Random fern descriptors, also called LBF, consist of some logical pairwise comparisons of the intensity or gradient levels of randomly selected pixels in images.14 However, such comparisons are not robust against rotation and scale variations because each pairwise pixel is randomly generated offline while remaining fixed in runtime. Therefore, a rotation-invariant descriptor with a high degree of stability in RGB-D images is defined as Display Formula
(1)where and are the ’th () feature channel15 obtained from a color image and the ’th depth channel obtained from the depth image, respectively, with both centered at pixel locations and . and are random pairwise pixel locations, and each comparison returns 0 or 1. In general, the pairwise pixels that are chosen map an image patch to a -dimensional space of binary descriptors in each fern. According to Eq. (1), RGB-D LBF can be computed as Display Formula
(2)where is the ’th fern and (or ) is the ’th binary feature. Therefore, the entire set of random ferns can be denoted by . A trade off between performance and memory can be made by changing the number of ferns and their sizes .