Visual Categorization Robust to Large Intra-Class Variations using Entropy-guided Codebook

Categorizing visual elements is fundamentally important for autonomous mobile robots to get intelligence such as new object acquisition and topological place classification. The main problem of visual categorization is how to reduce the large intra-class variations, especially surface markings of man-made objects. In this paper, we present a robust method by introducing intermediate blurring and entropy-guided codebook selection in a bag-of-words framework. Intermediate blurring can filter out the high frequency of surface markings and provide dominant shape information. Entropy of a hypothesized codebook can provide the necessary measure for the semantic parts among training exemplars. From the first step, a generative optimal codebook for each category is learned using the MDL (minimum description length) principle guided by entropy information. From the second step, a final set of codebook is learned using the discriminative method guided by the inter-category entropy of the codebook. We select the necessary parameters through various evaluations and validate the effect of the surface marking reduction method using a Caltech-101 DB, which has large intra-class variations. Finally, we briefly introduce the impact of the method to the object categorization and segmentation problem