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.
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.
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.
I'm not sure BT specifically stands for anything in particular, it just refers
to the series of standards which deals with broadcast TV stuff. In the opening
page of the standards document, it's annotated "Broadcasting service
(television)."
No, that's not an SMPTE standard; that's an ITU standard, from the Radio sector
of the International Telecommunication Union; hence, the current version is
properly titled ITU-R BT.709-6. The standard is free to download but it won't
help you much, probably.
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.
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). You may
need to scale the studio swing data to full swing to avoid washed-out shadows
and dull highlights.
Unfortunately the likelihood is you'll simply have to experiment until you find
the right solution, although I would expect it should be possible to fix it
using known scaling and remapping. Really, you should not have to start
eyeballing colour corrections in this scenario. If you find yourself having to
apply manually-configured filters I'd suspect you're not doing it right
somehow, and should step back and look at it again.
-P
On Monday, 6 November 2023 at 15:23:41 GMT, [email protected]
<[email protected]> wrote:
On 11/6/23 09:16, Devin Heitmueller wrote:
> On Sun, Nov 5, 2023 at 10:42 PM <[email protected]> wrote:
>>
>> Hello All,
>>
>> I have a 1990s TV show -- called 'SOURCE' here -- made by Paramount. The
>> show was renowned for its
>> production values. It's on Blu-ray from Paramount. The Blu-ray was made in
>> 2012 (may be a clue to a
>> colorspace variant used).
>
> If it is standard definition and from the 1990's then the original content is
> almost certainly in BT.601.
Thanks, Devin,
To add to the fun/mystery, though it was a TV show, Paramount shot it on film,
so maybe it was color
graded on film(?), whatever 'BT' that would be (probably not SMPTE). It looks
like too big a color
shift to simply be BT601 rendered via BT709. It's the saturation that clues me
to that. The reds are
saturated in play and in the ffmpeg HEVC encoding but they can't actually be
saturated on disc
because I can draw detail out of them. I think there's a 'limited' versus
'full' range thing going on.
I'm currently transcoding it with this:
-vf colorcorrect=saturation=0.85:rh=-0.06:bh=-0.1
It looks good, but that's to my eyes, on my laptop, with my laptop's video
settings. I'm out of my
depth with no oars. (Attenuating the blue bothers me, but hey, to my eyes the
discs have a blue cast
in addition to saturated reds.)
Paramount has done this to other TV shows. I'm hoping someone with experience
of Paramount's
film-to-TV-to-disc work will offer advice.
> Now if you're referring to the
> BluRay remaster, then who knows what they did. If done properly I
> would expect them to convert the colorspace to BT.709 ...
How convert? According to ffprobe, the discs have no colormatrix. So, I think,
ffmpeg has no choice
other than to accept it as BT709 -- 'conversion' not possible. I don't know how
to parse M2TS, so I
can't check on whether ffprobe is being truthful. Any parsing ideas would be
welcome.
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