Sharpening using unsharp masks

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I intend to post a few articles on sharpening images over the next week. This exercise should get you thinking about the subject.

One of the best methods in Photoshop is to use the unsharp mask filter. It initially seems a little peverse to have the term unsharp in a technique for sharpening, but if you work through the following procedure it should give you some insight into how an unsharp mask works.

1. Open your image in Photoshop and duplicate in a new layer.

2. Desaturate the new layer (Image - Adjustments - Desaturate).

3. Duplicate this desaturated layer, then invert the new layer (Image - Adjustments - Invert).

4. Change the blending mode to Colour Dodge.

5. In most cases the image will now appear completely white, but there may be some black areas if the original image had pure black in.

6. Slightly blur the image (Filter - Blur - Gaussian blur) by a few pixels radius.

7. Select the top two layers and merge them.

8. You should now see a soft ghost-like outline of the original image (as above) - this is your unsharp mask.

9. Change the blending mode of this layer to Multiply.

10. The image should appear sharper (since these images are reduced in size the effect here is not that overwhelming - on your full resolution image you should see a significant difference).

A full discussion will follow soon.

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