Swift 3：如何在设备上获得像素颜色？

Question

如何在设备上触摸像素颜色，下面的代码在模拟器上运行良好，但在设备上它返回错误的值。我不知道出了什么问题

要在触摸时获得像素颜色，我使用了代码

func getPixelColorAtPoint(point:CGPoint, sourceView: UIView) -> UIColor{

    let pixel = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
    let context = CGContext(data: pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)

    context!.translateBy(x: -point.x, y: -point.y)
    sourceView.layer.render(in: context!)
    let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0,
                                green: CGFloat(pixel[1])/255.0,
                                blue: CGFloat(pixel[2])/255.0,
                                alpha: CGFloat(pixel[3])/255.0)

    pixel.deallocate(capacity: 4)
    return colour
}

引自How to get the pixel color on touch?

任何建议都会有所帮助