Gray scale image data compression with code words a function of image history
US4369463A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 4, 1981 |
| Grant date | Jan 18, 1983 |
| Priority date | — |
| Expiry date | Jun 4, 2001 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N19/91
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
The present invention relates to a method and apparatus for compacting gray-scale image data which maintains extremely good picture quality and can result in typical images in a compression ratio of 5 to 1 and even better if a final step of arithmetic coding is used. The method is a special application of adaptive differential pulse code modulation (DPCM) which utilizes a prediction of smoothness surrounding a current pel to determine variable length codes to convey the quantized error. Thus, a continuously adaptive variable length code is produced which may be accurately decoded without using any further marker (code indicator) bits. For each pel and "error bit" is generated to indicate to the decoder if the predicted quantization range is adequate. These eroror bits can be further significantly compressed. This method permits the use of a "zero bit" per pel mode for the data transmission (1 "error bit" per pel actually transmitted) and provides for the automatic detection of the particular variable length compression code utilized for transmitting the quantized error (E.sub.Y) for a particular pel. Utilizing the concepts of the present invention the inventors have obtained compre…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.