Processing issue with NCG2024

[glatiak]

I am curious about a problem I am having with the fit files produced by my OSC -- I have only recently been using it with a Williams Z61 to capture wider fields -- M31, M45 and NCG2024 and notice a curious thing. The Bayer pattern is BGGR (I tried them all). But besides the green cast, which I gather is a feature, the detail in the green image for things like the nebulocity behind the Horsehead is much stronger than in the red image. I use the camera without a filter so I am guessing this comes from 2 green pixels and the broad tail of the green bayer filter in the red? Is there any reasonable way to clean this up in PI? I have been experimenting with using the green layer as red -- seems to work but leaves me with wonky colour balance issues. Or should I really be using a cutoff filter during exposure? Thoughts, anyone?

Greg Latiak

[wvanreeven]

Hi Greg,

Yes, twice the green pixels as compared to red and blue indeed makes the green signal stronger. Also, the pixels are closer together so the resolution in green is higher than in the other colours. What OSC do you use? Lack of red signal may be because of a clipped red pass band. I have a Canon DSLR and the standard ones have IR-cut filters that strongly reduce transmission in H-alpha, which is where most of the red emission of nebulae is. I had it modded so it is more sensitive to H-alpha now.

As for compensating the green hue: in some cases this may be the chrominance noise in the background. Try zooming into your images a LOT so you see the individual pixels. If you see many green ones in the background and some red and blue ones then that is chrominance noise. You can reduce that with the SNCR process.


HTH, Wouter