1. In a thermal printer apparatus including a print head having a number of thermal pixels, one for each image pixel, formed into a plurality of groups of thermal pixels, the thermal pixels of each group being simultaneously addressable in parallel and having N different possible temperature levels, the improvement comprising: a. a storage device having a plurality of stages, one for each thermal pixel; b. means for sequentially storing N digital signals in the stages of the storage device, in which the state of each stage corresponds to whether or not a corresponding thermal pixel is to be energized; c. means for sequentially addressing the groups of thermal pixels each time a digital signal is stored in the storage device with each group of thermal pixels being addressed N times; and d. means for selectively energizing each thermal pixel each time it is addressed depending upon the state of its corresponding stage until each thermal pixel is at one of N possible temperatures.