Patent ID: 7322665

Claim:
An inkjet printing system employing a printing head having a plurality of printing elements for ejecting ink to form an image on a printing medium in a movement relative to the printing head, comprising: means for converting multi-valued image data into gradation value data at a lower level at a predetermined resolution; means for selecting, according to the gradation value data, an index pattern from among a plurality of index patterns whose areas each corresponding to one pixel of the printing resolution of the printing head are defined to be printed or not based on the gradation value data to render the density of a region corresponding to one pixel of the predetermined resolution using a plurality of such areas arranged in at least the moving direction; and means for ejecting the ink from the printing element toward the printing medium according to the index pattern selected by the selecting means, wherein the ink ejected from the printing element is divided into a main droplet and a sub droplet ejected pursuant to the main droplet, and wherein the number of the areas of the index pattern arranged in the direction of the movement is determined such that the main droplet and the sub droplet are printed on the printing medium at an interval that is substantially an integral multiple of the width of the region corresponding to one pixel of the predetermined resolution in the moving direction.