1. A computer-implemented method comprising: receiving an image; extracting coarse features from the image; generating an object probability map based on the coarse features extracted from the image, the object probability map indicating high-probability object regions in the image that are likely to contain an object; and extracting dense features from the high-probability object regions of the image identified in the object probability map to enable detection of one or more objects in the image, wherein the dense features are features extracted using smaller sampling steps than sampling steps used to extract the coarse features.