A discrete cosine transformation circuit comprising a pipeline with a memory stage and an arithmetic stage. The arithmetic stage comprises first and second arithmetic logic units (ALU). Each of the ALUs receives from the memory a set of image data, performs a first calculation on the set of image data and outputs calculation result thereof in a first clock cycle. A path in the circuit directs the result to the memory stage, such that at least one ALU can selectively receive the result from the path in a clock cycle subsequent to the first clock cycle.