Color thermal printing method and apparatus

Abstract

Thermosensitive color recording paper includes a support and three thermosensitive coloring layers formed thereon for yellow, magenta and cyan colors. The uppermost yellow coloring layer has the highest heat sensitivity. The undermost cyan coloring layer has the lowest heat sensitivity. When the yellow or magenta coloring layer is colored at high density, the next-underlying coloring layer is inevitably colored at a small amount. A thermal head has heating elements which are respectively driven by a pulse train constituted of a bias pulse and gradation pulses. The bias pulse raises the temperature up to coloring temperature to record one pixel in each coloring layer. The number of the gradation pulses represents the density of recording on the pixel. The bias pulse is divided into two. The gradation pulses are grouped into two groups. To record the one pixel, the pulse train is generated so as to supply the thermal head with the first subsidiary bias pulse, the first gradation pulse group, the second subsidiary bias pulse, and then the second gradation pulse group, while the recording paper is moved. Although each gradation pulse group is related to a density lower than a desired final density of the pixel, the pixel is recorded to have appearance of such a final density, so as to obtain a well reproduced full-color image on the recording paper.