M39

[steviemac500]

Thought I'd try something different last night so as this high, I gave it  ago. 15L @ 300s, 8 RGB @ 225s each binned 2x2. 25 Bias, 15 flats each channel. DSS and PS for a bit of processing. Comments welcome as always.

 

[MattJenko]

Nicely framed and captured, but there is a big colour gradient across the image and the colour balance seems out of whack. Did the flats do their thing or has something not worked for one of the colour channels?

[steviemac500]

Thanks Matt. Could you explain more about the gradient as I'm not sure I can see what you mean (literally because I'm not sure I know what I'm looking for). I did have a bit more data in one of the channels but the histogram was lined up to the top left point. I used the healing brush on the left side in a diagonal line down to the right too. Thanks. 

[MattJenko]

Sure. As I see it, there is a changing in the background level of the colour channels as you move from the top left down to the bottom right. It is more blue at the top left of the image than at the bottom right of the image, and the change looks gradual, so a gradient. They can be tricky to remove, although there are photoshop actions which can minimise the effect to give a more even balance to the colours across the whole image.

[steviemac500]

Yep, I can see what you mean. Could the extra data in one of the channels be the cause of this and the colour balance?

[MattJenko]

If you use the histogram in PS and ensure that all the channels are lined up, then you will be able to see if the one of the colour's backgrounds is too bright, which can be adjusted in curves. Also, you have moved the background blackpoint very close to the data, clipping a bit (the background is very black) and when I took a look I think I can see why, in that there appears to be a plane flying right through your image on the left hand side! You could have a play with DSS settings to try and get that out of the L data when stacking as opposed to clipping the background to hide it.

Processing is fun

[steviemac500]

I normally use the kappa but I didn't this time so used the healing brush to remove the plane! I'm very impatient. I'll have another look at the histogram. Thanks.