A horizontal scan circuit comprises a column selector and a plurality of block selectors. A column selector is used to address particular columns of pixels within blocks. A block selector is used to select a particular block and to select the particular columns of the selected block that are addressed by the column selector. Each block selector typically comprises a single D-type flip-flop that is associated with a block of pixel columns. The block selectors are arranged such that the blocks can be scanned from left-to-right or right-to-left. The column selector comprises an asynchronous counter and a decoder that are further arranged to provide sub-sampling and horizontal adding functions. The use of block and column selectors reduces the number of relatively large D-type flip-flops (which conserves die area) and reduces the parasitic capacitance associated with the otherwise required relatively large number of inputs of the column selection circuit drivers.