Colors don't match images used when saving GIF

[julienguegan]

Hello all,

I have a weird behaviour when trying to save a .gif

Save a gif

I want to generate a gif from a sequence of image. I first create images with differents colors and transparence. Then, I save them. To generate a .gif, I read this images with Image.open() and then append them in a list.

Behaviour wanted

I want that the gif generated is exactly composed of the images I have generated/saved

What actually happened

The gif generated look a bit like that the images used but colors are not the same, I can see a frame where a part is completely black where it should be white/gray.

image in gif : image used :

I feel that it could be because of the transparency channel but I need to have transparency when I generate my images and also in my final .gif file ...

Configuration

• OS: Windows 10
• Python: 3.8.3
• Pillow: 8.1.2

Minimal Example

import numpy as np
import matplotlib.pyplot as plt
from PIL import Image
# generate images
alphas = np.linspace(0, 1, 10)
img = np.ones((200,200,4))
for i, a in enumerate(alphas):
    img[75:125,75:125,:] = a
    plt.imsave(str(i)+'.png', img)
# save as gif
images_gif = []
for i, a in enumerate(alphas):
    im = Image.open(str(i)+'.png')
    images_gif.append(im)
    plt.imshow(np.array(im))
    plt.show()
images_gif[0].save('file.gif', save_all=True, append_images=images_gif[1:], loop=0, duration=250)

[julienguegan]

Just saw that it seems to be related to some previous opened issues : (#4644 and #4640). The issue does not seem to be resolved but it might exist some workaround proposed in the previous opened issues ...

[lilisako]

@radarhere @julienguegan Could I take this issue? This seems interesting.

[radarhere]

@lilisako yeah, go for it

[julienguegan]

@radarhere Attention, I have been using Pillow: 8.1.2 and I just saw that the new version 8.2 (April) has some update concerning .gif files. I am still trying to understand if it helps my problem ...

[julienguegan]

I confirm it helps ! Plus https://gist.github.com/egocarib/ea022799cca8a102d14c54a22c45efe0