Quote:
Originally Posted by Shiraz
Jase, have not yet used star removal, but if you get rid of the stars, I guess that you infill from the surrounding regions. Deconvolution would then provide enhanced structure on the remaining extended objects, but you would not get any of the benefits on the stars - is that the case, or could you tidy them up before re-inserting?
regards ray
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Ray
Star removal is a little over-rated IMO. The issue with removing stars is that its near impossible to do so in a clean manner. Even using a continuum filter for narrowband data sets, there are always traces of where the stars were located requiring the image to be upscaled by and then manually cloned out. There are short cut solutions on the net that others have posted here. Deconvolution will wreck havoc if these traces are not sufficiently clean up, especially those with significant tonal differences from the surrounding area.
So instead of creating all that extra work with little gain by getting rid of the stars, work with them. Deconvolution can be applied at different strengths. You'll find the gains in reducing star sizes slowly decrease with the quantity of deconvolution passes. The difference between say 8 passes and 20 passes is much smaller than you think. Try it. You need to settle on a pass value where you maintain the stellar profile of a tight star, but don't butcher them completely blowing out the center. This is a fine line as you many not be able reach the desired pass value depending on the quality of data. No point sharpening noise as you're trying to get rid of it!
What about the extended object? You may find that the deconvolution applied simply to tighten up the stars was too weak to do your extend object justice. It may have a good signal so why not push it harder. In this case, load up your original master and increase the deconvolution passes to extract as much detail as possible without introducing artefacts. Don't focus on how the stars look, just the extended object.
So you now have two images, one where the stars look tight but not over done (cooked too long) and the extended object deconvolution where the stars look ridiculous, but the extend object is in full glory showing depth and detail. Time for some work in photoshop.
As deconvolution (or most sharpening routines in general) alters the contrast between shadows, midtones and highlights, the extend object is likely to be brighter than that of the master with a lower pass value to tighten the stars. If so, you can layer the extended object image as 'Lighten' blending mode to simply bring through the brighter highlights of the heavily deconvoluted extended object layer. 'Lighten" takes the larger of the each pair of RGB values. Note the stars will also break though in this mode given they'll be brighter so you'll need to create a mask to block them from coming through. Hide all will do the trick and simply paint in the highlights from the extended object layer. Be sure to blur the mask so the transition between layers is smooth. Experiment with the blending modes in photoshop. 'Soft light' is a favourite with me, but you need to be aware of what the blend does as some darken while others lighten. 'Soft light' darkens so the image being blended needs to be stretched. You can also perform a double layer (duplicating the layer) to increase the effect. Plenty of info online, but I recommend understanding them and know when to best use them.
Depending on how far you want to take it, you can also perform a variety of extra layers with even greater levels of deconvolution and sharpening, all while still maintaining a good stellar profile. Processing is one of those activities in what you put in is what you get out.