Messier 42 in Hydrogen bi-color

Messier 42 in Hydrogen bi-color, a photo by Mickut on Flickr.

Via Flickr:
Reprocessed data from last February, M42 shot in Ha and Hb to show the difference between hydrogen emission lines. The channels were linear fitted across the nebulous ADU range (leading to blue stars), then mapped R:Ha, G:Avg(Ha,Hb), B:Hb. The background was neutralized and gradients were removed, stretching was done with a histogram stretch in luminosity only and contrast and saturation was enhanecd to make the differences a bit more visible.