Method and apparatus for optimizing a JPEG image using regionally variable compression levels
US7430330B2 · kind B2 · utility
Inventor
Key dates
| Filing date | Mar 28, 2005 |
| Grant date | Sep 30, 2008 |
| Priority date | — |
| Expiry date | Nov 7, 2026 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06T9/005
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
A method of JPEG compression of an image frame divided up into a plurality of non-overlapping, tiled 8×8 pixel blocks Xi. A global quantization matrix Q is determined by either selecting a standard JPEG quantization table or selecting a quantization table such that the magnitude of each quantization matrix coefficient, Q[m,n] is inversely proportional to the aggregate visual importance in the image of the corresponding DCT basis vector. Next a linear scaling factor Si is selected for each block, bounded by user selected values Smin and Smax. Transform coefficients, Yi, obtained from a digital cosine transform of Xi, are quantized with global table Smin Q while emulated the effects of quantization with local table Si Q and the quantized coefficients Ti[m,n] and global quantization table Smin Q are entropy encoded , where Smin is a user selected minimum scaling factor, to create a JPEG Part 1 image file. The algorithm is unique in that it allows for the effect of variable-quantization to be achieved while still producing a fully compliant JPEG Part 1 file.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.