title: saving UIImage to file cost a lot of time
body: <p>I'm trying to load pictures in iPhone Photos app, then save the selected pictures in to my app's folder, using ALAssetsLibrary, and have two issues:
  1. the image file saved to disk is much bigger then original files in Photos app, for example, a picture is 2.8MB, but after saved to my app's folder, it's 6.4MB, following is the code:</p>
  
  <pre><code>        CGImageRef cgImage = [localPhoto thumbnail];
  
          NSString *path = @"/documents/test/1.jpeg";//the path is just an example
          BOOL succ;
          UIImage *image1 = [UIImage imageWithCGImage:cgImage];
  
          NSData *data1 = UIImageJPEGRepresentation(image1, 1.0);
          succ = [data1 writeToFile:path atomically:YES];
  </code></pre>
  
  <ol start="2">
  <li>the above code(saving 6.4MB image to file) costs about 1.6seconds, is it normal? is there anyway to make it faster?</li>
  </ol>