[Cin] possible patch for x265 on cmake 4.0?

[Georgy Salnikov]

On Thu, 3 Apr 2025, Andrea paz wrote:

> OK, I understand your explanation. Just one point: does it only apply
> to plugins that refer to color spaces (which by definition are limited
> (0, 1))? Or does it apply to all, e.g., Histogram and the like?
> Another question: generally conversions between color spaces are
> referred to CMS, i.e. via ICC color profiles; OpenColorIO; ACES, etc.
> Since CinGG does not have CMS how does the Color Space plugin work?
> And how does the \u201cYUV Color Space\u201d tool in \u201cPreferencies\u201d work?

An immanent property of a pixel is its color. All pixels have some color. If
there is some video in a clip (not only audio), it consists of video frames,
and each frame consists of pixels, and each pixel has some color.

Color is expressed as at least 3 values (usually 3 but it may be more) in
some coordinate system. This color coordinate system composes a color space.
Some color space always exists.

If some plugin alters only geometry (changes X and Y coords of pixels but
does not change colors), it still works in some color space, but in this
case the particular color space does not matter as pixel colors remain
constant.

If some other plugin changes colors or in some way accounts for colors, it
almost always must bear in mind the color coordinate system, the color space
pixels are in. Not just color perception CMS and ICC profiles are for, but
more fundamental.

Not all color spaces are limited to 0..1. For example, in YUV only Y is
0..1, U and V are -0.5 .. +0.5, while in HSV H is 0..360. Should you
calculate an Hue histogram in HSV color space (why not?), you must take into
account the particular range of Hue. Despite Hue has no ICC profile.

An MP4 video color space is some kind of YUV. If you wish to apply, let's
say, Chromakey, the latter works in HSV space. Therefore, you have to
convert pixels from YUV to HSV making use of some mathematical equations for
coordinate transformations.

The Color Space conversion plugin also uses some equations to do the job. If
you wish to extend it to a broader range to perform similar transformations
for HDR, you have to write the corresponding mathematical equations.

But as soon as you have the equations, you can easily express them in form
of one more blend program function, and you will have your HDR
transformation working.
_______________________________________________________________________________

Georgy Salnikov
NMR Group
Novosibirsk Institute of Organic Chemistry
Lavrentjeva, 9, 630090 Novosibirsk, Russia
Phone   +7-383-3307864
Email   sge at nmr.nioch.nsc.ru
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