A method of generating a feature descriptor includes determining a first output histogram of an input by processing a first group of pixels of the input to determine first contributions to bins of the first output histogram. The input image including gradient orientation values and gradient magnitude values of a portion of an image that is in a region of a detected feature. After processing the first group of pixels, the method includes determining a second output histogram of the input by processing a second group of pixels of the input to determine second contributions to bins of the second output histogram.