1. A method of detecting an object from an object class for use in an image sensor, the method comprising: storing, in an image buffer, image data in raster order; reading the image data from the image buffer in Z-order; computing a plurality of feature responses for the image data, wherein each of the feature responses corresponds to one of a plurality of features; determining whether an object from the object class is present in the image data based on the feature responses; and wherein the reading comprises obtaining a group of pixels from the image buffer substantially concurrently, and wherein computing the plurality of feature responses comprises computing one feature response for each of the plurality of features.