I was searching online for ways to encode an image into 8 bits, but I discovered that 8 bits only support 256 colors, so I am wrong. I am making a pixel art app, but I want to be limited to 16 different colors when making the picture. I have codes here, they work perfectly. I was able to zoom the image, color the pixel, etc., but I need to find the 16 top colours in the image. “colorsSet.count” is what I use to find colors from images. There are 15,653 different colors in total. There should only be 16. Any idea?

Here my full code:

let pixelNumber = 128

class TheDemo: UIViewController, UIScrollViewDelegate {
    let scrollImage = UIScrollView()
    let imageDemo = UIView()
    
    var originalImage = UIImage()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        originalImage = (UIImage(named: "Demo2")?.resizeUI(size: CGSize(width: pixelNumber, height: pixelNumber))!)!
        
        scrollImage.frame = view.bounds
        scrollImage.minimumZoomScale = 1
        scrollImage.maximumZoomScale = 25
        scrollImage.delegate = self
        
        imageDemo.frame = CGRect(x: 0, y: 0, width: view.frame.width, height: view.frame.width)
        imageDemo.center = view.center
        
        var numberOfBoxCreated = 0
        
        let boxSizeSet = view.frame.width / CGFloat(pixelNumber)
        
        DispatchQueue.main.async {
            let getColorPixel = self.findColors(self.originalImage)
            var colorsSet = [UIColor]()
            
            for checkColorSet in getColorPixel { if !colorsSet.contains(checkColorSet) { colorsSet.append(checkColorSet) } }
            print("Number of color: \(colorsSet.count)")
            
            for colX in 0..<pixelNumber {
                for rowX in 0..<pixelNumber {
                    let boxBtn = UIView()
                    boxBtn.frame = CGRect(x: CGFloat(colX) * boxSizeSet, y: CGFloat(rowX) * boxSizeSet, width: boxSizeSet, height: boxSizeSet)
                    boxBtn.backgroundColor = getColorPixel[numberOfBoxCreated]
                    self.imageDemo.addSubview(boxBtn)
                    
                    numberOfBoxCreated += 1
                }
            }
        }
        
        scrollImage.addSubview(imageDemo)
        view.addSubview(scrollImage)
        
    }
    
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        imageDemo
    }
    
    func findColors(_ image: UIImage) -> [UIColor] {
        let pixelsWide = pixelNumber
        let pixelsHigh = pixelNumber

        guard let pixelData = image.cgImage?.dataProvider?.data else { return [] }
        let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)

        var imageColors: [UIColor] = []
        for x in 0..<pixelsWide {
            for y in 0..<pixelsHigh {
                let point = CGPoint(x: x, y: y)
                let pixelInfo: Int = ((pixelsWide * Int(point.y)) + Int(point.x)) * 4
                let color = UIColor(red: CGFloat(data[pixelInfo]) / 255.0,
                                    green: CGFloat(data[pixelInfo + 1]) / 255.0,
                                    blue: CGFloat(data[pixelInfo + 2]) / 255.0,
                                    alpha: CGFloat(data[pixelInfo + 3]) / 255.0)
                imageColors.append(color)
            }
        }
        return imageColors
    }
}

extension UIImage {
    func resizeUI(size:CGSize) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(size, true, self.scale)
        self.draw(in: CGRect(origin: .zero, size: size))
        
        let resizedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return resizedImage
    }
}