Image loading with GCD receiving memory warning - ios

Question

I'm developing a photo gallery application using AssetsLibrary to load my device photos. When presenting a random image in another VC I've noticed the following : it takes about 1 or 2 seconds for my full res image to load on the imageView (way much longer than the native photosApp) and I also get from the log "Received memory warning" after loading a few images. If I set my representation to fullScreenImage the warnings stop but I don't want this. What must I change for a smooth performance and high quality images on the view ?
Here's the code,hope you can tell me what's the problem :
This is the VC where I want to present my image on the screen
- (void)viewDidLoad
{
[super viewDidLoad];
NSLog(#"%#",assetsController);
detailImageView = [[UIImageView alloc]initWithFrame:self.view.bounds];
[self.view addSubview:detailImageView];
detailImageView.image = smallImage; //small image is my asset thumbnail and is passed as an argument in my init function
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
ALAsset *asset = [assetsController.albumPics objectAtIndex:assetsController.index];
ALAssetRepresentation *representation = [asset defaultRepresentation];
bigImage = [[UIImage imageWithCGImage:[representation fullResolutionImage]]retain];
dispatch_async(dispatch_get_main_queue(), ^{
detailImageView.image = bigImage;
});
[pool release];
});
}
UPDATE 1
{
UIImageView *detailImageView = [[UIImageView alloc]initWithFrame:self.view.bounds];
[self.view addSubview:detailImageView];
detailImageView.image = smallImage;
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
ALAsset *asset = [assetsController.albumPics objectAtIndex:assetsController.index];
ALAssetRepresentation *representation = [asset defaultRepresentation];
UIImage *bigImage = [UIImage imageWithCGImage:[representation fullResolutionImage]];
dispatch_async(dispatch_get_main_queue(), ^{
detailImageView.image = bigImage;
});
[pool release];
});
}

Answer 1

Is bigImage an instance variable? Is it used in any place other than here? If it is not used anywhere else, then it should be a local variable, and you shouldn't retain it. If it is an instance variable that you retain, you need to release the previous value before assigning a new value to it.
Same discussion applies to detailImageView