Halftone image printing device

Abstract

A halftone image printing device for printing an image consisting of picture elements arrayed in a zig-zag fashioning. Each picture element is composed of dots forming a quasi-diamond-shaped matrix. The dot matrix is a 2 (row) x 3 (column) matrix with two additional dots located at the top and bottom, respectively. The range of optical density, within which the densities represented by the picture elements fall, is segmented into sub-ranges. Different heating-resistors are assigned to each sub-range of density. The dots printed by the heating-resistors assigned to any sub-range of density forms a 'dot pattern' of a specific shape. The first dot pattern has one dot printed on the upper-central part of the rectangular matrix. The second dot pattern has three dots forming an L-shaped pattern, the first dot printed on the upper-central part of the matrix, the second dot printed above the first dot, and the third dot printed to the right of the first dot. The third dot pattern consists of five dots forming a cross, the first dot printed on the upper-central part of the matrix, the second dot printed above the first dot, the third dot printed to the right of the first dot, the fourth dot printed below the first dot, and the fifth dot printed to the left of the first dot. And the fourth dot pattern consists of five dots forming a cross and an additional dot printed immediately below the cross. Of the dots of each dot pattern, the dot on which energy concentrates more than any other dot assumes the same location for all dot patterns.