Processing

M81 was tricky to process. The original images had a lot of sky glow, both from stray light and from light pollution. Unfortunately, the glow was not even across the picture and it was very difficult to remove digitally. In all cases, the way to remove sky glow is to obtain an image of the sky glow without the stars and galaxy. Then you can use Photoshop to subtract the sky glow from the original image. Of course, the hard part is obtaining an image of the sky glow without the stars and galaxy.

In this case, I tried isolating the different sky glow components. For example, there appeared to be a reddish glow spreading from the lower-left corner of the image. I tried simulating that glow using the cloning tool and lots of blurring. Once I removed the reddish glow, I noticed a bluish glow across the right-hand side and tried to remove that.

I didn't succeed entirely, and it is still possible to see some stray light on the left part of the image.

Adjusting the color was a little easier. The blue channel was very faint and noisy, so I just copied the green channel over it. I then adjusted the red channel down and the blue channel up until I got a reasonably pleasing image.