an image processing unit group including multiple image processing units that are connected in series to process first intermediate data of average RGB values of a plurality of pixels based on the input image data by respective series of image processing and sequentially transfer the processed first intermediate data through the multiple image processing units in the image processing unit group;

a pass unit group including multiple pass units that are connected in series to receive second intermediate data representing a black and white edge pattern and sequentially transfer the second intermediate data synchronously with transfer of the first intermediate data through the multiple image processing units;

an intermediate data generation unit that divides the input image data into at least one unit pixel group including a preset number of plural pixels, generates the first intermediate data and the second intermediate data according to a characteristic of the unit pixel group, generating an edge detection flag if the unit pixel group is from a black and white edge pattern, and outputs the generated first intermediate data to a first image processing unit on a first stage of the image processing unit group, while outputting the generated second intermediate data to a first pass unit on a first stage of the pass unit group;

a data selector that inputs both the first intermediate data that has gone through the respective series of image processing by the image processing unit group and the second intermediate data that has been sequentially transferred through the pass unit group and selects one of the input first and second intermediate data based on whether the edge detection flag is set;

a data storage module that stores the intermediate data selected by the data selector; and

an output image generation module that generates an output image, based on at least either of outputs from the image processing unit group and from the pass unit group;

wherein the intermediate data generation unit has a detection module that detects either presence or absence of an edge in the unit pixel group and a data generation module that, in response to detection of the presence of an edge by the detection module, generates the second intermediate data representing a black and white edge pattern; and

the data generation module of the intermediate data generation unit, in response to detection of the absence of an edge by the detection module, generates specific dummy data, as the second intermediate data;

the output image generation module uses the intermediate data stored in the data storage module to generate the output image; and

the output image generation module individually performs a different halftoning process for each of the processed first intermediate data which is output from the image processing unit group and the second intermediate data which is output from the pass unit group, so as to generate the output image.