Adding Ha to RGB Images

Many galaxies contain many nebula and bringing these out in an RGB Image can be difficult. One way to do this is to combine a Narrowband Channel image with one channel of the colour image.

One of the easiest to do is combining Ha with the red channel. A complication with the normal methods of achieving this is that the red channel can become overwhelming when the Ha is added to it.

One method to prevent this problem is continuum subtraction where the signal from the Ha channel has the Broadband Red channel subtracted to leave only the most prominent areas of Ha. 

These are the areas that astro-imagers want to bring out. Prior to the launch of a Pixinsight Script by Seti Astro, continuum subtraction required a set of complex formulae in Pixinsight Pixel Math or complex but clever trickery in Photoshop. 

Below is an image of Bodes Nebula (M81 & M82) that has been developed using LRGB+Ha and continuum subtraction. The Ha signal in this image ha been exaggerated to show the effect. 

However, i think it adds a lot to the interest of these galaxies.

Click on the image to get a closer view

M81 and M82

Paul Howat