Here is an adaptation of the routine that can be used for @2x images.

I have written it based on the sources I make reference to, including this page; thus please note the URL REF comments.

// BEGIN CODE

- (UIImage*) mergeTwoImages : (UIImage*) topImage : (UIImage*) bottomImage {
// URL REF: http://iphoneincubator.com/blog/windows-views/image-processing-tricks
// URL REF: http://stackoverflow.com/questions/1309757/blend-two-uiimages?answertab=active#tab-top
// URL REF: http://www.waterworld.com.hk/en/blog/uigraphicsbeginimagecontext-and-retina-display

int width = bottomImage.size.width;
int height = bottomImage.size.height;

CGSize newSize = CGSizeMake(width, height);
static CGFloat scale = -1.0;
if (scale= 4.0) {
scale = [screen scale];
}
else {
scale = 0.0; // Use the standard API
}
}
if (scale>0.0) {
UIGraphicsBeginImageContextWithOptions(newSize, NO, scale);
}
else {
UIGraphicsBeginImageContext(newSize);
}

[bottomImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
[topImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height) blendMode:kCGBlendModeNormal alpha:1.0];

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

return newImage;
}

// END CODE

- (UIImage *)addImage:(UIImage *)image1 toImage:(UIImage *)image2

It seems like this works perfectly on simulator and 320×480 screens, but if you jump to 640×960, image2’s dimensions are calculated at 320×480 sizes (even if you have the @2x file ready). This is only happening for image2; image1 is calculated at the correct Retina size. Curious.

Thanks

so I replaced `image` with `imageSavedToPhotosAlbum`, but it complained that `context`, which is at the end of your line, is an undeclared identifier. If I replace it with nil, the app crashes returning the following error: *** Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘+[NSInvocation invocationWithMethodSignature:]: method signature argument cannot be nil’ I’m using ios 4.3.3 and Xcode 4.0.2. Any suggestions?

Thanks!