PURPOSE: To control a quantization step size in detail, to control accurately a generated code quantity and to improve the picture quality by setting a gradient of an equation of relation between a residual code quantity and a quantization step size in response to an object code quantity of a block and using the residual code quantity calculated for each block so as to set the quantization step size.
CONSTITUTION: A relational equation setting section 40 obtains an object code quantity per block from an object code quantity of a frame or a field, sets the gradient A of the relational equation between a residual code quantity and a quantization step size to be 0.6/(object code quantity per block) and outputs a relational equation signal 41. A quantization step size calculation section 23 uses the relational equation signal 41 to obtain the relational equation between the residual code quantity and the quantization step size to decide a quantization step size Qb by equation, Qb=INT[A×Bcont]+2, where Bcont is a residual code quantity of a code memory section 24. Since the quantization step size is controlled for each block, the code quantity is controlled accurately and the picture quality of the entire picture is improved.
INOUE IKUO
TANAKA AKIYOSHI
