A structure descriptor for an m×n pixel block of an image may be determined. The m×n pixel block may contain a primary pixel having a primary pixel value and a plurality of secondary pixels having respective secondary pixel values. The structure descriptor may include a plurality of structure indicators each associated with a respective secondary pixel. The respective structure indicators may be based on the primary pixel value and the respective secondary pixel value of the associated secondary pixel. Based on the structure descriptor, a structure value for the m×n pixel block may be determined. Based on the structure value, image processing may be applied to the m×n pixel block.