Very low bit rate video compression using MPEG-4 sprite coding

The new MPEG-4 image coding standard that has recently been established offers higher image quality in low-bit-rate coding than conventional coding methods such as H.26X, MPEG-1, and MPEG-2, as well as coding for each object unit (a new function). This paper proposes an algorithm for the automatic extraction of video objects consisting of a foreground object and a background sprite. It is based on "sprite coding," which can greatly reduce the number of code bits compared to conventional methods. The foreground and background video objects processed by the proposed method are subjected to MPEG-4 object coding and sprite coding, respectively, and are compared with MPEG-4 simple profile (normal) coding. In particular, the influence of the frame rate and the foreground object rate on the number of code bits was investigated. It was found that the proposed method can reproduce images with the same quality while using about one-fourth to one-half as many code bits as the normal coding method when the foreground rate is 10 to 15% of the whole image, regardless of the frame rate. In addition, the proposed method can attain more than double the frame rate of the normal coding method at a very low bit rate (e.g., 128 and 64 kbit/s) with a similar SNR.