Measuring visual vocabulary appropriateness by dispersion index and its improvement by globalizing SIFT descriptors

Correct classification rates are often used to measure the appropriateness of a visual-word vocabulary. Appropriateness is also measured by the dispersion index, a technique in quantitative ecology that estimates the distribution pattern of individuals. In the bag-of-keypoints method of making a visual vocabulary, the size of the vocabulary is examined. In addition, a method to globalize a local feature is proposed. In this globalization method, each descriptor is modified to be similar to adjacent descriptors and therefore provides more opportunity for a visual word to form clumps on a test image. Although applying the index is limited by the classifier, we found that appropriateness is measured by estimating the average dispersion index for every visual word. In addition, this paper discusses another method for creating a visual-word vocabulary that is more appropriate for classification by globalization.