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#!/usr/bin/env python | |
from __future__ import print_function | |
# png.py - PNG encoder/decoder in pure Python | |
# | |
# Copyright (C) 2006 Johann C. Rocholl <[email protected]> | |
# Portions Copyright (C) 2009 David Jones <[email protected]> | |
# And probably portions Copyright (C) 2006 Nicko van Someren <[email protected]> | |
# | |
# Original concept by Johann C. Rocholl. | |
# | |
# LICENCE (MIT) | |
# | |
# Permission is hereby granted, free of charge, to any person | |
# obtaining a copy of this software and associated documentation files | |
# (the "Software"), to deal in the Software without restriction, | |
# including without limitation the rights to use, copy, modify, merge, | |
# publish, distribute, sublicense, and/or sell copies of the Software, | |
# and to permit persons to whom the Software is furnished to do so, | |
# subject to the following conditions: | |
# | |
# The above copyright notice and this permission notice shall be | |
# included in all copies or substantial portions of the Software. | |
# | |
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, | |
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF | |
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND | |
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS | |
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN | |
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN | |
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | |
# SOFTWARE. | |
""" | |
Pure Python PNG Reader/Writer | |
This Python module implements support for PNG images (see PNG | |
specification at http://www.w3.org/TR/2003/REC-PNG-20031110/ ). It reads | |
and writes PNG files with all allowable bit depths | |
(1/2/4/8/16/24/32/48/64 bits per pixel) and colour combinations: | |
greyscale (1/2/4/8/16 bit); RGB, RGBA, LA (greyscale with alpha) with | |
8/16 bits per channel; colour mapped images (1/2/4/8 bit). | |
Adam7 interlacing is supported for reading and | |
writing. A number of optional chunks can be specified (when writing) | |
and understood (when reading): ``tRNS``, ``bKGD``, ``gAMA``. | |
For help, type ``import png; help(png)`` in your python interpreter. | |
A good place to start is the :class:`Reader` and :class:`Writer` | |
classes. | |
Requires Python 2.3. Limited support is available for Python 2.2, but | |
not everything works. Best with Python 2.4 and higher. Installation is | |
trivial, but see the ``README.txt`` file (with the source distribution) | |
for details. | |
This file can also be used as a command-line utility to convert | |
`Netpbm <http://netpbm.sourceforge.net/>`_ PNM files to PNG, and the | |
reverse conversion from PNG to PNM. The interface is similar to that | |
of the ``pnmtopng`` program from Netpbm. Type ``python png.py --help`` | |
at the shell prompt for usage and a list of options. | |
A note on spelling and terminology | |
---------------------------------- | |
Generally British English spelling is used in the documentation. So | |
that's "greyscale" and "colour". This not only matches the author's | |
native language, it's also used by the PNG specification. | |
The major colour models supported by PNG (and hence by PyPNG) are: | |
greyscale, RGB, greyscale--alpha, RGB--alpha. These are sometimes | |
referred to using the abbreviations: L, RGB, LA, RGBA. In this case | |
each letter abbreviates a single channel: *L* is for Luminance or Luma | |
or Lightness which is the channel used in greyscale images; *R*, *G*, | |
*B* stand for Red, Green, Blue, the components of a colour image; *A* | |
stands for Alpha, the opacity channel (used for transparency effects, | |
but higher values are more opaque, so it makes sense to call it | |
opacity). | |
A note on formats | |
----------------- | |
When getting pixel data out of this module (reading) and presenting | |
data to this module (writing) there are a number of ways the data could | |
be represented as a Python value. Generally this module uses one of | |
three formats called "flat row flat pixel", "boxed row flat pixel", and | |
"boxed row boxed pixel". Basically the concern is whether each pixel | |
and each row comes in its own little tuple (box), or not. | |
Consider an image that is 3 pixels wide by 2 pixels high, and each pixel | |
has RGB components: | |
Boxed row flat pixel:: | |
list([R,G,B, R,G,B, R,G,B], | |
[R,G,B, R,G,B, R,G,B]) | |
Each row appears as its own list, but the pixels are flattened so | |
that three values for one pixel simply follow the three values for | |
the previous pixel. This is the most common format used, because it | |
provides a good compromise between space and convenience. PyPNG regards | |
itself as at liberty to replace any sequence type with any sufficiently | |
compatible other sequence type; in practice each row is an array (from | |
the array module), and the outer list is sometimes an iterator rather | |
than an explicit list (so that streaming is possible). | |
Flat row flat pixel:: | |
[R,G,B, R,G,B, R,G,B, | |
R,G,B, R,G,B, R,G,B] | |
The entire image is one single giant sequence of colour values. | |
Generally an array will be used (to save space), not a list. | |
Boxed row boxed pixel:: | |
list([ (R,G,B), (R,G,B), (R,G,B) ], | |
[ (R,G,B), (R,G,B), (R,G,B) ]) | |
Each row appears in its own list, but each pixel also appears in its own | |
tuple. A serious memory burn in Python. | |
In all cases the top row comes first, and for each row the pixels are | |
ordered from left-to-right. Within a pixel the values appear in the | |
order, R-G-B-A (or L-A for greyscale--alpha). | |
There is a fourth format, mentioned because it is used internally, | |
is close to what lies inside a PNG file itself, and has some support | |
from the public API. This format is called packed. When packed, | |
each row is a sequence of bytes (integers from 0 to 255), just as | |
it is before PNG scanline filtering is applied. When the bit depth | |
is 8 this is essentially the same as boxed row flat pixel; when the | |
bit depth is less than 8, several pixels are packed into each byte; | |
when the bit depth is 16 (the only value more than 8 that is supported | |
by the PNG image format) each pixel value is decomposed into 2 bytes | |
(and `packed` is a misnomer). This format is used by the | |
:meth:`Writer.write_packed` method. It isn't usually a convenient | |
format, but may be just right if the source data for the PNG image | |
comes from something that uses a similar format (for example, 1-bit | |
BMPs, or another PNG file). | |
And now, my famous members | |
-------------------------- | |
""" | |
__version__ = "0.0.18" | |
import itertools | |
import math | |
import re | |
# http://www.python.org/doc/2.4.4/lib/module-operator.html | |
import operator | |
import struct | |
import sys | |
# http://www.python.org/doc/2.4.4/lib/module-warnings.html | |
import warnings | |
import zlib | |
from array import array | |
from functools import reduce | |
try: | |
# `cpngfilters` is a Cython module: it must be compiled by | |
# Cython for this import to work. | |
# If this import does work, then it overrides pure-python | |
# filtering functions defined later in this file (see `class | |
# pngfilters`). | |
import cpngfilters as pngfilters | |
except ImportError: | |
pass | |
__all__ = ['Image', 'Reader', 'Writer', 'write_chunks', 'from_array'] | |
# The PNG signature. | |
# http://www.w3.org/TR/PNG/#5PNG-file-signature | |
_signature = struct.pack('8B', 137, 80, 78, 71, 13, 10, 26, 10) | |
_adam7 = ((0, 0, 8, 8), | |
(4, 0, 8, 8), | |
(0, 4, 4, 8), | |
(2, 0, 4, 4), | |
(0, 2, 2, 4), | |
(1, 0, 2, 2), | |
(0, 1, 1, 2)) | |
def group(s, n): | |
# See http://www.python.org/doc/2.6/library/functions.html#zip | |
return list(zip(*[iter(s)]*n)) | |
def isarray(x): | |
return isinstance(x, array) | |
def tostring(row): | |
return row.tostring() | |
def interleave_planes(ipixels, apixels, ipsize, apsize): | |
""" | |
Interleave (colour) planes, e.g. RGB + A = RGBA. | |
Return an array of pixels consisting of the `ipsize` elements of | |
data from each pixel in `ipixels` followed by the `apsize` elements | |
of data from each pixel in `apixels`. Conventionally `ipixels` | |
and `apixels` are byte arrays so the sizes are bytes, but it | |
actually works with any arrays of the same type. The returned | |
array is the same type as the input arrays which should be the | |
same type as each other. | |
""" | |
itotal = len(ipixels) | |
atotal = len(apixels) | |
newtotal = itotal + atotal | |
newpsize = ipsize + apsize | |
# Set up the output buffer | |
# See http://www.python.org/doc/2.4.4/lib/module-array.html#l2h-1356 | |
out = array(ipixels.typecode) | |
# It's annoying that there is no cheap way to set the array size :-( | |
out.extend(ipixels) | |
out.extend(apixels) | |
# Interleave in the pixel data | |
for i in range(ipsize): | |
out[i:newtotal:newpsize] = ipixels[i:itotal:ipsize] | |
for i in range(apsize): | |
out[i+ipsize:newtotal:newpsize] = apixels[i:atotal:apsize] | |
return out | |
def check_palette(palette): | |
"""Check a palette argument (to the :class:`Writer` class) | |
for validity. Returns the palette as a list if okay; raises an | |
exception otherwise. | |
""" | |
# None is the default and is allowed. | |
if palette is None: | |
return None | |
p = list(palette) | |
if not (0 < len(p) <= 256): | |
raise ValueError("a palette must have between 1 and 256 entries") | |
seen_triple = False | |
for i,t in enumerate(p): | |
if len(t) not in (3,4): | |
raise ValueError( | |
"palette entry %d: entries must be 3- or 4-tuples." % i) | |
if len(t) == 3: | |
seen_triple = True | |
if seen_triple and len(t) == 4: | |
raise ValueError( | |
"palette entry %d: all 4-tuples must precede all 3-tuples" % i) | |
for x in t: | |
if int(x) != x or not(0 <= x <= 255): | |
raise ValueError( | |
"palette entry %d: values must be integer: 0 <= x <= 255" % i) | |
return p | |
def check_sizes(size, width, height): | |
"""Check that these arguments, in supplied, are consistent. | |
Return a (width, height) pair. | |
""" | |
if not size: | |
return width, height | |
if len(size) != 2: | |
raise ValueError( | |
"size argument should be a pair (width, height)") | |
if width is not None and width != size[0]: | |
raise ValueError( | |
"size[0] (%r) and width (%r) should match when both are used." | |
% (size[0], width)) | |
if height is not None and height != size[1]: | |
raise ValueError( | |
"size[1] (%r) and height (%r) should match when both are used." | |
% (size[1], height)) | |
return size | |
def check_color(c, greyscale, which): | |
"""Checks that a colour argument for transparent or | |
background options is the right form. Returns the colour | |
(which, if it's a bar integer, is "corrected" to a 1-tuple). | |
""" | |
if c is None: | |
return c | |
if greyscale: | |
try: | |
len(c) | |
except TypeError: | |
c = (c,) | |
if len(c) != 1: | |
raise ValueError("%s for greyscale must be 1-tuple" % | |
which) | |
if not isintance(c[0], int): | |
raise ValueError( | |
"%s colour for greyscale must be integer" % which) | |
else: | |
if not (len(c) == 3 and | |
isinstance(c[0], int) and | |
isinstance(c[1], int) and | |
isinstance(c[2]), int): | |
raise ValueError( | |
"%s colour must be a triple of integers" % which) | |
return c | |
class Error(Exception): | |
def __str__(self): | |
return self.__class__.__name__ + ': ' + ' '.join(self.args) | |
class FormatError(Error): | |
"""Problem with input file format. In other words, PNG file does | |
not conform to the specification in some way and is invalid. | |
""" | |
class ChunkError(FormatError): | |
pass | |
class Writer: | |
""" | |
PNG encoder in pure Python. | |
""" | |
def __init__(self, width=None, height=None, | |
size=None, | |
greyscale=False, | |
alpha=False, | |
bitdepth=8, | |
palette=None, | |
transparent=None, | |
background=None, | |
gamma=None, | |
compression=None, | |
interlace=False, | |
bytes_per_sample=None, # deprecated | |
planes=None, | |
colormap=None, | |
maxval=None, | |
chunk_limit=2**20, | |
x_pixels_per_unit = None, | |
y_pixels_per_unit = None, | |
unit_is_meter = False): | |
""" | |
Create a PNG encoder object. | |
Arguments: | |
width, height | |
Image size in pixels, as two separate arguments. | |
size | |
Image size (w,h) in pixels, as single argument. | |
greyscale | |
Input data is greyscale, not RGB. | |
alpha | |
Input data has alpha channel (RGBA or LA). | |
bitdepth | |
Bit depth: from 1 to 16. | |
palette | |
Create a palette for a colour mapped image (colour type 3). | |
transparent | |
Specify a transparent colour (create a ``tRNS`` chunk). | |
background | |
Specify a default background colour (create a ``bKGD`` chunk). | |
gamma | |
Specify a gamma value (create a ``gAMA`` chunk). | |
compression | |
zlib compression level: 0 (none) to 9 (more compressed); | |
default: -1 or None. | |
interlace | |
Create an interlaced image. | |
chunk_limit | |
Write multiple ``IDAT`` chunks to save memory. | |
x_pixels_per_unit | |
Number of pixels a unit along the x axis (write a | |
`pHYs` chunk). | |
y_pixels_per_unit | |
Number of pixels a unit along the y axis (write a | |
`pHYs` chunk). Along with `x_pixel_unit`, this gives | |
the pixel size ratio. | |
unit_is_meter | |
`True` to indicate that the unit (for the `pHYs` | |
chunk) is metre. | |
The image size (in pixels) can be specified either by using the | |
`width` and `height` arguments, or with the single `size` | |
argument. If `size` is used it should be a pair (*width*, | |
*height*). | |
`greyscale` and `alpha` are booleans that specify whether | |
an image is greyscale (or colour), and whether it has an | |
alpha channel (or not). | |
`bitdepth` specifies the bit depth of the source pixel values. | |
Each source pixel value must be an integer between 0 and | |
``2**bitdepth-1``. For example, 8-bit images have values | |
between 0 and 255. PNG only stores images with bit depths of | |
1,2,4,8, or 16. When `bitdepth` is not one of these values, | |
the next highest valid bit depth is selected, and an ``sBIT`` | |
(significant bits) chunk is generated that specifies the | |
original precision of the source image. In this case the | |
supplied pixel values will be rescaled to fit the range of | |
the selected bit depth. | |
The details of which bit depth / colour model combinations the | |
PNG file format supports directly, are somewhat arcane | |
(refer to the PNG specification for full details). Briefly: | |
"small" bit depths (1,2,4) are only allowed with greyscale and | |
colour mapped images; colour mapped images cannot have bit depth | |
16. | |
For colour mapped images (in other words, when the `palette` | |
argument is specified) the `bitdepth` argument must match one of | |
the valid PNG bit depths: 1, 2, 4, or 8. (It is valid to have a | |
PNG image with a palette and an ``sBIT`` chunk, but the meaning | |
is slightly different; it would be awkward to press the | |
`bitdepth` argument into service for this.) | |
The `palette` option, when specified, causes a colour | |
mapped image to be created: the PNG colour type is set to 3; | |
`greyscale` must not be set; `alpha` must not be set; | |
`transparent` must not be set; the bit depth must be 1,2,4, | |
or 8. When a colour mapped image is created, the pixel values | |
are palette indexes and the `bitdepth` argument specifies the | |
size of these indexes (not the size of the colour values in | |
the palette). | |
The palette argument value should be a sequence of 3- or | |
4-tuples. 3-tuples specify RGB palette entries; 4-tuples | |
specify RGBA palette entries. If both 4-tuples and 3-tuples | |
appear in the sequence then all the 4-tuples must come | |
before all the 3-tuples. A ``PLTE`` chunk is created; if there | |
are 4-tuples then a ``tRNS`` chunk is created as well. The | |
``PLTE`` chunk will contain all the RGB triples in the same | |
sequence; the ``tRNS`` chunk will contain the alpha channel for | |
all the 4-tuples, in the same sequence. Palette entries | |
are always 8-bit. | |
If specified, the `transparent` and `background` parameters must | |
be a tuple with three integer values for red, green, blue, or | |
a simple integer (or singleton tuple) for a greyscale image. | |
If specified, the `gamma` parameter must be a positive number | |
(generally, a `float`). A ``gAMA`` chunk will be created. | |
Note that this will not change the values of the pixels as | |
they appear in the PNG file, they are assumed to have already | |
been converted appropriately for the gamma specified. | |
The `compression` argument specifies the compression level to | |
be used by the ``zlib`` module. Values from 1 to 9 specify | |
compression, with 9 being "more compressed" (usually smaller | |
and slower, but it doesn't always work out that way). 0 means | |
no compression. -1 and ``None`` both mean that the default | |
level of compession will be picked by the ``zlib`` module | |
(which is generally acceptable). | |
If `interlace` is true then an interlaced image is created | |
(using PNG's so far only interace method, *Adam7*). This does | |
not affect how the pixels should be presented to the encoder, | |
rather it changes how they are arranged into the PNG file. | |
On slow connexions interlaced images can be partially decoded | |
by the browser to give a rough view of the image that is | |
successively refined as more image data appears. | |
.. note :: | |
Enabling the `interlace` option requires the entire image | |
to be processed in working memory. | |
`chunk_limit` is used to limit the amount of memory used whilst | |
compressing the image. In order to avoid using large amounts of | |
memory, multiple ``IDAT`` chunks may be created. | |
""" | |
# At the moment the `planes` argument is ignored; | |
# its purpose is to act as a dummy so that | |
# ``Writer(x, y, **info)`` works, where `info` is a dictionary | |
# returned by Reader.read and friends. | |
# Ditto for `colormap`. | |
width, height = check_sizes(size, width, height) | |
del size | |
if width <= 0 or height <= 0: | |
raise ValueError("width and height must be greater than zero") | |
if not isinstance(width, int) or not isinstance(height, int): | |
raise ValueError("width and height must be integers") | |
# http://www.w3.org/TR/PNG/#7Integers-and-byte-order | |
if width > 2**32-1 or height > 2**32-1: | |
raise ValueError("width and height cannot exceed 2**32-1") | |
if alpha and transparent is not None: | |
raise ValueError( | |
"transparent colour not allowed with alpha channel") | |
if bytes_per_sample is not None: | |
warnings.warn('please use bitdepth instead of bytes_per_sample', | |
DeprecationWarning) | |
if bytes_per_sample not in (0.125, 0.25, 0.5, 1, 2): | |
raise ValueError( | |
"bytes per sample must be .125, .25, .5, 1, or 2") | |
bitdepth = int(8*bytes_per_sample) | |
del bytes_per_sample | |
if not isinstance(bitdepth, int) or bitdepth < 1 or 16 < bitdepth: | |
raise ValueError("bitdepth (%r) must be a positive integer <= 16" % | |
bitdepth) | |
self.rescale = None | |
palette = check_palette(palette) | |
if palette: | |
if bitdepth not in (1,2,4,8): | |
raise ValueError("with palette, bitdepth must be 1, 2, 4, or 8") | |
if transparent is not None: | |
raise ValueError("transparent and palette not compatible") | |
if alpha: | |
raise ValueError("alpha and palette not compatible") | |
if greyscale: | |
raise ValueError("greyscale and palette not compatible") | |
else: | |
# No palette, check for sBIT chunk generation. | |
if alpha or not greyscale: | |
if bitdepth not in (8,16): | |
targetbitdepth = (8,16)[bitdepth > 8] | |
self.rescale = (bitdepth, targetbitdepth) | |
bitdepth = targetbitdepth | |
del targetbitdepth | |
else: | |
assert greyscale | |
assert not alpha | |
if bitdepth not in (1,2,4,8,16): | |
if bitdepth > 8: | |
targetbitdepth = 16 | |
elif bitdepth == 3: | |
targetbitdepth = 4 | |
else: | |
assert bitdepth in (5,6,7) | |
targetbitdepth = 8 | |
self.rescale = (bitdepth, targetbitdepth) | |
bitdepth = targetbitdepth | |
del targetbitdepth | |
if bitdepth < 8 and (alpha or not greyscale and not palette): | |
raise ValueError( | |
"bitdepth < 8 only permitted with greyscale or palette") | |
if bitdepth > 8 and palette: | |
raise ValueError( | |
"bit depth must be 8 or less for images with palette") | |
transparent = check_color(transparent, greyscale, 'transparent') | |
background = check_color(background, greyscale, 'background') | |
# It's important that the true boolean values (greyscale, alpha, | |
# colormap, interlace) are converted to bool because Iverson's | |
# convention is relied upon later on. | |
self.width = width | |
self.height = height | |
self.transparent = transparent | |
self.background = background | |
self.gamma = gamma | |
self.greyscale = bool(greyscale) | |
self.alpha = bool(alpha) | |
self.colormap = bool(palette) | |
self.bitdepth = int(bitdepth) | |
self.compression = compression | |
self.chunk_limit = chunk_limit | |
self.interlace = bool(interlace) | |
self.palette = palette | |
self.x_pixels_per_unit = x_pixels_per_unit | |
self.y_pixels_per_unit = y_pixels_per_unit | |
self.unit_is_meter = bool(unit_is_meter) | |
self.color_type = 4*self.alpha + 2*(not greyscale) + 1*self.colormap | |
assert self.color_type in (0,2,3,4,6) | |
self.color_planes = (3,1)[self.greyscale or self.colormap] | |
self.planes = self.color_planes + self.alpha | |
# :todo: fix for bitdepth < 8 | |
self.psize = (self.bitdepth/8) * self.planes | |
def make_palette(self): | |
"""Create the byte sequences for a ``PLTE`` and if necessary a | |
``tRNS`` chunk. Returned as a pair (*p*, *t*). *t* will be | |
``None`` if no ``tRNS`` chunk is necessary. | |
""" | |
p = array('B') | |
t = array('B') | |
for x in self.palette: | |
p.extend(x[0:3]) | |
if len(x) > 3: | |
t.append(x[3]) | |
p = tostring(p) | |
t = tostring(t) | |
if t: | |
return p,t | |
return p,None | |
def write(self, outfile, rows): | |
"""Write a PNG image to the output file. `rows` should be | |
an iterable that yields each row in boxed row flat pixel | |
format. The rows should be the rows of the original image, | |
so there should be ``self.height`` rows of ``self.width * | |
self.planes`` values. If `interlace` is specified (when | |
creating the instance), then an interlaced PNG file will | |
be written. Supply the rows in the normal image order; | |
the interlacing is carried out internally. | |
.. note :: | |
Interlacing will require the entire image to be in working | |
memory. | |
""" | |
if self.interlace: | |
fmt = 'BH'[self.bitdepth > 8] | |
a = array(fmt, itertools.chain(*rows)) | |
return self.write_array(outfile, a) | |
nrows = self.write_passes(outfile, rows) | |
if nrows != self.height: | |
raise ValueError( | |
"rows supplied (%d) does not match height (%d)" % | |
(nrows, self.height)) | |
def write_passes(self, outfile, rows, packed=False): | |
""" | |
Write a PNG image to the output file. | |
Most users are expected to find the :meth:`write` or | |
:meth:`write_array` method more convenient. | |
The rows should be given to this method in the order that | |
they appear in the output file. For straightlaced images, | |
this is the usual top to bottom ordering, but for interlaced | |
images the rows should have already been interlaced before | |
passing them to this function. | |
`rows` should be an iterable that yields each row. When | |
`packed` is ``False`` the rows should be in boxed row flat pixel | |
format; when `packed` is ``True`` each row should be a packed | |
sequence of bytes. | |
""" | |
# http://www.w3.org/TR/PNG/#5PNG-file-signature | |
outfile.write(_signature) | |
# http://www.w3.org/TR/PNG/#11IHDR | |
write_chunk(outfile, b'IHDR', | |
struct.pack("!2I5B", self.width, self.height, | |
self.bitdepth, self.color_type, | |
0, 0, self.interlace)) | |
# See :chunk:order | |
# http://www.w3.org/TR/PNG/#11gAMA | |
if self.gamma is not None: | |
write_chunk(outfile, b'gAMA', | |
struct.pack("!L", int(round(self.gamma*1e5)))) | |
# See :chunk:order | |
# http://www.w3.org/TR/PNG/#11sBIT | |
if self.rescale: | |
write_chunk(outfile, b'sBIT', | |
struct.pack('%dB' % self.planes, | |
*[self.rescale[0]]*self.planes)) | |
# :chunk:order: Without a palette (PLTE chunk), ordering is | |
# relatively relaxed. With one, gAMA chunk must precede PLTE | |
# chunk which must precede tRNS and bKGD. | |
# See http://www.w3.org/TR/PNG/#5ChunkOrdering | |
if self.palette: | |
p,t = self.make_palette() | |
write_chunk(outfile, b'PLTE', p) | |
if t: | |
# tRNS chunk is optional. Only needed if palette entries | |
# have alpha. | |
write_chunk(outfile, b'tRNS', t) | |
# http://www.w3.org/TR/PNG/#11tRNS | |
if self.transparent is not None: | |
if self.greyscale: | |
write_chunk(outfile, b'tRNS', | |
struct.pack("!1H", *self.transparent)) | |
else: | |
write_chunk(outfile, b'tRNS', | |
struct.pack("!3H", *self.transparent)) | |
# http://www.w3.org/TR/PNG/#11bKGD | |
if self.background is not None: | |
if self.greyscale: | |
write_chunk(outfile, b'bKGD', | |
struct.pack("!1H", *self.background)) | |
else: | |
write_chunk(outfile, b'bKGD', | |
struct.pack("!3H", *self.background)) | |
# http://www.w3.org/TR/PNG/#11pHYs | |
if self.x_pixels_per_unit is not None and self.y_pixels_per_unit is not None: | |
tup = (self.x_pixels_per_unit, self.y_pixels_per_unit, int(self.unit_is_meter)) | |
write_chunk(outfile, b'pHYs', struct.pack("!LLB",*tup)) | |
# http://www.w3.org/TR/PNG/#11IDAT | |
if self.compression is not None: | |
compressor = zlib.compressobj(self.compression) | |
else: | |
compressor = zlib.compressobj() | |
# Choose an extend function based on the bitdepth. The extend | |
# function packs/decomposes the pixel values into bytes and | |
# stuffs them onto the data array. | |
data = array('B') | |
if self.bitdepth == 8 or packed: | |
extend = data.extend | |
elif self.bitdepth == 16: | |
# Decompose into bytes | |
def extend(sl): | |
fmt = '!%dH' % len(sl) | |
data.extend(array('B', struct.pack(fmt, *sl))) | |
else: | |
# Pack into bytes | |
assert self.bitdepth < 8 | |
# samples per byte | |
spb = int(8/self.bitdepth) | |
def extend(sl): | |
a = array('B', sl) | |
# Adding padding bytes so we can group into a whole | |
# number of spb-tuples. | |
l = float(len(a)) | |
extra = math.ceil(l / float(spb))*spb - l | |
a.extend([0]*int(extra)) | |
# Pack into bytes | |
l = group(a, spb) | |
l = [reduce(lambda x,y: | |
(x << self.bitdepth) + y, e) for e in l] | |
data.extend(l) | |
if self.rescale: | |
oldextend = extend | |
factor = \ | |
float(2**self.rescale[1]-1) / float(2**self.rescale[0]-1) | |
def extend(sl): | |
oldextend([int(round(factor*x)) for x in sl]) | |
# Build the first row, testing mostly to see if we need to | |
# changed the extend function to cope with NumPy integer types | |
# (they cause our ordinary definition of extend to fail, so we | |
# wrap it). See | |
# http://code.google.com/p/pypng/issues/detail?id=44 | |
enumrows = enumerate(rows) | |
del rows | |
# First row's filter type. | |
data.append(0) | |
# :todo: Certain exceptions in the call to ``.next()`` or the | |
# following try would indicate no row data supplied. | |
# Should catch. | |
i,row = next(enumrows) | |
try: | |
# If this fails... | |
extend(row) | |
except: | |
# ... try a version that converts the values to int first. | |
# Not only does this work for the (slightly broken) NumPy | |
# types, there are probably lots of other, unknown, "nearly" | |
# int types it works for. | |
def wrapmapint(f): | |
return lambda sl: f([int(x) for x in sl]) | |
extend = wrapmapint(extend) | |
del wrapmapint | |
extend(row) | |
for i,row in enumrows: | |
# Add "None" filter type. Currently, it's essential that | |
# this filter type be used for every scanline as we do not | |
# mark the first row of a reduced pass image; that means we | |
# could accidentally compute the wrong filtered scanline if | |
# we used "up", "average", or "paeth" on such a line. | |
data.append(0) | |
extend(row) | |
if len(data) > self.chunk_limit: | |
compressed = compressor.compress(tostring(data)) | |
if len(compressed): | |
write_chunk(outfile, b'IDAT', compressed) | |
# Because of our very witty definition of ``extend``, | |
# above, we must re-use the same ``data`` object. Hence | |
# we use ``del`` to empty this one, rather than create a | |
# fresh one (which would be my natural FP instinct). | |
del data[:] | |
if len(data): | |
compressed = compressor.compress(tostring(data)) | |
else: | |
compressed = b'' | |
flushed = compressor.flush() | |
if len(compressed) or len(flushed): | |
write_chunk(outfile, b'IDAT', compressed + flushed) | |
# http://www.w3.org/TR/PNG/#11IEND | |
write_chunk(outfile, b'IEND') | |
return i+1 | |
def write_array(self, outfile, pixels): | |
""" | |
Write an array in flat row flat pixel format as a PNG file on | |
the output file. See also :meth:`write` method. | |
""" | |
if self.interlace: | |
self.write_passes(outfile, self.array_scanlines_interlace(pixels)) | |
else: | |
self.write_passes(outfile, self.array_scanlines(pixels)) | |
def write_packed(self, outfile, rows): | |
""" | |
Write PNG file to `outfile`. The pixel data comes from `rows` | |
which should be in boxed row packed format. Each row should be | |
a sequence of packed bytes. | |
Technically, this method does work for interlaced images but it | |
is best avoided. For interlaced images, the rows should be | |
presented in the order that they appear in the file. | |
This method should not be used when the source image bit depth | |
is not one naturally supported by PNG; the bit depth should be | |
1, 2, 4, 8, or 16. | |
""" | |
if self.rescale: | |
raise Error("write_packed method not suitable for bit depth %d" % | |
self.rescale[0]) | |
return self.write_passes(outfile, rows, packed=True) | |
def convert_pnm(self, infile, outfile): | |
""" | |
Convert a PNM file containing raw pixel data into a PNG file | |
with the parameters set in the writer object. Works for | |
(binary) PGM, PPM, and PAM formats. | |
""" | |
if self.interlace: | |
pixels = array('B') | |
pixels.fromfile(infile, | |
(self.bitdepth/8) * self.color_planes * | |
self.width * self.height) | |
self.write_passes(outfile, self.array_scanlines_interlace(pixels)) | |
else: | |
self.write_passes(outfile, self.file_scanlines(infile)) | |
def convert_ppm_and_pgm(self, ppmfile, pgmfile, outfile): | |
""" | |
Convert a PPM and PGM file containing raw pixel data into a | |
PNG outfile with the parameters set in the writer object. | |
""" | |
pixels = array('B') | |
pixels.fromfile(ppmfile, | |
(self.bitdepth/8) * self.color_planes * | |
self.width * self.height) | |
apixels = array('B') | |
apixels.fromfile(pgmfile, | |
(self.bitdepth/8) * | |
self.width * self.height) | |
pixels = interleave_planes(pixels, apixels, | |
(self.bitdepth/8) * self.color_planes, | |
(self.bitdepth/8)) | |
if self.interlace: | |
self.write_passes(outfile, self.array_scanlines_interlace(pixels)) | |
else: | |
self.write_passes(outfile, self.array_scanlines(pixels)) | |
def file_scanlines(self, infile): | |
""" | |
Generates boxed rows in flat pixel format, from the input file | |
`infile`. It assumes that the input file is in a "Netpbm-like" | |
binary format, and is positioned at the beginning of the first | |
pixel. The number of pixels to read is taken from the image | |
dimensions (`width`, `height`, `planes`) and the number of bytes | |
per value is implied by the image `bitdepth`. | |
""" | |
# Values per row | |
vpr = self.width * self.planes | |
row_bytes = vpr | |
if self.bitdepth > 8: | |
assert self.bitdepth == 16 | |
row_bytes *= 2 | |
fmt = '>%dH' % vpr | |
def line(): | |
return array('H', struct.unpack(fmt, infile.read(row_bytes))) | |
else: | |
def line(): | |
scanline = array('B', infile.read(row_bytes)) | |
return scanline | |
for y in range(self.height): | |
yield line() | |
def array_scanlines(self, pixels): | |
""" | |
Generates boxed rows (flat pixels) from flat rows (flat pixels) | |
in an array. | |
""" | |
# Values per row | |
vpr = self.width * self.planes | |
stop = 0 | |
for y in range(self.height): | |
start = stop | |
stop = start + vpr | |
yield pixels[start:stop] | |
def array_scanlines_interlace(self, pixels): | |
""" | |
Generator for interlaced scanlines from an array. `pixels` is | |
the full source image in flat row flat pixel format. The | |
generator yields each scanline of the reduced passes in turn, in | |
boxed row flat pixel format. | |
""" | |
# http://www.w3.org/TR/PNG/#8InterlaceMethods | |
# Array type. | |
fmt = 'BH'[self.bitdepth > 8] | |
# Value per row | |
vpr = self.width * self.planes | |
for xstart, ystart, xstep, ystep in _adam7: | |
if xstart >= self.width: | |
continue | |
# Pixels per row (of reduced image) | |
ppr = int(math.ceil((self.width-xstart)/float(xstep))) | |
# number of values in reduced image row. | |
row_len = ppr*self.planes | |
for y in range(ystart, self.height, ystep): | |
if xstep == 1: | |
offset = y * vpr | |
yield pixels[offset:offset+vpr] | |
else: | |
row = array(fmt) | |
# There's no easier way to set the length of an array | |
row.extend(pixels[0:row_len]) | |
offset = y * vpr + xstart * self.planes | |
end_offset = (y+1) * vpr | |
skip = self.planes * xstep | |
for i in range(self.planes): | |
row[i::self.planes] = \ | |
pixels[offset+i:end_offset:skip] | |
yield row | |
def write_chunk(outfile, tag, data=b''): | |
""" | |
Write a PNG chunk to the output file, including length and | |
checksum. | |
""" | |
# http://www.w3.org/TR/PNG/#5Chunk-layout | |
outfile.write(struct.pack("!I", len(data))) | |
outfile.write(tag) | |
outfile.write(data) | |
checksum = zlib.crc32(tag) | |
checksum = zlib.crc32(data, checksum) | |
checksum &= 2**32-1 | |
outfile.write(struct.pack("!I", checksum)) | |
def write_chunks(out, chunks): | |
"""Create a PNG file by writing out the chunks.""" | |
out.write(_signature) | |
for chunk in chunks: | |
write_chunk(out, *chunk) | |
def filter_scanline(type, line, fo, prev=None): | |
"""Apply a scanline filter to a scanline. `type` specifies the | |
filter type (0 to 4); `line` specifies the current (unfiltered) | |
scanline as a sequence of bytes; `prev` specifies the previous | |
(unfiltered) scanline as a sequence of bytes. `fo` specifies the | |
filter offset; normally this is size of a pixel in bytes (the number | |
of bytes per sample times the number of channels), but when this is | |
< 1 (for bit depths < 8) then the filter offset is 1. | |
""" | |
assert 0 <= type < 5 | |
# The output array. Which, pathetically, we extend one-byte at a | |
# time (fortunately this is linear). | |
out = array('B', [type]) | |
def sub(): | |
ai = -fo | |
for x in line: | |
if ai >= 0: | |
x = (x - line[ai]) & 0xff | |
out.append(x) | |
ai += 1 | |
def up(): | |
for i,x in enumerate(line): | |
x = (x - prev[i]) & 0xff | |
out.append(x) | |
def average(): | |
ai = -fo | |
for i,x in enumerate(line): | |
if ai >= 0: | |
x = (x - ((line[ai] + prev[i]) >> 1)) & 0xff | |
else: | |
x = (x - (prev[i] >> 1)) & 0xff | |
out.append(x) | |
ai += 1 | |
def paeth(): | |
# http://www.w3.org/TR/PNG/#9Filter-type-4-Paeth | |
ai = -fo # also used for ci | |
for i,x in enumerate(line): | |
a = 0 | |
b = prev[i] | |
c = 0 | |
if ai >= 0: | |
a = line[ai] | |
c = prev[ai] | |
p = a + b - c | |
pa = abs(p - a) | |
pb = abs(p - b) | |
pc = abs(p - c) | |
if pa <= pb and pa <= pc: | |
Pr = a | |
elif pb <= pc: | |
Pr = b | |
else: | |
Pr = c | |
x = (x - Pr) & 0xff | |
out.append(x) | |
ai += 1 | |
if not prev: | |
# We're on the first line. Some of the filters can be reduced | |
# to simpler cases which makes handling the line "off the top" | |
# of the image simpler. "up" becomes "none"; "paeth" becomes | |
# "left" (non-trivial, but true). "average" needs to be handled | |
# specially. | |
if type == 2: # "up" | |
type = 0 | |
elif type == 3: | |
prev = [0]*len(line) | |
elif type == 4: # "paeth" | |
type = 1 | |
if type == 0: | |
out.extend(line) | |
elif type == 1: | |
sub() | |
elif type == 2: | |
up() | |
elif type == 3: | |
average() | |
else: # type == 4 | |
paeth() | |
return out | |
# Regex for decoding mode string | |
RegexModeDecode = re.compile("(LA?|RGBA?);?([0-9]*)", flags=re.IGNORECASE) | |
def from_array(a, mode=None, info={}): | |
"""Create a PNG :class:`Image` object from a 2- or 3-dimensional | |
array. One application of this function is easy PIL-style saving: | |
``png.from_array(pixels, 'L').save('foo.png')``. | |
Unless they are specified using the *info* parameter, the PNG's | |
height and width are taken from the array size. For a 3 dimensional | |
array the first axis is the height; the second axis is the width; | |
and the third axis is the channel number. Thus an RGB image that is | |
16 pixels high and 8 wide will use an array that is 16x8x3. For 2 | |
dimensional arrays the first axis is the height, but the second axis | |
is ``width*channels``, so an RGB image that is 16 pixels high and 8 | |
wide will use a 2-dimensional array that is 16x24 (each row will be | |
8*3 = 24 sample values). | |
*mode* is a string that specifies the image colour format in a | |
PIL-style mode. It can be: | |
``'L'`` | |
greyscale (1 channel) | |
``'LA'`` | |
greyscale with alpha (2 channel) | |
``'RGB'`` | |
colour image (3 channel) | |
``'RGBA'`` | |
colour image with alpha (4 channel) | |
The mode string can also specify the bit depth (overriding how this | |
function normally derives the bit depth, see below). Appending | |
``';16'`` to the mode will cause the PNG to be 16 bits per channel; | |
any decimal from 1 to 16 can be used to specify the bit depth. | |
When a 2-dimensional array is used *mode* determines how many | |
channels the image has, and so allows the width to be derived from | |
the second array dimension. | |
The array is expected to be a ``numpy`` array, but it can be any | |
suitable Python sequence. For example, a list of lists can be used: | |
``png.from_array([[0, 255, 0], [255, 0, 255]], 'L')``. The exact | |
rules are: ``len(a)`` gives the first dimension, height; | |
``len(a[0])`` gives the second dimension; ``len(a[0][0])`` gives the | |
third dimension, unless an exception is raised in which case a | |
2-dimensional array is assumed. It's slightly more complicated than | |
that because an iterator of rows can be used, and it all still | |
works. Using an iterator allows data to be streamed efficiently. | |
The bit depth of the PNG is normally taken from the array element's | |
datatype (but if *mode* specifies a bitdepth then that is used | |
instead). The array element's datatype is determined in a way which | |
is supposed to work both for ``numpy`` arrays and for Python | |
``array.array`` objects. A 1 byte datatype will give a bit depth of | |
8, a 2 byte datatype will give a bit depth of 16. If the datatype | |
does not have an implicit size, for example it is a plain Python | |
list of lists, as above, then a default of 8 is used. | |
The *info* parameter is a dictionary that can be used to specify | |
metadata (in the same style as the arguments to the | |
:class:`png.Writer` class). For this function the keys that are | |
useful are: | |
height | |
overrides the height derived from the array dimensions and allows | |
*a* to be an iterable. | |
width | |
overrides the width derived from the array dimensions. | |
bitdepth | |
overrides the bit depth derived from the element datatype (but | |
must match *mode* if that also specifies a bit depth). | |
Generally anything specified in the | |
*info* dictionary will override any implicit choices that this | |
function would otherwise make, but must match any explicit ones. | |
For example, if the *info* dictionary has a ``greyscale`` key then | |
this must be true when mode is ``'L'`` or ``'LA'`` and false when | |
mode is ``'RGB'`` or ``'RGBA'``. | |
""" | |
# We abuse the *info* parameter by modifying it. Take a copy here. | |
# (Also typechecks *info* to some extent). | |
info = dict(info) | |
# Syntax check mode string. | |
match = RegexModeDecode.match(mode) | |
if not match: | |
raise Error("mode string should be 'RGB' or 'L;16' or similar.") | |
mode, bitdepth = match.groups() | |
alpha = 'A' in mode | |
if bitdepth: | |
bitdepth = int(bitdepth) | |
# Colour format. | |
if 'greyscale' in info: | |
if bool(info['greyscale']) != ('L' in mode): | |
raise Error("info['greyscale'] should match mode.") | |
info['greyscale'] = 'L' in mode | |
if 'alpha' in info: | |
if bool(info['alpha']) != alpha: | |
raise Error("info['alpha'] should match mode.") | |
info['alpha'] = alpha | |
# Get bitdepth from *mode* if possible. | |
if bitdepth: | |
if info.get("bitdepth") and bitdepth != info['bitdepth']: | |
raise Error("bitdepth (%d) should match bitdepth of info (%d)." % | |
(bitdepth, info['bitdepth'])) | |
info['bitdepth'] = bitdepth | |
# Fill in and/or check entries in *info*. | |
# Dimensions. | |
if 'size' in info: | |
assert len(info["size"]) == 2 | |
# Check width, height, size all match where used. | |
for dimension,axis in [('width', 0), ('height', 1)]: | |
if dimension in info: | |
if info[dimension] != info['size'][axis]: | |
raise Error( | |
"info[%r] should match info['size'][%r]." % | |
(dimension, axis)) | |
info['width'],info['height'] = info['size'] | |
if 'height' not in info: | |
try: | |
info['height'] = len(a) | |
except TypeError: | |
raise Error("len(a) does not work, supply info['height'] instead.") | |
planes = len(mode) | |
if 'planes' in info: | |
if info['planes'] != planes: | |
raise Error("info['planes'] should match mode.") | |
# In order to work out whether we the array is 2D or 3D we need its | |
# first row, which requires that we take a copy of its iterator. | |
# We may also need the first row to derive width and bitdepth. | |
a,t = itertools.tee(a) | |
row = next(t) | |
del t | |
try: | |
row[0][0] | |
threed = True | |
testelement = row[0] | |
except (IndexError, TypeError): | |
threed = False | |
testelement = row | |
if 'width' not in info: | |
if threed: | |
width = len(row) | |
else: | |
width = len(row) // planes | |
info['width'] = width | |
if threed: | |
# Flatten the threed rows | |
a = (itertools.chain.from_iterable(x) for x in a) | |
if 'bitdepth' not in info: | |
try: | |
dtype = testelement.dtype | |
# goto the "else:" clause. Sorry. | |
except AttributeError: | |
try: | |
# Try a Python array.array. | |
bitdepth = 8 * testelement.itemsize | |
except AttributeError: | |
# We can't determine it from the array element's | |
# datatype, use a default of 8. | |
bitdepth = 8 | |
else: | |
# If we got here without exception, we now assume that | |
# the array is a numpy array. | |
if dtype.kind == 'b': | |
bitdepth = 1 | |
else: | |
bitdepth = 8 * dtype.itemsize | |
info['bitdepth'] = bitdepth | |
for thing in ["width", "height", "bitdepth", "greyscale", "alpha"]: | |
assert thing in info | |
return Image(a, info) | |
# So that refugee's from PIL feel more at home. Not documented. | |
fromarray = from_array | |
class Image: | |
"""A PNG image. You can create an :class:`Image` object from | |
an array of pixels by calling :meth:`png.from_array`. It can be | |
saved to disk with the :meth:`save` method. | |
""" | |
def __init__(self, rows, info): | |
""" | |
.. note :: | |
The constructor is not public. Please do not call it. | |
""" | |
self.rows = rows | |
self.info = info | |
def save(self, file): | |
"""Save the image to *file*. If *file* looks like an open file | |
descriptor then it is used, otherwise it is treated as a | |
filename and a fresh file is opened. | |
In general, you can only call this method once; after it has | |
been called the first time and the PNG image has been saved, the | |
source data will have been streamed, and cannot be streamed | |
again. | |
""" | |
w = Writer(**self.info) | |
try: | |
file.write | |
def close(): pass | |
except AttributeError: | |
file = open(file, 'wb') | |
def close(): file.close() | |
try: | |
w.write(file, self.rows) | |
finally: | |
close() | |
class _readable: | |
""" | |
A simple file-like interface for strings and arrays. | |
""" | |
def __init__(self, buf): | |
self.buf = buf | |
self.offset = 0 | |
def read(self, n): | |
r = self.buf[self.offset:self.offset+n] | |
if isarray(r): | |
r = r.tostring() | |
self.offset += n | |
return r | |
try: | |
str(b'dummy', 'ascii') | |
except TypeError: | |
as_str = str | |
else: | |
def as_str(x): | |
return str(x, 'ascii') | |
class Reader: | |
""" | |
PNG decoder in pure Python. | |
""" | |
def __init__(self, _guess=None, **kw): | |
""" | |
Create a PNG decoder object. | |
The constructor expects exactly one keyword argument. If you | |
supply a positional argument instead, it will guess the input | |
type. You can choose among the following keyword arguments: | |
filename | |
Name of input file (a PNG file). | |
file | |
A file-like object (object with a read() method). | |
bytes | |
``array`` or ``string`` with PNG data. | |
""" | |
if ((_guess is not None and len(kw) != 0) or | |
(_guess is None and len(kw) != 1)): | |
raise TypeError("Reader() takes exactly 1 argument") | |
# Will be the first 8 bytes, later on. See validate_signature. | |
self.signature = None | |
self.transparent = None | |
# A pair of (len,type) if a chunk has been read but its data and | |
# checksum have not (in other words the file position is just | |
# past the 4 bytes that specify the chunk type). See preamble | |
# method for how this is used. | |
self.atchunk = None | |
if _guess is not None: | |
if isarray(_guess): | |
kw["bytes"] = _guess | |
elif isinstance(_guess, str): | |
kw["filename"] = _guess | |
elif hasattr(_guess, 'read'): | |
kw["file"] = _guess | |
if "filename" in kw: | |
self.file = open(kw["filename"], "rb") | |
elif "file" in kw: | |
self.file = kw["file"] | |
elif "bytes" in kw: | |
self.file = _readable(kw["bytes"]) | |
else: | |
raise TypeError("expecting filename, file or bytes array") | |
def chunk(self, seek=None, lenient=False): | |
""" | |
Read the next PNG chunk from the input file; returns a | |
(*type*, *data*) tuple. *type* is the chunk's type as a | |
byte string (all PNG chunk types are 4 bytes long). | |
*data* is the chunk's data content, as a byte string. | |
If the optional `seek` argument is | |
specified then it will keep reading chunks until it either runs | |
out of file or finds the type specified by the argument. Note | |
that in general the order of chunks in PNGs is unspecified, so | |
using `seek` can cause you to miss chunks. | |
If the optional `lenient` argument evaluates to `True`, | |
checksum failures will raise warnings rather than exceptions. | |
""" | |
self.validate_signature() | |
while True: | |
# http://www.w3.org/TR/PNG/#5Chunk-layout | |
if not self.atchunk: | |
self.atchunk = self.chunklentype() | |
length, type = self.atchunk | |
self.atchunk = None | |
data = self.file.read(length) | |
if len(data) != length: | |
raise ChunkError('Chunk %s too short for required %i octets.' | |
% (type, length)) | |
checksum = self.file.read(4) | |
if len(checksum) != 4: | |
raise ChunkError('Chunk %s too short for checksum.' % type) | |
if seek and type != seek: | |
continue | |
verify = zlib.crc32(type) | |
verify = zlib.crc32(data, verify) | |
# Whether the output from zlib.crc32 is signed or not varies | |
# according to hideous implementation details, see | |
# http://bugs.python.org/issue1202 . | |
# We coerce it to be positive here (in a way which works on | |
# Python 2.3 and older). | |
verify &= 2**32 - 1 | |
verify = struct.pack('!I', verify) | |
if checksum != verify: | |
(a, ) = struct.unpack('!I', checksum) | |
(b, ) = struct.unpack('!I', verify) | |
message = "Checksum error in %s chunk: 0x%08X != 0x%08X." % (type, a, b) | |
if lenient: | |
warnings.warn(message, RuntimeWarning) | |
else: | |
raise ChunkError(message) | |
return type, data | |
def chunks(self): | |
"""Return an iterator that will yield each chunk as a | |
(*chunktype*, *content*) pair. | |
""" | |
while True: | |
t,v = self.chunk() | |
yield t,v | |
if t == b'IEND': | |
break | |
def undo_filter(self, filter_type, scanline, previous): | |
"""Undo the filter for a scanline. `scanline` is a sequence of | |
bytes that does not include the initial filter type byte. | |
`previous` is decoded previous scanline (for straightlaced | |
images this is the previous pixel row, but for interlaced | |
images, it is the previous scanline in the reduced image, which | |
in general is not the previous pixel row in the final image). | |
When there is no previous scanline (the first row of a | |
straightlaced image, or the first row in one of the passes in an | |
interlaced image), then this argument should be ``None``. | |
The scanline will have the effects of filtering removed, and the | |
result will be returned as a fresh sequence of bytes. | |
""" | |
# :todo: Would it be better to update scanline in place? | |
# Yes, with the Cython extension making the undo_filter fast, | |
# updating scanline inplace makes the code 3 times faster | |
# (reading 50 images of 800x800 went from 40s to 16s) | |
result = scanline | |
if filter_type == 0: | |
return result | |
if filter_type not in (1,2,3,4): | |
raise FormatError('Invalid PNG Filter Type.' | |
' See http://www.w3.org/TR/2003/REC-PNG-20031110/#9Filters .') | |
# Filter unit. The stride from one pixel to the corresponding | |
# byte from the previous pixel. Normally this is the pixel | |
# size in bytes, but when this is smaller than 1, the previous | |
# byte is used instead. | |
fu = max(1, self.psize) | |
# For the first line of a pass, synthesize a dummy previous | |
# line. An alternative approach would be to observe that on the | |
# first line 'up' is the same as 'null', 'paeth' is the same | |
# as 'sub', with only 'average' requiring any special case. | |
if not previous: | |
previous = array('B', [0]*len(scanline)) | |
def sub(): | |
"""Undo sub filter.""" | |
ai = 0 | |
# Loop starts at index fu. Observe that the initial part | |
# of the result is already filled in correctly with | |
# scanline. | |
for i in range(fu, len(result)): | |
x = scanline[i] | |
a = result[ai] | |
result[i] = (x + a) & 0xff | |
ai += 1 | |
def up(): | |
"""Undo up filter.""" | |
for i in range(len(result)): | |
x = scanline[i] | |
b = previous[i] | |
result[i] = (x + b) & 0xff | |
def average(): | |
"""Undo average filter.""" | |
ai = -fu | |
for i in range(len(result)): | |
x = scanline[i] | |
if ai < 0: | |
a = 0 | |
else: | |
a = result[ai] | |
b = previous[i] | |
result[i] = (x + ((a + b) >> 1)) & 0xff | |
ai += 1 | |
def paeth(): | |
"""Undo Paeth filter.""" | |
# Also used for ci. | |
ai = -fu | |
for i in range(len(result)): | |
x = scanline[i] | |
if ai < 0: | |
a = c = 0 | |
else: | |
a = result[ai] | |
c = previous[ai] | |
b = previous[i] | |
p = a + b - c | |
pa = abs(p - a) | |
pb = abs(p - b) | |
pc = abs(p - c) | |
if pa <= pb and pa <= pc: | |
pr = a | |
elif pb <= pc: | |
pr = b | |
else: | |
pr = c | |
result[i] = (x + pr) & 0xff | |
ai += 1 | |
# Call appropriate filter algorithm. Note that 0 has already | |
# been dealt with. | |
(None, | |
pngfilters.undo_filter_sub, | |
pngfilters.undo_filter_up, | |
pngfilters.undo_filter_average, | |
pngfilters.undo_filter_paeth)[filter_type](fu, scanline, previous, result) | |
return result | |
def deinterlace(self, raw): | |
""" | |
Read raw pixel data, undo filters, deinterlace, and flatten. | |
Return in flat row flat pixel format. | |
""" | |
# Values per row (of the target image) | |
vpr = self.width * self.planes | |
# Make a result array, and make it big enough. Interleaving | |
# writes to the output array randomly (well, not quite), so the | |
# entire output array must be in memory. | |
fmt = 'BH'[self.bitdepth > 8] | |
a = array(fmt, [0]*vpr*self.height) | |
source_offset = 0 | |
for xstart, ystart, xstep, ystep in _adam7: | |
if xstart >= self.width: | |
continue | |
# The previous (reconstructed) scanline. None at the | |
# beginning of a pass to indicate that there is no previous | |
# line. | |
recon = None | |
# Pixels per row (reduced pass image) | |
ppr = int(math.ceil((self.width-xstart)/float(xstep))) | |
# Row size in bytes for this pass. | |
row_size = int(math.ceil(self.psize * ppr)) | |
for y in range(ystart, self.height, ystep): | |
filter_type = raw[source_offset] | |
source_offset += 1 | |
scanline = raw[source_offset:source_offset+row_size] | |
source_offset += row_size | |
recon = self.undo_filter(filter_type, scanline, recon) | |
# Convert so that there is one element per pixel value | |
flat = self.serialtoflat(recon, ppr) | |
if xstep == 1: | |
assert xstart == 0 | |
offset = y * vpr | |
a[offset:offset+vpr] = flat | |
else: | |
offset = y * vpr + xstart * self.planes | |
end_offset = (y+1) * vpr | |
skip = self.planes * xstep | |
for i in range(self.planes): | |
a[offset+i:end_offset:skip] = \ | |
flat[i::self.planes] | |
return a | |
def iterboxed(self, rows): | |
"""Iterator that yields each scanline in boxed row flat pixel | |
format. `rows` should be an iterator that yields the bytes of | |
each row in turn. | |
""" | |
def asvalues(raw): | |
"""Convert a row of raw bytes into a flat row. Result will | |
be a freshly allocated object, not shared with | |
argument. | |
""" | |
if self.bitdepth == 8: | |
return array('B', raw) | |
if self.bitdepth == 16: | |
raw = tostring(raw) | |
return array('H', struct.unpack('!%dH' % (len(raw)//2), raw)) | |
assert self.bitdepth < 8 | |
width = self.width | |
# Samples per byte | |
spb = 8//self.bitdepth | |
out = array('B') | |
mask = 2**self.bitdepth - 1 | |
shifts = [self.bitdepth * i | |
for i in reversed(list(range(spb)))] | |
for o in raw: | |
out.extend([mask&(o>>i) for i in shifts]) | |
return out[:width] | |
return map(asvalues, rows) | |
def serialtoflat(self, bytes, width=None): | |
"""Convert serial format (byte stream) pixel data to flat row | |
flat pixel. | |
""" | |
if self.bitdepth == 8: | |
return bytes | |
if self.bitdepth == 16: | |
bytes = tostring(bytes) | |
return array('H', | |
struct.unpack('!%dH' % (len(bytes)//2), bytes)) | |
assert self.bitdepth < 8 | |
if width is None: | |
width = self.width | |
# Samples per byte | |
spb = 8//self.bitdepth | |
out = array('B') | |
mask = 2**self.bitdepth - 1 | |
shifts = list(map(self.bitdepth.__mul__, reversed(list(range(spb))))) | |
l = width | |
for o in bytes: | |
out.extend([(mask&(o>>s)) for s in shifts][:l]) | |
l -= spb | |
if l <= 0: | |
l = width | |
return out | |
def iterstraight(self, raw): | |
"""Iterator that undoes the effect of filtering, and yields | |
each row in serialised format (as a sequence of bytes). | |
Assumes input is straightlaced. `raw` should be an iterable | |
that yields the raw bytes in chunks of arbitrary size. | |
""" | |
# length of row, in bytes | |
rb = self.row_bytes | |
a = array('B') | |
# The previous (reconstructed) scanline. None indicates first | |
# line of image. | |
recon = None | |
for some in raw: | |
a.extend(some) | |
while len(a) >= rb + 1: | |
filter_type = a[0] | |
scanline = a[1:rb+1] | |
del a[:rb+1] | |
recon = self.undo_filter(filter_type, scanline, recon) | |
yield recon | |
if len(a) != 0: | |
# :file:format We get here with a file format error: | |
# when the available bytes (after decompressing) do not | |
# pack into exact rows. | |
raise FormatError( | |
'Wrong size for decompressed IDAT chunk.') | |
assert len(a) == 0 | |
def validate_signature(self): | |
"""If signature (header) has not been read then read and | |
validate it; otherwise do nothing. | |
""" | |
if self.signature: | |
return | |
self.signature = self.file.read(8) | |
if self.signature != _signature: | |
raise FormatError("PNG file has invalid signature.") | |
def preamble(self, lenient=False): | |
""" | |
Extract the image metadata by reading the initial part of | |
the PNG file up to the start of the ``IDAT`` chunk. All the | |
chunks that precede the ``IDAT`` chunk are read and either | |
processed for metadata or discarded. | |
If the optional `lenient` argument evaluates to `True`, checksum | |
failures will raise warnings rather than exceptions. | |
""" | |
self.validate_signature() | |
while True: | |
if not self.atchunk: | |
self.atchunk = self.chunklentype() | |
if self.atchunk is None: | |
raise FormatError( | |
'This PNG file has no IDAT chunks.') | |
if self.atchunk[1] == b'IDAT': | |
return | |
self.process_chunk(lenient=lenient) | |
def chunklentype(self): | |
"""Reads just enough of the input to determine the next | |
chunk's length and type, returned as a (*length*, *type*) pair | |
where *type* is a string. If there are no more chunks, ``None`` | |
is returned. | |
""" | |
x = self.file.read(8) | |
if not x: | |
return None | |
if len(x) != 8: | |
raise FormatError( | |
'End of file whilst reading chunk length and type.') | |
length,type = struct.unpack('!I4s', x) | |
if length > 2**31-1: | |
raise FormatError('Chunk %s is too large: %d.' % (type,length)) | |
return length,type | |
def process_chunk(self, lenient=False): | |
"""Process the next chunk and its data. This only processes the | |
following chunk types, all others are ignored: ``IHDR``, | |
``PLTE``, ``bKGD``, ``tRNS``, ``gAMA``, ``sBIT``, ``pHYs``. | |
If the optional `lenient` argument evaluates to `True`, | |
checksum failures will raise warnings rather than exceptions. | |
""" | |
type, data = self.chunk(lenient=lenient) | |
method = '_process_' + as_str(type) | |
m = getattr(self, method, None) | |
if m: | |
m(data) | |
def _process_IHDR(self, data): | |
# http://www.w3.org/TR/PNG/#11IHDR | |
if len(data) != 13: | |
raise FormatError('IHDR chunk has incorrect length.') | |
(self.width, self.height, self.bitdepth, self.color_type, | |
self.compression, self.filter, | |
self.interlace) = struct.unpack("!2I5B", data) | |
check_bitdepth_colortype(self.bitdepth, self.color_type) | |
if self.compression != 0: | |
raise Error("unknown compression method %d" % self.compression) | |
if self.filter != 0: | |
raise FormatError("Unknown filter method %d," | |
" see http://www.w3.org/TR/2003/REC-PNG-20031110/#9Filters ." | |
% self.filter) | |
if self.interlace not in (0,1): | |
raise FormatError("Unknown interlace method %d," | |
" see http://www.w3.org/TR/2003/REC-PNG-20031110/#8InterlaceMethods ." | |
% self.interlace) | |
# Derived values | |
# http://www.w3.org/TR/PNG/#6Colour-values | |
colormap = bool(self.color_type & 1) | |
greyscale = not (self.color_type & 2) | |
alpha = bool(self.color_type & 4) | |
color_planes = (3,1)[greyscale or colormap] | |
planes = color_planes + alpha | |
self.colormap = colormap | |
self.greyscale = greyscale | |
self.alpha = alpha | |
self.color_planes = color_planes | |
self.planes = planes | |
self.psize = float(self.bitdepth)/float(8) * planes | |
if int(self.psize) == self.psize: | |
self.psize = int(self.psize) | |
self.row_bytes = int(math.ceil(self.width * self.psize)) | |
# Stores PLTE chunk if present, and is used to check | |
# chunk ordering constraints. | |
self.plte = None | |
# Stores tRNS chunk if present, and is used to check chunk | |
# ordering constraints. | |
self.trns = None | |
# Stores sbit chunk if present. | |
self.sbit = None | |
def _process_PLTE(self, data): | |
# http://www.w3.org/TR/PNG/#11PLTE | |
if self.plte: | |
warnings.warn("Multiple PLTE chunks present.") | |
self.plte = data | |
if len(data) % 3 != 0: | |
raise FormatError( | |
"PLTE chunk's length should be a multiple of 3.") | |
if len(data) > (2**self.bitdepth)*3: | |
raise FormatError("PLTE chunk is too long.") | |
if len(data) == 0: | |
raise FormatError("Empty PLTE is not allowed.") | |
def _process_bKGD(self, data): | |
try: | |
if self.colormap: | |
if not self.plte: | |
warnings.warn( | |
"PLTE chunk is required before bKGD chunk.") | |
self.background = struct.unpack('B', data) | |
else: | |
self.background = struct.unpack("!%dH" % self.color_planes, | |
data) | |
except struct.error: | |
raise FormatError("bKGD chunk has incorrect length.") | |
def _process_tRNS(self, data): | |
# http://www.w3.org/TR/PNG/#11tRNS | |
self.trns = data | |
if self.colormap: | |
if not self.plte: | |
warnings.warn("PLTE chunk is required before tRNS chunk.") | |
else: | |
if len(data) > len(self.plte)/3: | |
# Was warning, but promoted to Error as it | |
# would otherwise cause pain later on. | |
raise FormatError("tRNS chunk is too long.") | |
else: | |
if self.alpha: | |
raise FormatError( | |
"tRNS chunk is not valid with colour type %d." % | |
self.color_type) | |
try: | |
self.transparent = \ | |
struct.unpack("!%dH" % self.color_planes, data) | |
except struct.error: | |
raise FormatError("tRNS chunk has incorrect length.") | |
def _process_gAMA(self, data): | |
try: | |
self.gamma = struct.unpack("!L", data)[0] / 100000.0 | |
except struct.error: | |
raise FormatError("gAMA chunk has incorrect length.") | |
def _process_sBIT(self, data): | |
self.sbit = data | |
if (self.colormap and len(data) != 3 or | |
not self.colormap and len(data) != self.planes): | |
raise FormatError("sBIT chunk has incorrect length.") | |
def _process_pHYs(self, data): | |
# http://www.w3.org/TR/PNG/#11pHYs | |
self.phys = data | |
fmt = "!LLB" | |
if len(data) != struct.calcsize(fmt): | |
raise FormatError("pHYs chunk has incorrect length.") | |
self.x_pixels_per_unit, self.y_pixels_per_unit, unit = struct.unpack(fmt,data) | |
self.unit_is_meter = bool(unit) | |
def read(self, lenient=False): | |
""" | |
Read the PNG file and decode it. Returns (`width`, `height`, | |
`pixels`, `metadata`). | |
May use excessive memory. | |
`pixels` are returned in boxed row flat pixel format. | |
If the optional `lenient` argument evaluates to True, | |
checksum failures will raise warnings rather than exceptions. | |
""" | |
def iteridat(): | |
"""Iterator that yields all the ``IDAT`` chunks as strings.""" | |
while True: | |
try: | |
type, data = self.chunk(lenient=lenient) | |
except ValueError as e: | |
raise ChunkError(e.args[0]) | |
if type == b'IEND': | |
# http://www.w3.org/TR/PNG/#11IEND | |
break | |
if type != b'IDAT': | |
continue | |
# type == b'IDAT' | |
# http://www.w3.org/TR/PNG/#11IDAT | |
if self.colormap and not self.plte: | |
warnings.warn("PLTE chunk is required before IDAT chunk") | |
yield data | |
def iterdecomp(idat): | |
"""Iterator that yields decompressed strings. `idat` should | |
be an iterator that yields the ``IDAT`` chunk data. | |
""" | |
# Currently, with no max_length parameter to decompress, | |
# this routine will do one yield per IDAT chunk: Not very | |
# incremental. | |
d = zlib.decompressobj() | |
# Each IDAT chunk is passed to the decompressor, then any | |
# remaining state is decompressed out. | |
for data in idat: | |
# :todo: add a max_length argument here to limit output | |
# size. | |
yield array('B', d.decompress(data)) | |
yield array('B', d.flush()) | |
self.preamble(lenient=lenient) | |
raw = iterdecomp(iteridat()) | |
if self.interlace: | |
raw = array('B', itertools.chain(*raw)) | |
arraycode = 'BH'[self.bitdepth>8] | |
# Like :meth:`group` but producing an array.array object for | |
# each row. | |
pixels = map(lambda *row: array(arraycode, row), | |
*[iter(self.deinterlace(raw))]*self.width*self.planes) | |
else: | |
pixels = self.iterboxed(self.iterstraight(raw)) | |
meta = dict() | |
for attr in 'greyscale alpha planes bitdepth interlace'.split(): | |
meta[attr] = getattr(self, attr) | |
meta['size'] = (self.width, self.height) | |
for attr in 'gamma transparent background'.split(): | |
a = getattr(self, attr, None) | |
if a is not None: | |
meta[attr] = a | |
if self.plte: | |
meta['palette'] = self.palette() | |
return self.width, self.height, pixels, meta | |
def read_flat(self): | |
""" | |
Read a PNG file and decode it into flat row flat pixel format. | |
Returns (*width*, *height*, *pixels*, *metadata*). | |
May use excessive memory. | |
`pixels` are returned in flat row flat pixel format. | |
See also the :meth:`read` method which returns pixels in the | |
more stream-friendly boxed row flat pixel format. | |
""" | |
x, y, pixel, meta = self.read() | |
arraycode = 'BH'[meta['bitdepth']>8] | |
pixel = array(arraycode, itertools.chain(*pixel)) | |
return x, y, pixel, meta | |
def palette(self, alpha='natural'): | |
"""Returns a palette that is a sequence of 3-tuples or 4-tuples, | |
synthesizing it from the ``PLTE`` and ``tRNS`` chunks. These | |
chunks should have already been processed (for example, by | |
calling the :meth:`preamble` method). All the tuples are the | |
same size: 3-tuples if there is no ``tRNS`` chunk, 4-tuples when | |
there is a ``tRNS`` chunk. Assumes that the image is colour type | |
3 and therefore a ``PLTE`` chunk is required. | |
If the `alpha` argument is ``'force'`` then an alpha channel is | |
always added, forcing the result to be a sequence of 4-tuples. | |
""" | |
if not self.plte: | |
raise FormatError( | |
"Required PLTE chunk is missing in colour type 3 image.") | |
plte = group(array('B', self.plte), 3) | |
if self.trns or alpha == 'force': | |
trns = array('B', self.trns or []) | |
trns.extend([255]*(len(plte)-len(trns))) | |
plte = list(map(operator.add, plte, group(trns, 1))) | |
return plte | |
def asDirect(self): | |
"""Returns the image data as a direct representation of an | |
``x * y * planes`` array. This method is intended to remove the | |
need for callers to deal with palettes and transparency | |
themselves. Images with a palette (colour type 3) | |
are converted to RGB or RGBA; images with transparency (a | |
``tRNS`` chunk) are converted to LA or RGBA as appropriate. | |
When returned in this format the pixel values represent the | |
colour value directly without needing to refer to palettes or | |
transparency information. | |
Like the :meth:`read` method this method returns a 4-tuple: | |
(*width*, *height*, *pixels*, *meta*) | |
This method normally returns pixel values with the bit depth | |
they have in the source image, but when the source PNG has an | |
``sBIT`` chunk it is inspected and can reduce the bit depth of | |
the result pixels; pixel values will be reduced according to | |
the bit depth specified in the ``sBIT`` chunk (PNG nerds should | |
note a single result bit depth is used for all channels; the | |
maximum of the ones specified in the ``sBIT`` chunk. An RGB565 | |
image will be rescaled to 6-bit RGB666). | |
The *meta* dictionary that is returned reflects the `direct` | |
format and not the original source image. For example, an RGB | |
source image with a ``tRNS`` chunk to represent a transparent | |
colour, will have ``planes=3`` and ``alpha=False`` for the | |
source image, but the *meta* dictionary returned by this method | |
will have ``planes=4`` and ``alpha=True`` because an alpha | |
channel is synthesized and added. | |
*pixels* is the pixel data in boxed row flat pixel format (just | |
like the :meth:`read` method). | |
All the other aspects of the image data are not changed. | |
""" | |
self.preamble() | |
# Simple case, no conversion necessary. | |
if not self.colormap and not self.trns and not self.sbit: | |
return self.read() | |
x,y,pixels,meta = self.read() | |
if self.colormap: | |
meta['colormap'] = False | |
meta['alpha'] = bool(self.trns) | |
meta['bitdepth'] = 8 | |
meta['planes'] = 3 + bool(self.trns) | |
plte = self.palette() | |
def iterpal(pixels): | |
for row in pixels: | |
row = [plte[x] for x in row] | |
yield array('B', itertools.chain(*row)) | |
pixels = iterpal(pixels) | |
elif self.trns: | |
# It would be nice if there was some reasonable way | |
# of doing this without generating a whole load of | |
# intermediate tuples. But tuples does seem like the | |
# easiest way, with no other way clearly much simpler or | |
# much faster. (Actually, the L to LA conversion could | |
# perhaps go faster (all those 1-tuples!), but I still | |
# wonder whether the code proliferation is worth it) | |
it = self.transparent | |
maxval = 2**meta['bitdepth']-1 | |
planes = meta['planes'] | |
meta['alpha'] = True | |
meta['planes'] += 1 | |
typecode = 'BH'[meta['bitdepth']>8] | |
def itertrns(pixels): | |
for row in pixels: | |
# For each row we group it into pixels, then form a | |
# characterisation vector that says whether each | |
# pixel is opaque or not. Then we convert | |
# True/False to 0/maxval (by multiplication), | |
# and add it as the extra channel. | |
row = group(row, planes) | |
opa = map(it.__ne__, row) | |
opa = map(maxval.__mul__, opa) | |
opa = list(zip(opa)) # convert to 1-tuples | |
yield array(typecode, | |
itertools.chain(*map(operator.add, row, opa))) | |
pixels = itertrns(pixels) | |
targetbitdepth = None | |
if self.sbit: | |
sbit = struct.unpack('%dB' % len(self.sbit), self.sbit) | |
targetbitdepth = max(sbit) | |
if targetbitdepth > meta['bitdepth']: | |
raise Error('sBIT chunk %r exceeds bitdepth %d' % | |
(sbit,self.bitdepth)) | |
if min(sbit) <= 0: | |
raise Error('sBIT chunk %r has a 0-entry' % sbit) | |
if targetbitdepth == meta['bitdepth']: | |
targetbitdepth = None | |
if targetbitdepth: | |
shift = meta['bitdepth'] - targetbitdepth | |
meta['bitdepth'] = targetbitdepth | |
def itershift(pixels): | |
for row in pixels: | |
yield [p >> shift for p in row] | |
pixels = itershift(pixels) | |
return x,y,pixels,meta | |
def asFloat(self, maxval=1.0): | |
"""Return image pixels as per :meth:`asDirect` method, but scale | |
all pixel values to be floating point values between 0.0 and | |
*maxval*. | |
""" | |
x,y,pixels,info = self.asDirect() | |
sourcemaxval = 2**info['bitdepth']-1 | |
del info['bitdepth'] | |
info['maxval'] = float(maxval) | |
factor = float(maxval)/float(sourcemaxval) | |
def iterfloat(): | |
for row in pixels: | |
yield [factor * p for p in row] | |
return x,y,iterfloat(),info | |
def _as_rescale(self, get, targetbitdepth): | |
"""Helper used by :meth:`asRGB8` and :meth:`asRGBA8`.""" | |
width,height,pixels,meta = get() | |
maxval = 2**meta['bitdepth'] - 1 | |
targetmaxval = 2**targetbitdepth - 1 | |
factor = float(targetmaxval) / float(maxval) | |
meta['bitdepth'] = targetbitdepth | |
def iterscale(): | |
for row in pixels: | |
yield [int(round(x*factor)) for x in row] | |
if maxval == targetmaxval: | |
return width, height, pixels, meta | |
else: | |
return width, height, iterscale(), meta | |
def asRGB8(self): | |
"""Return the image data as an RGB pixels with 8-bits per | |
sample. This is like the :meth:`asRGB` method except that | |
this method additionally rescales the values so that they | |
are all between 0 and 255 (8-bit). In the case where the | |
source image has a bit depth < 8 the transformation preserves | |
all the information; where the source image has bit depth | |
> 8, then rescaling to 8-bit values loses precision. No | |
dithering is performed. Like :meth:`asRGB`, an alpha channel | |
in the source image will raise an exception. | |
This function returns a 4-tuple: | |
(*width*, *height*, *pixels*, *metadata*). | |
*width*, *height*, *metadata* are as per the | |
:meth:`read` method. | |
*pixels* is the pixel data in boxed row flat pixel format. | |
""" | |
return self._as_rescale(self.asRGB, 8) | |
def asRGBA8(self): | |
"""Return the image data as RGBA pixels with 8-bits per | |
sample. This method is similar to :meth:`asRGB8` and | |
:meth:`asRGBA`: The result pixels have an alpha channel, *and* | |
values are rescaled to the range 0 to 255. The alpha channel is | |
synthesized if necessary (with a small speed penalty). | |
""" | |
return self._as_rescale(self.asRGBA, 8) | |
def asRGB(self): | |
"""Return image as RGB pixels. RGB colour images are passed | |
through unchanged; greyscales are expanded into RGB | |
triplets (there is a small speed overhead for doing this). | |
An alpha channel in the source image will raise an | |
exception. | |
The return values are as for the :meth:`read` method | |
except that the *metadata* reflect the returned pixels, not the | |
source image. In particular, for this method | |
``metadata['greyscale']`` will be ``False``. | |
""" | |
width,height,pixels,meta = self.asDirect() | |
if meta['alpha']: | |
raise Error("will not convert image with alpha channel to RGB") | |
if not meta['greyscale']: | |
return width,height,pixels,meta | |
meta['greyscale'] = False | |
typecode = 'BH'[meta['bitdepth'] > 8] | |
def iterrgb(): | |
for row in pixels: | |
a = array(typecode, [0]) * 3 * width | |
for i in range(3): | |
a[i::3] = row | |
yield a | |
return width,height,iterrgb(),meta | |
def asRGBA(self): | |
"""Return image as RGBA pixels. Greyscales are expanded into | |
RGB triplets; an alpha channel is synthesized if necessary. | |
The return values are as for the :meth:`read` method | |
except that the *metadata* reflect the returned pixels, not the | |
source image. In particular, for this method | |
``metadata['greyscale']`` will be ``False``, and | |
``metadata['alpha']`` will be ``True``. | |
""" | |
width,height,pixels,meta = self.asDirect() | |
if meta['alpha'] and not meta['greyscale']: | |
return width,height,pixels,meta | |
typecode = 'BH'[meta['bitdepth'] > 8] | |
maxval = 2**meta['bitdepth'] - 1 | |
maxbuffer = struct.pack('=' + typecode, maxval) * 4 * width | |
def newarray(): | |
return array(typecode, maxbuffer) | |
if meta['alpha'] and meta['greyscale']: | |
# LA to RGBA | |
def convert(): | |
for row in pixels: | |
# Create a fresh target row, then copy L channel | |
# into first three target channels, and A channel | |
# into fourth channel. | |
a = newarray() | |
pngfilters.convert_la_to_rgba(row, a) | |
yield a | |
elif meta['greyscale']: | |
# L to RGBA | |
def convert(): | |
for row in pixels: | |
a = newarray() | |
pngfilters.convert_l_to_rgba(row, a) | |
yield a | |
else: | |
assert not meta['alpha'] and not meta['greyscale'] | |
# RGB to RGBA | |
def convert(): | |
for row in pixels: | |
a = newarray() | |
pngfilters.convert_rgb_to_rgba(row, a) | |
yield a | |
meta['alpha'] = True | |
meta['greyscale'] = False | |
return width,height,convert(),meta | |
def check_bitdepth_colortype(bitdepth, colortype): | |
"""Check that `bitdepth` and `colortype` are both valid, | |
and specified in a valid combination. Returns if valid, | |
raise an Exception if not valid. | |
""" | |
if bitdepth not in (1,2,4,8,16): | |
raise FormatError("invalid bit depth %d" % bitdepth) | |
if colortype not in (0,2,3,4,6): | |
raise FormatError("invalid colour type %d" % colortype) | |
# Check indexed (palettized) images have 8 or fewer bits | |
# per pixel; check only indexed or greyscale images have | |
# fewer than 8 bits per pixel. | |
if colortype & 1 and bitdepth > 8: | |
raise FormatError( | |
"Indexed images (colour type %d) cannot" | |
" have bitdepth > 8 (bit depth %d)." | |
" See http://www.w3.org/TR/2003/REC-PNG-20031110/#table111 ." | |
% (bitdepth, colortype)) | |
if bitdepth < 8 and colortype not in (0,3): | |
raise FormatError("Illegal combination of bit depth (%d)" | |
" and colour type (%d)." | |
" See http://www.w3.org/TR/2003/REC-PNG-20031110/#table111 ." | |
% (bitdepth, colortype)) | |
def isinteger(x): | |
try: | |
return int(x) == x | |
except (TypeError, ValueError): | |
return False | |
# === Support for users without Cython === | |
try: | |
pngfilters | |
except NameError: | |
class pngfilters(object): | |
def undo_filter_sub(filter_unit, scanline, previous, result): | |
"""Undo sub filter.""" | |
ai = 0 | |
# Loops starts at index fu. Observe that the initial part | |
# of the result is already filled in correctly with | |
# scanline. | |
for i in range(filter_unit, len(result)): | |
x = scanline[i] | |
a = result[ai] | |
result[i] = (x + a) & 0xff | |
ai += 1 | |
undo_filter_sub = staticmethod(undo_filter_sub) | |
def undo_filter_up(filter_unit, scanline, previous, result): | |
"""Undo up filter.""" | |
for i in range(len(result)): | |
x = scanline[i] | |
b = previous[i] | |
result[i] = (x + b) & 0xff | |
undo_filter_up = staticmethod(undo_filter_up) | |
def undo_filter_average(filter_unit, scanline, previous, result): | |
"""Undo up filter.""" | |
ai = -filter_unit | |
for i in range(len(result)): | |
x = scanline[i] | |
if ai < 0: | |
a = 0 | |
else: | |
a = result[ai] | |
b = previous[i] | |
result[i] = (x + ((a + b) >> 1)) & 0xff | |
ai += 1 | |
undo_filter_average = staticmethod(undo_filter_average) | |
def undo_filter_paeth(filter_unit, scanline, previous, result): | |
"""Undo Paeth filter.""" | |
# Also used for ci. | |
ai = -filter_unit | |
for i in range(len(result)): | |
x = scanline[i] | |
if ai < 0: | |
a = c = 0 | |
else: | |
a = result[ai] | |
c = previous[ai] | |
b = previous[i] | |
p = a + b - c | |
pa = abs(p - a) | |
pb = abs(p - b) | |
pc = abs(p - c) | |
if pa <= pb and pa <= pc: | |
pr = a | |
elif pb <= pc: | |
pr = b | |
else: | |
pr = c | |
result[i] = (x + pr) & 0xff | |
ai += 1 | |
undo_filter_paeth = staticmethod(undo_filter_paeth) | |
def convert_la_to_rgba(row, result): | |
for i in range(3): | |
result[i::4] = row[0::2] | |
result[3::4] = row[1::2] | |
convert_la_to_rgba = staticmethod(convert_la_to_rgba) | |
def convert_l_to_rgba(row, result): | |
"""Convert a grayscale image to RGBA. This method assumes | |
the alpha channel in result is already correctly | |
initialized. | |
""" | |
for i in range(3): | |
result[i::4] = row | |
convert_l_to_rgba = staticmethod(convert_l_to_rgba) | |
def convert_rgb_to_rgba(row, result): | |
"""Convert an RGB image to RGBA. This method assumes the | |
alpha channel in result is already correctly initialized. | |
""" | |
for i in range(3): | |
result[i::4] = row[i::3] | |
convert_rgb_to_rgba = staticmethod(convert_rgb_to_rgba) | |
# === Command Line Support === | |
def read_pam_header(infile): | |
""" | |
Read (the rest of a) PAM header. `infile` should be positioned | |
immediately after the initial 'P7' line (at the beginning of the | |
second line). Returns are as for `read_pnm_header`. | |
""" | |
# Unlike PBM, PGM, and PPM, we can read the header a line at a time. | |
header = dict() | |
while True: | |
l = infile.readline().strip() | |
if l == b'ENDHDR': | |
break | |
if not l: | |
raise EOFError('PAM ended prematurely') | |
if l[0] == b'#': | |
continue | |
l = l.split(None, 1) | |
if l[0] not in header: | |
header[l[0]] = l[1] | |
else: | |
header[l[0]] += b' ' + l[1] | |
required = [b'WIDTH', b'HEIGHT', b'DEPTH', b'MAXVAL'] | |
WIDTH,HEIGHT,DEPTH,MAXVAL = required | |
present = [x for x in required if x in header] | |
if len(present) != len(required): | |
raise Error('PAM file must specify WIDTH, HEIGHT, DEPTH, and MAXVAL') | |
width = int(header[WIDTH]) | |
height = int(header[HEIGHT]) | |
depth = int(header[DEPTH]) | |
maxval = int(header[MAXVAL]) | |
if (width <= 0 or | |
height <= 0 or | |
depth <= 0 or | |
maxval <= 0): | |
raise Error( | |
'WIDTH, HEIGHT, DEPTH, MAXVAL must all be positive integers') | |
return 'P7', width, height, depth, maxval | |
def read_pnm_header(infile, supported=(b'P5', b'P6')): | |
""" | |
Read a PNM header, returning (format,width,height,depth,maxval). | |
`width` and `height` are in pixels. `depth` is the number of | |
channels in the image; for PBM and PGM it is synthesized as 1, for | |
PPM as 3; for PAM images it is read from the header. `maxval` is | |
synthesized (as 1) for PBM images. | |
""" | |
# Generally, see http://netpbm.sourceforge.net/doc/ppm.html | |
# and http://netpbm.sourceforge.net/doc/pam.html | |
# Technically 'P7' must be followed by a newline, so by using | |
# rstrip() we are being liberal in what we accept. I think this | |
# is acceptable. | |
type = infile.read(3).rstrip() | |
if type not in supported: | |
raise NotImplementedError('file format %s not supported' % type) | |
if type == b'P7': | |
# PAM header parsing is completely different. | |
return read_pam_header(infile) | |
# Expected number of tokens in header (3 for P4, 4 for P6) | |
expected = 4 | |
pbm = (b'P1', b'P4') | |
if type in pbm: | |
expected = 3 | |
header = [type] | |
# We have to read the rest of the header byte by byte because the | |
# final whitespace character (immediately following the MAXVAL in | |
# the case of P6) may not be a newline. Of course all PNM files in | |
# the wild use a newline at this point, so it's tempting to use | |
# readline; but it would be wrong. | |
def getc(): | |
c = infile.read(1) | |
if not c: | |
raise Error('premature EOF reading PNM header') | |
return c | |
c = getc() | |
while True: | |
# Skip whitespace that precedes a token. | |
while c.isspace(): | |
c = getc() | |
# Skip comments. | |
while c == '#': | |
while c not in b'\n\r': | |
c = getc() | |
if not c.isdigit(): | |
raise Error('unexpected character %s found in header' % c) | |
# According to the specification it is legal to have comments | |
# that appear in the middle of a token. | |
# This is bonkers; I've never seen it; and it's a bit awkward to | |
# code good lexers in Python (no goto). So we break on such | |
# cases. | |
token = b'' | |
while c.isdigit(): | |
token += c | |
c = getc() | |
# Slight hack. All "tokens" are decimal integers, so convert | |
# them here. | |
header.append(int(token)) | |
if len(header) == expected: | |
break | |
# Skip comments (again) | |
while c == '#': | |
while c not in '\n\r': | |
c = getc() | |
if not c.isspace(): | |
raise Error('expected header to end with whitespace, not %s' % c) | |
if type in pbm: | |
# synthesize a MAXVAL | |
header.append(1) | |
depth = (1,3)[type == b'P6'] | |
return header[0], header[1], header[2], depth, header[3] | |
def write_pnm(file, width, height, pixels, meta): | |
"""Write a Netpbm PNM/PAM file. | |
""" | |
bitdepth = meta['bitdepth'] | |
maxval = 2**bitdepth - 1 | |
# Rudely, the number of image planes can be used to determine | |
# whether we are L (PGM), LA (PAM), RGB (PPM), or RGBA (PAM). | |
planes = meta['planes'] | |
# Can be an assert as long as we assume that pixels and meta came | |
# from a PNG file. | |
assert planes in (1,2,3,4) | |
if planes in (1,3): | |
if 1 == planes: | |
# PGM | |
# Could generate PBM if maxval is 1, but we don't (for one | |
# thing, we'd have to convert the data, not just blat it | |
# out). | |
fmt = 'P5' | |
else: | |
# PPM | |
fmt = 'P6' | |
header = '%s %d %d %d\n' % (fmt, width, height, maxval) | |
if planes in (2,4): | |
# PAM | |
# See http://netpbm.sourceforge.net/doc/pam.html | |
if 2 == planes: | |
tupltype = 'GRAYSCALE_ALPHA' | |
else: | |
tupltype = 'RGB_ALPHA' | |
header = ('P7\nWIDTH %d\nHEIGHT %d\nDEPTH %d\nMAXVAL %d\n' | |
'TUPLTYPE %s\nENDHDR\n' % | |
(width, height, planes, maxval, tupltype)) | |
file.write(header.encode('ascii')) | |
# Values per row | |
vpr = planes * width | |
# struct format | |
fmt = '>%d' % vpr | |
if maxval > 0xff: | |
fmt = fmt + 'H' | |
else: | |
fmt = fmt + 'B' | |
for row in pixels: | |
file.write(struct.pack(fmt, *row)) | |
file.flush() | |
def color_triple(color): | |
""" | |
Convert a command line colour value to a RGB triple of integers. | |
FIXME: Somewhere we need support for greyscale backgrounds etc. | |
""" | |
if color.startswith('#') and len(color) == 4: | |
return (int(color[1], 16), | |
int(color[2], 16), | |
int(color[3], 16)) | |
if color.startswith('#') and len(color) == 7: | |
return (int(color[1:3], 16), | |
int(color[3:5], 16), | |
int(color[5:7], 16)) | |
elif color.startswith('#') and len(color) == 13: | |
return (int(color[1:5], 16), | |
int(color[5:9], 16), | |
int(color[9:13], 16)) | |
def _add_common_options(parser): | |
"""Call *parser.add_option* for each of the options that are | |
common between this PNG--PNM conversion tool and the gen | |
tool. | |
""" | |
parser.add_option("-i", "--interlace", | |
default=False, action="store_true", | |
help="create an interlaced PNG file (Adam7)") | |
parser.add_option("-t", "--transparent", | |
action="store", type="string", metavar="#RRGGBB", | |
help="mark the specified colour as transparent") | |
parser.add_option("-b", "--background", | |
action="store", type="string", metavar="#RRGGBB", | |
help="save the specified background colour") | |
parser.add_option("-g", "--gamma", | |
action="store", type="float", metavar="value", | |
help="save the specified gamma value") | |
parser.add_option("-c", "--compression", | |
action="store", type="int", metavar="level", | |
help="zlib compression level (0-9)") | |
return parser | |
def _main(argv): | |
""" | |
Run the PNG encoder with options from the command line. | |
""" | |
# Parse command line arguments | |
from optparse import OptionParser | |
version = '%prog ' + __version__ | |
parser = OptionParser(version=version) | |
parser.set_usage("%prog [options] [imagefile]") | |
parser.add_option('-r', '--read-png', default=False, | |
action='store_true', | |
help='Read PNG, write PNM') | |
parser.add_option("-a", "--alpha", | |
action="store", type="string", metavar="pgmfile", | |
help="alpha channel transparency (RGBA)") | |
_add_common_options(parser) | |
(options, args) = parser.parse_args(args=argv[1:]) | |
# Convert options | |
if options.transparent is not None: | |
options.transparent = color_triple(options.transparent) | |
if options.background is not None: | |
options.background = color_triple(options.background) | |
# Prepare input and output files | |
if len(args) == 0: | |
infilename = '-' | |
infile = sys.stdin | |
elif len(args) == 1: | |
infilename = args[0] | |
infile = open(infilename, 'rb') | |
else: | |
parser.error("more than one input file") | |
outfile = sys.stdout | |
if sys.platform == "win32": | |
import msvcrt, os | |
msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY) | |
if options.read_png: | |
# Encode PNG to PPM | |
png = Reader(file=infile) | |
width,height,pixels,meta = png.asDirect() | |
write_pnm(outfile, width, height, pixels, meta) | |
else: | |
# Encode PNM to PNG | |
format, width, height, depth, maxval = \ | |
read_pnm_header(infile, (b'P5',b'P6',b'P7')) | |
# When it comes to the variety of input formats, we do something | |
# rather rude. Observe that L, LA, RGB, RGBA are the 4 colour | |
# types supported by PNG and that they correspond to 1, 2, 3, 4 | |
# channels respectively. So we use the number of channels in | |
# the source image to determine which one we have. We do not | |
# care about TUPLTYPE. | |
greyscale = depth <= 2 | |
pamalpha = depth in (2,4) | |
supported = [2**x-1 for x in range(1,17)] | |
try: | |
mi = supported.index(maxval) | |
except ValueError: | |
raise NotImplementedError( | |
'your maxval (%s) not in supported list %s' % | |
(maxval, str(supported))) | |
bitdepth = mi+1 | |
writer = Writer(width, height, | |
greyscale=greyscale, | |
bitdepth=bitdepth, | |
interlace=options.interlace, | |
transparent=options.transparent, | |
background=options.background, | |
alpha=bool(pamalpha or options.alpha), | |
gamma=options.gamma, | |
compression=options.compression) | |
if options.alpha: | |
pgmfile = open(options.alpha, 'rb') | |
format, awidth, aheight, adepth, amaxval = \ | |
read_pnm_header(pgmfile, 'P5') | |
if amaxval != '255': | |
raise NotImplementedError( | |
'maxval %s not supported for alpha channel' % amaxval) | |
if (awidth, aheight) != (width, height): | |
raise ValueError("alpha channel image size mismatch" | |
" (%s has %sx%s but %s has %sx%s)" | |
% (infilename, width, height, | |
options.alpha, awidth, aheight)) | |
writer.convert_ppm_and_pgm(infile, pgmfile, outfile) | |
else: | |
writer.convert_pnm(infile, outfile) | |
if __name__ == '__main__': | |
try: | |
_main(sys.argv) | |
except Error as e: | |
print(e, file=sys.stderr) |
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