Filter

• Photoshop comes with a variety of filters. There is also an entire industry of companies who publish after-market Photoshop filters, or "plug-ins." A filter can be applied to an entire digital image or a selection of an image. Some filters are very basic. Some are sophisticated. One of the great stock filters in Photoshop renders any digital image as a watercolor painting --- quite believably.
  
  

Distortion

• Adobe's categorization of its effects into "filters, distortion and adjustments" seems a little arbitrary. Under distortion, the lens correction effect is anti-distortion. It allows you to digitally undo the distortion your lens created on the image. You can straighten horizons and take exaggerated perspective out of buildings. Or, you can exaggerate them if you want.
  
  

Adjustment

• Some of Photoshop's most commonly used effects allow users to essentially change the development of the image, after it's taken. Adjustments allow the brightness and contrast of an image to be increased and decreased. The color balance can be adjusted. The saturation of hues can be increased, or colors can be muted.
  
  

Custom Techniques and Effects

• Each effect so far has been an effect engineered by Photoshop. In other words, the effect you get is the effect Adobe intended. Many of the greatest effects available to the photoshop user are custom effects derived from the application of several effects. Myriad books have been written on how to use Photoshop and achieve certain effects. One example is to use the Gaussian blur effect and the layers feature to create a shadow effect.