ALAssetsLibrary accessing all photos 1000 + from camera roll app crashes

I want to access all photos from camera roll my code is working fine if i have few images in camera roll then app is working fine but if i have more than 1000 photos then app crashes here is my code

ALAssetsLibrary *al = [[ALAssetsLibrary alloc] init];

     [al enumerateGroupsWithTypes:ALAssetsGroupAll

                      usingBlock:^(ALAssetsGroup *group, BOOL *stop)
     {
         NSMutableArray *arrImages=[[NSMutableArray alloc]init];
         NSString *albumName = [group valueForProperty:ALAssetsGroupPropertyName];
         if (albumName !=nil) {


         [arrGroupsNames addObject:albumName];
         [group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop)
          {
              if (asset)
              {

                  UIImage *img=[self imageForAsset:asset];


                  [arrImages addObject:img];

              }
          }
           ];

         [arrGroups addObject:arrImages];
         }



         [self.tableVieww reloadData];

     }



                    failureBlock:^(NSError *error)
     {
         // User did not allow access to library
         NSLog(@"error");
      }
     ];

and here is the function which return image from ALAsset

-(UIImage*) imageForAsset:(ALAsset*) aAsset{

    ALAssetRepresentation *rep;

    rep = [aAsset defaultRepresentation];

    return [UIImage imageWithCGImage:[rep fullResolutionImage]];
}