On 11/6/23 11:16, Phil Rhodes via ffmpeg-user wrote:
A number of potentially complex interactions govern what's going on here.
FFmpeg has never been particularly smart about how it interprets colour and
brightness encoding, and it is not very well documented in that regard, but to
be fair, files are not always (or even often) marked correctly with flags
indicating what they contain, the flags may be nonstandard, etc. It's tricky.
Hello, Phil, Nice to 'speak' with you again. I agree with you. Color is a
wilderness.
Below is what x265 expects, so it's what ffmpeg must give it:
--video-signal-type-preset <string>
Specify combinations of 'colorprim' 'transfer' 'colormatrix' 'range'
& 'chromaloc'.
String format: <system>
This has higher precedence than individual VUI parameters.
If any individual VUI option is specified together with this, which
changes the values set corresponding to the system or color-volume,
it will be discarded.
<system> colorprim transfer colormatrix range chromaloc
=============== ========= ============ =========== ======= =========
BT601_525 smpte170m smpte170m smpte170m limited 0
BT601_626 bt470bg smpte170m bt470bg limited 0
BT709_YCC bt709 bt709 bt709 limited 0
BT709_RGB bt709 bt709 gbr limited
BT2020_YCC_NCL bt2020 bt2020-10 bt709 limited 2
BT2020_RGB bt2020 smpte2084 bt2020nc limited
BT2100_HLG_YCC bt2020 arib-std-b67 bt2020nc limited 2
BT2100_HLG_RGB bt2020 arib-std-b67 gbr limited
FR709_RGB bt709 bt709 gbr full
FR2020_RGB bt2020 bt2020-10 gbr full
FRP3D65_YCC smpte432 bt709 smpte170m full 1
String format: <system>:<color-volume>
The color-volume options can be used only with the system options
BT2100_PQ_YCC, BT2100_PQ_ICTCP, and BT2100_PQ_RGB. It is
incompatible with other options.
<system> colorprim transfer colormatrix range chromaloc
=============== ========= ============ =========== ======= =========
BT2100_PQ_YCC bt2020 smpte2084 bt2020nc limited 2
BT2100_PQ_ICTCP bt2020 smpte2084 ictcp limited 2
BT2100_PQ_RGB bt2020 smpte2084 gbr limited
<color-volume> master-display
===============
=====================================================================
P3D65x1000n0005
G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,5)
P3D65x4000n005
G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(40000000,50)
BT2100x108n0005
G(8500,39850)B(6550,2300)R(34000,146000)WP(15635,16450)L(10000000,1)
--colorprim <integer|string>
Specify color primaries to use when converting to RGB. Default
undefined (not signaled)
0 bt709 3 bt470m 6 smpte240m 9 smpte428
1 unknown 4 bt470bg 7 film 10 smpte431
2 reserved 5 smpte170m 8 bt2020 11 smpte432
--transfer <integer|string>
Specify transfer characteristics. Default undefined (not signaled)
0 bt709 5 smpte170m 10 iec61966-2-4 15 smpte2084
1 unknown 6 smpte240m 11 bt1361e 16 smpte428
2 reserved 7 linear 12 iec61966-2-1 17 arib-std-b67
3 bt470m 8 log100 13 bt2020-10
4 bt470bg 9 log316 14 bt2020-12
--colormatrix <integer|string>
Specify color matrix setting i.e set the matrix coefficients used in
deriving the luma and chroma. Default undefined (not signaled)
0 gbr 4 fcc 8 ycgco 12 chroma-derived-nc
1 bt709 5 bt470bg 9 bt2020nc 13 chroma-derived-c
2 unknown 6 smpte170m 10 bt2020c 14 ictcp
3 reserved 7 smpte240m 11 smpte2085
If it's a blu-ray it'll generally be in 709, unless it's one of the Sony 4K
Blu-Rays which uses xvYCC. It's hard to prove a negative but those are the only
situations I'm aware of. Assume what's on the disc will be studio swing 709
unless it is a 4K blu-ray.
It's 1920x1080. I 'heard' of "studio swing". What is it relative to what x265 expects (above)? Do
you know?
If it's a blu-ray of a TV show which was shot on film, it will have been
scanned and electronically colour corrected for the blu-ray.
Film scanned. Yes. So that's a 1st-level coloration. But red could not have saturated during
scanning. Otherwise, I couldn't pull more detail from the 'saturated' regions.
Oversaturation particularly of reds is one of the issues that will arise from
mixing up 601 and 709 and scaling issues are another, but there are so many
ways this can be wrong, and places to change settings, that I hesitate to
speculate further without further info. You are likely to be facing several
confounding issues at once.
I feel a headache coming on. Let's assume ffprobe is correct and colormatrix is undefined on the
discs. That limits things, eh? That limits things a lot.
If you intend to watch the resulting file on a computer, you should not need to
change the colourspace as sRGB and 709 have identical primaries (they do not
have identical brightness mapping but it should not look wildly wrong).
Right now I'm watching it on computer.
Well, I'll tell you. Watching 1: my transcode, and 2: the original (with no colormatrix?), and 3:
the Criterion "Fanny and Alexander", the skin tones in my transcode look a lot more like "Fanny and
Alexander" than it looks like the original (with no colormatrix?). The original looks bluish in
addition to red saturating from bright light emitters.
I'd love to tag the original as 'film' and let the bt709 encoding happen and see what results, but I
don't know how to do that in ffmpeg. Do you?
FFmpeg doesn't have any 'film' color setting, and ffmpeg colormatrix makes no sense if the source's
colormatrix is 'unknown'.
I'm kinda happy with what I've done: cutting contrast, reducing red and blue, but that's not very
satisfying or scientific.
Key may be what you mean by 'studio swing'.
From ffprobe:
level=41
color_range=unknown
color_space=unknown
color_transfer=unknown
color_primaries=unknown
What do you think of this: Paramount did not limit chroma (i.e., 'range=full'). Is there any way I
could confirm such a statement?
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