Region proposal and object detection using HoG-based CNN feature map

Abstract

Object region proposal has a wide application on various domains, such as object detection, object tracking, robot navigation, and anomaly detection. Widely used region proposal methods are based on either grouping superpixels or sliding windows. Previous studies have been done by grouping either convolution features, superpixels, or windows. Moreover, histogram of gradients (HoGs) of lower-level features (pixels) can be used for the region proposal task. In this study, both the concepts of HoGs and convolution features are used for proposing object(s) region(s) in an image. Region proposal is done by HoGs of convolution features and statistical application on the gradient data of different feature maps. First, a sized image is passed through one convolution layer to generate reduced feature maps. Then, a window slides over each feature map and HoG is applied over each window. Thereafter, the histogram is analysed using the concept of Coefficient of Variation (CV) and angle (slope) applied on histogram data values. A window is considered as the object region if the CV and angle of its histogram data exceed some thresholds. For all feature maps, we have obtained several widows that represent approximated object regions. These windows are grouped to obtain the possible region(s) proposal. The effectiveness of the proposed method is demonstrated over one of the benchmark datasets, called `PASCAL VOC'. Our method is found superior to two other state-of-the-art, namely region-based segmentation (RBS), and combining efficient object localization and image classification (CEOLIC) in terms of recall.