Patent ID: 7570392

Claim:
A printing device that prints an image on a medium with a print head having nozzles capable of forming dots, the device comprising: an image data acquisition portion that acquires image data having an M-value (M≧3) pixel value, the M-value corresponding to a first number of possible grayscale levels that are represented by the pixel value; a nozzle information storage portion that stores nozzle information indicating a characteristic of each nozzle; an error diffusion matrix storage portion that stores plural error diffusion matrices having different diffusion ratios of an error assigned to pixel data as diffusion targets, the plural error diffusion matrices including a diagonally weighted error diffusion matrix in which a diffusion ratio of the error assigned to the pixel data corresponding to pixels as diffusion targets positioned in a diagonal direction, which is a direction other than a pixel selecting direction and a direction perpendicular to the pixel selecting direction, is made larger than the diffusion ratio assigned to pixels as diffusion targets positioned in a direction other than the diagonal direction; a pixel data selecting portion that selects specific pixel data in the image data; an N-value conversion processing portion that performs N-value conversion processing to convert the M-value pixel value indicated by the selected pixel data to an N (M>N≧2) value, the N-value corresponding to a second number of possible grayscale levels that are represented by the pixel value; an error diffusion portion that diffuses the error to pixel data that has not been subjected to the N-value conversion processing in the image data according to the error diffusion matrix by using a difference between: a value of the selected pixel data; and a value of the selected pixel data after the N-value conversion processing as the error, thereby updating pixel values in the image data; a print data generation portion that generates print data that defines information about a dot formation content of the nozzles corresponding to the image data after the N-value conversion processing; and a printing portion that prints the image on the medium using the print head according to the print data, wherein the error diffusion portion selects a specific error diffusion matrix for each selected pixel data from the error diffusion matrix storage portion according to the nozzle information, and diffuses the error to the pixel data that has not been subjected to the N-value conversion processing according to the selected error diffusion matrix, the error diffusion portion selecting the diagonally weighted error diffusion matrix when the nozzle information corresponding to the selected pixel data indicates a nozzle failure and selecting an error diffusion matrix other than the diagonally weighted error diffusion matrix when the nozzle information corresponding to the selected pixel data does not indicate a nozzle failure.