Any possibility to get CGPoint from particular color of UIImage in iOS?

Question

Consider the below sample irregular shape of images.How to get CGPoint from the border color. All are separate images. i'm trying to get border path.

Answer 1

Following method finds the points of the color approximately(Swift 4):

extension UIImage {
    func getPoints(displayP3Red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) -> [CGPoint] {
        var points = [CGPoint]()

        if let imageData = self.cgImage?.dataProvider?.data {
            let data: UnsafePointer<UInt8>  = CFDataGetBytePtr(imageData)
            let allowDiff:CGFloat = 0.5

            for x in 0 ..< Int(self.size.width) {
                for y in 0 ..< Int(self.size.height) {
                    let pixelInfo: Int = ((Int(self.size.width) * y) + x) * 4

                    let diffRed = CGFloat(data[pixelInfo]) / 255.0 - displayP3Red
                    let diffGreen = CGFloat(data[pixelInfo+1]) / 255.0 - green
                    let diffBlue = CGFloat(data[pixelInfo+2]) / 255.0 - blue
                    let diffAlpha = CGFloat(data[pixelInfo+3]) / 255.0 - alpha

                    if abs(diffRed) < allowDiff
                        && abs(diffGreen) < allowDiff
                        && abs(diffBlue) < allowDiff
                        && abs(diffAlpha) < allowDiff { // compare the color approximately
                        points.append(CGPoint(x: x, y: y))
                    }
                }
            }
        }

        return points
    }
}

Use it like:

let image = UIImage(named: "yourImage.png")
let pointsOfColor = image?.getPoints(displayP3Red: 204.0/255.0, green: 33.0/255.0, blue: 50.0/255.0, alpha: 1.0)

The posted image is tested:

Maybe you need to reduce the array size by getting average values, and then calculate the paths.

Answer 2

-(NSMutableArray *)getPointsfromRGB:(CGFloat)Red :(CGFloat)Green :(CGFloat)Blue andAlpha:(CGFloat)Alpha
{
    NSMutableArray* resultPoint = [NSMutableArray new];

    CFDataRef pixelData = CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage));
    const UInt8* data = CFDataGetBytePtr(pixelData);
    CGFloat allowDiff = 0.015;

    for (int x=0; x<self.size.width; x++) {

        for (int y=0; y<self.size.width; y++) {

            int pixelInfo = ((self.size.width  * y) + x ) * 4; // The image is png
            UInt8 red = (data[pixelInfo] / 255.0 ) - Red;
            UInt8 green = (data[(pixelInfo + 1)] / 255.0) - Green;
            UInt8 blue = (data[pixelInfo + 2] / 255.0) - Blue;
            UInt8 alpha = (data[pixelInfo + 3] / 255.0) - Alpha;
            if ((red) < allowDiff && (green) < allowDiff && (blue) < allowDiff && (alpha) < allowDiff) {
                [resultPoint addObject:[NSValue valueWithCGPoint:CGPointMake(x, y)]];
            }

        }

    }

    return resultPoint;
}