There are many reasons to explore blur in your images: remove distractions, direct attention, enhance space, modify mood and add interesting visual artifacts are a few among many. Blur can be controlled at the point of capture and in postprocessing. Thoroughly understanding your postprocessing options will help you make choices about when and how to control blur in your images before, during and after exposure.
When it comes to postprocessing, you have options! Photoshop currently offers 14: Field Blur, Iris Blur, Tilt-Shift, Average, Blur, Blur More, Box Blur, Gaussian Blur, Lens Blur, Motion Blur, Radial Blur, Shape Blur, Smart Blur, Surface Blur—in order of appearance in the Filter > Blur drop-down menu. (If you want to extend your software palette even further, explore onOne Software’s FocalPoint.)
At first glance, the list is overwhelming. Where do you start? Get started with this quick survey of available options.
First, play process of elimination. Forget Blur and Blur More; they’re just fixed settings of Gaussian Blur. Put Average at the back of the back shelf; it averages all colors in an image into one, producing a flat field of color; it has extremely limited usefulness.
Second, start with the simple tools, grouping them by similar functions, and work your way up to the more complex ones.
Gaussian Blur is the ultra-simple workhorse everyone needs. It has one slider, Radius, which makes the effect stronger. It averages neighboring pixels; the higher the Radius, the farther its reach. At maximum, it can reduce an image to a flat field of color, a somewhat different color than Average. It’s extremely useful for modifying masks and special effects. It can be synthetically uniform and doesn’t convincingly simulate the more complex aspects of analog lens blurs or bokeh.
Many other blur filters are essentially Gaussian Blur with additional modifiers to alter the effect.
Box Blur produces a blur with a square shape. Rather than uniform, it’s linear, but not as gestural as Motion Blur and offering only 90º angles.
Shape Blur lets you choose from many different shapes, both geometric (these are the most useful—try circles, spirals, grids, triangles, etc.)—and iconic (they’re gimmicky—cats and dogs? Really? Why not?).
Surface Blur preserves contours. Like other blur filters, Radius controls the strength, but unlike others, Threshold controls the modifying effect. With Threshold set at the minimum of 2, no effect takes place. Even with Threshold at a maximum, the original image can be seen through a haze of color.