On Sat, Sep 25, 2021 at 10:23:56AM +0200, Hendrik Leppkes wrote: > On Sat, Sep 25, 2021 at 5:00 AM Soft Works <softwo...@hotmail.com> wrote: > > > > > > > > > -----Original Message----- > > > From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of > > > Soft Works > > > Sent: Friday, 24 September 2021 19:03 > > > To: FFmpeg development discussions and patches <ffmpeg- > > > de...@ffmpeg.org> > > > Subject: Re: [FFmpeg-devel] Scaling PAL8 images with alpha > > > > > > > > > > > > > -----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- > > > de...@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. > > > > I've put a few thing together to illustrate what I'm talking about: > > > > https://gist.github.com/softworkz/deef5c2a43d3d629c3e17f9e21544a8f > > > > > > Meanwhile I found what I need: https://github.com/ImageOptim/libimagequant > > > > Interestingly, they are comparing their lib specifically to the > > Photoshop feature that I mentioned: https://pngquant.org/vsphotoshop.html > > In the 2000's, the PS implementation for image quantization, optimization > > and compression (profanely named "Save for Web") had remained > > unparalleled for years, that's why it was one of my first thoughts. > > > > I hadn't heard about libimagequant before, but it seems to do exactly > > what is needed for rescaling PAL8 to PAL8 at a high quality. > > > > Before spending any time on it, I wanted ask whether that library > > would be acceptable for adding it as a (GPLv3) reference to the > > project and as a dependency to my filter? > > > > External dependencies for what is supposed to be a rather base feature > are not ideal.
+1 i see no reason why this would need an external dependancy we have filters implementing much more complex things than scaling a pal8 image [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Its not that you shouldnt use gotos but rather that you should write readable code and code with gotos often but not always is less readable
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