On Thu, 24 May 2018 08:58:22 +0000, "Song, Ruiling" <ruiling.s...@intel.com> wrote: > Where comes the "1000 cd/m² is the reference display peak"? seems no clear > statement in BT2100?
The concept of there being a "standard" 1000 cd/m² display is introduced in multiple places. Refer to Table 5 of ITU-R BT.2100, specifically the section called "HLG Reference EOTF, in particular this definition: > γ = 1.2 at the nominal display peak luminance of 1 000 cd/m². [5d, 5e, 5f] And also the Note 5e below it, which explains how to adjust the gamma if you are displaying on a display with a peak luminance that is different from 1000 cd/m². This is pretty much as close to saying that a reference HLG display should have a peak of 1000 cd/m² as you can get without explicitly saying it, since that value is essentially the assumption they hard-coded into their formula. In addition to this, the ITU-R further reinforces this concept heavily throughout their ITU-R Report BT.2390, which includes e.g. such sentences: > In order to determine the appropriate system gamma for a 1 000 cd/m² > reference display, NHK conducted a series of experiments with an > indoor test scene. So the concept of a “HLG reference display” is not something I made up. (Incidentally, 1000 cd/m² is also the value you hard-code in your OOTF) > If that is true, my code is wrong to detect peak of untagged source. > if (!peak) > peak = in->color_trc == AVCOL_TRC_SMPTE2084 ? 100.0f : 12.0f; > so here I should change it from 12.0f to 10.0f? Yes, given that you're defaulting the OOTF to 1000 this is definitely a good idea, otherwise white won't map to white. (Observe that you have the scaling factor in your ootf_hlg hard-coded as 1000.0f / REFERENCE_WHITE = 10.0) > Thanks for point this out. I mis-understand the code in libplacebo, because > inverse_ootf() was also called if need_ootf is true, which makes I fail to > understand it correctly. pl_shader_inverse_ootf() is parametrized by the actual OOTF to use. Observe that the inverse_ootf() definition in libplacebo is a no-op if the `enum pl_color_light` is given as PL_COLOR_LIGHT_DISPLAY. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
