Abstract: An adaptive quantizing apparatus and method in HDTV according to the invention is capable of modifying a quantization spacing for the individual blocks to be processed in accordance with the human visual system, such as motion, complicatedness, brightness, etc. of a picture. To this end, a picture portion which is prone to present any conspicuous visual undesirable effects is tracked down and assigned a modified bit rate so that a bit rate is lowered for a picture portion where such undesirable effects, if they occur, should not be very conspicuous, decreasing the probability of enhancing the subject picture quality.