Determine if CGPoint is within image area

Question

I'm trying to figure out whether a CGPoint lies within the shape of an image. The image is a simple black shape such as the two attached below. I'd like to create a method that determines whether or not a CGPoint lies within the black area of that shape.

I think this needs two things: 1) Turning the image into something that can be read with code (not sure what kind of image processing this would use or how)

2) Using that as a reference to determine whether or not a CGPoint lies within it.

Any help or ideas appreciated. I've never done image processing type of coding before. Thanks!

Answer 1

Take a look at Ole Begemann's OBShapedButton. There you'll find an UIImage category that contains ColorAtPixel method. Guess that's what you're looking for.

You can then get UIColor of certain pixel with:

UIImage *image = [UIImage imageWithCGImage:yourCGImage];
CGPoint point = CGPointMake(pointx,pointy);
UIColor *pixelColor = [image colorAtPixel:point];

To simplify getting RGB values you could also take a look at uicolor-utilities. Using UIColor-Expanded category you can simply determine let's say red and blue component. If they are low (pixel is dark) then tested point is inside shape.

CGFloat redComp = [pixelColor red];
CGFloat blueComp = [pixelColor blue];

BOOL isInsideShape = ((redComp < 0.5) && (blueComp < 0.5));