vImage.MultidimensionalLookupTable

struct · iOS 16.0+ · SDK 27.1

struct MultidimensionalLookupTable

A multidimensional lookup table. Use a multidimensional lookup table to transform the colors in an image. The lookup table defines an output color based on the input color values. The vImage multidimensional lookup table provides interpolation to compute output color values that don't have an explicit entry in the table for a given input color. `MultidimensionalLookupTable` applies transforms to 32-bit planar pixel buffers. There are pixel buffer functions available to convert between bit depths and interleaved to planar buffers. The following is an example of a simple lookup table that implements the Rec. 709 luma coefficients to convert from a 3-channel RGB image to a single-channel grayscale image. The lookup table is a 3D cube with 32 entries per channel. ``` let entriesPerChannel = UInt8(32) let srcChannelCount = 3 let destChannelCount = 1 let lookupTableElementCount = Int(pow(Float(entriesPerChannel), Float(srcChannelCount))) * Int(destChannelCount) let tableData = [UInt16](unsafeUninitializedCapacity: lookupTableElementCount) { buffer, count in let multiplier = Float(UInt16.max) var bufferIndex = 0 for red in ( 0 ..< entriesPerChannel) { for green in ( 0 ..< entriesPerChannel) { for blue in ( 0 ..< entriesPerChannel) { let normalizedRed = Float(red) / Float(entriesPerChannel - 1) let normalizedGreen = Float(green) / Float(entriesPerChannel - 1) let normalizedBlue = Float(blue) / Float(entriesPerChannel - 1) let gray = (normalizedRed * 0.2126) + (normalizedGreen * 0.7152) + (normalizedBlue * 0.0722) buffer[ bufferIndex ] = UInt16(gray * multiplier) bufferIndex += 1 } } } count = lookupTableElementCount } ``` Use the lookup table data to create a `MultidimensionalLookupTable`. ``` let entryCountPerSourceChannel = [UInt8](repeating: entriesPerChannel, count: srcChannelCount) let lookupTable = vImage.MultidimensionalLookupTable( entryCountPerSourceChannel: entryCountPerSourceChannel, destinationChannelCount: destChannelCount, data: tableData) ``` Call the `apply` function to transform a 3-channel RGB image to a grayscale image. In this example, the source is interleaved. The code demonstrates calling `planarBuffers()` to deinterleave the source. ``` let src = vImage.PixelBuffer<vImage.InterleavedFx3>( ... ) let planarSources = src.planarBuffers() let dest = vImage.PixelBuffer<vImage.PlanarF>(size: src.size) lookupTable.apply(sources: planarSources, destinations: [dest], interpolation: .none) ``` On return, `dest` contains a grayscale representation of the soufce RGB image.

Members (5)

get sourceChannelCount(): number

let sourceChannelCount: Int

get destinationChannelCount(): number

let destinationChannelCount: Int

static init(entryCountPerSourceChannel: Array<number>, destinationChannelCount: number, data: Array<number>): vImage_MultidimensionalLookupTable

init<T>(entryCountPerSourceChannel: [UInt8], destinationChannelCount: Int, data: T) where T : AccelerateBuffer, T.Element == UInt16

get entryCountPerSourceChannel(): Array<number>

let entryCountPerSourceChannel: [UInt8]

apply(sources: Array<vImage_PixelBuffer<vImage_PlanarF>>, destinations: Array<vImage_PixelBuffer<vImage_PlanarF>>, interpolation: vImage_MultidimensionalLookupTable_InterpolationMethod): void

func apply(sources: [vImage.PixelBuffer<vImage.PlanarF>], destinations: [vImage.PixelBuffer<vImage.PlanarF>], interpolation: vImage.MultidimensionalLookupTable.InterpolationMethod)

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