How do I view the Y channel?

[rec]

I'm sorry to ask such an elementary question, but how can I view the Y channel? And I don't mean using "Greyscale". I don't want to do any conversion. I simply want to view the Y channel as it exists on footage that's been captured with a video camera.

[Gavino]

Greyscale doesn't do any conversion of the Y channel if the input is YUV. It just sets U=V=128.