保存在python中时，为什么GIF像素值会更改？

Question

I'm trying to write a steganography applcation using the LSB method and it works so far well enough for a few image formats .

However it doesn't work for GIF images since i have noticed that the saved gif has a few different pixel values (usually +- 1) and the LSB method relies on changing the least significant bit so a few different values throws the decoding algorithm off.

i have tried using both imageio and PIL.Image and it's the same problem in both cases

So basically my question is : Why does the pixel values change when saved and is it even possible to use LSB for encoding and decoding a GIF ?

Thanks for your help.

Answer 1

Gif is lossless it should not change the pixels, I recently did a little application using LSB method with gif format here is few things you should do:

• make sure when you encoded right, try replacing the pixel(0,0) then verify if the value is change if not so check the decoding

• make sure that the gif color is 255

• you will encounter this later but you should put the original metadata and delay time when assembling the frames

These are the main issues, other than that as I said earlier it is a lossless compression just like png it should not change the pixels so the problem is either in coding/decoding or type of the RGB color.