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contrastStretch(binCount:destination:)

Stretches the histogram of a 32-bit planar pixel buffer.

Declaration

func contrastStretch(binCount: Int, destination: vImage.PixelBuffer<vImage.PlanarF>)

Parameters

  • binCount:

    The number of histogram entries for each channel.

  • 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: 32,
    bitsPerPixel: 32 * 1,
    colorSpace: CGColorSpaceCreateDeviceGray(),
    bitmapInfo: CGBitmapInfo(rawValue: kCGBitmapByteOrder32Host.rawValue |
                             CGBitmapInfo.floatComponents.rawValue |
                             CGImageAlphaInfo.none.rawValue))!

let buffer = try vImage.PixelBuffer(
    cgImage: srcImage,
    cgImageFormat: &cgImageFormat,
    pixelFormat: vImage.PlanarF.self)

buffer.contrastStretch(binCount: 1024,
                       destination: buffer)

let outputImage = buffer.makeCGImage(cgImageFormat: cgImageFormat)

See Also

Related Documentation

Contrast stretching