Alpha Channel

Updated 22 Sep 2026

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What it is
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  an additional image channel representing opacity or coverage for compositing
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Common interpretation
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  normalized $\alpha=0$ - fully transparent
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  normalized $\alpha = 1$ - fully opaque
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Simple compositing
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  over an opaque background, with straight colors in an appropriate linear working space: $C_{\text{out}}=\alpha C_{\text{foreground}}+(1-\alpha)C_{\text{background}}$
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Caution
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  alpha is not an adidtional color component
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  straight and premultiplied-alpha represntations use different stored-color conventions
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Related
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  RGB Color Model

Linked references 2