Processing DSLR H alpha - help!

[ollypenrice]

Hi all,

I have a guest who has shot some Ha in his unmodded DSLR and has done pretty well for signal. However, what is the best way to process this data? I've heard of people stripping out just the red channel but my guesses as to how this might be done haven't worked!

I can see that one can just go into greyscale mode but it strikes me that this will retain the noise inherent in the unused channels?

What's the best way to work with Ha from a Bayer Matrix chip?

Cheers,

Olly

[anthony]

http://www.astro-nut.com/SolarPrimer.pdf

there is some info here from about page 11. Don't know how helpful it'll be.

[JohnC64]

I've split the rgb in a dlsr fit in nebulosity using the Batch Conversion -> RGB to 3 separate Colour menu. Just point at the rgb fit and it will produce a red_filename, blue_filename and green_filename.

Hope this helps

Cheers John

[russellhq]

Couldn't you just copy the red channel from photoshop somehow?

[JohnC64]

And to answer your (actual) question - Yes removing the red channel from the rgb image gave me better results than just doing a greyscale. I did get mostly noise in the blue and green channels and once removed, the image looked cleaner and (to my eye) appeared to be better when stretched

John

[melsky]

Hi Olly, in Photoshop go the channels drop down menu (top right corner of the palette) and select "split channels" then simply discard the blue and green and save the red, this can then be stacked in DSS etc.

Mel

[GlassWalker]

I've used nebulosity to do a batch channel extraction before. I assume other software can do similar. However I find if the goal is to eventually add it to OIII data, it helps to leave the Ha (and SII if that's attempted) interpolated at the nominal camera resolution as opposed to only keeping the red sensor pixels. Although computationally wasteful, I do a stack of the debayered all channels and only discard the other channels keeping the red channel as Ha after that is done. Note my mount alignment is not the best so I get a nice dose of free dither thrown in.

[laser_jock99]

And to answer your (actual) question - Yes removing the red channel from the rgb image gave me better results than just doing a greyscale. I did get mostly noise in the blue and green channels and once removed, the image looked cleaner and (to my eye) appeared to be better when stretched

John

Using just the red channel data does seem to strip out some of the green/blue noise in a DSLR Ha image but there will still be noise left in the red data. It might be possible to use the green channel data (if it is free of residual star images) to cancel out some of the remaining red noise in layers?

Edit- 3 channel Ha image with red channel only (inset) definitely cleaner.

[ollypenrice]

Thanks all. Much appreciated. I did try Mel's method by guesswork but got a bizarre result. If I discarded one of the other colour channels the remaining ones instantly swapped to a different colour palette, no longer RGB. I guess I should have split the channels and just saved the red one under a new name. I wasn't on my own computer at this time and didn't like to mess with any settings or investigate further.

I'm sure I'll get this to work now. It was just a hunch that the red alone would be less noisy.

Again, thanks.

Olly

[JohnC64]

Using just the red channel data does seem to strip out some of the green/blue noise in a DSLR Ha image but there will still be noise left in the red data. It might be possible to use the green channel data (if it is free of residual star images) to cancel out some of the remaining red noise in layers?

Thats an interesting Idea of using the green as a dark to reduce the noise. Hadn't though of that. Although looking at mine, i find that some of the brighter stars have punched through to the green . So if i used it as a "Dark", i would probably end up with a tiny dark dot at the centre of the bright stars.

Cheers John

[laser_jock99]

Thats an interesting Idea of using the green as a dark to reduce the noise. Hadn't though of that. Although looking at mine, i find that some of the brighter stars have punched through to the green . So if i used it as a "Dark", i would probably end up with a tiny dark dot at the centre of the bright stars.

Cheers John

That's exactly what happened when I tried it later. I suppose you could edit them out manually if they were few in number?