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Old 29 October 2016, 01:18   #50
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Join Date: Mar 2012
Location: Norfolk, UK
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Originally Posted by Jack Burton View Post
So to reach ~262144 colors we need a 16M pixels image, which can't be displayed on a standard Amiga. So finally these HAM8 256K colors are nothing more than a theoretical number...
Not really, it's just that your particular test image doesn't cover the RGB range very well when you crop out just a small part of it.
If you're taking the top left 5x5 squares then you're only going to be testing with 25 blue levels out of 256, and some of those will be mapped to the same blue level after colour-reduction to 18-bit, so you'd probably only have 10 unique blue levels out of 64 represented.

Therefore your potential colour range of 262144 colours is reduced to 262144*10/64 = 40960, which is pretty close to the result you got.
If instead of cropping you do a nearest-neighbour scaling on your test image to reduce it to 512x512 pixels, then repeat your test I think you'll get a result much closer to 262144.
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