Why does a GIF increase in size when I add a logo although number of colors stays the same?

I have an animated GIF that’s about 2 MB large. When I open it in Photoshop CS 5, add a layer with a logo, then save it for web, its suddenly 4 MB large.

Why? There aren’t more colors or anything, so why does the size increase?

The image in question is NSFW and I cannot post it here.


Color number is just half the game. The other is to compress the picture after color reduction. This lossless compression, searches for repeated patterns in scanline order.

Long story, in short: When you add the logo you are increasing the image variability, entropy. Compression gets worse the more entropy there is in the image, as the computer can nolonger find as many repeated patterns. Thus doubling complexity of image roughly speaking doubles your file size.

Source : Link , Question Author : Community , Answer Author : joojaa

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