Birdlets: Subordinate categorization using volumetric primitives and pose-normalized appearance

  • Authors:
  • Ryan Farrell;Om Oza; Ning Zhang;Vlad I. Morariu;Trevor Darrell;Larry S. Davis

  • Affiliations:
  • University of Maryland, College Park, USA;University of Maryland, College Park, USA;University of California, Berkeley, USA;University of Maryland, College Park, USA;University of California, Berkeley, USA;University of Maryland, College Park, USA

  • Venue:
  • ICCV '11 Proceedings of the 2011 International Conference on Computer Vision
  • Year:
  • 2011

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Abstract

Subordinate-level categorization typically rests on establishing salient distinctions between part-level characteristics of objects, in contrast to basic-level categorization, where the presence or absence of parts is determinative. We develop an approach for subordinate categorization in vision, focusing on an avian domain due to the fine-grained structure of the category taxonomy for this domain. We explore a pose-normalized appearance model based on a volumetric poselet scheme. The variation in shape and appearance properties of these parts across a taxonomy provides the cues needed for subordinate categorization. Training pose detectors requires a relatively large amount of training data per category when done from scratch; using a subordinate-level approach, we exploit a pose classifier trained at the basic-level, and extract part appearance and shape information to build subordinate-level models. Our model associates the underlying image pattern parameters used for detection with corresponding volumetric part location, scale and orientation parameters. These parameters implicitly define a mapping from the image pixels into a pose-normalized appearance space, removing view and pose dependencies, facilitating fine-grained categorization from relatively few training examples.