RFC: new module pixeldeblur

[weltyj]

Also addressed style problems found by Pascal Obry on Feb 21., and cleaned out a little more unused code.

Another thought -- the "sharpen" module only works on the "L" component in Lab colorspace. This could do the same, but with an option to additionally deblur the "ab" components too. Personally I think the right way is to deblur all three components, in order to catch the cases where "L" is the same between some pixels but the "a" or "b" is more different than "L".

It would run about 2x faster if only deblurring the "L" component based on an extensive test of 1 image ;-).

[weltyj]

Just another thought I had while out walking, the real genesis of this module was literally thinking about deblurring a slightly out of focus image or slightly soft lens. It is not intented to provide perceptual sharpening (like the traditional unsharp mask). Looking at how images are downscaled (via bilinear,bicubic,lanczos), and particularly how lanzcos will create slight halos, I really wonder if this should be in the processing chain before any pixel scaling happens -- as @jenshannoschwalm was thinking on the other PR.

Thanks all (especially @TurboGit) for your help/guidance.

FYI -- I'll be "off the grid" for a week.

[github-actions]

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[github-actions]

This pull request has been marked as stale due to inactivity for the last 60 days. It will be automatically closed in 300 days if no update occurs. Please verify it has no conflicts with the master branch and rebase if needed. Mention it now if you need help or give permission to other people to finish your work.