A Better Method of Sharpening Pictures in Photoshop
This technique will be completely different than any picture sharpening technique you have seen before. Properly used, it will produce a picture that appears distinctly sharper when viewed from a normal viewing distance, but which will show no obvious sharpening artifacts, even viewed close up. In fact, if you do a close-up side-by-side comparison with small parts of the original the differences – even the added sharpness – will not be obvious. I currently use this technique on the majority of photos from which I intend to make large prints, and it is especially useful when trying to stretch the resolution of a picture to make a convincing large print. I have used it several times to make convincing prints covering most of 13" x 19" paper from originals that are 1000 to 1600 pixels in the major dimension. However, that should not be expected to work satisfactorily for every picture.
First, prepare the picture. Do any image content corrections that are planned, fixing scratches, etc. Do any gross corrections in levels, color, brightness, etc. that are necessary to bring the picture to the approximate overall final state for printing. I do not use layers to do these initial gross corrections, but if you do, flatten the image. Resize the picture to sufficient pixels to make a good print. My own nominal standard for this is 300 pixels per inch in the final print. If you normally do some "regular" sharpening, this is the time to do it. In fact, any regular sharpening that is not overdone will be enhanced by the method. I sometimes do this, but I recommend first trying the method without regular sharpening.
Now use the technique. First, make a duplicate layer of the Background layer. I usually call the duplicate layer "Sharp." With the duplicate layer selected, set up an extreme unsharp mask. Settings which might be considered typical for this step are: Amount 150%, Radius 250 pixels, Threshold 5 levels. Those are not typographical errors. They really are the appropriate settings for an image with a nominal 5000 pixels on the major side. For different pixel counts, try a Radius of about 0.05 times the maximum pixel dimension.
Unlike the normal usage of the unsharp mask, you will find this takes a very long time. You may have to wait many seconds or even minutes for a preview and even if you skip on waiting for that, it will take a long time to perform the filter function – again perhaps minutes. Do not be alarmed by the result. What you want at this stage is an image that appears very sharp although parts may be lacking in detail and will have apparent high contrast and patches of exaggerated color. About the only significant problem that I have seen at this point is wide, very light, halos around large dark areas of the picture, and I have only seen that once or twice. The proper way to solve that is to select out the dark area and separately sharpen the two parts of the picture, combining the results. But if this happens, select another picture for a first test of the method.
The next step is to change the opacity of the Sharp (or whatever you called the duplicate) layer. Select the Layers tab in the Layers-Channels-Paths box and select the Sharp layer. Make sure "Normal" is selected on the pulldown at top left of the box and in the top right of the box use the Opacity pulldown to select an opacity of 20%. That setting should be approximately correct, but you will need to experiment with setting it at values between about 10% and 40%, switching the Sharp layer on and off to compare with the original. I usually leave it at a point where the overall sharpening effect is obvious during on/off comparisons but close examination does not reveal any annoying artifacts. Usually this is 15% to 20%, but it varies a lot for different pictures. It is likely that at first you may select opacities that are a little too high for best print results. Once you are satisfied, you can merge the Background and Sharp layers, although I often leave them separate. Then continue on to make any further layers adjustments, masking, etc., to bring the picture to its final appearance. The sharpening process will increase apparent image contrast somewhat. Often this is beneficial, but if it is not, use standard adjustment techniques to remove it.
While it is necessary to experiment with the opacity setting to get the best result, you may also find it interesting to experiment with the unsharp mask settings. You may find that somewhat different settings work better with your setup. If you are interested in why this technique works, send me an e-mail. The technique has more history behind it than you might think. As this method of implementation is original with us, you are welcome to use it in an article, a course, or a book but please credit C F Systems and www.c-f-systems.com
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