Creative Sharpening with a Layer Mask
Here at Earthbound Light, I've been covering Photoshop masking the last couple of weeks. I've also written a fair bit about sharpening in the past. This week, it's time to put the two together to create a great tool for selectively sharpening just the parts of an image that need it the most.
The idea is to create a duplicate copy of an image on a layer that we then sharpen but hide with a completely black layer mask. We can then use a soft-edged white brush on the mask to selectively "paint in" sharpness where it is needed and to the degree it is needed.
To see this in action, open your favorite image in Photoshop. Now drag the image layer down to the "new layer icon" that looks like a piece of paper with one corner folded over at the bottom of the Layers palette to create a copy. If you have any adjustment layers on top of your image, they will automatically end up on top of both image copies so that their effect will remain unchanged.
Then sharpen the top image copy as you see fit. Smart Sharpening is a great choice, but most any other method will work including standard unsharp masking. Whatever method you choose though, be a bit more aggressive in your sharpening than you might ordinarily be. Adding the mask later will allow you to dial the effect back down to where you need it in each part of the image. Don't get completely ridiculous with it of course since halos and other artifacts will cause problems that no mask can hide. Aim for as sharp as you can get without causing artifacts.
Once that has been done, it's time to hide the sharpened layer completely by adding a black layer mask. With the sharpened layer selected, hold down the Alt key (Option key on Mac OS) and click on the "add layer mask" icon that looks like an empty circle within a square at the bottom of the Layers palette. When you do, all your hard work at sharpening will disappear since the black mask hides the entire layer. As such, your image will now look the same as it did before you created the duplicate image layer.
Everything so far was just to get us ready for the magic that happens next.
Select a soft-edged white brush and set the brush opacity to around ten percent. Use this brush to paint on the sharpening layer's mask wherever you want to add sharpness. You can easily control how much sharpness since each stroke of the brush will add more as you build up white on the originally black mask at that point. Remember, with layer masks, black hides, and white reveals. Once you get to pure white you can't make things any sharper off course, but since we started with the layer being a bit too sharp, there should be no danger of running out of headroom. If you accidentally sharpen something more than you'd like, simply switch your brush color to black and darken down the mask at that point.
The eye is naturally drawn to sharpness. When deciding what to selectively sharpen, think about what you want the viewer to notice in your image. Limit your sharpening to just those areas that really need it. Your goal should be to add impact, something that would be lost if you sharpened too much of the image. This technique is for creative sharpening, not output sharpening as you normally would do to an entire image to get it ready for printing.
Selective sharpening lets you combine two very useful Photoshop tools to give you a powerful technique that would be hard to do any other way. Using masking and sharpening together allows you to creatively emphasize what you want people to look at in an image, without adding undue attention to everything else.