Merging multiple images into 1 - ios

Question

I'm trying to overlay picture taken from camera with some other preset images. Problem is, picture from camera might be 8MP which is huge in term of memory usage. Some of the overlays might try to cover the whole image.
I tried multiple way to merge them all into one image.
UIGraphicsBeginImageContextWithOptions(_imageView.image.size, NO, 1.0f);
[_containerView.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
or
CGContextDrawImage(UIGraphicsGetCurrentContext(), (CGRect){CGPointZero, _imageView.image.size}, _imageView.image.CGImage);
CGContextDrawImage(UIGraphicsGetCurrentContext(), (CGRect){CGPointZero, _imageView.image.size}, *other image views*);
or
UIImage* image = _imageView.image;
CGImageRef imageRef = image.CGImage;
size_t imageWidth = (size_t)image.size.width;
size_t imageHeight = (size_t)image.size.height;
CGContextRef context = CGBitmapContextCreate(NULL, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef), CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), CGImageGetColorSpace(imageRef), CGImageGetBitmapInfo(imageRef));
CGRect rect = (CGRect){CGPointZero, {imageWidth, imageHeight}};
CGContextDrawImage(context, rect, imageRef);
CGContextDrawImage(context, rect, **other images**);
CGImageRef newImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
UIImage* resultImage = nil;
NSURL* url = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:#"x.jpg"]];
CFURLRef URLRef = CFBridgingRetain(url);
CGImageDestinationRef destination = CGImageDestinationCreateWithURL(URLRef, kUTTypeJPEG, 1, NULL);
if (destination != NULL)
{
CGImageDestinationAddImage(destination, newImageRef, NULL);
if (CGImageDestinationFinalize(destination))
{
resultImage = [[UIImage alloc] initWithContentsOfFile:url.path];
}
CFRelease(destination);
}
CGImageRelease(newImageRef);
all of these work but essentially, doubling the current memory usage.
Is there anyway to compose them all together without the need to create new context? Maybe save all images in file system and doing the merging there without actually consuming tons of memory? Or maybe even rendering into filesystem tile per tile?
Any suggestion or pointer where do I go from this?
Thanks

Answer 1

Check out the following code. You can send multiple images to the following method, however as you are facing memory issues, I suggest you to call the same method repetitively to merge multiple images. This process might take more time though.
-(CGImageRef )mergedImageFromImageOne:(UIImage *)imageOne andImageTwo:(UIImage *)imageTwo
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
CGSize imageSize = imageOne.size;
UIGraphicsBeginImageContext(sizeVideo);
[imageOne drawInRect:CGRectMake(0,0,imageSize.width,imageSize.height)];
[imageTwo drawInRect:CGRectMake(0,0,imageSize.width,imageSize.height) alpha:1];
CGImageRef imageRefNew = CGImageCreateWithImageInRect(UIGraphicsGetImageFromCurrentImageContext().CGImage, CGRectMake(0,0,imageOne.width,imageOne.height));
UIGraphicsEndImageContext();
[pool release];
return imageRefNew;
}
Hope this helps.