Adobe Photoshop CS2 On Demand [Electronic resources]

Using a Channel Mask to Control Filter Effects

Photoshop's filters can be applied to any raster image. In addition, filters can be controlled with the use of selections. You can use any of Photoshop's selection tools to define a working area. However, sometimes selections are somewhat limited in what they can do. Although selections can be feathered, they basically represent a cookie-cutter work area. What if you want to apply a filter in a completely different way? For example, you want to apply a filter that is more aggressive on the right side of the image, and slowly tapers off from left to right? In that case a simple selection won't help, but a Channel mask will do exactly what you need.

Use a Channel Mask to Control Filter Effects

Open a document.

Click the

Channels palette, and then click the

Add New Channel button.

Select the

Gradient tool on the toolbox, click a linear gradient, default the foreground and background colors to black and white, and then drag left to right across the new channel mask.

Photoshop creates a horizontal black to white, channel mask.

Select the

Layers palette, and then select the layer containing the image you want to modify.

See Also See Chapter 10,"Creating Layer and Channel Masks," on page 231 for information on using Channel Masks.

Click the

Select menu, and then click

Load Selection .

Click the

Channel list arrow, select the new channel, and leave the other options at their default values.

Click

OK .

Click the

Filters menu, and then click

Filter Gallery .

Click any of the available filters, and then adjust the options until you see what you want.

Click

OK .

The gradient mask (black to white) creates a ramped percentage selection. The white area of the mask is fully selected and the black area is fully masked. As the mask moves to black, the image became less and less selected. When the filter was applied, it lost strength from left to right (matching the shades of gray in the mask).

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