I watched a video on image processing, and it motivated me to try again with my image of M42.
The first step was to mess with the levels in a more careful way. I would start by moving the middle clamp setting closer to the peaks in the histogram. This would bring out the detail in dim parts of the picture. As I would do this incrementally, I would also move up the “shadow” slider in the level close to the start of the peak in the histogram. This worked very nicely for brightening up the nebula, while also keeping the background and some noise low.
After getting the levels to something that I thought looked nice, I then copied the image. I used a Gaussian blur to remove as many stars as I could. I then used the clone tool to remove any remaining stars and the entire nebula. This gave me a base that was solely light pollution.
I was then able to subtract this layer from the leveled layer to remove the pinkish light pollution. This really pulled it together nicely.
The finally obstacle was to denoise the image. I again copied the base layer and set it to “darken only.” I then ran a more aggressive noise reduction on it. This greatly removed the random color noise from the image.
After all of this, I ended up with a significantly better result.
The following picture combines a layer with a lot of blur added to remove noise, and another layer to spice up the colors.