Hmm LRGB combine and background extraction = greyscale?

[NickK]

I've been so busy with work that I've not managed to get out and take more images so I'm back to processing old data.

Now I've done the usual stack of channels, align and LRGB combine at which point I can see the orange swamp of light pollution. So after using dynamic background extraction and subtracting it from the image I'm left with below:

Now this is the screen shot from PI of a mag 15.1 Seyfert_1 galaxy (08:15:16.77 +46:04:33.8). The main bar is 23" across.

Now there's noise (the big whit blips) but that's not what is annoying me - it's the lack of any colour other than grey..

[ollypenrice]

I don't combine L in PI. I use DBE on both the L and the RGB and then go into Ps. (Looks like you need to hit the RGB with SCNR green as well.)

Then I can up the saturation. Don't use saturation, though, go into Lab colour and lift the contrast in a and b channels by 30 or more. Then return to RGB.

Now apply your L to the RGB.

Washed out? Fear not. Drop the L opacity, flatten, up the saturation, blur slightly and re-apply the L. This time uit will take a bit more.

And repeat!

It's a Gendler idea.

Olly

[NickK]

Thanks Olly i'll read up on what the function is in PP and emulate it with PI - I can't justify a PP purchase at the moment..

[NickK]

PI has a CIE l*a*b colour space and I think this is the equivalent - I'll have a play over the weekend.

[NickK]

I don't combine L in PI. I use DBE on both the L and the RGB and then go into Ps. (Looks like you need to hit the RGB with SCNR green as well.)

Then I can up the saturation. Don't use saturation, though, go into Lab colour and lift the contrast in a and b channels by 30 or more. Then return to RGB.

Now apply your L to the RGB.

Washed out? Fear not. Drop the L opacity, flatten, up the saturation, blur slightly and re-apply the L. This time uit will take a bit more.

And repeat!

Ok by switching to CIE*a*b (wiki page here)... a being red:green ratio, b being the yellow:blue. So it shifting to red-blue to bring out the red/blue colours that are very common in astro-targets. Applying L back in then gives you the luminance for the colour shifts.

Still thinking of the next bit and why that's working..

[NickK]

The next bit is effectively fattening up/flattening the variations in colour - so it creates more solid block of colour, then reapplying it colours the luminance again.

[ollypenrice]

Yes, this sounds like the same sort of thing.

Olly

[nigelg]

Hi Nick

Have you had a look at Harry's Video Tutorial on combining LRGB.

Nigel