Any Filter, Any Mode

Here's one of my favorite tricks.

Most of the tools in Photoshop can work in different modes. The Blur tool, for example, can be set to Lighten or Darken. In Lighten mode, the Blur tool will only make things lighter, never darker.

Here's the original photo, the results of the Blur tool applied in Lighten mode, and the results of the Blur tool applied in Darken mode.

What you can't do is apply a blur filter, such as Gaussian Blur, in a given blending mode.

Well, actually, you can. You can apply any filter or any tool in (almost) any blending mode with a little trick: the Fade tool.

Apply any filter to your photo. Now, from the menu, select Edit | Fade.

The Fade dialog lets you fade the effect of the last tool or filter, but you can also change its mode. Choose the blending mode of your choice from the Mode drop down menu.

Leave the slider set to 100% ... or drag it to the left to fade the effect. Click OK to apply your filter in its new blending mode.

Note: You can use this trick for tools such as the paintbrush, too, but it only works on the last stroke. If you paint 15 or 20 strokes, you'll have to use a different trick to change their blending mode after the fact.