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

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开发者_运维百科 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.

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)];
...

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()

SWIFT 4

let backgroundImage = imageData!
let watermarkImage = #imageLiteral(resourceName: "jodi_url_icon")

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: 10, y: 10, width: watermarkImage.size.width, height: backgroundImage.size.height - 40))

let result = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
self.imgaeView.image = result

Use result to UIImageView, tested.

You can use this method, which is very dynamic and you can specify the starting position of the second image and total size of the image.

-(UIImage *) addImageToImage:(UIImage *)img withImage2:(UIImage *)img2 andRect:(CGRect)cropRect withImageWidth:(int) width{

    CGSize size = CGSizeMake(width,40);
    UIGraphicsBeginImageContext(size);

    CGPoint pointImg1 = CGPointMake(0,0);
    [img drawAtPoint:pointImg1];

    CGPoint pointImg2 = cropRect.origin;
    [img2 drawAtPoint: pointImg2];

    UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return result;

}

SWIFT 5 Function:

func addWaterMark(image: UIImage) -> UIImage {
        let backgroundImage = image//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()
        return result!
    }