Correcting Red from an Unmodified DSLR

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.

Now this is a reasonable image in its own right, but it lacks a little red. In order to brighten the red a bit, the curve to the right is applied to the red channel only. The idea here is to increase the narrow range of brightness values occupied by the nebula. The bottom point is placed below that to prevent the sky background from being shifted to red and the upper point does the same for the stars.

The result is shown in the image below. Be careful, as it is easy to overdo and end up with overpowering red in the image. If the curve is applied with an adjustment layer, masking can be applied to areas of the image that you do not want to enhance.