If you’re a Lightroom user you’ll know that in Lightroom you can mask the sharpening you apply to an image so it is applied to the edges in the image only. This same feature is not yet available in Photoshop and the sharpening filters there are applied to the entire image rather than just edge detail.
However you can achieve a reasonable approximation of the Lightroom masking feature in Photoshop using the Photoshop Find Edges filter. The benefit of this is you can apply more sharpening to the image than you would do without the masking effect and areas of flat color like skies and skin tones won’t be sharpened. Here’s how to do this.
How to Sharpen Image Edges in Photoshop
Once you have finished processing your image in Photoshop, flatten the image to a single layer or make a single layer of the edited image by adding a new layer at the top of the Layer palette and press Ctrl + Alt + Shift + E (Command + Option + Shift + E on the Mac) to create a flattened version of the image on that layer.
Duplicate the flattened layer twice.
Target the topmost layer – you will create your sharpening mask from this layer. Choose Image > Adjustments > Desaturate to convert it to black and white then choose Filter > Stylize > Find Edges to isolate the edges in the image.
Choose Image > Adjustments > Invert to invert the colors so that what is black is white and vice versa.
Choose Image > Adjustments > Levels and adjust the mask so that it shows white in the areas that you want to sharpen and black in those areas that you do not want to sharpen.
Once you have a good mask, blur its edges slightly by choosing Filter > Blur > Gaussian Blur and apply a 1 or 2 pixel blur to it. When this is done, hide the sharpening mask layer by turning its visibility icon off in the Layer palette.
Now target the second topmost layer in the image and click the Add Layer Mask icon at the foot of the Layer palette.
Click the mask thumbnail on this layer to target it and choose Image > Apply Image to open the Apply Image dialog. From the Layer dropdown list select the layer that contains the hidden sharpening mask, and click Ok.
Click on the image thumbnail on this layer to target it and apply your sharpening to this layer – use Smart Sharpen or Unsharp Mask as desired. When you set the slider values, view the result on the image and not using the preview in the sharpening dialog. The preview in the dialog doesn’t take into account the mask you have applied – the image itself does. Click Ok when you’re done.
To compare the before and after result of sharpening the image with an edge mask, Shift + Click on the mask layer thumbnail to disable it and see the image as it would look sharpened and without the masking effect. Click the mask thumbnail again to enable the mask again. You can discard the hidden mask layer now, if desired as it is no longer needed.
While this sharpening mask takes some effort to create once you’ve done it a few times you will find the process quite straightforward and some of its creation can be automated using Actions.