Maximum Sampling Region Acquisition and Contrast Calculation of Intensified Charge-Coupled Device Rectangular Target Image Under Low Illumination

Accurate acquisition of image contrast is an important factor for measuring modulation transfer function and minimum resolvable contrast of camera. Under low illumination, image from intensified charge-coupled device exhibits ion feedback noise with high brightness, resulting in lower signal-to-noise ratio of the image. Thus, one cannot obtain easily the accurate image contrast results by using the conventional contrast calculation method. In this paper, the ion feedback noise of the rectangular target image under low illumination is first reduced by means of constrained noise screening method and asymmetrical orientation window weighted mean filling algorithm. According to the spatial height correlation of the rectangular target image, the maximum sampling region is then founded by using spatial one-way statistical average algorithm combined with Otsu binarization. The image contrast is finally calculated after removing the fuzzy interval in the boundary between black and white stripes. It is shown that the method proposed can achieve the maximum sampling region acquisition and the contrast calculation for the image captured under low illumination, which reduces the error of calculation contrast caused by manually selecting the sampling region.