Dynamic range compensation by filter cascade
US7899267B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | May 23, 2007 |
| Grant date | Mar 1, 2011 |
| Priority date | — |
| Expiry date | Oct 26, 2029 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N23/88
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A local method uses a cascade of multiple nonlinear edge preserving filters, and nonlinear pixel point operations, to calculate the pixel gain. Multiple low-pass filters are used, being applied to surrounding neighborhoods of the current pixel of narrow and of wide extent. The number of filter stages may be determined based on the image content. The coefficients used to combine a gray level image extracted from the input image with the ascending scale regions can be automatically extracted from high-pass filtered images of the ascending scale regions. Multiplying each color component of the input image by one or more pixel dependent gain or attenuation factors, using a nonlinear mapping function that can lighten shadow regions as well as darken bright regions, generates the output image.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.