iPhone - How do you color an image?

I would love to know how to color an image (make a white .png red, for example). I have seen various suggestions but never any confirmation that this is actually possible. I have tried this:

-(UIImage *)colorizeImage:(UIImage *)baseImage color:(UIColor *)theColor {
    UIGraphicsBeginImageContext(baseImage.size);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, baseImage.size.width, baseImage.size.height);

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);
    CGContextSaveGState(ctx);
    CGContextClipToMask(ctx, area, baseImage.CGImage);
    [theColor set];
    CGContextFillRect(ctx, area);
    CGContextRestoreGState(ctx);
    CGContextSetBlendMode(ctx, kCGBlendModeNormal);
    CGContextDrawImage(ctx, area, baseImage.CGImage);
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

myImageView.image = [self colorizeImage:[UIImage imageNamed:@"whiteImage.png"] color:[UIColor redColor]];

But it doesn't work - the image is still white on the screen.

Make this a UIImage category. It also takes into account the scale factor with iOS 4.

- (UIImage *)imageWithOverlayColor:(UIColor *)color
{        
    CGRect rect = CGRectMake(0.0f, 0.0f, self.size.width, self.size.height);

    if (UIGraphicsBeginImageContextWithOptions) {
        CGFloat imageScale = 1.0f;
        if ([self respondsToSelector:@selector(scale)])  // The scale property is new with iOS4.
            imageScale = self.scale;
        UIGraphicsBeginImageContextWithOptions(self.size, NO, imageScale);
    }
    else {
        UIGraphicsBeginImageContext(self.size);
    }

    [self drawInRect:rect];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(context, kCGBlendModeSourceIn);

    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextFillRect(context, rect);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

UPDATE - Swift version:

func imageWithColor(color: UIColor) -> UIImage {
    let rect = CGRect(x: 0.0, y: 0.0, width: size.width, height: size.height)
    UIGraphicsBeginImageContextWithOptions(self.size, false, 0.0);
    drawInRect(rect)
    let context = UIGraphicsGetCurrentContext()
    CGContextSetBlendMode(context, .SourceIn)
    CGContextSetFillColorWithColor(context, color.CGColor)
    CGContextFillRect(context, rect);
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
}

Change your blend mode to multiply and your code will work:

CGContextSetBlendMode(ctx, kCGBlendModeMultiply);

As of iOS 7 you can tint images with a single colour like so

Objective C

UIImage *image = [UIImage imageNamed:@"myImage.png"];
UIImageView *imageView = [[UIImageView alloc]initWithImage:[image imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate]];
imageView.tintColor = [UIColor redColor];

Swift 3

let image = UIImage(named:"myImage.png")?.withRenderingMode(.alwaysTemplate)
let imageView = UIImageView(image:image)
imageView.tintColor = .red

This will colour an entire image with a single colour and preserve the alpha channel.

I think that the best way to colorize an image from iOS7 is by specifying the property UIImageRenderingModeAlwaysTemplate on your image:

myImageView.image = [[UIImage imageNamed:@"myImage"] imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];

and then colorize it with the tintColor of the imageView

myImageView.tintColor = [UIColor purpleColor]; //Maybe purple is not the best choice ;)

I think it's easier (no category needed) and of course optimized!

Note: if you are using xcassets, you can set the rendering property to UIImageRenderingModeAlwaysTemplate in XCode, like in this screenshot: