How to use a UIImage as a mask over a color in Objective-C

Question

I have a UIImage that is all black with an alpha channel so some parts are grayish and some parts are completely see-through. I want to use that images as a mask over some o

Answer 1

Translating Jano's answer into Swift:

func ipMaskedImageNamed(name:String, color:UIColor) -> UIImage {
    let image = UIImage(named: name)
    let rect:CGRect = CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: image!.size.width, height: image!.size.height))
    UIGraphicsBeginImageContextWithOptions(rect.size, false, image!.scale)
    let c:CGContextRef = UIGraphicsGetCurrentContext()
    image?.drawInRect(rect)
    CGContextSetFillColorWithColor(c, color.CGColor)
    CGContextSetBlendMode(c, kCGBlendModeSourceAtop)
    CGContextFillRect(c, rect)
    let result:UIImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return result
}

Usage:

myButton.setImage(ipMaskedImageNamed("grayScalePNG", color: UIColor.redColor()), forState: .Normal)

Edit: According to this article, you can turn an image into a mask whose opaque areas are represented by the tint color. Within the asset catalog, under the Attributes Inspector of the image, change Render As to Template Image. No code necessary.