1989 年 13 巻 43 号 p. 31-36
Standardization for highly efficient video coding system is in progress at CCITT. In this paper, loop and post filters used in the video coding system are studied to be contributed to the standardization work by the Specialist Group on Coding of Visual Telephony, which is substantially responsible for making the recommendation. Through previous study for n×384kbps codec standardization, a simple loop filter with 3×3 pixel window has been proven to show good performance with a reasonable hardware cost at 384kbps. In lower bit-rate operations, however, some improvements on the loop filter have been felt required because noticeable block-shape and granular noises have been observed in the reproduced pictures. Aiming at improving the reproduced image quality, extensive experimants have been carried out. From the experimantal results, the followings have been obtained: (1) Considering perfomance, hardware cost and IDCT mismatch condition, the 3×3 low-pass filter is the most suitable as loop filter in 64-1920kbps video codec specification. (2) In lower bit-rate operations, an adaptive noise filter for post processing significantly improves reproducesed image quality.