Thermal printing apparatus

Abstract

A thermal printing apparatus prints input gradational images, characters and figures by using multilevel density regulates the levels of the densities representing the gradiational images etc. to be printed by a linear thermal head having n heating resistors arranged in a row. The printing apparatus is provided with a density control unit for regulating, for example, the multilevel durations for energizing the heating resistors in accordance with n gradational printing data each corresponding to a respective one of said resistors, and a data conversion unit, receiving as printing data a set of n original data for each a plurality of lines parallel with the row of n resistors, for producing p sets of n data for p split lines on the basis of the n original data, where p is an integer equal to or greater than two, each of the p split lines being disposed in an area in which the line corresponding to the printing data should be printed, in parallel with the row of n resistors, the p sets of n data being sequentially supplied to the density control unit set by set to print the original line corresponding to the printing data by printing the split lines corresponding to the original line split line by split line so by shifting the linear thermal head in a direction perpendicular to the row of n resistors every time each of the split lines is printed, that each of the n printing data is represented by p dots.