Wednesday, February 16, 2005

When to best use Unsharp Mask?

I like to increase my file sizes using Photoshop's Bicubic Interpolation system. This involves increasing a 200 ppi file up to 300 ppi. I do this in small increments at a time. Up to now, I have been adding Unsharp Mask at the end using about 200-250%. While I have no complaints with my final results, I thought that I would be better off using a small amount of Unsharp Mask, maybe 40-50% with each incremental increase.

Of course there are as many strategies as there are users; but my suggestion is as follows:

1) If the files are from a digital camera, I would perform some light unsharp mask on the files after the first incremental interpolation: and then after the final incremental interpolation. I would perform the final unsharp mask based on the final image size to be printed. If there is a possibility that the image will be resized in the future to different sizes for different uses, I would make a duplicate copy of the file without the final application of the unsharp mask to keep as an archive copy and use copies of the archive file as the base upon which the final unsharp mask will be applied according to the sizing of the image required for the purposes at hand.

2) If the files are not from a digital camera but from scanner or another source, I would skip the preliminary application of the unsharp mask and then proceed with the rest of the steps suggested in 1).

Here is another take:

1. Always apply your unsharp mask to a separate duplicated layer above your main layer (change the duplicated layer to "luminosity" blend mode). This way you won't end up with any color shifts.

You also may want to apply unsharp mask selectively to the channels (usually your blue channel will need more masking than the other channels).

2. Always make your color corrections, file edits, touchups and general work on your photo BEFORE you make any size changes, or use unsharp mask at all. This goes hand in hand with keeping an original untouched file as your starting point. Always work on a copy of this original, not the original itself. This way you can always go back to it later.

3. Apply unsharp mask very sparingly after each incremental shift upwards. VERY sparingly. If you are going down in size, unsharp masking is not quite as important, but can still give you some good results.

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