How to save ALAsset image to disk fast on iOS?

Question

I am using ALAsset to retrieve images like that:

[[asset defaultRepresentation] fullResolutionImage]]

This return CGImageRef which I want to save to disk as fast as possible...

Solution 1:

UIImage *currentImage = [UIImage imageWithCGImage:[[asset defaultRepresentation] fullResolutionImage]];
NSData *currentImageData = UIImagePNGRepresentation(currentImage);
[currentImageData writeToFile:filePath atomically:YES];

Solution 2:

CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath];
CGImageDestinationRef destination = CGImageDestinationCreateWithURL(url, kUTTypePNG, 1, NULL);
CGImageDestinationAddImage(destination, [[asset defaultRepresentation] fullResolutionImage], nil);
CGImageDestinationFinalize(destination);

The problem is that both methods are very slow performing on a device. I takes about 2 seconds per image to perform this. And this is absolutely to long.

Question: How can I speed up this image saving process? Or perhaps is there a better solution for this?

UPDATE: The best performance improvements in both solutions is to save images to JPEG format instead of PNG. So for solution 1 have replaced UIImagePNGRepresentation with UIImageJPEGRepresentation. For solution 2 have replaced kUTTypePNG with kUTTypeJPEG.

Also worth noting that second solution is way more memory efficient that first one.

Answer 1

That's because of PNG compression is slow process, and takes a while on iPhone's processor, especially for full-size photography.