Get pixel data as array from UIImage/CGImage in swift

Question

I have an app so far that allows the user to free draw (like a sketch pad) on a UIImageView element.

I want to get the raw RGB pixel data (as 0 to 255 integer values) as a multidimensional array so I can feed it into a machine learning algorithm . Or is there some other way I can send the raw image data over to separate C++ function?

Is there an easy way to do this in Swift?

Answer 1

In Swift 3 and Swift 4, using Core Graphics, it is quite easy to do what you want:

extension UIImage {
    func pixelData() -> [UInt8]? {
        let size = self.size
        let dataSize = size.width * size.height * 4
        var pixelData = [UInt8](repeating: 0, count: Int(dataSize))
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let context = CGContext(data: &pixelData,
                                width: Int(size.width),
                                height: Int(size.height),
                                bitsPerComponent: 8,
                                bytesPerRow: 4 * Int(size.width),
                                space: colorSpace,
                                bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue)
        guard let cgImage = self.cgImage else { return nil }
        context?.draw(cgImage, in: CGRect(x: 0, y: 0, width: size.width, height: size.height))

        return pixelData
    }
 }