I’m trying to fix up a scan of an old newspaper. It’s in grayscale, I’ve tried doing the below in both .tif and .psd, makes no difference. I’m working on the background layer, in fact there is only the background layer, so that’s not the problem.
When I adjust levels or (even more distinctly) use unsharp mask, I can see the effect of the changes I’m making in preview. The changes are distinct and effective. But once I finish fiddling about with settings and hit OK to process the change, it goes away. Clicking backwards and forward on “history” to see before and after show distinctly that (particularly) applying unsharp mask has made no noticeable difference. And yet when I actually have the unsharp mask dialog box open, on preview I can see very distinct change (and change much for the better).
First off, NEVER work on the backround layer. Go ahead and duplicate the backround layer, and then turn off the backround layer and work on the new layer. If you screw something up, you won’t have to start over. Second, for some reason there’s certain things you just can’t do to the backround layer. I’ll bet if you try this on a new layer it’ll take.
Just a WAG, but is the photo a high-res scan from a newspaper?
If so, the luminence isn’t coming from actual greyscale values, but from a halftone screen. (Zoom in – do you see shades of grey, or black dots of varying density?)
I would not expect unsharp or levels adjustments to yield great results on a high-res halftone image, but you may see the expected results on the preview image.
If this is the case, try applying a gaussian blur first to break up the granularity of the image, so that your pixels come in actual shades of grey instead of black or white.
Larry’s explanation sounds the most reasonable to me… you might be sharpening the printed halftone dots of the page. Sharpening filter works by increasing the contrast of adjacent pixels, after a certain threshold. That works best on a continuous-tone image.
Other than that, I can’t imagine a scenario that would show you results in the preview, but doesn’t apply to the image as a whole, short of a bug.
I agree with others that the problem is probably the newspapers ‘dots’. When you look at preview I think you are seeing a much lower resolution photo, which is actually grey and can be sharpened. Your hi-res photo is made of dots. When you sharpen it, all you are doing is sharpening the ‘dots’. I’ve found that with newspapers and magazines, you get a better scan by using as low a resolution as you can without hurting the image. This seems to blend the dots together and helps avoid getting those weird circular patterns( moiré pattern ) in the large grey areas.
One trick I learned for halftone images was blur it a little then sharpen it. Repeat until the pattern is diminished. The tough part is figuring out how much to blur it.
Some scanner software comes with a halftone correction setting. You can also try scanning it at an angle, but that usually only works if the tone pattern is all horizontal.
Whenever I’m fiddling with photoshop and I can’t tell if what I’m doing is having any effect, I use this trick: before doing the effect, “duplicate” the image so you have another copy of it in another window. Then after doing the effect, use “calculate -> difference” using the two images as the sources and “new document” as the destination. What you end up with is a mostly black or very dark image that has lighter spots where the before-and-after images differ. Cranking the contrast of this really helps you see the impact of your effect. If others’ theories about your problem are correct, I would expect this to result in a black image with little white donuts that define the edges of all your halftone dots.
The background layer is often locked by default. It should indicate that in the layers palette with a little padlock icon. If so, you cannot edit that layer. Make a copy of the layer, or remove the lock by double clicking it, which will call it “layer 0”.
