One problem when imaging with an unmodified DSLR is the lack of H alpha response. When imaging those deep red emission nebula that we all love, an unmodified camera produces more of a pastel result than the bright red we see in all the CCD images. While this image is closer to true colour as seen by the eye, it is not what many have come to expect. Fortunatly it is easy to fix with a simple curve adjustment to the red channel.
First let's start with a North American Nebula image that has not been corrected.