Help With Noisy DSLR R & B Channels

[russellhq]

I was playing about with Photoshop and noticed the red and blue channels were far more noisy than the green channel in my M51 data. I'm wondering if this is normal or if it's something I've done? As a side note, I tried using the green channel as a synthetic luminosity layer (as it was less noisy) and I think it worked better than using RGB for the synthetic lum layer.

Red Channel

Blue Channel

Green Channel

Maybe it's something to do with the DSLR sensor having twice as many green pixels? Though I'm sure I read that DSS discards the data from the second pixel with it's debayering.

[rfdesigner]

Yup.. twice as many pixels makes a noticable difference.

I've been playing with LRGB techniques that seem to work quite well at reducing colour noise... Make RGB image, produce a luminance from it, save it. go back to RGB image, apply gaussian blur, combine blurred RGB with sharp luminance the end result is a sharp image with much reduced colour noise.

Derek

[russellhq]

Derek, have you tried using just the green channel to make the luminance image? As it has least noise, maybe that would be a better option?

[rfdesigner]

No, I did some maths recently on adding images for optimum noise (i.e. a string of images taken going up to dawn), this is a similar problem

For OSC RGB images, The R & B frames have the same SNR.. so can be added together straight. The result of the combined RB image and the G frame should also have the same SNR so can be added together.

In other words, try making a luminance immediately after debayering, before colour balancing

Derek