Patent ID: 7369708

Claim:
An image data compression device used to compress image data, the image data compression device comprising: a quantization section which quantizes image data in frame units; a FIFO buffer section which buffers quantized data for at least N frames (N is an integer greater than one) from the quantization section; an encoded data generation section which reads the quantized data from the FIFO buffer section asynchronously from writing into the FIFO buffer section, and generates encoded data by encoding the quantized data; and a rate control section which changes a quantization step of the quantization section by using the data size of the encoded data to change a data size of encoded data to be processed, wherein the rate control section calculates a quantization parameter to be equal to or less than an upper threshold of the quantization parameter or to be equal to or greater than a lower threshold of the quantization parameter by using an average data size obtained by averaging the data size of the encoded data for N frames preceding a frame of image data to be quantized by the quantization section; and wherein the rate control section changes the quantization step based on the quantization parameter.