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Thermal and night vision image visibility and enhancement

This paper offers a review of effective methods of image representation, or visibility images in enhancement applied to the thermal images and night vision images. The quality of images is estimated by quantitative enhancement measures, which are based on the Weber-Fechner, Michelson, and other parameterized ratio and entropy-type measures. We also apply the concept of visibility images, by using different types of gradient operators which allow for extracting and enhancing features in images. Examples of gradient visibility images, Weber-Fechner, and Michelson contrast, log and power Michelson and Weber visibility images are given. Experimental results show the effectiveness of visibility images in enhancing thermal and night vision images. Different methods of image enhancement in spatial and frequency domains are analyzed on the thermal and night vision images, by using the visibility images. Experimental results show that visibility images can be used in processing in spatial and frequency domains. Here, we mention the alpha-rooting by the classical discrete Fourier transform (DFT) and quaternion DFT, the retinex method, and new gradient based histogram equalization.