---
title: "applyGamma(linearParameters:exponentialParameters:boundary:destination:)"
framework: accelerate
role: symbol
role_heading: Instance Method
path: "accelerate/vimage/pixelbuffer/applygamma(linearparameters:exponentialparameters:boundary:destination:)-249w5"
---

# applyGamma(linearParameters:exponentialParameters:boundary:destination:)

Applies a piecewise gamma calculation to an 8-bit pixel buffer.

## Declaration

```swift
func applyGamma(linearParameters: (scale: Float, bias: Float), exponentialParameters: (scale: Float, preBias: Float, gamma: Float, postBias: Float), boundary: Pixel_8, destination: vImage.PixelBuffer<Format>)
```

## 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

Discussion This function computes the output value of each pixel using the following pseudocode: For each source `Pixel_8` pixel value x:  if x < boundary:      scale = linearParameters.scale      bias = linearParameters.bias

x = x * (1/255.0)                   // scale pixel to 0...1

r = x * scale + bias  else:      scale = exponentialParameters.scale      preBias = exponentialParameters.preBias      gamma = exponentialParameters.gamma      postBias = exponentialParameters.postBias

x = x * (1/255.0)                   // scale pixel to 0...1

t = x * scale + preBias      r = pow(t, gamma) + postBias  output pixel value = r * 255.0          // scale pixel to 0...255 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. let buffer = vImage.PixelBuffer<vImage.Interleaved8x2>(     pixelValues: [64, 191],     size: vImage.Size(width: 1,                       height: 1))

buffer.applyGamma(linearParameters: (scale: 2,                                      bias: 0),                   exponentialParameters: (scale: 1,                                           preBias: 0,                                           gamma: 2,                                           postBias: 0),                   boundary: 127,                   destination: buffer)

// Prints "[128, 143]" ≅ [ 0.25 * 2 * 255, 0.75² * 255 ]. print(buffer.array)

## See Also

### Applying piecewise gamma

- [applyGamma(linearParameters:exponentialParameters:boundary:destination:)](accelerate/vimage/pixelbuffer/applygamma(linearparameters:exponentialparameters:boundary:destination:)-8r0ro.md)