Video signal quantizing apparatus and method thereof

A video signal quantizing apparatus for quantizing a video signal in each equal length unit composed of a plurality of blocks within a target code amount, the apparatus comprising:

• total code amount detecting means for obtaining a total code amount generated in the equal length unit of the video signal with each of a plurality of quantizing steps when the video signal is quantized with the plurality of different quantizing steps;
• first deciding means for deciding a first quantizing step from the plurality of quantizing steps, the first quantizing step being a quantizing step with which the total code amount is smaller than a target code amount and a difference of the total code amount and the target code amount is minimum;
• activity detecting means for detecting an activity for each block of the video signal, said activity being a variance of a plurality of pixel values constituting the block;
• second deciding means for deciding a second quantizing step by varying the first quantizing step according to the activity of each block;
• residue code amount detecting means for detecting a residue code amount that is a difference between a code amount of which all of the plurality of blocks in the equal length unit of the video signal are quantized with the first quantizing step and the total code amount;
• priority rank deciding means for deciding a priority rank of each block according to an error by rounding when the second quantizing step is decided in consideration of the activity;
• third deciding means for deciding a third quantizing step by varying the second quantizing step for a block selected according to the priority rank;
• and
• quantizing means for quantizing each block with a quantizing step decided by the second deciding means or the third deciding means.