Good evening, F irstly, thanks for creating and maintaining such a fantastic library, the PIL is awesome!
I've got an interesting problem and I'd really appreciate if someone could point me in the right direction. I'm a reasonable developer but I've become out of my depth in image science :) I've got greyscale images which I have dithered (Floyd-Steinberg) so that they contain exactly 8 shades. The pixel values present in the images are 0, 36, 73, 109, 146, 182, 219, 255 - so 8 levels with pure-white and pure-black being represented. Naturally, most of the 256 possible pixel values in the histogram are empty. I want to reduce the size of this image by 3x in both directions, ie (300, 300) => (100, 100) *with* anti-aliasing but *without* creating pixels outside of those 8 shades. Of course, the Lanczos implementation in PIL doesn't know to only use values 0, 36, 73 etc, so it uses the full 256 range, thereby undoing my dithering work. Can anyone suggest a good approach to this? Would it be possible to modify the resampling algorithm to work in 8 shades rather than 256? Or is there a way I could put the pixel values back into the 8 "buckets" afterwards without wrecking the colour accuracy? I have tried the latter and gradients become steps, as you'd expect. It doesn't seem right to apply dithering again somehow. I have considered re-ordering my process from: *High-res image -> Dithering -> Resampling* to *High-res image -> Resampling -> Dithering* but I then think the dithering process wreaks havoc on the beautifully antialiased edges in the image. Any thoughts would be very gratefully received. Kind regards, Paul
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