Patent US 5,768,403

An image-area identifying system for a color image processing apparatus comprises: image area identifying means for identifying a character area or a half-tone image area by using characteristic values of pixels in each pixel block of an image area; hue determining means for determining, every pixel, hue of received color image data to produce a necessary color switch signal or an unnecessary color switch signal; and data reset means for resetting unnecessary image data on the basis of the results of the block-basis area identifying determination by the image area identifying means and the pixel-basis hue determination by the hue determining means. The image area identifying means may be nonlinear quantitizers for quantitizing three characteristic values, "in-block average value", "number of in-block high-level pixels" (Ph), and "number of in-block medium-level pixels" (Pm) for reducing the quantities of data representing the three characteristic values, and a three-dimensional look-up table accessed by the output data of the nonlinear quantitizers, to produce a character area data signal or a half-tone image data signal.