Imaging apparatus offering dynamic range that is expandable by weighting two image signals produced during different exposure times with two coefficients whose sum is 1 and adding them up

Abstract

An object is imaged continuously during a first exposure time and a second exposure time shorter than the first exposure time. Weights, one of which decreases monotonously and the other of which increases monotonously, are applied to first and second resultant image signals under the condition that the sum of the weights is 1. The first and second image signals that have been weighted are added up, thus producing a synthetic picture signal. When a luminance level is low, the ratio of the first image signal, which has been produced during the longer exposure time, to the second image signal is increased. This results in an image demonstrating a high signal-to-noise ratio. When the luminance level is high, the ratio of the second image signal, which has been produced during the shorter exposure time, to the first image signal is increased. This results in a synthetic image that proves a wide dynamic range, depicts a smoothly varying brightness level, and exhibits a characteristic of being seen as almost natural. Moreover, the first and second image signals are produced to resemble those produced during mutually different exposure times by controlling an amount of light incident on an imaging device or by varying an amount of illumination light.