Divide the image into small connected regions called cells,
and for each cell compute a histogram of gradient directions or edge
orientations for the pixels within the cell.
Discretize each cell into angular bins according to the
Each cell's pixel contributes weighted gradient to its
corresponding angular bin.
Groups of adjacent cells are considered as spatial regions
called blocks. The grouping of cells into a block is the basis for grouping and
normalization of histograms.
Normalized group of histograms represents the block
histogram. The set of these block histograms represents the descriptor.