     
     private func sizeForAsset(asset: PHAsset) -> CGSize {
         let proportion = CGFloat(asset.pixelWidth)/CGFloat(asset.pixelHeight)
-        let height = self.tableView(self.tableView, heightForRowAtIndexPath: NSIndexPath(forRow: 0, inSection: 0)) - 2.0 * BRNImagePickerSheet.collectionViewInset
+        
+        let height: CGFloat = {
+            var rowHeight: CGFloat = 0.0
+            if (self.enlargedPreviews) {
+                rowHeight = BRNImagePickerSheet.tableViewEnlargedPreviewRowHeight
+            }
+            else {
+                rowHeight = BRNImagePickerSheet.tableViewPreviewRowHeight
+            }
+            
+            return rowHeight-2.0*BRNImagePickerSheet.collectionViewInset
+        }()
         
         return CGSize(width: proportion*height, height: height)
     }
     
     private func requestImageForAsset(asset: PHAsset, size: CGSize, completion: (image: UIImage) -> Void) {
-        let manager = PHImageManager.defaultManager()
-        
         let options = PHImageRequestOptions()
         options.resizeMode = .None
         
-        manager.requestImageForAsset(asset, targetSize: size, contentMode: .AspectFit, options: options) { (image, _) -> Void in
+        self.imageManager.requestImageForAsset(asset, targetSize: size, contentMode: .AspectFit, options: options) { (image, _) -> Void in
             completion(image: image)
         }
+    }
+    
+    private func prefetchImagesForAsset(asset: PHAsset, size: CGSize) {
+        let options = PHImageRequestOptions()
+        options.resizeMode = .None
+        
+        self.imageManager.startCachingImagesForAssets([asset], targetSize: size, contentMode: .AspectFit, options: options)
     }
     
     func getSelectedImagesWithCompletion(completion: (images:[UIImage]) -> Void) {

            return
        }
        
        self.fetchImages()
        self.tableView.reloadData()
        
        self.delegate?.willPresentImagePickerSheet?(self)

    
    // MARK: - Images
    
    private func fetchAssets() {
        let options = PHFetchOptions()
        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
        let result = PHAsset.fetchAssetsWithMediaType(.Image, options: options)
