On the fly postprocessing (sharpening)OverviewStacking alone usually does not suffice to produce an impressive picture. A lot of algorithms exist which aim at modifying the image data in a way to enhance fine details and/or contrast. Of course, if one applies these methods too strongly or in an otherwise not fitting way, artifacts can be generated. Also, sharpening algorithms not only enhance the image detail, but also the noise. Nevertheless, sharpening is almost a must in planetary imaging.In PEAAnuts, 3 postprocessing algorithms are integrated:
It is possible to execute one or more of the available modules directly after completion of a new stack. If more than one module is selected, their order of application can be chosen, too. Cascading applicationThe LR deconvolution and unsharp masking modules both offer the option to be applied multiple times in a cascading manner, with stepwise modified parameters. For example, one can perform LR deconvolution three times, with decreasing radii. How much the parameters should change with each cascading step can be specified with factors. So for a start radius of 2, a radius factor of 0.8 and 3 cascading steps, the LR dec. module will be applied once with r=2.0, then with r=2.0*0.8, and finally with r=2.0*0.8*0.8.Contrast sensitivityThis option is available for LR deconvolution and unsharp masking. It is a rather simple means which adapts the sharpening effect according to the locally detected contrast in the image. This can help in reducing artifacts, esp. at the planet limb (the so called ring artifact). It works quite good for planets with natural limb darkening, like Jupiter and Saturn. However, the ring artifact is also diffraction related, so, to be exact, its complete supression needs more elaborate methods. This problem is of course more apparent when imaging Mercury, Venus and Mars with their bright rims on the illuminated side. So, naturally the performance of the simple contrast sensitivity feature in terms of ring artifact suppression depends on the situation.Example: Sharpening with the unsharp mask tool only. Left side without, right side with active contrast sensitivity option: ![]() Applying parameter changesDuring a running live stacking session, parameter changes will have an effect upon the next arriving stack. So one way of adjusting parameters is to run a session with a lower stack count, resulting in stacks arriving quickly. Then tweak parameters, look at the result on the next stack, and so on, until one is satisfied with the setting. The other way is to stop the live stacking with the 'S' button. Then parameter changes in the dialog can be applied immediately with the so-named button in the dialog. After deciding upon a specific parameter combination, the live stacking can be continued by clicking the '>' button, all further stacks will then be processed with the new parameters.Special hintsThe unsharp masking module allows to set a strength factor < 1.0, meaning a softening rather than a sharpening. Esp. with cascading execution, on may use this for a simple denoising. Just set strength, strength multiplier and cascading steps such that for the last step, a strength value < 1.0 results.State of developmentAll sharpening modules are still in an experimental state, and in need of more or less development. Usually they work quite OK already. One sign of the unfinished state is the frame like appearence which will occur at the image border. As this does not have an effect on the planet image in the center, the issue might be acceptable for the moment.Certainly, more tests are necessary to see if the currently implemented ranges for the parameters are sufficient, or if they need to be increased/decreased. |