Image treatment method and apparatus with error dispersion and controllable quantization

Claim 1

An image processing apparatus comprising: input means for inputting image data; setting means for setting a reference value to serve as a reference for use in quantizing the image data, said setting means setting the reference value based on the image data input by said input means; quantizing means for quantizing the image data; means for outputting an image in accordance with the result of the processing performed by said quantizing means; judgment means for judging whether or not a dot is present in a region consisting of quantized data of plural pixels which has been quantized by said quantizing means; and error determining means for determining an error between input image data, input prior to an object pixel input by said input means, and output image data, wherein said quantizing means performs the quantizing in accordance with: the image data of an object pixel input by said input means; the error between input image data, input prior to the object pixel, and the output image data; and the judgment by said judgment means, wherein said setting means is so structured and arranged as to set the reference value to be smaller when the value of the image data input by said input means is small than when the value of the image data is large, and wherein said setting means is structured and arranged as to generate plural random numbers in a predetermined region in accordance with the image data and to set one of those numbers as the reference value.