Sharpening Images With the High Pass Filter in Photoshop

By Doug Nelson

Dateline: June 13, 2006
Version: Photoshop 7

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Unsharp masking is considered standard practice for sharpening a soft image. It exaggerates the edge contrast of details, but can also inappropriately exaggerate textures, faults, and other artifacts. The High Pass filter offers a more controllable alternative.
Download the mousegirl.zip archive, extract the mousegirl.jpg file, open it and save it as a Photoshop document. Create a duplicate of the background layer by pressing Command/Ctrl-J, then name the new layer High Pass. Set the blending mode of the High Pass layer to Overlay, which temporarily increases the overall contrast of the image.
Select Filter > Other > High Pass and arrange the filter dialog box so you can clearly see it alongside your image; make sure the Preview option is checked, too. Now concentrate on one critical area, such as the girl’s face, and reduce Radius to 0.1 pixels. Slowly drag the Radius slider toward the right and keep an eye on the image as it begins to sharpen. Zoom in and out by pressing Command/Ctrl-+ and Command/Ctrl-–. To maneuver inside the preview, click-drag while pressing Space. The High Pass dialog box preview only shows details that will be sharpened, a significant advantage over Unsharp Mask. Inspecting this allows you to avoid undesirable texture exaggeration in smooth areas like skin. Once you’ve found the optimal Radius, in this instance 10 pixels, click OK.
When you toggle the High Pass layer’s visibility you can see that the girl’s face looks appropriately sharpened, but her hat has been oversharpened. Add a mask and select the mask thumbnail. Hide the oversharpening by painting over the hat and background area with a soft black brush. Restore any accidentally removed sharpness, such as the mouse’s fur, by painting over it with a soft white brush.
At this point, her shirt could use a bit more sharpening, so duplicate the High Pass layer. But this makes everything too sharp! Fix this by selecting the layer mask thumbnail and painting over everything but her shirt with a soft black brush. Even now her shirt is still a bit too sharp, so finish off by lowering the layer’s Opacity. Compare your final version to the unsharpened original by Option/Alt-clicking on the background layer’s visibility icon. The original image is shown at left, with the final one below.
Sharpening Tips
  • Determine the amount of sharpening by your print size and viewing distance.
  • The smaller the final output and the closer it will be viewed, the less sharpening the image will tolerate. An image may need several sharpening passes.
  • Highly textured areas such as foliage need the least sharpening, while faces need the most.
  • Watch for halos. These pale outlines that trace around details are tell-tale evidence of oversharpening.

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Doug Nelson is a freelance writer, technical editor, and founder of RetouchPRO.com, an online community for photo retouchers.