Quantization step selection for image coding in digital video recorders

摘要

A quantization step size selecting unit comprises a multi-step quantization unit 402 for performing quantization on the small blocks output from an orthogonal transform coding unit (figure 1,104) according to a plurality of predetermined quantization step sizes. A multi-step accumulating unit 408 accumulates the code length output from said variable length coding unit 406 in units of small blocks, and also predetermined reference small blocks in units of large blocks (figure 7.720). Normalisation unit 410 uses said code length accumulated in small block units and said code length accumulated in the reference large block unit to allot a new target code length to each small block so that the difference between the accumulated small blocks and the reference large block is a minimum. A quantization step size selecting unit 412 selects a quantization step size capable of outputting the closest value to said target code length of said normalizing unit.