Nonuniformity correction of an imaging sensor using region-based correction terms

Abstract

A scene based nonuniformity correction method (40) that computes and applies offset correction errors to a video signal corresponding to an image derived from a imaging sensor (11). A video signal derived from the sensor (11) is processed such that a vector representing offset correction terms is formed, and this vector is initially set to zero. Each element in this vector represents a correction term for a particular detector of the sensor (11). The vector is applied to each pixel of the image by a processor (13) as the pixels are read from the sensor (11). To measure the offset error, the image is separated into vertically oriented regions, each comprising a plurality of channels. The average of each channel within a region is computed (42), and a set of region vectors is foraged, such that there is one region vector for each region. Each region vector is then globally high-pass filtered and then edges larger than a predefined threshold are detected (43), and marked (44). Then, each region vector is further separated into sub-regions (45). The isolated sub-regions are locally high-pass filtered. In one embodiment, the correction terms for each vertical region vector are averaged together, resulting in a single correction vector (48). The correction terms calculated for each vertical region may also be applied individually to each detector of the sensor (11). In this second embodiment, the offset level error in each region for each channel is calculated (49), wherein the offset level error at boundary edges is undefined. The correction terms corresponding to a region are applied as the detector (11) scans the scene and views a portion corresponding to that particular region. The correction terms are smoothed at region boundaries to eliminate noise due to boundary transitions.

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