Agricultural Soil Carbon Sequestration: Economic Issues and Research Needs

An image processing method that employs a threshold matrix to binarize image signals obtained by reading an image recorded on a film such as microfilm. A middle tone image brightness range, which corresponds to a middle or half tone image, is discriminated by referring a brightness histogram for image signals. The upper- and lower-most brightness values of the middle tone image brightness range are used to convert the elements of a threshold matrix in accordance with a predetermined conversion expression, and the converted threshold matrix used for binarization processing. Even if a film density variation occurs or if there is a background density change, binary conversion (a dithering process) can be performed, without deterioration of image quality, within a middle tone density area of, for example, a photograph.