【python图像处理】gif动态图的解析与合成

gif动态图是在现在已经司空见惯，朋友圈里也经常是一言不合就斗图。这里，就介绍下如何使用python来解析和生成gif图像。

一、gif动态图的合成

如下图，是一个gif动态图。



gif动态图的解析可以使用PIL图像模块即可，具体代码如下：

#-*- coding: UTF-8 -*-

import os
from PIL import Image

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('test_gif.gif')

if __name__ == "__main__":
main()

解析结果如下，由此可见改动态图实际上是由14张相同分辨率的静态图组合而成



二、gif动态图的合成

gif图像的合成，使用imageio库（https://pypi.python.org/pypi/imageio）

代码如下：

#-*- coding: UTF-8 -*-

import imageio

def create_gif(image_list, gif_name):

frames = []
for image_name in image_list:
frames.append(imageio.imread(image_name))
# Save them as frames into a gif
imageio.mimsave(gif_name, frames, 'GIF', duration = 0.1)

return

def main():
image_list = ['test_gif-0.png', 'test_gif-2.png', 'test_gif-4.png',
'test_gif-6.png', 'test_gif-8.png', 'test_gif-10.png']
gif_name = 'created_gif.gif'
create_gif(image_list, gif_name)

if __name__ == "__main__":
main()

这里，使用第一步解析出来的图像中的8幅图，间副的间隔时间为0.1s，合成新的gif动态图如下：



2017.08.24