Nonlinear technique for the enhancement of extremely high contrast images
Numan Ünaldı, Saibabu Arigela, Vijayan K. Asari, Zia-ur Rahman · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2008
An adaptive technique for image enhancement based on a specifically designed nonlinear function is presented in this paper. The enhancement technique constitutes three main processes-adaptive intensity enhancement, contrast adjustment, and color restoration. A sine function with an image dependent parameter is used to tune the intensity of each pixel in the luminance image. This process provides dynamic range compression by boosting the luminance of darker pixels while reducing the intensity of brighter pixels and maintaining local contrast. The normalized reflectance image is added to the enhanced image to preserve the details. The quality of the enhanced image is improved by applying a local contrast enhancement followed by a contrast stretch process. A basic linear color restoration process based on the chromatic information of the original image is employed to convert the enhanced intensity image back to a color image. The performance of the algorithm is compared with other state of the art enhancement techniques and evaluated using a statistical image quality evaluation method.