Swift - Compare colors at CGPoint

Question

I have 2 pictures which I want to compare, if pixel color is the same to save it. I detect the color of the pixel by this UIImage extension function:

func getPixelColor(pos: CGPoint) -> ??? {

    let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage))
    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 ???
}

For example, I run the scanner on picture 1 and save it in an array? Or dictionary? And after that I run the scanner on picture 2 and when I have the information from 2 pictures to compare it with what function?

I want to see on which CGPoint the pixels colors are identical from 2 images?

UPDATE: I update getPixelColor to return me "(pos)(r)(g)(b)(a)" and after that I created this function which left only duplicates (BEFORE USING THIS FUNCTION YOU HAVE TO .sort() THE ARRAY!)

extension Array where Element : Equatable {
    var duplicates: [Element] {
        var arr:[Element] = []
        var start = 0
        var start2 = 1
        for _ in 0...self.count{
            if(start2<self.count){
                if(self[start] == self[start2]){
                    if(arr.contains(self[start])==false){
                        arr.append(self[start])
                    }
                }
                start+=1
                start2+=1
            }
        }
        return arr
    }
}

This returns me something like this: "(609.0, 47.0)1.01.01.01.0" I know that the color is black at this point I do x-536 to fit iPhone 5 screen and when I make an attempt to draw it again it draws something wrong... maybe I can't do it properly.. help?

Answer 1

have the UIImage extension return a UIColor. use this method to compare each pixel of the two images. if both pixels match, add the color to an array of arrays.

extension UIImage {
    func getPixelColor(pos: CGPoint) -> UIColor {

        let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage))
        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)
    }
}


func findMatchingPixels(aImage: UIImage, _ bImage: UIImage) -> [[UIColor?]] {
    guard aImage.size == bImage.size else { fatalError("images must be the same size") }

    var matchingColors: [[UIColor?]] = []
    for y in 0..<Int(aImage.size.height) {
        var currentRow = [UIColor?]()
        for x in 0..<Int(aImage.size.width) {
            let aColor = aImage.getPixelColor(CGPoint(x: x, y: y))
            let colorsMatch = bImage.getPixelColor(CGPoint(x: x, y: y)) == aColor
            currentRow.append(colorsMatch ? aColor : nil)
        }
        matchingColors.append(currentRow)
    }
    return matchingColors
}

used like this:

let matchingPixels = findMatchingPixels(UIImage(named: "imageA.png")!, UIImage(named: "imageB.png")!)
if let colorForOrigin = matchingPixels[0][0] {
   print("the images have the same color, it is: \(colorForOrigin)")
} else {
   print("the images do not have the same color at (0,0)")
}

for simplicity i made findMatchingPixels() require the images be the same size, but it wouldn't take much to allow different sized images.

UPDATE

if you want ONLY the pixels that match, i'd return a tuple like this:

func findMatchingPixels(aImage: UIImage, _ bImage: UIImage) -> [(CGPoint, UIColor)] {
    guard aImage.size == bImage.size else { fatalError("images must be the same size") }

    var matchingColors = [(CGPoint, UIColor)]()
    for y in 0..<Int(aImage.size.height) {
        for x in 0..<Int(aImage.size.width) {
            let aColor = aImage.getPixelColor(CGPoint(x: x, y: y))
            guard bImage.getPixelColor(CGPoint(x: x, y: y)) == aColor else { continue }

            matchingColors.append((CGPoint(x: x, y: y), aColor))
        }
    }
    return matchingColors
}