simple tools to write (block) data to png files

blocktoimg.py

#!/usr/bin/env python3
# Distributed under the MIT software license
import binascii, struct, sys
from PIL import Image

def div_roundup(x,y):
    return (x+y-1)//y

f = open(sys.argv[1], 'r')
outfilename = sys.argv[2]
blockdata = binascii.a2b_hex(f.read().strip())

metaheader = struct.pack('>II', len(blockdata), binascii.crc32(blockdata))

data = metaheader + blockdata

pixels=div_roundup(len(data), 4)
width=512 # could be made adaptive...
height=div_roundup(pixels, width)

print('exporting %d×%d to %s' % (width,height,outfilename))

padding_len = width*height*4 - len(data)
data += b'\x00' * padding_len

img = Image.frombytes("RGBA", (width, height), data)
img.save(outfilename)

imgtoblock.py

#!/usr/bin/env python3
# Distributed under the MIT software license
import binascii, struct, sys
from PIL import Image

img = Image.open(sys.argv[1])
outfilename = sys.argv[2]
assert(img.format == 'PNG' and img.mode == 'RGBA')
imgdata = img.tobytes()

metaheader = imgdata[0:8]
(blocksize,crc) = struct.unpack('>II', metaheader)
print('size {:d}×{:d}'.format(img.width, img.height))
print('metaheader:')
print('  size  : {:d}'.format(blocksize))
print('  CRC32 : {:x}'.format(crc))

assert(8+blocksize <= len(imgdata))
blockdata = imgdata[8:8+blocksize]

assert(binascii.crc32(blockdata) == crc)

with open(outfilename, 'w') as f:
    f.write(binascii.b2a_hex(blockdata).decode())
    f.write('\n')