iOS: How to get pixel data array from CGImage in Swift

Question

I need to get pixel data as byte array from a CGImage that can be RGB8, RGB16, GRAYSCALE8 or GRAYSCALE16. Previous solutions such as this one produce a dark or distorted image.

Answer 1

Per the link provided in your question, you can get the pixelData by doing

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
    }
 }

However, as a developer, the concerning objects here are the bitmapInfo and colorSpace. Your image may be getting distorted or colored differently depending on the information provided. The exact solution will be dependent upon how you obtained the image and what color schemes were provided from the image. You may just need to play with the variables.

I've never had an issue using CGColorSpaceCreateDeviceRGB() as my colorSpace but I have had to alter my bitmapInfo many times as my images were coming in as a different value.

Here is the location to reference the different types of bitmaps. More than likely though, you only need a variation of the CGImageAlphaInfo which can be located here.

If necessary, you can change the colorSpace. The default CGcolorSpace webpage can be found here. However, you could probably get away with one of the default ones located here