Photoshop® CS4 Bible

20.3. Blurring and Sharpening

A pair of complementary techniques — blurring and sharpening — are often used to repair or correct images. Blurring works by reducing contrast between pixels, thereby smoothing out trouble spots, while sharpening enhances contrast between pixels, producing crisp images. In this section, these two techniques are examined in detail.

20.3.1. Blur

Two of the powerhouses of the Blur family of filters — Gaussian Blur and Lens Blur — have already been covered in Chapter 17, in the context of removing noise and pixelization. To recap quickly, the Gaussian Blur filter analyzes pixels in relation to their neighbors, and reduces the contrast between them based on a bell-shaped curve. Enter a value from 1.0 to 250 to increase the intensity of the blur.

Lens Blur, a more complex filter, is used to bring specific areas of an image into or out of focus, giving you the ability to simulate shallow depth-of-field effects that are normally performed by photographers in-camera, through the use of lenses with wide apertures. The areas of the photo that are in focus can be determined either by a depth map based on a layer's transparency, its layer mask, or an alpha channel.

In the following sections, the remaining variations of the blur filters are covered in more detail.

NOTE

For more on the Gaussian Blur and Lens Blur filters, refer to Chapter 17.

20.3.1.1. Smart Blur

Smart Blur is designed to blur low-contrast areas in a photo while preserving edges, making it useful ...