@urban-toolkit/autk-core

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@urban-toolkit/autk-core / computeAlphaByte

Function: computeAlphaByte()

computeAlphaByte(value, context): number

Defined in: transfer-function.ts:146

Computes alpha as an 8-bit channel value for a scalar value.

NaN values are always mapped to 0 (transparent). The mapping uses the precomputed context bounds and the resolved transfer-function configuration, applies gamma shaping when config.gamma differs from 1, and clamps the result to the byte range [0, 255].

Parameters

value

number

Scalar value to map into an alpha byte.

context

TransferContext

Precomputed transfer-function context from buildTransferContext.

Returns

number

Alpha channel value in the integer range [0, 255].

Throws

Never throws. Returns 0 for NaN input.

Example

const ctx = buildTransferContext([0, 100], { mode: 'linear' });
computeAlphaByte(50, ctx);  // → 128 (midpoint)
computeAlphaByte(NaN, ctx); // → 0   (transparent)