Method and apparatus for gray level signal processing

摘要

A gray level signal processing method determines whether an image signal derived from an original document belongs to the character image area which needs high resolution or the continuous-tone image area which needs gray level reproduction such as for photographs, and quantizes the signal in a quantization method suitable for the image area to which the signal belongs. The process comprises the steps: (a) picture image is divided into blocks each composed of m-by-n picture elements; (b) the maximum optical density level (Pmax) and the minimum optical density level (Pmin) are detected in each block; (c) the difference value (P DELTA =¦Pmax-Pmin¦) between the maximum and minimum optical density levels is calculated; (d) the image area to which the block belongs is determined according to the difference value (P DELTA ); and (e) the optimum one of quantization processing methods is selected according to the result of the determination, and the optical density level of each picture element in the block is quantized in the selected processing quantization method. The method can be applied to the process of facsimile system including continuous-tone or halftone information or also to the process in a copy machine which reads and records a picture in units of picture elements.