Adaptive graylevel image compression system
US4725885A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Dec 22, 1986 |
| Grant date | Feb 16, 1988 |
| Priority date | — |
| Expiry date | Dec 22, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N19/593
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Apparatus and method for modelling differential pulse code modulation (DPCM) input data for entropy coding. In particular, the sign and magnitude of one piece of DPCM data after another are modelled to provide a magnitude state input and a sign state input to provide context for DPCM magnitude input and DPCM sign input, respectively, to an entropy encoder or decoder. That is, the DPCM magnitudes of earlier pieces of (context) DPCM magnitude data are re-mapped for each such earlier piece of data, the re-mapped data being aggregated to form a combined value indicative of the magnitude state input. Similarly, the DPCM signs of earlier pieces of (context) DPCM sign data are re-mapped for each such earlier piece of data, the re-mapped data being aggregated to form a combined value indicative of the sign state input. In an image data compression system, the magnitude state input serves as an activity indicator for picture elements (pixels) neighboring a "subject" pixel. According to the invention, the DPCM signal is derived from a difference value calculated by subtracting one of a plurality of predictor values from the graylevel value X of the subject pixel. The selection of predictor v…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.