默认的相机iPhone应用程序如何设置如此快速地保存照片？

Question

So far I've managed to create an app for iPhone that takes multiple images with about a 3 second interval between each. I`m processing each image in a separate thread asynchronously and everything is great till it gets to the moment for saving the image on the iPhone disk. Then it takes about 12 seconds to save the image to the disk using JPEG representation.

How does Apple do it, how do they manage to save a single image so fast to the disk is there a trick they are using? I saw that the animations distract the user for a while, but still the time needed is below 12 seconds!

Thanks in advance.

Answer 1

Actually apple uses its kernal driver AppleJPEGDriver, It is a hardware jpeg encoding api and is much faster than software encoding (JPEGRepresnetaion) and some of the people using it in their jailbreak apps(cycorder video recording application). Apple should give the same functionality to its users but they are apple :)

Answer 2

I haven't tried this but I wouldn't be so sure that Apple isn't using the same methods. A big part of the Apple design philosophy relies on hiding operational interruptions from the user. The Apple code may take as much time as yours but simply be adroit at hiding the entire save time from the perception of the user.

If someone can't tell you how Apple actually does save faster I would suggest looking at ways to disguise the save time.

Answer 3

I was having this problem in my app, on saving it would hang so I used Grand central dispatch.

Below is the setImage method out of my image cache class, if UIImage has a image it saves it otherwise it deletes it. You can adapt this to suit your needs hopefully, will only work on iOS 4+. The code is ARC enabled.

-(void)setImage:(UIImage *)image{
    if (image == nil){
    NSLog(@"Deleting Image");
    // Since we have no image let's remove the cached image if it exists
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                   NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory,
                   NSUserDomainMask, YES) objectAtIndex:0];
                   [[NSFileManager defaultManager] removeItemAtPath:[cachePath
                   stringByAppendingPathComponent:@"capturedimage.jpg"] error:nil];
                 });
    }
else {
      NSLog(@"Saving Image");
      // We've got an image, let's save it to flash memory.
      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                     NSString *cachePath = 
                    [NSSearchPathForDirectoriesInDomains(NSCachesDirectory,
                    NSUserDomainMask, YES) objectAtIndex:0];
                    NSData *dataObj = UIImagePNGRepresentation(image);
                    [dataObj writeToFile:[cachePath 
                    stringByAppendingPathComponent:@"capturedimage.jpg"] atomically:NO];
                  });
     }

imageCache = image;

}

Answer 4

If you google around a bit... there is a whole bunch of people with the same problem.

I didn't find an answer. The general conclusion seems to be that apple either uses some internal api and bypass public api overhead or some hardware encoder.

Guess you are out of luck for fast image saving