Vitor, Frankly, I can hardly relate your problem description to font rendering. Can you possibly rephrase it? In FreeType speak LCD rendering is just triplicated for 3 arbitrary color channels with slight differences depending how these channels are spatially shifted. Regular antialiasing is just a special case assuming that three channels are not shifted at all. Note that FreeType does not assign color to the channels.
Alexei > On Jun 6, 2025, at 09:35, VÍTOR RAMOS <vitor.ra...@ufrn.br> wrote: > > All, > > I have been studying the subpixel rendering code and I could spot a > few improvement areas and I would like to hear your opinion about it. > In this message I discuss one of them. > > There are a few issues people face with subpixel antialiasing that > yield artifacts on their setup. The most common culprit is gamma > mismatches, but quite a few other less obvious factors are involved, > such as geometry which is partially addressed. > > One factor that is not addressed (or even mentioned in discussions at > all) is lossy color format and space transformations in display output > pipelines. > > It has become increasingly common that display adapters may > autoconfigure the output to use compressed video streams under a lossy > (chroma-subsampled) YUV output color format. This is usually done in > the context of a trade-off to achieve higher resolutions, refresh > rates or bit depths. As an example, many high-DPI panels only offer > UHD at 60 Hz under a chroma-subsampled YUV 4:2:0 stream. As another > example, many high-refresh rate panels only offer their maximum rates > under a likewise compressed format. As yet another example, higher bit > depth may also only be available under a chroma-subsampled format. In > general, video throughput may be limited by panels, adapters and even > physical channels, and the display output may be automatically > configured to use a compressed format. > > As is, the project implicitly assumes an RGB 4:4:4 uncompressed output > video format and performs excellently, but if the output has chroma > subsampling then subpixel antialiased rendering can exhibit color > fringe artifacts. Indeed, several complaints about fringing may very > well be caused by chroma subsampling rather than gamma issues. > > Exposing a subpixel antialiasing filter that addresses cases where the > output format has subsampled chroma is quite a large undertaking but > is feasible. Though the simpler solution in this case is to switch to > grayscale antialiasing. > > To my knowledge, no libraries commercial or otherwise currently > address this issue. > > Vítor >
