Color pixel with tap recognizer

Question

Hello everyone I need help with my iOS app. How can I get the background color of the image (that I insert in UIImageView) exactly where I tap. I create a Tap Gesture Recognizer but I do not know how to read the background color where I tap.

You don't mean background colour, you mean just the colour, right? At the pixel which the user tapped? — Pekka, Jul 29 '15 at 13:12
Googling `ios tapped image pixel color` seems to yield a lot of hits — Pekka, Jul 29 '15 at 13:13
e.g. http://stackoverflow.com/questions/9270923/how-to-read-rgb-pixel-data-on-iphone — Pekka, Jul 29 '15 at 13:13
http://stackoverflow.com/questions/3284185/get-pixel-color-of-uiimage — Pekka, Jul 29 '15 at 13:14
http://stackoverflow.com/questions/144250/how-to-get-the-rgb-values-for-a-pixel-on-an-image-on-the-iphone — Teja Nandamuri, Jul 29 '15 at 13:14
I'll leave it to the tag experts to determine which is the best duplicate — Pekka, Jul 29 '15 at 13:14
I read this: http://stackoverflow.com/questions/3284185/get-pixel-color-of-uiimage but the latest code don't work... — Neoxxx, Jul 29 '15 at 13:16

score 5 · Answer 1 · answered Jul 29 '15 at 13:38

add gesture in your control

UITapGestureRecognizer * tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapGesture:)];
        [lblSlider addGestureRecognizer:tapRecognizer];
        lblSlider.userInteractionEnabled = YES;

after add this method

 - (void)tapGesture:(UITapGestureRecognizer *)recognizer
    {
        CGPoint point1 = [recognizer locationInView:recognizer.view];

        UIGraphicsBeginImageContext(recognizer.view.bounds.size);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [recognizer.view.layer renderInContext:context];

        int bpr = (int)CGBitmapContextGetBytesPerRow(context);
        unsigned char * data = CGBitmapContextGetData(context);
        if (data != NULL)
        {
            int offset = bpr*round(point1.y) + 4*round(point1.x);
            int blue = data[offset+0];
            int green = data[offset+1];
            int red = data[offset+2];
            int alpha =  data[offset+3];

            NSLog(@"%d %d %d %d", alpha, red, green, blue);

            if (alpha == 0)
            {
                // Here is tap out of text
            }
            else
            {
                // Here is tap right into text
            }
        }

        UIGraphicsEndImageContext();
    }

Nothing. Error: cannot initialize a variable of type 'unsigned char *' with an r value of type 'void *' — Neoxxx, Jul 29 '15 at 13:53

Color pixel with tap recognizer

1 Answers1