How do I apply a denoiser to only one channel?

[rec]

How do I apply a denoiser (such as dfttest) to say, only the red channel?

This is what I've got, and I know it's not right.

converttorgb()
MergeRGB(converttoyuy2().dfttest(),last,last)

I really didn't want to put converttoyuy2 in front of dfttest, but I couldn't see any other way to make it work. It does denoise the red channel, but the luma value of the red channel is all screwed up.

[Gavino]

ConvertToRGB()
MergeRGB(ShowRed("YUY2").dfttest(), last, last)

[rec]

Thank you! It works!
If it's not asking too much, could you explain conceptually what's going on? I'm having a hard time reconciling the red channel with YUY2 color space.

[Wilbert]

You should look at the documentation for ShowRed and MergeRGB and what happens when feeding a YCbCr clip:

ShowRed("YUY2"): red channel is copied to the luma channel of the resulting YUY2 clip (chroma is set to grey). When using MergeRGB, the red channel is filled with luma channel of the first clip (since that clip is YCbCr).