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Chapter 7. Transparency > Basic Compositing Computations

7.2. Basic Compositing Computations

This section describes the basic computations for compositing a single object with its backdrop. These computations are extended in Section 7.3, “Transparency Groups,” to cover groups consisting of multiple objects.

7.2.1. Basic Notation for Compositing Computations

In general, variable names in this chapter consisting of a lowercase letter denote a scalar quantity, such as an opacity. Uppercase letters denote a value with multiple scalar components, such as a color. In the descriptions of the basic color compositing computations, color values are generally denoted by the letter C, with a mnemonic subscript indicating which of several color values is being referred to; for instance, Cs stands for “source color.” Shape and opacity values are denoted respectively by the letters f (for “form factor”) and q (for “opaqueness”)—again with a mnemonic subscript, such as qs for “source opacity.” The symbol (alpha) stands for a product of shape and opacity values.


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