Why is it recommended to denoise the luma plane only?

[ACKR]

I have a bunch of anime blu rays i want to encode and all the guides say to only denoise the luma plane(Y) why is it? Should other frames be left as is?

[amichaelt]

I have a bunch of anime blu rays i want to encode and all the guides say to only denoise the luma plane(Y) why is it? Should other frames be left as is?

Why not ask the people writing the guides? Maybe it's for some sort of slight speed gain? What do these guides you are reading say specifically?

[lansing]

Usually you're not going to see any visual difference when denoising Cr and Cb plane unless there's a color noise.

[MysteryX]

There's the fact that in the standard YV12 format, there is 1 chroma pixel for every 4 lima pixels. The information is much more grossian and thus much less noise. It would in fact just blur it out further?

[Asmodian]

The information is much more grossian and thus much less noise. It would in fact just blur it out further?

I think this is the most significant reason.

(You meant Gaussian I assume? It is not really Gaussian, that is a particular shape, but that is getting pedantic; you meant it is smooth and low detail, like video after a gaussian blur, which is true).

Then even if there is some noise humans are bad at noticing chroma noise.

Also performance considerations, all the above is true and then on top of that it takes a lot of CPU time to work on. All in all it is almost never worth it but weird sources always exist. For example, if over compressed there can be compression artifacts in the chroma planes, these are usually better handled by deblocking the chroma not denoising it, but there can still be reasons to do it.