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Old 15 January 2020, 20:58   #1
sparhawk
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Image conversion from RGB to indexed color

I found some website where one could upload some RGB Image and it converted it to an indexed color image for download. You could choose from 2, 4, 8, ... also 12 bit RGB with 32 colors, etc. as on Amiga.


Unfortunately I don't remember where I found this, it was in some thread in a forum, but I don't remember where (not sure if it was this forum or some other). So does anybody know such a site, or a tool that can do this?
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Old 15 January 2020, 21:21   #2
ross
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http://tool.anides.de/
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Old 15 January 2020, 21:25   #3
sparhawk
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Yes! That was the site. I was shocked to find that I didn't bookmark the page, and couldn't find it anymore.
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Old 15 January 2020, 22:53   #4
jotd
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Without any internet, I'm using ImageMagick "convert" utility and "amigeconv" to convert BMP images to bitplanes and palette.

Also python & PIL to merge all images so they'll share the same palette when cutting them back.

My process:

1) concatenate all images (python PIL/Pillow lib)
2) reduce colors (with imagemagick), turn off dithering or this is horrible
3) extract palette with amigeconv (extract copperlist => you have the palette)
4) cut back the images as PNG (Python Pillow)
5) convert the images to bitplanes. They'll use the palette extracted at 3), and add extra info in the header so your game knows the dimensions, depth...

python script used for Bagman game here: https://github.com/jotd666/bagman/bl...hop_sprites.py

(next version to come is able to create sprites too)

Sometimes the algorithm reduces colors too much. I used 2 passes, progressively reducing to 32 then to 16 and it worked well… With Python PIL you can also create your own color reduction algorithm but it's not trivial
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