Swift - Picking pixel colour of UIImage - memory crash - swift

Question

I want to pick colour of specific pixel of UIImage in Swift 3 and this method is called ~10k times.
func pixelColour(_ pixelPosition: CGPoint) {
if !CGRect(x: 0.0, y: 0.0, width: self.size.width, height: self.size.height).contains(pixelPosition) {
return false
}
let pointX = trunc(pixelPosition.x);
let pointY = trunc(pixelPosition.y);
let cgImage = self.cgImage;
let width = self.size.width;
let height = self.size.height;
let colorSpace = CGColorSpaceCreateDeviceRGB();
let bytesPerPixel = 4;
let bytesPerRow = bytesPerPixel * 1;
let bitsPerComponent = 8;
let pixelData = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
let context = CGContext(data: pixelData, width: 1, height: 1, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
context?.setBlendMode(CGBlendMode.copy);
context?.translateBy(x: -pointX, y: pointY-CGFloat(height));
// This line takes too much memory, how to release memory here?
context?.draw(cgImage!, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)));
print("\(pixelData[0]) \(pixelData[1]) \(pixelData[2]) ")
pixelData.deallocate(capacity: 4)
}
Unfortunately it seems that memory is not released, because it crashes after checking ~500 pixels. How I can solve this problem?

Answer 1

You have not shown how pixelColour is called, but I presume that it is in some sort of loop. If so, surround your repeated call to pixelColour with an autoreleasepool{...} call to release the accumulated memory each time through your loop:
let p = // next CGPoint
autoreleasepool {
pixelColour(p)
}

Answer 2

Taken from How do I get the color of a pixel in a UIImage with Swift?
and converted to Swift 3
extension UIImage{
func getPixelColor(pos: CGPoint) -> UIColor? {
guard let provider=cgImage?.dataProvider else{
return nil
}
let pixelData = provider.data
let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)
let pixelInfo: Int = ((Int(self.size.width) * Int(pos.y)) + Int(pos.x)) * 4
let r = CGFloat(data[pixelInfo]) / CGFloat(255.0)
let g = CGFloat(data[pixelInfo+1]) / CGFloat(255.0)
let b = CGFloat(data[pixelInfo+2]) / CGFloat(255.0)
let a = CGFloat(data[pixelInfo+3]) / CGFloat(255.0)
return UIColor(red: r, green: g, blue: b, alpha: a)
}
}
This should not take to much memory, since it uses pointers so it doesn't load the entire image.
hope it helps