Add JPEG artifact removal filter
Submitted by David R Tribble
Link to original bug (#768462)
Description
Created attachment 330926 PaintShop Pro dialog: JPEG Artifact Removal
The current accepted technique for removing (or at least reducing) JPEG artifacts from images is generally a two-step process of 1) applying a smoothing filter, typically a Selective Gaussian Blur filter with a fairly large radius (more than 2 or 3 pixels wide) and a small delta (10 or less); and then 2) applying a sharpening filter, typically an Unsharp Mask with a fairly large radius (5 pixels or so) and a small effect (0.5 or so). The first step smooths out the larger JPEG artifact jaggies, and the second step restores some of the crispness of the edges in the image.
See, for example, the one-page description at http://plasmasturm.org/log/124 . There is also a guy with a PhD thesis about cleaning up JPEG images (and other lossy compression schemes) which might be worth digging into, at http://www.logarithmic.net/pfh/blog/01068940800 .
Some of the recommended techniques found in the web also add noise or apply the Gaussian blur multiple times with different parameters, but the idea is basically the same: filtering to smooth the JPEG noise artifacts, and then filtering to restore the edges.
It would be nice to combine these two steps into a single filter dialog, one having two basic settings: 'strength' or 'effect', which controls how wide and how much smoothing to apply; and 'crispness' or 'preserve edges', which controls how much to sharpen the smoothed image. Another possible control value could be 'JPEG block width', which could be 8 or 16 to reflect the underlying image's JPEG block size, which could be used to control where the edges are in the image blocks and where the JPEG artifacts are more likely to be concentrated.
An existing example of this kind of filter can be found in Paint Shop Pro (v7) (which I've been keeping alive for several years as long as it will still run on MS/Windows), which has a filter called, appropriately, 'JPEG Artifact Removal' which apparently performs the same kind of 2-step filtering process (see attached dialog image).
Note that this new filter would (probably) not add any new mathematical image manipulation functionality that does already exist in GIMP, but it would be a time-saver by combining multiple filtering steps into a single dialog.
Attachment 330926, "PaintShop Pro dialog: JPEG Artifact Removal":
Version: git master