Contrast control for intensity deformation removal in greyscale and color images

We present a method for elimination of global intensity deformation in greyscale and color images of any size using contrast control. The method is based on image resolution manipulation and uses a representation of an image in the form of a difference-of-low-pass pyramid (DoLP). In the first step, a Gaussian pyramid representation of the input image is prepared through low-pass filtration and sampling of successive pyramid levels. In the second step, the DoLP pyramid is built, and finally all levels in the DoLP pyramid are expanded to the original image size and added with weights, to reconstruct the image. Proper choice of the weights is crucial for efficient elimination of global intensity deformation and leads to contrast enhancement at certain levels of the pyramid. Color images and images of a size different than 2 N +1 x 2 N +1, where N = 2, 3, ?., require additional processing. They are converted to and from hue-saturation-value (HSV) color space model and geometrically transformed, which can be performed using two proposed methods. An algorithm and a computer routines library written in object programming language C++ are developed. The proposed method is useful in digital archiving of airborne, scanned, photo-copied and optical camera-made photographs, degraded due to ageing processes.