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by spookthesunset
1682 days ago
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As has been said, dithering is something that people did back in the bad old days of 256 (or 16!) color palletized displays. It is a way to "fake" more colors than available. It was never meant for image compression. I don't even remember the last time I saw a dithered image anywhere on the internet.... it's been quite some time. |
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Dithering was used to make GIFs smaller, since the reduced palette could fit into a smaller bit depth per pixel. So in that sense it is a type of compression. This was useful and used even when 24-bit colour displays became common.
The issue of 256 colour palette display modes is separate and caused other problems - i.e. you might specify one palette of 16 colours in your GIF, but they might not exactly match the colours provided by the operating system.
That is where the (I imagine now long forgotten...) notion of a "web safe" colour palette came from - these were the 216 colours you could expect any 256 colour OS to provide (produced by dividing up the colour space evenly using only combinations of 00 33 66 99 CC FF values for R, G, B)
You could use colours outside the safe palette in your GIF but the OS would use the nearest available colour from its own palette to display them, and often it did a bad/unpredictable job of choosing a substitute. So it was common to deliberately adjust colours in your image to align with the "web safe" palette, so as not to risk garish substitutions when displayed on a 256 colour display.