Bit rate control system based on object

PURPOSE: A method and an apparatus for controlling an object-based bit rate are provided to adaptively assign quantization parameters of a macro block unit to an object region and a background region and control the bit rate. CONSTITUTION: A target bit setup unit(302) sets target bit quantity from an object segmentation result(301) and a result in which the state of an output buffer(306) is checked. A quantization parameter setup unit(303) receives the set target bit quantity and the object segmentation result from the target bit setup unit(302), and adaptively sets a quantization parameter of an object region and a quantization parameter of a background region. A quantization mode setup unit(304) judges whether a macro block to be quantized belongs in a boundary region of the object region and the background region, and sets a quantization mode so that the quantization is performed using an arbitrary quantization parameter selection mode in the boundary region. A quantizer(305) quantizes an input image according to quantization parameters set according to the background region, the object region and the boundary region. The output buffer(306) outputs the quantized image signal as a bit stream.