[Cin] Some tests on blending

[Georgy Salnikov]

On Fri, 28 Mar 2025, Andrew Randrianasulu wrote:

> > No, I didn't. I knew that Blend Algebra uses float and RGB by default,

Not exactly so. Blend Algebra uses float always, doing the conversions if
the color model is not float already. Also it uses alpha always, imitating
it if the color model itself does not have it. And between RGB, YUV, HSV it
uses by default that mode which is declared in the function (or the
project's color model if the function declares nothing).

The user can override the function's color model in the plugin dialog. He
cannot override float and alpha usage, but it is possible to inquire inside
the function which native color space is used in the project and if it has
alpha channel or not (outside the function).

> > and it just seemed interesting to me to see the differences this makes
> > from patchbay (I chose YUV media on purpose, for the test, because
> > they are the most common). I would actually like to see all parts of
> > CinGG unified to the internal float engine and RGB color space, but I
> > know that is impossible, as each tool/plugin goes its own way.

> If I understand correctly most  non-ffmpeg plugins should technically work
> in all modes, due to their history. But clipping probably occur in some of
> them even in rgba-float mode as you discovered earlier?

Many plugins work in all modes just because the particular color model does
not matter (like plugins that transform only geometry and do not transform
colors). Other plugins also work in all modes because they do the necessary
color space conversions (like Chromakeys). I'd expect, there are also a few
color model dependent ones.

In RGBA-Float some plugins can clip internally, to investigate it is a
distinct work. But clipping can occur later depending on the output format
when rendering, or on the display driver, or on the usage of opengl
accelerators. For example, unclipped R = -1.0 is displayed as black by the
opengl driver and as red by the X11 driver.

_______________________________________________________________________________

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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