[Cin] Colors tip from forum

[Andrew Randrianasulu]

чт, 4 авг. 2022 г., 09:28 Andrea paz <gamberucci.andrea at gmail.com>:

> Thank you for the explanations.
> I am trying to write a color section for the CGG manual.
> I have a doubt: a long time ago GG said that on the
> timeline/compositor we always see an sRGB output:
>
> "CinGG, works internally at 32 bits in RGB, but the output in timeline
> is sRGB, and performs a first conversion from YUV of the original file
> to RGB with the scaler (matrix function, not primaries or transfer
> characteristic function), using its internal settings."
>
> Does this mean that it is useless to have wide-gamut monitors? And
> that it is useless to have ICCs or LUTs unless they are limited to
> sRGB only?


I think some ffmpeg plugins work internally in rgba-float, so correction
happens with high precision, just display truncate/dither image. So yes,
not truely 'what you see is what you get' {as far as I understand all image
processing happens in linear space ? Because converting back and forth at
each effect sounds wasteful on cpu ...}

I wonder if mpv can read those yuv4mpeg raw streams with color transfer
info? May be you can render to pipe and add mpv as gl accelerated and
color-corrected external player?

But I think fixing display stage will be as 'simple'  as using specialised
color-corrected rgba-float-> 10bit rgb (or may be dithered/tonemapped 8bit
rgb) function, as long as display driver support 30 bit color. I commented
in  few bugs in the past:

https://www.cinelerra-gg.org/bugtracker/view.php?id=297
https://www.cinelerra-gg.org/bugtracker/view.php?id=294
https://www.cinelerra-gg.org/bugtracker/view.php?id=238


If so, it would be extremely limiting for color correction
> in CGG.
> My other doubt: what is the purpose of the "YUV color space" in
> Preferences, just for encoding?




I think it also used indirectly via FFVideoConvert::convert_vframe_picture
in convert_cmodel function, in turn used by FFVideoStream::load


all those in cinelerra/ffmpeg.C

Any use of YUV type color spaces
> should be discouraged since the signal on the screen is always sRGB.
>

Well, there is Xv (yuv) output, and encoded video tend to be variation of
subsampled yuv (because it takes less space this way)

>
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