How to use LUT png for CIColorCube filter?

Question

I would like to use a lookup table png (example) as color cube data for the CIColorCube filter in Swift. All I tried (and found) so far are examples with a computed

Answer 1

Thought I would update this for Swift 3.0 also this works for JPG's and PNG's 3D Color LUTs

fileprivate func colorCubeFilterFromLUT(imageName : String) -> CIFilter? {

    let size = 64

    let lutImage    = UIImage(named: imageName)!.cgImage
    let lutWidth    = lutImage!.width
    let lutHeight   = lutImage!.height
    let rowCount    = lutHeight / size
    let columnCount = lutWidth / size

    if ((lutWidth % size != 0) || (lutHeight % size != 0) || (rowCount * columnCount != size)) {
        NSLog("Invalid colorLUT %@", imageName);
        return nil
    }

    let bitmap  = getBytesFromImage(image: UIImage(named: imageName))!
    let floatSize = MemoryLayout.size

    let cubeData = UnsafeMutablePointer.allocate(capacity: size * size * size * 4 * floatSize)
    var z = 0
    var bitmapOffset = 0

    for _ in 0 ..< rowCount {
        for y in 0 ..< size {
            let tmp = z
            for _ in 0 ..< columnCount {
                for x in 0 ..< size {

                    let alpha   = Float(bitmap[bitmapOffset]) / 255.0
                    let red     = Float(bitmap[bitmapOffset+1]) / 255.0
                    let green   = Float(bitmap[bitmapOffset+2]) / 255.0
                    let blue    = Float(bitmap[bitmapOffset+3]) / 255.0

                    let dataOffset = (z * size * size + y * size + x) * 4

                    cubeData[dataOffset + 3] = alpha
                    cubeData[dataOffset + 2] = red
                    cubeData[dataOffset + 1] = green
                    cubeData[dataOffset + 0] = blue
                    bitmapOffset += 4
                }
                z += 1
            }
            z = tmp
        }
        z += columnCount
    }

    let colorCubeData = NSData(bytesNoCopy: cubeData, length: size * size * size * 4 * floatSize, freeWhenDone: true)

    // create CIColorCube Filter
    let filter = CIFilter(name: "CIColorCube")
    filter?.setValue(colorCubeData, forKey: "inputCubeData")
    filter?.setValue(size, forKey: "inputCubeDimension")

    return filter
}


fileprivate func getBytesFromImage(image:UIImage?) -> [UInt8]?
{
    var pixelValues: [UInt8]?
    if let imageRef = image?.cgImage {
        let width = Int(imageRef.width)
        let height = Int(imageRef.height)
        let bitsPerComponent = 8
        let bytesPerRow = width * 4
        let totalBytes = height * bytesPerRow

        let bitmapInfo = CGImageAlphaInfo.premultipliedLast.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        var intensities = [UInt8](repeating: 0, count: totalBytes)

        let contextRef = CGContext(data: &intensities, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)
        contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)))

        pixelValues = intensities
    }
    return pixelValues!
}