BigglesZX · November 5, 2012 10:31 · fjania · Oct 18, 2013 · BigglesZX · Oct 28, 2013
diff --git a/gifextract.py b/gifextract.py
 import os
 from PIL import Image


 '''
 I searched high and low for solutions to the "extract animated GIF frames in Python"
 problem, and after much trial and error came up with the following solution based
 on several partial examples around the web (mostly Stack Overflow).

 There are two pitfalls that aren't often mentioned when dealing with animated GIFs -
 firstly that some files feature per-frame local palettes while some have one global
 palette for all frames, and secondly that some GIFs replace the entire image with
 each new frame ('full' mode in the code below), and some only update a specific
 region ('partial').

 This code deals with both those cases by examining the palette and redraw
 instructions of each frame. In the latter case this requires a preliminary (usually
 partial) iteration of the frames before processing, since the redraw mode needs to
 be consistently applied across all frames. I found a couple of examples of
 partial-mode GIFs containing the occasional full-frame redraw, which would result
 in bad renders of those frames if the mode assessment was only done on a
 single-frame basis.

 Nov 2012
 '''


 def analyseImage(path):
    '''
    Pre-process pass over the image to determine the mode (full or additive).
    Necessary as assessing single frames isn't reliable. Need to know the mode 
    before processing all frames.
    '''
    im = Image.open(path)
    results = {
        'size': im.size,
        'mode': 'full',
    }
    try:
        while True:
            if im.tile:
                tile = im.tile[0]
                update_region = tile[1]
                update_region_dimensions = update_region[2:]
                if update_region_dimensions != im.size:
                    results['mode'] = 'partial'
                    break
            im.seek(im.tell() + 1)
    except EOFError:
        pass
    return results


 def processImage(path):
    '''
    Iterate the GIF, extracting each frame.
    '''
    mode = analyseImage(path)['mode']
    
    im = Image.open(path)

    i = 0
    p = im.getpalette()
    last_frame = im.convert('RGBA')
    
    try:
        while True:
            print "saving %s (%s) frame %d, %s %s" % (path, mode, i, im.size, im.tile)
            
            '''
            If the GIF uses local colour tables, each frame will have its own palette.
            If not, we need to apply the global palette to the new frame.
            '''
            if not im.getpalette():
                im.putpalette(p)
            
            new_frame = Image.new('RGBA', im.size)
            
            '''
            Is this file a "partial"-mode GIF where frames update a region of a different size to the entire image?
            If so, we need to construct the new frame by pasting it on top of the preceding frames.
            '''
            if mode == 'partial':
                new_frame.paste(last_frame)
            
            new_frame.paste(im, (0,0), im.convert('RGBA'))
            new_frame.save('%s-%d.png' % (''.join(os.path.basename(path).split('.')[:-1]), i), 'PNG')

            i += 1
            last_frame = new_frame
            im.seek(im.tell() + 1)
    except EOFError:
        pass


 def main():
    processImage('foo.gif')
    processImage('bar.gif')
    

 if __name__ == "__main__":
    main()
	import os
	from PIL import Image


	'''
	I searched high and low for solutions to the "extract animated GIF frames in Python"
	problem, and after much trial and error came up with the following solution based
	on several partial examples around the web (mostly Stack Overflow).

	There are two pitfalls that aren't often mentioned when dealing with animated GIFs -
	firstly that some files feature per-frame local palettes while some have one global
	palette for all frames, and secondly that some GIFs replace the entire image with
	each new frame ('full' mode in the code below), and some only update a specific
	region ('partial').

	This code deals with both those cases by examining the palette and redraw
	instructions of each frame. In the latter case this requires a preliminary (usually
	partial) iteration of the frames before processing, since the redraw mode needs to
	be consistently applied across all frames. I found a couple of examples of
	partial-mode GIFs containing the occasional full-frame redraw, which would result
	in bad renders of those frames if the mode assessment was only done on a
	single-frame basis.

	Nov 2012
	'''


	def analyseImage(path):
	'''
	Pre-process pass over the image to determine the mode (full or additive).
	Necessary as assessing single frames isn't reliable. Need to know the mode
	before processing all frames.
	'''
	im = Image.open(path)
	results = {
	'size': im.size,
	'mode': 'full',
	}
	try:
	while True:
	if im.tile:
	tile = im.tile[0]
	update_region = tile[1]
	update_region_dimensions = update_region[2:]
	if update_region_dimensions != im.size:
	results['mode'] = 'partial'
	break
	im.seek(im.tell() + 1)
	except EOFError:
	pass
	return results


	def processImage(path):
	'''
	Iterate the GIF, extracting each frame.
	'''
	mode = analyseImage(path)['mode']

	im = Image.open(path)

	i = 0
	p = im.getpalette()
	last_frame = im.convert('RGBA')

	try:
	while True:
	print "saving %s (%s) frame %d, %s %s" % (path, mode, i, im.size, im.tile)

	'''
	If the GIF uses local colour tables, each frame will have its own palette.
	If not, we need to apply the global palette to the new frame.
	'''
	if not im.getpalette():
	im.putpalette(p)

	new_frame = Image.new('RGBA', im.size)

	'''
	Is this file a "partial"-mode GIF where frames update a region of a different size to the entire image?
	If so, we need to construct the new frame by pasting it on top of the preceding frames.
	'''
	if mode == 'partial':
	new_frame.paste(last_frame)

	new_frame.paste(im, (0,0), im.convert('RGBA'))
	new_frame.save('%s-%d.png' % (''.join(os.path.basename(path).split('.')[:-1]), i), 'PNG')

	i += 1
	last_frame = new_frame
	im.seek(im.tell() + 1)
	except EOFError:
	pass


	def main():
	processImage('foo.gif')
	processImage('bar.gif')


	if __name__ == "__main__":
	main()