Thermal recording apparatus capable of gradation recording

Claim 1

A thermal recording apparatus adapted to perform a thermosensitive recording process capable of controlling the calorific value of each of a plurality of heating elements constituting a printing head by setting the time during which power is supplied to the heating elements in a multistage manner and thereby providing the multistage expression of gradation by picture elements each corresponding to the heating elements, a thermal recording apparatus for implementing the aforesaid process comprising: (1) image data storage means for storing image data as a recording unit comprising a plurality of picture elements; (2) gradation level comparison means for comparing the gradation level representing each of the picture elements constituting one recording unit of picture data with a reference gradation level; (3) counting means for counting the number of picture elements whose gradation level exceeds the aforesaid reference gradation level based on the comparison means; and (4) gradation level correcting means for correcting the gradation level expressed by the image data stored in the aforesaid image data storage means in accordance with the results counted by the counting means representing the cumulative gradations of the picture elements.