Photoshop® CS4 Bible

17.4. Blurring

Instinctively, blurring seems like the last thing you would want to do to enhance a photograph — after all, it's usually ingrained in us very early on that most pictures look their best when they are crystal clear and everything is in focus.

Nevertheless, blurring can be a useful way to reduce the appearance of grain or other artifacts in an image. Blurring can also be used creatively to emphasize specific areas of an image or to create a specific atmosphere by toning down distracting background elements.

Blurring works by reducing the contrast between pixels and smoothing out transitions between colored areas. Pixels are examined and manipulated in relation to their neighbors. Two of the major blurring tools — Gaussian Blur and Lens Blur — are covered in this chapter, while the remaining filters in the Blur subcategory of the Filter menu are covered in Chapter 20.

17.4.1. Gaussian blur

Despite (or maybe because of) its simplicity, the Gaussian Blur filter is the one that most Photoshop users reach for first to satisfy their blurring needs. Selecting it from the FiltersBlur menu produces a rather simplistic dialog box with a Preview window and single slider labeled Radius, which controls the amount of blur that is applied to the image.

Enter a value from 1.0 to 250, and a blur is calculated based on a bell-shaped curve. To illustrate the effect of the Gaussian Blur ...