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Wednesday, 27 March 2013

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Thanks Ctein,
very useful tip.

Seriously useful tip. I'll have to remember this next time I'm dealing with a battered old print I need to scan properly.

a remarkable coincidence (if it is one) that you and Thom Hogan talk about the stack-and-mean technique on the same day!

Thanks Ctein, I do alot of restoration and I appreciate finding new methods that work to deal with problems, (or, rather, challenges). I actually turned away a large and very complexly cracked hand coloured photograph recently because my methods would have made the restoration beyond the clients budget - this may have helped, though the damage was more crater like rather than linear. With black and white photos I often find that a slight difference in reflectance can be reduced by the same methods as those to deal with tarnishing, i.e. more often through the blue channel or more crudely using the blue or cyan in Hue/Saturation. Adjusting Lightness, for example, in the hues changes density for uneven areas and is a quick way of reducing stains on black and white photos: I don't think I can tell you anything new, Ctein, your book on Digital Restoration has been a great help. The interesting thing about restoring is that there are many varied techniques that can be used effectively for different levels of finish - mainly dictated, for me, by the size of reproduction that is asked for. Many small faults are often useen in a finished print, so it is often the case to not work on areas at too great a screen magnification or it becomes too time consuming - and not many customers want to pay me for more than an hour or twos work.
Thankyou, Mark Walker.

Dear almost...,

Yes, total coincidence; Thom and I don't even much correspond with each other.

What this trick did teach me is that I need to look a lot more closely at Photoshop's "Statistics" functions, which I'd been pretty much ignoring.

pax / Ctein

Wow! Nice one Ctien. I guess I'm gonna have to go ahead and buy your book on photo restoration. I've been putting it off for a couple of years. If congress were full of critters like myself, the spending problem would be solved! But could you please tell Mike to stop renting, reviewing, and then buying cameras. My defenses are weakening.

Huh; how does that work? I guess the actual lighting at the moment of sampling is more complex than the model in my head (no real surprise there). Ah; but the light and the sensors can't be exactly aligned for reflective materials, so there's an angle one way or the other. Yep, okay, makes sense now.

Anyway it clearly does work, those are good illustrations.

Can I ask your readers "Can it be done without an Extended version of PS?".

Very clever trick to stash away. Thank you.

Unfortunately, while I may remember having stashed such a tip it's unlikely that I'll be able to recall where.

Very nice. I have CS5 (not extended), so I put the second image as a new layer over the first and set opacity to 50%--seemed to do the trick.

@Steven House.... the Thom Hogan article linked to above in a comment explains how to do his averaging with layers too, in regular Photoshop. He is using it for noise, but I suspect you can do this as well.

Dear Mark,

Although the illustration for this article shows cracks, this technique really isn't about cracks, it's about any ripples or other deviations from flatness in the print. Basically, if the print doesn't lie perfectly flat on the platen of the scanner, there will be variations in brightness and this technique will largely eliminate those variations. So, depending on the nature the “craters” in your prints, it may considerably help with those.

It's powerful enough that unless I start off with a print that I know is perfectly flat, I make two scans in reverse directions as a matter of course.

~~~~

Dear Walt,

Well, this particular trick isn't in the book; I learned of it after I wrote the most recent edition (which is well over two years old and, no, there isn't going to be a third edition for at least another 18 months).

But there are plenty of other cool tricks!


pax \ Ctein
[ Please excuse any word-salad. MacSpeech in training! ]
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-- Ctein's Online Gallery http://ctein.com 
-- Digital Restorations http://photo-repair.com 
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Throw the scanner out the window for this type of picture. Use a copy stand and cross-polarize.

Dear Bob,

If you reread my book, you'll find I cover that in detail.

Here's the thing. It doesn't work any better than the scanning trick (although it is a lot better for tarnish and other reflective blemishes). So, depends on your setup.

If you don't have a cross-polarized copy stand permanently set up (more photographers have scanners ready to go than copy stands ) it's a lot more time and effort consuming. If you do it's definitely faster.

Note: some restoration work is best done with much higher resolution images than you may get from an ordinary digital camera.

pax / Ctein

For the honeycomb papers you need the Fast Fourier Transform that is only available for Windows. I could retouch a reproduction of an old photo with that pattern using Imagej for Mac OSX. Is for those times you have not the original photo to rescan. But I don't believe if it works with a cracked photo.

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