title: google app engine get_serving_url 16-bit
body: <p>I am building a GAE app where user's photo uploads are written to Google Cloud Storage and served from the Blobstore, and thumbnails are served using the get_serving_url() method, which generally works very well.  </p>
  
  <p>But I've hit an issue for uploaded images that are 16-bit tiffs; using parse_file_info() after my BlobstoreUploadHandler ( self.get_uploads('file') ) I can read the metadata in the FileInfo class and see that the Content_Type is an image/tiff, which can be thumbnailed ( by get_serving_url() ) if they are 8-bit, so the file is sent off to be thumbnailed but this returns an error for 16-bit tiffs.  Any ideas on how I can verify the bit-depth to prevent these files being sent off for thumbnailing, given the bit-depth of the tiff isn't part of the metadata picked up by the get_uploads() method?</p>
  
  <p>I also tried passing parse_source_metadata=True to execute_transforms and then reading the metadata, but it is just width and height and colorspace and colorprofile but not bit depth.</p>