Chris Peterson wrote:I'd be very cautious making any rigorous color analysis of this image. First of all, the colors we see in the tail and coma of this nearly dust-free comet are from a handful of C and CN narrowband emissions, which are not recorded accurately in a broadband image.
Any color analysis has to always be based on at least two variables ... more actually, but these two at the very least: 1) bandpass filters used and 2) the criteria used by the person producing the image. The first is known, L+RGB, and I wouldn't expect anyone doing an analysis ignoring this fact. The image is presenting the broadband colors that were recorded. Recording at any other bandpass and produding a (RGB) image is a translation/interpretation. Neither is accurate or inaccurate, they're just different representations, and that's the only "caution" required
Whether RGB are the best filters for this object, that's a different question I think. In this case, color saturation has been enhanced, absolutely, but there's no color shift (intentional at least!).
Chris Peterson wrote:(the processing is excellent, but you can still see that the stars behind the tail are brighter than the stars in other areas).
I know many people - particularly those with some experience processing astroimages - think that the brighter stars behind the tail "reveal" that the area of the tail has been stretched selectively. However, if you pay very close attention, you may notice that the reason the stars are brighter in the tail has nothing to do with that.
The stars behind the tail appear brighter (they certainly do) because after most of the post-processing, the stars all over the image were too rough (no question processing was aggressive overall), so, using a star mask, I toned them all down to bring back a bit of their usual Gaussian profile, EXCEPT those in the area of the tail. I could not include the stars behind the tail without producing dark ringing around them, so I left them out. This process does not affect background sky, comet or tail, only the stars. Experienced eyes always see more in an image than most people, but sometimes their interpretation can too be inaccurate. I should know, it's happened to me before!