Coding apparatus
US5432556A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jan 31, 1994 |
| Grant date | Jul 11, 1995 |
| Priority date | — |
| Expiry date | Jan 31, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N19/91
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A coding apparatus reduces a digital image signal. The coding apparatus includes a block formatting circuit for dividing the digital image signal into blocks of a plurality of picture elements, an orthogonal transforming circuit for transforming the blocks of plurality of picture elements into a plurality of coefficients, an adaptive quantizing unit for quantizing the plurality of coefficients with a quantization table, a calculating circuit that divides each block of the digital image signal into a plurality of sub-blocks and obtains a plurality of indexes, and a detecting circuit that obtains a maximum index and a minimum index from the plurality of indexes. Each index indicates a degree of change between the picture elements in a sub-block of the plurality of sub-blocks. The coding apparatus further includes a subtracting unit that obtains a difference between the maximum index and the minimum index, and a selecting unit that obtains the quantization table from a plurality of quantization tables according to the minimum index and the difference. As a result, the image quality of the background having little change in the signal is kept good.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.