Patent Number: 6,167,161

Title: Lossless transform coding system having compatibility with lossy coding

Abstract: A reversible eight-element discrete cosine transform coding system which provides transform values near to transform values of the original eight-element discrete cosine transform. In a 4.times.4 matrix transform which appears when an eight-element discrete cosine transform is decomposed in accordance with a fast calculation method, transform coefficients (X1, X7, X3, X5) are separated into (X1, X7) and (X3, X5), which are quantized individually making use of the fact that, if (X1, X7) are determined, then values which can be taken by (X3, X5) are limited. (X1, X7) are quantized with step sizes k1, k7 by linear quantizers to obtain quantization values (Xq1, Xq7). Meanwhile, (X3, X5) are divided into global signals and local signals, and the global signals are quantized with step sizes L3, L5 by linear quantizers while quantization values of the local signals are determined using a table. The quantization values are added by adders to obtain quantization values (Xq3, Xq5) of (X3, X5). The reversible transform quantization for a 4.times.4 matrix and conventional reversible quantization of 2.times.2 matrices are combined to construct a reversible eight-element discrete cosine transform system.

Inventors: Oami; Ryoma (Tokyo, JP)

Assignee: NEC Corporation

International Classification: G06T 9/00 (20060101); G06K 009/36 (); G06K 009/46 ()

Expiration Date: 12/26/2017