I have put together a few images which demonstrate in a nutshell how I get from raw input data to the panes I throw into AutoStitch64.
It all starts with the AVI, I typically gather 1000 frames per pane. With the Solar Spectrum filter, even a single frame can show a good deal of detail. Carefully tweaking focus until sharpness is optimal is essential. A frame obtained today is shown below.
Although it looks decent, this is not a good starting point for mosaic stitching. One reason is the fact that there is a distinct uneven illumination (or shading) visible. By taking flats this can be corrected. Various approaches can be used, I tend to defocus, take an AVI of the same length as the ones for the panes, and create a master stack in AS!2 (under image calibration). I often apply a smoothing filter (100 pixel diameter flat averaging often works) to get rid of residuals of sunspots or bright plage. A caveat is that dust bunnies are not well corrected for if you smooth the flat. Fortunately, the camera shows no sign of them (yet). Loading the master flat into AS!2 ensures all frames are corrected. Not that if you take AVIs of an ROI rather than full frame, you must create flats for that ROI. The result of flat-field correction is shown below.
This looks more promising. I then stack 100 (typically) of the frames (letting AS!2 pick out the best ones). The result appears to be not much different from the previous, as can be seen below.
Looks can be deceiving, however. If we apply Lucy-Richardson deconvolution (sigma = 1.15, 50 iterations works for these data) and unsharp masking (sigma = 1.15, strength 2.75) in ImPPG to the stack of 100 images, we get a very decent result.
I frequently work with higher strength values (3.75) in ImPPG, as can be seen in this screenshot
The parameter values used depend heavily on the optical system and camera used. I have recently found that the smaller sigma values work best for my current Solar Spectrum filter, whereas in my previous LS35THa and also SolarMax-II 60mm I tended to use much larger values of sigma for unsharp masking, and slightly larger ones for LR deconvolution. The reason for the small sigma value for unsharp masking in the new set-up might be that the contrast for large structures is good enough, and they do not need to be boosted, so I can focus on small detail. Just experimenting in ImPPG is the way to find what suits you best. The image above is the kind that I use for mosaic stitching. My procedure for that is VERY easy: open AutoStich64, click on the "open files" button, select all your panes, and sit back. Any tweaks of contrast after stitching is done in GIMP.
Applying the same settings for sharpening to the flat-field corrected frame yields this:
Result ≠ good
The noise in a single frame just explodes. By stacking 100 frames we can increase the signal-to-noise ratio by a factor of 10 (square root of the number of frames stacked).
I might also want to use a single pane as a detail shot. In that case I like to apply contrast stretching or (partial) invertion of contrast in ImPPG, not GIMP. The reason is that AS!2 outputs 16-bit TIFF files, and ImPPG allows me to work in 16 bit mode with the curves. The results of applying a sigmoidal curve to stretch the contrast in the mid-tones look like this:
The exact degree of contrast stretching is entirely a matter of taste.
One of my favourite contrast tweaks is partial inversion of the contrast. The aim here is to have the region outside the disk in positive contrast (but heavily stretched to bring out proms and spicule detail), and everything on the disk in negative contrast. To achieve this I create a convex curve with a single maximum near the grey level of the spicule layer. The original black and white values are both mapped to zero. I then insert an extra control point to set the apex of the curve at the grey level of the layer of spicules, or a bit above. This point is set to just below white (255) as output value to avoid saturation. The resulting curve is roughly a parabola, which I then correct with two additional control points on either side of the apex. I move these to make the curve on the right a bit concave, and on the left nearly straight. I then tweak until satisfied. The result looks like the one below, and has a 3D feel to it.
A screenshot of ImPPG shows the curves used:
Finally, I might want to turn the image into a pseudo-colour version. To do this I open the image in GIMP, and apply a series of curves for red green and blue to achieve this:
The latter is done with curves that look more-or-less like this
I will add more detail (including screenshots) in due course.