# applyGamma(linearParameters:exponentialParameters:boundary:destination:) Applies a piecewise gamma calculation to a 32-bit pixel buffer. ``` func applyGamma(linearParameters: (scale: Float, bias: Float), exponentialParameters: (scale: Float, preBias: Float, gamma: Float, postBias: Float), boundary: Float, destination: vImage.PixelBuffer) ``` ## Parameters `linearParameters` The scale and bias applied to pixels with a value below `boundary`. `exponentialParameters` The boundary value that defines whether the function transforms pixels with the linear or the exponential calculation. `boundary` The parameters that the function uses for the exponential calculation. `destination` The destination pixel buffer. ## Discussion This function computes the output value of each pixel using the following pseudocode: ```swift For each source pixel value x: if x < boundary: scale = linearParameters.scale bias = linearParameters.bias r = x * scale + bias else: scale = exponentialParameters.scale preBias = exponentialParameters.preBias gamma = exponentialParameters.gamma postBias = exponentialParameters.postBias t = x * scale + preBias r = pow(t, gamma) + postBias output pixel value = r ``` For example, the following code applies piecewise gamma to a one-pixel, two-channel pixel buffer. The first channel’s value is below the boundary and the second channel’s value is above the boundary. The operation mutliplies the first channel’s value by two and squares the second channel’s value. ```swift let buffer = vImage.PixelBuffer( pixelValues: [0.25, 0.75], size: vImage.Size(width: 1, height: 1)) buffer.applyGamma(linearParameters: (scale: 2, bias: 0), exponentialParameters: (scale: 1, preBias: 0, gamma: 2, postBias: 0), boundary: 0.5, destination: buffer) // Prints "[0.5, 0.5625]" = [ 0.25 * 2, 0.75² ]. print(buffer.array) ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)