The Blur menu has six entries. All but the first one end with an ellipsis, which indicates that those filters bring up a dialog to set their parameters before acting on the image.
The Blur filter has no parameters and operates instantly. It works by computing the average of each pixel and its immediate neighbors. On a large image, its effect is imperceptible. Figure 17-3 shows only a small part of a photograph, which is zoomed in to make the effect visible. Figure 17-4 shows the same image after three applications of the Blur filter. This a rather clunky way to adjust the amount of blur on an image, but it is very fast.
Figure 17-3. The initial image
Figure 17-4. After using Blur three times
Figure 17-5. The Gaussian Blur ...