iPhone, how does one overlay one image onto another to create a new image to save? (watermark)

Question

Basically I want to take an image that the user chooses from their photo library and then apply a watermark, a triangle in the lower right that has the app name on it. I have the second image already made with a transparent layer in photoshop.

I tried a function, which I can't remember the exact name, but it involved CGIImages and masks. This combines the two images, but as a mask, which made the image darker where the transparent layer was and the images were not merged per se, just masked.

How would I get the watermark image to merge with another image, to make a UIImage, without displaying the images on the screen?

Thank you.

Answer 1

It's pretty easy:

UIImage *backgroundImage = [UIImage imageNamed:@"image.png"]; UIImage *watermarkImage = [UIImage imageNamed:@"watermark.png"];  UIGraphicsBeginImageContext(backgroundImage.size); [backgroundImage drawInRect:CGRectMake(0, 0, backgroundImage.size.width, backgroundImage.size.height)]; [watermarkImage drawInRect:CGRectMake(backgroundImage.size.width - watermarkImage.size.width, backgroundImage.size.height - watermarkImage.size.height, watermarkImage.size.width, watermarkImage.size.height)]; UIImage *result = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); 

If you want the background and watermark to be of the same size then use this code

... [backgroundImage drawInRect:CGRectMake(0, 0, backgroundImage.size.width, backgroundImage.size.height)]; [watermarkImage drawInRect:CGRectMake(0, 0, backgroundImage.size.width, backgroundImage.size.height)]; ... 

Answer 2

The solution provided by omz also works in Swift, like so:

let backgroundImage = UIImage(named: "image.png")! let watermarkImage = UIImage(named: "watermark.png")!  UIGraphicsBeginImageContextWithOptions(backgroundImage.size, false, 0.0) backgroundImage.draw(in: CGRect(x: 0.0, y: 0.0, width: backgroundImage.size.width, height: backgroundImage.size.height)) watermarkImage.draw(in: CGRect(x: backgroundImage.size.width - watermarkImage.size.width, y: backgroundImage.size.height - watermarkImage.size.height, width: watermarkImage.size.width, height: watermarkImage.size.height)) let result = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext()