Adaptive gray scale mapping to reduce registration noise in difference images

Abstract

Difference images are used in various image processing applications such as change detection, radar imaging, remote sensing, and biomedical image analysis. The difference image, or difference picture, is found by subtracting one image from another. One practical problem with difference images is that, if the images are not in perfect spatial registration before subtraction, their difference image will contain artifacts caused by incomplete cancellation of the unchanged background objects. These artifacts (registration noise) show up as extraneous light and dark regions on either side of the background objects. Usually, this noise is reduced by either smoothing (blurring), or thresholding the difference image. This paper describes a new method to reduce registration noise using adaptive gray scale mapping. This simple digital filter reduces registration noise as well as, or better than, previous methods, with less degradation of the actual differences between the images.