Halftone image printing device

Abstract

A halftone image printing device represents an image using a pixel matrix, prints each pixel as a dot pattern constituted by predetermined dots in a dot matrix, and controls the dot pattern and the printing density (multilevel density) of each dot included in the dot pattern in accordance with the density (multilevel) of the pixel. An overall printing density range is divided into four density ranges, i.e., from the lowest to the highest density ranges, and each pixel is defined by a 3.times.3 dot matrix. A dot pattern in the lowest density range has a dot at the center of the matrix, a dot pattern in the next lowest range has dots at the center of the matrix and at positions above and to the right of the center, a dot pattern in the next highest density range has dots at the center of the matrix and at positions above, below, and to the right and left of the center, and a dot pattern in the highest density range has dots at the center of the matrix and at positions above, below, to the right, left, and upper right of the center. In order to print each dot at each density level in each density range, the level of energy supplied to the heating element of the thermal head corresponding to each dot is precisely controlled.