Why does compressing an image or GIF create noise in previously-solid areas? Surely that requires MORE information to be stored?
In: Technology
GIFs are limited to 256 colours. This was a common thing back in the day to save space and because many PC monitors ran in 8 bit colour mode – start with a table of colours (called the palette) then each pixel is only a single byte even before you compressed it. Many image formats were palette based or at least supported it.
But if your source image has more colours than 256 then you have a problem. Standard solution method is called dithering, where you replace a solid chunk of a colour which isn’t available with a mixture of colours you do. This results in the noise. If you see a dark brown with slightly light brown noise, then the original colour was actually darkish brown slightly lighter than the main colour. Suffice to say, Gif is a bad choice for photo-realistic images.
The good news is gifs are mostly phased out from the internet. Their only real advantage is both transparency and animation in the same image, but with web videos covering animation needs these days gif is dying.
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