- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGSize innerSize = CGSizeMake(galleryView.frame.size.width - 80, galleryView.frame.size.height - 40);
    GLPhotoAsset *photo = [(PCOpticsPhotoPoint *)_cluster.points[indexPath.row] photo];
    CGFloat ratio = MIN(innerSize.width / photo.size.width, innerSize.height / photo.size.height);

    return CGSizeMake(photo.size.width * ratio, photo.size.height * ratio);
}