contrastStretch(destination:)
Stretches the histogram of a multiple-plane 8-bit pixel buffer.
Declaration
func contrastStretch(destination: vImage.PixelBuffer<Format>)Parameters
- destination:
The destination pixel buffer.
Discussion
Use this function to evenly distributes a histogram’s pixel values across the full range of available pixel values.
For example, the following code stretches the contrast of an image:
let srcImage = imageLiteral(resourceName: "Landscape_28_lowContrast.jpg").cgImage(
forProposedRect: nil,
context: nil,
hints: nil)!
var cgImageFormat = vImage_CGImageFormat(
bitsPerComponent: 8,
bitsPerPixel: 8 * 3,
colorSpace: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue))!
let interleavedBuffer = try vImage.PixelBuffer(
cgImage: srcImage,
cgImageFormat: &cgImageFormat,
pixelFormat: vImage.Interleaved8x3.self)
let multiplaneBuffer = vImage.PixelBuffer<vImage.Planar8x3>(
interleavedBuffer: interleavedBuffer)
multiplaneBuffer.contrastStretch(destination: multiplaneBuffer)
multiplaneBuffer.convert(to: interleavedBuffer)
let outputImage = interleavedBuffer.makeCGImage(cgImageFormat: cgImageFormat)