вс, 18 мая 2025 г., 04:36 Mark Filipak <markfilipak.i...@gmail.com>:
> For people who are wondering what this is all about, I have a summary at > the bottom. > > On 17/05/2025 16.46, Andrew Randrianasulu wrote: > > On Sun, May 18, 2025 at 2:37 AM Mark Filipak <markfilipak.i...@gmail.com> > wrote: > >> ... > >> I tried a few 'cubes'. I was unsure which 'cubes' to use based solely > on their names -- for example, > >> what does 'linear' mean in this context > > > > As far as I understand "linear" here means linear light, without any > > gamma curve applied, mostly for further processing? > > For example, HLG_BT2020_to_Linear_BT709.cube. What does "Linear_BT709" > mean? Linear... how? BT709 is > not linear, so what's Linear_BT709? > Try to ask this question on github, where this project hosted? Or at doom9 forum .... I suspect (from name patterns) linear is opposed to HLG/PQ *gamma* (EOTF?) and BT2020/BT709 is colour primaries etc. > To sum-up to this point... > > Let's call the next lines "tonemap-based". > > set _TWEAK_=eq=contrast=1.28:brightness=0.0725 > ffmpeg^ > ... > -filter_complex^ > "[0:v]scale=w=iw/2:h=ih/2^ > ,zscale=transfer=linear:npl=100,format=gbrpf32le^ > ,tonemap=tonemap=hable:desat=0^ > ,zscale=primaries=bt709:transfer=bt709:matrix=bt709:range=tv^ > ,%_TWEAK_%^ > ,format=yuv420p[v]"^ > -map "[v]"^ > ... > > as you see, that's not much tweaking. > > Now, let's call the next lines "LUT-based". > > ffmpeg^ > ... > -filter_complex^ > "[0:v]scale=w=iw/2:h=ih/2^ > ,lut3d=file='BT2100_HDR_PQ_to_BT2020_SDR.cube'^ > ,lut3d=file='BT2020_to_BT709.cube' > ,format=yuv420p[v]"^ > -map "[v]"^ > ... > > In contrast to tonemap-based, LUT-based conversions needed a lot more > tweaking -- not shown because > I didn't actually waste my time tweaking what obviously required much more > tweaking. > > But LUT-based conversions are not supposed to need tweaking! > > My understanding is that your friends in France took various Hybrid > Log-Gamma (HLG) curves for > BT2100, BT2020, BT709, etc. and made LUTs of them for use doing > conversions. > My understanding is that the LUTs are formatted to work with FFmpeg's > 'lut3d' filter. > Something is wrong with my understandings, methinks. > > What do you think? Or do I need to go to France? :-) > > > For people who are wondering what this is all about, I have a summary: HLG > acts like ordinary gamma > (almost 1:1 source-to-target transfer) for low-to-mid input luminance: > 0.0..0.5, but acts like a > logarithm (like compression) for mid-to-high input luminance: 0.5..1.0. > Basically, it smoothly and > progressively reduces the HDR values that are 'tending' to go whiter than > SDR white, HDR values that > blow out skies and sun-glints when in SDR, without losing HDR's deep > blacks very much and without > SDR's gray banding. The alternative to all this curve stuff is taking the > HDR values that don't fit > into SDR, and just clipping-to-white, blowing out skies and glints and > highlights, etc. > > Of course, if you don't have an HDL source, then you're stuck with > ordinary SDL and there's nothing > you can do about it. > > As a bonus that's unrelated to color tones, HDR means UHD resolution (i.e. > 2160x2040 or more), so > you'll be able to transcode to HD (i.e. 1920x1080) and not only _not_ lose > resolution, but actually > get better resolution (better textures, cleaner edges) than most HD > Blu-rays have. > > I have taken a 55 GiB, 2 hour 36 minute UHD movie -- HEVC encoded -- and > made a 3.5 GiB HD copy -- > AVC encoded -- that looks better than the native HD Blu-ray of the same > movie, better in every way. > > > _______________________________________________ > ffmpeg-user mailing list > ffmpeg-user@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
