2D Pixel Trigrams for Content-Based Image Retrieval

The problem of nding similar images and images with a similar sub-image given a search image or part of a search image is addressed in this article by using 3x3 local pattern statistics in thresholded gradient images of scanned portraits normalized for scale, orientation, position and lighting. Pattern frequencies sorted on magnitude are closely linked to a spatial frequency ordering. The 2D trigram feature vector is formed by a weighing of the pattern frequencies. Several weighing functions were applied to a database of 3014 image les: the results indicate that a sort of band pass approach, suppressing both ends of the sorted pattern frequency distribution works best. The method works well on full image comparison and will be applied to sub-image search in the near future.