IM 6.3.9 - YUV combine broken or not implemented?

I'm trying to get rid of chroma noise; my idea is to recompose image in
color space with separate luma channel (e.g. YUV), then denoise chroma
channels, maybe resize all parts, sharpen luma a bit and finally
recompose everything back.

I can do YUV decompose with IM:

   $ convert photo.jpg -colorspace YUV -separate yuv-channel-%d.png

but on recomposing

   $ convert yuv-channel-0.png yuv-channel-1.png yuv-channel-2.png -colorspace YUV -combine total.jpg

IM works as if channels were RGB components, not YUV. Is there any way
I can persuade IM to treat compoment images as YUV channels and recompose
correctly? Maybe IM supports combine in another luma based colorspace (which one)?

I'm using IM 6.3.9.


Vit