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Chapter 14. Manipulating Images with Fil... > Using a Channel Mask to Control Filt...

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 209 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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