Relighting Backlight and Spotlight Images using the von Kries Model

Improving the quality of backlight and spotlight images is a challenging task. Indeed, these pictures include both very bright and very dark regions with unreadable content and details. Restoring the visibility in these regions has to be performed without over-enhancing the bright regions, thus without generating unpleasant artifacts. To this end, some algorithms segment the image in bright and dark regions, re-work them separately by different enhancing functions. Other algorithms process the input image at multiple scales or with different enhancement techniques. All these methods merge the results together paying attention to the edge areas. The present work proposes a novel approach, called REK and implementing a relighting technique based on the von Kries model. REK linearly increases the channel intensities of the input image, obtaining a new brighter image, which is then summed up to the input one with weights computed from the input image and taking high values on the dark regions while low values on the bright ones. In this way, REK improves the quality of backlight and spotlight pictures without needing for segmentation and multiple analysis, while granting satisfactory performance at a computational complexity proportional to the number of image pixels.