Chapter 22. Compositing with Channels


  • Applying images

  • Using calculations

Much of Photoshop's power lies in its ability to combine images. Multiple images can be collaged together as layers, and their trans-parency can be precisely controlled with opacity adjustments, blending modes, and with layer masks. The shape of layer content can be altered with clipping groups. Selections and alpha channels can also be combined as can other types of masks.

The two Photoshop channel operations that this chapter covers, Apply Image and Calculations, were essential in earlier versions of Photoshop to produce many of the effects that Layer Styles and Blend modes now can do with con-siderably more ease. Still, these commands can still be extremely useful for accurate compositing and making accurate selections. Because they use for-mulas that compare the brightness values of channels they are sometimes called Chops short for channel operations. Chops affect the core color or selection information that constitute Photoshop documents. Compositing information from multiple channels can produce amazing results.

Applying Images

Many of the Apply images features are similar to the blending modes in the Layers palette. But there are two big differences. Apply image combines the contents of two separate documents into a single document. Within the dia-log box you have the ability to target individual layers and channels that give it additional functionality.

The Apply Image command can apply the ...

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