How to get the pixel color on touch?

Question

I know this is a common question and there are a lot of answers of this question. I\'ve used some of this. Although many of them are the same. But the sad thing for me is th

Answer 1

Swift 4, Xcode 9 - With a UIImageView Extension

This is a combination of all of the answers above but in an extension

extension UIImageView {
    func getPixelColorAt(point:CGPoint) -> UIColor{
        
        let pixel = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
        let context = CGContext(data: pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
        
        context!.translateBy(x: -point.x, y: -point.y)
        layer.render(in: context!)
        let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0,
                                    green: CGFloat(pixel[1])/255.0,
                                    blue: CGFloat(pixel[2])/255.0,
                                    alpha: CGFloat(pixel[3])/255.0)
        
        pixel.deallocate(capacity: 4)
        return color
    }
}

How to use

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    let touch = touches.first
    if let point = touch?.location(in: view) {
        let color = myUIImageView.getPixelColorAt(point: point)
        print(color)
    }
}

Answer 2

Thank you for @Aggressor's post the code above

Swift 2.1

func getPixelColorAtPoint(point:CGPoint) -> UIColor{

   let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
   let colorSpace = CGColorSpaceCreateDeviceRGB()
   let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)
   let context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, bitmapInfo.rawValue)

   CGContextTranslateCTM(context, -point.x, -point.y)
   view.layer.renderInContext(context!)
   let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0)

   pixel.dealloc(4)
   return color
}

Swift 3, Xcode Version 8.2 (8C38) and Swift 4, Xcode Version 9.1 (9B55)

 func getPixelColorAtPoint(point:CGPoint, sourceView: UIView) -> UIColor{

    let pixel = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
    let context = CGContext(data: pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
    var color: UIColor? = nil

    if let context = context {
        context.translateBy(x: -point.x, y: -point.y)
        sourceView.layer.render(in: context)

        color = UIColor(red: CGFloat(pixel[0])/255.0,
                        green: CGFloat(pixel[1])/255.0,
                        blue: CGFloat(pixel[2])/255.0,
                        alpha: CGFloat(pixel[3])/255.0)

        pixel.deallocate(capacity: 4)
    }
    return color
}

Answer 3

First, I'd like to thank the author of this code, it helped me a lot for my game project, as I was looking for this function to do a pixel-perfect hitbox (excluding where the aplha is O). Here's a little update for Swift 5:

// Fonction permettant de retourner les valeurs RGBA d'un pixel d'une vue
func getPixelColor(atPosition:CGPoint) -> UIColor{

    var pixel:[CUnsignedChar] = [0, 0, 0, 0];
    let colorSpace = CGColorSpaceCreateDeviceRGB();
    let bitmapInfo = CGBitmapInfo(rawValue:    CGImageAlphaInfo.premultipliedLast.rawValue);
    let context = CGContext(data: &pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue);

    context!.translateBy(x: -atPosition.x, y: -atPosition.y);
    layer.render(in: context!);
    let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0,
                                green: CGFloat(pixel[1])/255.0,
                                blue: CGFloat(pixel[2])/255.0,
                                alpha: CGFloat(pixel[3])/255.0);

    return color;

}

I had somme issues with pixel.dealloc(4), as in Swift 5 it seems that you can't dealloc with capacity parameter anymore. I removed the (4), but it had some weird behavior (as the dealloc() didn't dealloc the whole array).

I didn't do an extension of UIView as in my project I have my own subclass, but this can be easily done.

The way I implement the code:

// Méthode déterminant si le "touch" est validé par l'objet (par défaut, exclut les zones transparentes et les objets invisibles). A surcharger si nécessaire.
func isHit(atPosition position:CGPoint) -> Bool
{

    // Si l'objet n'est pas caché (paramètre isHidden) et si la zone touchée correspond à une zone effectivement dessinée (non transparente), retourne true.
    if (!self.isHidden && self.getPixelColor(atPosition: position).cgColor.alpha != 0) {return true}
    else {return false}

}

I hope this can help.

Answer 4

Great answer rdelmar this helped me A LOT!

Here is how I did the above in Swift:

override func touchesBegan(touches: NSSet, withEvent event: UIEvent)
    {
        var touch:UITouch = event.allTouches()!.anyObject() as UITouch
        var loc = touch.locationInView(self)
        var color:UIColor = getPixelColorAtPoint(loc)
        println(color)
    }

    //returns the color data of the pixel at the currently selected point
    func getPixelColorAtPoint(point:CGPoint)->UIColor
    {
        let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
        var colorSpace = CGColorSpaceCreateDeviceRGB()
        let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
        let context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, bitmapInfo)

        CGContextTranslateCTM(context, -point.x, -point.y)
        layer.renderInContext(context)
        var color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0)

        pixel.dealloc(4)
        return color
    }

Answer 5

This is the one I've used, and it looks simpler than the methods you've tried.

In my custom view class, I have this:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    CGPoint loc = [touch locationInView:self];
    self.pickedColor = [self colorOfPoint:loc];
}

colorOfPoint is a method in a category on UIView, with this code:

#import "UIView+ColorOfPoint.h"
#import <QuartzCore/QuartzCore.h>

@implementation UIView (ColorOfPoint)

-(UIColor *) colorOfPoint:(CGPoint)point
    {
    unsigned char pixel[4] = {0};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pixel,
            1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);

    CGContextTranslateCTM(context, -point.x, -point.y);

    [self.layer renderInContext:context];

    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    UIColor *color = [UIColor colorWithRed:pixel[0]/255.0
        green:pixel[1]/255.0 blue:pixel[2]/255.0
        alpha:pixel[3]/255.0];
    return color;
    }

Don't forget to import the category into the custom view class and add the QuartzCore framework.

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Trivial note for 2013: cast that last argument as (CGBitmapInfo) to avoid an implicit conversion warning: example here. Hope it helps.