> -----Original Message----- > From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of Michael > Niedermayer > Sent: Friday, 24 September 2021 17:40 > To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org> > Subject: Re: [FFmpeg-devel] Scaling PAL8 images with alpha > > On Fri, Sep 24, 2021 at 10:30:31AM +0000, Soft Works wrote: > > Hi, > > > > for a new filter, I want to rescale PAL8 subtitle bitmaps where the palette > includes > > colors with alpha. > > > > From what I’ve seen, swscale doesn’t support PAL8-to-PAL8, only PAL8-to- > BGR8 > > which doesn’t support alpha and the palette is fixed with 256 entries > defined by > > convention, while I would ideally like to be able to allow the following: > > > > - constrain the output to use the same palette as the input > > - adaptively quantize it to a palette with a configurable number of colors > > > > Thus it's about the palette quantization (with or without dithering) after > > scaling in RGBA. (or some cool algorithmic trick I'm not aware of) > > > > Is there any existing code that I could reuse? The closest I could find > > is pngenc, but I'm wondering whether there's something else/better > > somewhere in the ffmpeg libs that I haven't seen? > > There are some non linear scaling filters which may make sense when you do > not have the full linear space available see: > hqx, epx, xbr > you could also try some neural net stuff
Photoshop can perfectly do what is needed, but their algorithms are not public. > or the insane solution, OCR, scale text, render font into RGBA and then back > to PAL8 LOL, for a moment I had thought the same after the great OCR results I had seen recently... softworkz _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
