Photoshop Tutorial: One of the basic problems with sharpening is the so-called halo effect. It is a luminous border around the edges, broader than the sharpening area, that springs to life as a side-effect of contrast differences at the edges (i.e., sharpening). You can easily observe the phenomenon when using Unsharp Mask a great deal. If the effect is too strong, the photo is oversharpened. Now we introduce High Pass sharpening that can bring better results when used appropriately, and produces less halo.
We want to apply a bit of sharpening to this slightly soft photo.
All you need to do is to duplicate the original Background layer by dragging its row upon the indicated icon on the Layers palette. Select the duplicate layer and set the general effect mode from Normal to Overlay.
The original image gets a lot of contrast. We need to refine it so that the high difference in contrasts is strong only along the edges, but weaker in all other areas.
We’ll use Filter/Other/High Pass for this purpose. The appearing dialog lets you set the Radius value for the High Pass filter. If you want to sharpen very fine, tiny details, or the photo is relatively small, use a Radius value of 1 or less. Use a higher value when you want to sharpen the edges more strongly. Of course, the rule of thumb is once again “decide according to taste”.
We have set a Radius of 1.5, a rather high value for such a small picture, to demonstrate the sharpening effect better for you, Dear Reader.
In fact, you could already merge the two layers and sit back, but you may also take another step forward. Never mind that you’ve set the sharpening effect a bit too harsh, now it’s time for some refining.
Stay on the same layer, and activate the High Pass filter again to process the photo once more. Use the previous Radius value, or a lower one. This way, more fine details will get emphasized. We have used a value of 1 the second time. If you want to refine the sharpening even more, select the Soft Light effect mode instead of Overlay, or drag the Opacity slider to a lower value.
When you’re done, click Layer/Flatten Image to merge the layers, and there you go:
before / after