Reads a png file and convert it to planar raw byte file.

PNG to Plananr Binary

#!/usr/bin/env python

'''
Reads a png file and convert it to planar raw byte file. 

Requires Python3 and pypng.

Please use
```
#pip install pypng
```
to install the required png library.
'''

import sys
import png
import os
import itertools

if __name__ == "__main__":

    if len(sys.argv) < 2:
        print(r'usage: "py -3 png_to_channel_maps.py input.png"')

    OUTPUT_FN = r"output.bin" if len(sys.argv) < 3 else sys.argv[2]

    with open(sys.argv[1], "rb") as f:
        with open(OUTPUT_FN, "wb") as o:
            png = png.Reader(file = f)
            (width, height, frame_data, meta) = png.asRGB8()
            print("width, height = %d, %d" % (width, height))
            '''
            the format is boxed row, flat pixel
            list([ (R,G,B), (R,G,B), (R,G,B) ],
                 [ (R,G,B), (R,G,B), (R,G,B) ],
                 ...)
            '''

            # for each channel (r, g, b)
            channelNum = 3
            for c in (0, 1, 2):
                # note that frame_data is a generator -
                # so we "clone" the generator before iterating through it.
                frame_data, frame_data_copy = itertools.tee(frame_data)
                for row in frame_data_copy:
                    # skipping channels
                    for pixel_value in row[c::channelNum]:
                        o.write(pixel_value.to_bytes(1, 'little'))

            print("expected size = %d" % (width * height * channelNum,))

    # f and o auto-closes.
    print("resulting file '%s' size = %d" % (OUTPUT_FN, os.path.getsize(OUTPUT_FN)))