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Image cleanup (descreening, levelling, stitching, scanning)
Important topics on moe, and info is pretty scattered, so maybe we should gather what we know. If anyone knows of an active forum thread on another board for these topics, we can just go there instead of duplicating it, but I havn't found any.

scanning, descreening GREYc (hi, admin2): http://uruchai.com/2007/10/26/high-res-scanning-for-dummies

scanning, descreening, Neat Image: http://www.pireze.org/blog/?p=250

Descreening without a high res source (eg. image recovery): This is hard, and will probably never turn a noisy image into a very clear one without destroying the resolution, but it must be possible to at last improve things a bit. I've yet to have any success, though, and the descreening tutorials out there are all for making very clean 300 DPI images from prestine 600-1200 DPI scans, not for improving those noisy 300 DPI scans.

Stitching: For poster scans in multiple, overlapping parts (the easiest things to stich), what's a good method for color matching layers in PS? Sometimes they've been levelled separately, resulting in them not matching each other. The "match color" adjustment doesn't seem to fix it; manual levels never really matches (likely a skill problem on my part).

Stitching: for images with missing parts, is filling in the image something the non-artists among us should even consider? Filling in color is sometimes fairly easy, but I've never been able to fill in outlines on even the simplest of images. This may be an "if you have to ask, you can't do it" topic, but when an image is missing 1/8" in the middle, it feels like I should be able to do something.
I can only remove noise for the most part, but I'm not that great. I will try to get someone who's good at it to post here eventually.

Anyways, I've sorta stopped scanning at the moment, turns out my random lockups while using GREYc is due to my q6600 overheating (it idles at 55c[!?!?!]), so I gotta replace the heatsink/fan before I can figure out a good combo for wraith's scans on GREYc. Besides that, cleaning scans is a lot like black magic to be honest. Before using GREYc I used to just play around with built in photoshop filters. If I remember right I used blur, blur more, median after resizing a 600dpi scan in to 300 or 150.
is GREYc better than noiseninja?
(Went to post this in a comment re: post #16774, then remembered there's a better place ...)

Watch out for those little white lines at the edges of images when cleaning up images--they really stand out when there's a sharp color contrast at the edge, and it's really easy to miss in Photoshop. I try to remember to view cleanups in something like ACDSee (with a dark background), and it's usually just a couple pixels to crop.
Petopeto? Personally I don't see anything wrong with those white lines. On average i would say most users would have some kind of graphic software and removing those would be a sinch, but if you're looking for perfection, then it would be ok.

If they don't the image wouldn't be editable for them anyway.

But like you said, just crop it larger than the image and sitck it above a pure black background and you'll see the white spots, and vice verse for dark spots.
I view images on a black background (even in browser, I use a CSS override to change the post/show page to black), so when an image has a white line a few pixels thick on the edge, it sticks out.

("Users can do that themselves"--of course they can, they can also denoise and remove dust spots and relevel images themselves, but if you're cleaning up an image for upload, it's an easy thing to do while you're in there.)

(Of course, the image being cleaned up was uploaded initially by me, so this is a reminder to myself as much as a suggestion to others ...)