title: App crash while downloading large images using SDWebImage?
body: <p>I'm using <code>SDWebImage</code> to download image async from server.Some images on server are of size ~1.5 to 2. MB.I'm showing these images on <code>UICollectionView</code>. I'm getting memory warning and app crashes after several run.Some times it happens when images downloaded first time and some time when i scroll the collection view up and down.
  Here is my code-</p>
  
  <pre><code>-(void)setImageWithUrl:(NSURL*)imgurl onImageView:(UIImageView*)image prograssive:(BOOL)progressive
  {
      __block UIActivityIndicatorView *activityIndicator;
      __weak UIImageView *weakImageView = image;
      SDWebImageOptions opt;
      if (progressive) {
  
          opt = SDWebImageProgressiveDownload;
      }
      else
          opt = SDWebImageRetryFailed;
      [image sd_setImageWithURL:imgurl placeholderImage:[UIImage imageNamed:@"default_image"] options:opt progress:^(NSInteger receivedSize, NSInteger expectedSize)
       {
           if (!activityIndicator)
           {
               [weakImageView addSubview:activityIndicator = [UIActivityIndicatorView.alloc initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]];
               activityIndicator.center = CGPointMake(weakImageView.frame.size.width /2, weakImageView.frame.size.height/2);
               // activityIndicator.center = weakImageView.center;
               [activityIndicator setBackgroundColor:[UIColor clearColor]];
               [activityIndicator startAnimating];
           }
       }
                      completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL)
       {
           [activityIndicator removeFromSuperview];
           activityIndicator = nil;
       }];
  }
  </code></pre>
  
  <p>and in <code>AppDelegate</code>-</p>
  
  <pre><code>- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application
  {
  
      [[SDImageCache sharedImageCache] clearMemory];
      [[SDImageCache sharedImageCache] cleanDisk];
      [[SDImageCache sharedImageCache] clearDisk];
      [[SDImageCache sharedImageCache] setValue:nil forKey:@"memCache"];
  }
  </code></pre>
  
  <p>Please not the images are high resolution(more than 3000 pixel width).For example one of them has 4256*2832 and size 979KB produce the memory warning.Any help or suggestion would be appreciated. 
  <strong>EDIT:-</strong> my App is being killed due to memory pressure, but only on iPhone 4s and lower versions(working fine on iPhone5 and above).when a large image is being downloaded(or complete download) i got a sudden memory spike(it goes from ~25mb to ~90mb) and app crashes.Any suggestion what to do?</p>