91 lines
2.5 KiB
Python
91 lines
2.5 KiB
Python
from io import BytesIO
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from PIL import Image
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def resize_gif(mem, path, resize_to):
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frames, result = extract_and_resize_frames(mem, resize_to)
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if len(frames) == 1:
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frames[0].save(path, optimize=True)
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else:
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frames[0].save(path,
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optimize=True,
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save_all=True,
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append_images=frames[1:],
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duration=result['duration'],
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loop=1000)
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def analyse_image(mem):
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"""
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Pre-process pass over the image to determine the mode (full or additive).
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Necessary as assessing single frames isn't reliable. Need to know the mode
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before processing all frames.
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"""
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image = Image.open(BytesIO(mem))
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results = {
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'size': image.size,
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'mode': 'full',
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'duration': image.info["duration"]
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}
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try:
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while True:
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if image.tile:
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tile = image.tile[0]
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update_region = tile[1]
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update_region_dimensions = update_region[2:]
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if update_region_dimensions != image.size:
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results['mode'] = 'partial'
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break
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image.seek(image.tell() + 1)
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except EOFError:
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pass
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return results
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def extract_and_resize_frames(mem, resize_to):
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result = analyse_image(mem)
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image = Image.open(BytesIO(mem))
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i = 0
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palette = image.getpalette()
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last_frame = image.convert('RGBA')
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frames = []
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try:
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while True:
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'''
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If the GIF uses local colour tables,
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each frame will have its own palette.
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If not, we need to apply the global palette to the new frame.
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'''
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if not image.getpalette():
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image.putpalette(palette)
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new_frame = Image.new('RGBA', image.size)
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'''
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Is this file a "partial"-mode GIF where frames update a region
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of a different size to the entire image?
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If so, we need to construct the new frame by
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pasting it on top of the preceding frames.
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'''
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if result['mode'] == 'partial':
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new_frame.paste(last_frame)
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new_frame.paste(image, (0, 0), image.convert('RGBA'))
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# This method preservs aspect ratio
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new_frame.thumbnail(resize_to, Image.ANTIALIAS)
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frames.append(new_frame)
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i += 1
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last_frame = new_frame
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image.seek(image.tell() + 1)
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except EOFError:
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pass
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return frames, result
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