[Cin] Some tests on blending

[Andrew Randrianasulu]

чт, 3 апр. 2025 г., 22:03 Andrea paz via Cin <cin at lists.cinelerra-gg.org>:

> I tried again to test Color Space plugin and noticed some peculiarities:
> If I set Input: BT709 and Output BT709, and also BT2020 -> BT2020;
> then the result is not clipped. Any other combination of Input/Output
> leads to a clipped result instead. How can this be explained? Perhaps
> the input is not clipped (apart from BT601 which is always clipped),
> but every transformation is always clipped. 709 -> 709 and 2020 ->
> 2020 does not perform transformations and thus remains unclipped.
> This argument can perhaps also be carried over to the “YUV Color
> Space” tool:


my understanding this is not a tool per se, more like switch for ffmpeg
(libswscale) colour conversions ...

happens on both input (if ffmpeg selected) and output ....

As I noted there is some CMS/floating point/swscale rework in upcoming
ffmpeg 8.0 , so if things will not break in many other ways we might try to
convince swscale to not clip on import at least.


if we leave the source color space unchanged then we can
> keep the pipeline without clipping (if it was already unclipped to
> begin with), if we convert to any other color space then clipping will
> occur.
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