# specifyHistogram(_:destination:) Performs a histogram specification operation on a 32-bit-per-channel, 3-channel multiple-plane pixel buffer. ``` func specifyHistogram(_ histogram: vImage.PixelBuffer.HistogramFFF, destination: vImage.PixelBuffer) ``` ## 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:  The code below initializes the source and reference buffers from the instances `sourceImage` and `referenceImage` respectively: ```swift 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( planarBuffers: interleavedSource.planarBuffers()) let interleavedReference = try vImage.PixelBuffer( cgImage: referenceImage, cgImageFormat: &cgImageFormat, pixelFormat: vImage.InterleavedFx3.self) let multiplePlaneReference = vImage.PixelBuffer( planarBuffers: interleavedReference.planarBuffers()) ``` The following code calls [`histogram()`](/documentation/Accelerate/vImage/PixelBuffer/histogram()-14a38) to calculate the histogram of the reference image and passes the histogram to [`specifyHistogram(_:destination:)`](/documentation/Accelerate/vImage/PixelBuffer/specifyHistogram(_:destination:)-7xiz4) to generate the specification result. This function works in place, that is, the input and output can share the same underlying memory. ```swift let histogram = multiplePlaneReference.histogram(binCount: 1024) multiplePlaneSource.specifyHistogram(histogram, destination: multiplePlaneSource) ``` ## See Also --- 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)