iOS - Merging two images of different size

I'm facing the following problem : I have to merge two images A and B to create a new image C as a result of the merging.
I already know how to merge two images but in this case my goal is a little bit different.
I would like that image A will be the background for Image B.
For instance if image A size is 500x500 and image B size is 460x460 I would like that image C (the image result of the merging) will be 500x500, with image B (460x460) centered in it.

Thanks in advance for any help or suggestion

Solution 1:

This is what I've done in my app, but without using UIImageView:

UIImage *bottomImage = [UIImage imageNamed:@"bottom.png"]; //background image
UIImage *image       = [UIImage imageNamed:@"top.png"]; //foreground image

CGSize newSize = CGSizeMake(width, height);
UIGraphicsBeginImageContext( newSize );

// Use existing opacity as is
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

// Apply supplied opacity if applicable
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.8];

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

If the image already has opacity, you do not need to set it (as in bottomImage) otherwise you can set it (as with image).

After this UIImage is created then you can embed it in your UIImageView

UPDATE: Thanks to Ahmet AkkoK - for Swift (2.2) users blend mode macro has changed. CGBlendMode .kCGBlendModeNormal is replaced with CGBlendMode.Normal

Solution 2:

Hey i got multiple images add same background with different foreground This is my code

UIImage *bottomImage = [UIImage imageNamed:@"photo 2.JPG"]; //background image
UIImage *image       = [UIImage imageNamed:@"photo 3.JPG"]; //foreground image
UIImage *image1      = [UIImage imageNamed:@"photo 4.JPG"]; //foreground image
UIImage *image2      = [UIImage imageNamed:@"photo 5.JPG"]; //foreground image

CGSize newSize = CGSizeMake(320, 480);
UIGraphicsBeginImageContext( newSize );

// Use existing opacity as is
[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

// Apply supplied opacity if applicable
[image drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.4];
[image1 drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.3];
[image2 drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:0.2];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

resultView = [[UIImageView alloc] initWithImage:newImage];
resultView.frame = CGRectMake(0, 0,320,460);
[self.view addSubview:resultView];

Solution 3:

Swift version

Copy/Paste to Playground

var bottomImage:UIImage = UIImage(named:"avatar_4.png") //background image

var imageTop:UIImage  = UIImage(named:"group_4.png")    //top image

var newSize = CGSizeMake(bottomImage.size.width, bottomImage.size.height)
UIGraphicsBeginImageContext( newSize )
    
bottomImage.drawInRect(CGRectMake(0,0,newSize.width,newSize.height))

// decrease top image to 36x36 
imageTop.drawInRect(CGRectMake(18,18,36,36), blendMode:kCGBlendModeNormal, alpha:1.0)

var newImage:UIImage = UIGraphicsGetImageFromCurrentImageContext()
var imageData = UIImagePNGRepresentation(newImage)

To load images from playground:

• Open playground file and create there folder Resources
• copy images to this folder

Solution 4:

Just made quick paste function for those of you who wanted to use Srikar Appal answer. (if in case background & foreground images are of different sizes)

- (UIImage *) mergeImages:(NSString *)bgImageFileName foreGround:(NSString *)fgImageFileName  {
    UIImage *bottomImage = [UIImage imageNamed:bgImageFileName]; //background image
    UIImage *image       = [UIImage imageNamed:fgImageFileName]; //foreground image

    CGSize newSize = CGSizeMake(bottomImage.size.width, bottomImage.size.height);
    UIGraphicsBeginImageContext(newSize);

    // Use existing opacity as is
    [bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];

    // Apply supplied opacity if applicable
    // Change xPos, yPos if applicable
    [image drawInRect:CGRectMake(11,11,image.size.width,image.size.height) blendMode:kCGBlendModeNormal alpha:1.0];

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    return newImage;
}