[Rafael Amador] "As FCPX does.
To simply tweak your luma on any YUV stuff you need to go RGB.
Some time ago people would have said "overkills"."
Sure, luma adjustments are mathematically easier in YUV than RGB.
However, here's a counterexample: compositing is traditionally done in RGB. Performing the same composite math on two images in YUV may yield different results than on the same images in RGB. For blend modes to yield the "correct" expected results, they must be processed in RGB.
That said, these are computer problems, not user problems. Users care how the image looks, and users care about having all the tools they need to adjust the image. Users do not care how an image's colors are encoded.
The key is that with sufficient precision, RGB and YUV can be converted back and forth without clipping or rounding errors, so developers are free to use whichever color encoding is most convenient for a particular processing algorithm without incurring any quality loss. On modern systems, the speed penalty for converting RGB/YUV is negligible.
FCPX is not alone in processing in RGB, either: it joins apps like After Effects, Color, Flame, Fusion, Nuke, Resolve, SCRATCH, Shake, and Smoke.
Walter Soyka
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