Filter Basics

It would take several entire issues of Photoshop User to even begin to cover all of the filters in Photoshop. Instead, let's take a look at some key strategies to using filters in general - then you can explore the wonderful world of filters on your own.

The first thing you probably want to consider with any filter is whether you want to apply the filter to the entire image or just certain portions. If you want the filter to affect the entire image, don't select anything; just go to the Filter menu and choose your “weapon.” (In an odd quirk of Photoshop, having nothing selected is actually the same as choosing Select All. Go figure.)

To restrict the effects of a filter to a particular area, you'll need to make a selection before using the filter, or use a layer mask (see “Use a Layer Mask to Control a Filter”). If you're going to make a selection, you'll have to decide if you want to feather the selection to make the filter effect blend in with the surrounding area or create a hard-edged effect with little or no feathering on your selection.

Whether you want to use a layer mask or not, it's a good idea to duplicate the Background before applying a filter. That opens up many options, including changing the blend mode, lowering the opacity, or deleting the layer to start over again. Here's one example: We duplicated the Background layer and applied a Gaussian Blur filter. By lowering the filtered layer's Opacity, the effect changes quite dramatically.

After you run a filter, that filter will appear at the top of the Filter menu: Choose it to run the filter again with the same settings you just used. You can also press Command-F (PC: Control-F) to reapply the filter, or Command-Option-F (PC: Control-Alt-F) to open the last filter and choose the settings.

Use a layer mask to control a filter

The following technique offers a high level of flexibility because you can adjust the mask to affect different areas or throw away the duplicated layer completely to return to the original image:

Step 1: Duplicate the Background layer by pressing Command-J (PC: Control-J).
Step 2: Apply the filter (or filters) to the duplicated layer.
Step 3: Click on the Add a Layer Mask icon at the bottom of the Layers palette and then use the Brush tool (B) to paint with black and “hide” the filtered areas.

A few filters, such as Blur and Sharpen, give you several choices. In general, it's best to use filters that offer a dialog rather than those that simply run and produce some result. For example, look under the Sharpen filters (Filter>Sharpen) and you'll see the filter names: Sharpen, Sharpen Edges, Sharpen More. When you click on any of these filters, it will run without a dialog. A filter with an ellipsis after its name, such as Smart Sharpen… or Unsharp Mask…, will open a filter dialog, and many of those dialogs have a preview option.

If you have the option of using a preview, why not use it to see what effect the filter will have on your image before clicking OK to run the filter? Try this: In a filter dialog that has a preview area, click-and-hold in the preview thumbnail to see the before filter image and let go to see the effects of the filter.

You can also click-and-drag with the Hand tool (H) in the preview area to look at a different area of the image. In many (but not all) of these filters, you can drag your mouse onto the image and click to preview that area of the image.

Filter Gallery

One way to experiment with multiple filters is with the Filter Gallery. This dialog lets you add multiple filters, change the order of the filters, or hide filters, and then see the results of these different combinations. Note: It's not the same as using layers, because once you click OK you cannot return and make changes.

Let's look at the steps to using the Filter Gallery:

Click on the triangle beside the filter set name to see the list of individual filters.

Click on the filter thumbnail and enter the settings.

To add another filter, click on the New Effect Layer button at the bottom of the dialog, then choose the filter; otherwise, you'll change the existing filter.

If you want to change the filter order, click-and-drag them up or down in the list. To hide a filter, click the Eye icon beside its name in the list. To hide all of the filters except the current one, Option-click (PC: Alt-click) the Eye icon beside the current filter in the list. And, if you want a bigger preview area, just click on the arrow at the top-right of the filter list.

Finally, here are a few troubleshooting tips when working with filters:

Some filters only work in RGB mode, so if you change the image mode, some filters will be grayed out in the menu.

• You cannot apply a filter to a type layer—you'll first have to rasterize the type. You may want to duplicate the type layer first so that you'll still have an editable type layer.
• If the Filter menu is grayed out, there can be a couple of reasons: your document is in Indexed Color or Bitmap mode, or you're using Free Transform and you need to commit the transformation.

Without question, one of the best ways to learn about filters is to experiment, so with these guidelines in mind, experiment away!

Courtesy of Layers magazine.