Making Templates Rotationally Invariant. An Application to Rotated Digit Recognition

Part of Advances in Neural Information Processing Systems 11 (NIPS 1998)

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Shumeet Baluja


This paper describes a simple and efficient method to make template-based object classification invariant to in-plane rotations. The task is divided into two parts: orientation discrimination and classification. The key idea is to perform the orientation discrimination before the classification. This can be accom(cid:173) plished by hypothesizing, in turn, that the input image belongs to each class of interest. The image can then be rotated to maximize its similarity to the train(cid:173) ing images in each class (these contain the prototype object in an upright orien(cid:173) tation). This process yields a set of images, at least one of which will have the object in an upright position. The resulting images can then be classified by models which have been trained with only upright examples. This approach has been successfully applied to two real-world vision-based tasks: rotated handwritten digit recognition and rotated face detection in cluttered scenes.