How to get pixel color at location from UIimage scaled within a UIimageView

Question

I\'m currently using this technique to get the color of a pixel in a UIimage. (on Ios)

- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
UIColor* color =         


        

Answer 1

Here's a pointer:

0x3A28213A //sorry, I couldn't resist the joke

---

For real now: after going through the comments on the page at markj.net, a certain James has suggested to make the following changes:

size_t w = CGImageGetWidth(inImage); //Written by Mark
size_t h = CGImageGetHeight(inImage); //Written by Mark
float xscale = w / self.frame.size.width;
float yscale = h / self.frame.size.height;
point.x = point.x * xscale;
point.y = point.y * yscale;

(thanks to http://www.markj.net/iphone-uiimage-pixel-color/comment-page-1/#comment-2159)

This didn't actually work for me... Not that I did much testing, and I'm not the world's greatest programmer (yet)...

My solution was to scale the UIImageView in such a way that each pixel of the image in it was the same size as a standard CGPoint on the screen, then I took my color like normal (using getPixelColorAtLocation:(CGPoint)point) , then I scaled the image back to the size I wanted.

Hope this helps!

Answer 2

try this for swift3

func getPixelColor(image: UIImage, x: Int, y: Int, width: CGFloat) -> UIColor 
{

    let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage))
    let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)

    let pixelInfo: Int = ((Int(width) * y) + 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)
}

Answer 3

Use the UIImageView Layer:

- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
    UIColor* color = nil;

    UIGraphicsBeginImageContext(self.frame.size);
    CGContextRef cgctx = UIGraphicsGetCurrentContext();
    if (cgctx == NULL) { return nil; /* error */ }

    [self.layer renderInContext:cgctx];

    unsigned char* data = CGBitmapContextGetData (cgctx);
    /*
    ...
    */
    UIGraphicsEndImageContext();
    return color;
}