J. M. Quan and S. C. Tai
Instutite of Electrical Engineering
National Cheng Kung University
Tainan, Taiwan, R.O.C.
In this paper, we present a compression technique which preserves edges in the compressed image and adapts itself to the local nature of the image. Inter block redundancies were seldom considered in the earlier design of compressors. We take this into acount, achieve a good compression ratio and also preserve good visual quality at the same time. In this paper, the range value presented by Nosiopoulos is used to classity the image blocks into four coding techniques, respectively, which are used to compress the associated class image block. The four coding algorithms are: mean coding, 2_level MMSE quantizer for blodk truncation coding (BTC), hybrid BTC (HBTC) and quad-tree coding. Experimental results show that considerable improvements over the work by Nasiopoulus can be achieved. As for complex images which contain sharp edges and even single-pixel-width grey level sudden changes, their visual quality is very well-preserved. Thus,our technique is suitable for practical applications if image quality is requested.
Keywords: adaptive compression coding, quad-tree coding, block truncation coding, hybrid block truncation coding
Received May 16, 1992; revised November 18, 1993.
Communicated by Jhing-Fa Wang.
*This research work was supported by the National Science Council fo the Republic of China under contract NSC 83-0420-E-006-002.