Downscaling and Colorimetry
Posted: Thu Dec 09, 2021 7:23 pm
Hi Don, I have a question regarding the "Colorimetry" field reported by your tools. As I understand it, HD (720p+) video uses BT.709, while SD video uses various standards, depending on the source format. DGIndexNV will report e.g. "Colorimetry: BT.709 [1]*" for HD, where the star means BT.709 is assumed based on the resolution and not explicitly declared.
If you're downscaling an HD source to SD, I believe you're supposed to indicate that the video is BT.709, so the playback device doesn't incorrectly assume BT.601 or some other SD standard; however, x264 has three related settings:
Are you supposed to set all three to bt709, only the --colormatrix flag, or something else? The x264 help says you invoke the VUI settings at your own risk, so I'd rather not make things worse compared to not declaring anything at all, if I can help it.
If you're downscaling an HD source to SD, I believe you're supposed to indicate that the video is BT.709, so the playback device doesn't incorrectly assume BT.601 or some other SD standard; however, x264 has three related settings:
Code: Select all
--colorprim <string> Specify color primaries ["undef"]
- undef, bt709, bt470m, bt470bg, smpte170m,
smpte240m, film, bt2020, smpte428,
smpte431, smpte432
--transfer <string> Specify transfer characteristics ["undef"]
- undef, bt709, bt470m, bt470bg, smpte170m,
smpte240m, linear, log100, log316,
iec61966-2-4, bt1361e, iec61966-2-1,
bt2020-10, bt2020-12, smpte2084, smpte428,
arib-std-b67
--colormatrix <string> Specify color matrix setting ["???"]
- undef, bt709, fcc, bt470bg, smpte170m,
smpte240m, GBR, YCgCo, bt2020nc, bt2020c,
smpte2085, chroma-derived-nc,
chroma-derived-c, ICtCp