specifyHistogram(_:destination:)
Performs a histogram specification operation on a 32-bit-per-channel, 3-channel multiple-plane pixel buffer.
Declaration
func specifyHistogram(_ histogram: vImage.PixelBuffer<Format>.HistogramFFF, destination: vImage.PixelBuffer<Format>)Parameters
- histogram:
The histogram.
- destination:
The destination pixel buffer.
Discussion
Histogram specification is a technique that allows you to calculate the histogram of a reference image and apply it to an input image.
The example below shows a source image (bottom left) and a histogram reference image (top left), with the histogram specification output on the right:
[Image]
The code below initializes the source and reference buffers from the CGImage instances sourceImage and referenceImage respectively:
var cgImageFormat = vImage_CGImageFormat(
bitsPerComponent: 32,
bitsPerPixel: 32 * 3,
colorSpace: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: CGBitmapInfo(rawValue: CGBitmapInfo.byteOrder32Little.rawValue |
CGBitmapInfo.floatComponents.rawValue |
CGImageAlphaInfo.none.rawValue))!
let interleavedSource = try vImage.PixelBuffer(
cgImage: sourceImage,
cgImageFormat: &cgImageFormat,
pixelFormat: vImage.InterleavedFx3.self)
let multiplePlaneSource = vImage.PixelBuffer<vImage.PlanarFx3>(
planarBuffers: interleavedSource.planarBuffers())
let interleavedReference = try vImage.PixelBuffer(
cgImage: referenceImage,
cgImageFormat: &cgImageFormat,
pixelFormat: vImage.InterleavedFx3.self)
let multiplePlaneReference = vImage.PixelBuffer<vImage.PlanarFx3>(
planarBuffers: interleavedReference.planarBuffers())The following code calls histogram() to calculate the histogram of the reference image and passes the histogram to specifyHistogram(_:destination:) to generate the specification result. This function works in place, that is, the input and output can share the same underlying memory.
let histogram = multiplePlaneReference.histogram(binCount: 1024)
multiplePlaneSource.specifyHistogram(histogram,
destination: multiplePlaneSource)