Switched Keys

There is a tool a filter actually in Photoshop that is useful for a number of things. Recently I've been experimenting and reading more about the High Pass filter. It is most useful for sharpening. Yet there are numerous ways it can be used. Basic High Pass One of the easiest ways to use it is as a separate layer.

1. Once the image is ready to sharpen you need to make a copy of the image. If the image is multiple layers you may need to make a stamp a layer with all layers flattened. Using that layer select Filter > Other > High Pass.
2. Adjust the radius until you see a good outline of the image. It looks like a grayscale image except that the detail edges are lightened or darkened. 1 to 4 pixels is usually enough.
3. The next step is simply to set the layer blend mode to overlay. And you're done. Unless you want to experiment with some other ways to use High Pass.

Intermediate High Pass Another way to use High Pass is to use it as a mask.

1. Duplicate or Stamp your image two times.
2. On the top duplicate select Filter > Other > High Pass. This creates the high pass layer.
3. Next turn all layers off except this one. Go to the Channels palette and Ctrl-click on the RGB channel. That creates a selection of the High Pass layer.
4. Then go to the second duplicate image you made and click the layer mask icon. That essentially turns the High Pass layer into a mask. Then you can sharpen the image.

Extreme High Pass Of course you may not be done there either. There are many other things you can do with the High Pass or the High Pass mask.

• You can possibly improve the effect if you sharpen the mask. Select the mask and then sharpen like you would an image.
• You could also outline the mask by either using Image > Adjustments > Threshold or by using Filter > Stylize > Find Edges.
• If you want a more subtle effect you can either blur any of these masks or adjust opacity.
• You might also want to reverse the mask for special effects or use it as a mask for softening the other parts of the image.
• You can also spread or compress the mask by using Image > Adjustments > Minimize or Image > Adjustments > Maximize.

BTW you can select and display the image in a mask by Alt-clicking on the mask. This may be needed to cleanup the mask. Photoshop is still not that magical that you don't need to do some touchup.