Quote:
Originally Posted by skysurfer
Well, the Tarantula is blue. I captured it recently with a 110mm/5.6 ED telescope and saw the nebula in blue with other red nebulas around it. These red nebulas are a bit missing in your photo and too blue, probably you should push up the red channel something.
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The point of a narrowband image is to study the underlying physics of the area. The colours are chosen arbitrarily, most commonly according to the NASA/Hubble convention of red for SII, green for H-alpha, and blue for OIII. Octane has used this standard convention here.
There is no reason at all to try to make the colours natural, and to attempt to do so misses the point.
Very briefly, H-alpha shows the distribution of easily ionized hydrogen as a tracer of bulk stuff. The OIII shows the distribution of hard ultraviolet light, and/or shock energy, biased toward areas of particularly high vacuum. The SII shows more heavily processed material, particularly from long-past supernova remnants. The details are much more complicated than this.