Expanding a color gamut of a direct thermal printer

A direct thermal printer comprising

• a control circuit;
• and
• one or more print heads linked to the control circuit, each of the one or more print heads containing a linear array of print head elements that print on a direct thermal output medium, the output medium transported past the print head elements to produce a two-dimensional print image, the print image resulting from heating of the output medium by dynamically adjusting an average power of a pulse stream applied to the individual print head elements to heat them,
• wherein the output medium comprises three color forming layers, each capable of forming a different color when heated above a respective threshold temperature T1, T2 and T3, the three color forming layers separated by chemically inert spacing layers, and
• wherein dynamically adjusting the average applied power comprises evaluating pixel color data prior to printing each pixel of an image to determine whether a hue and saturation of the color to be printed will be compromised by unintended printing on a first and second color forming layers when issuing pulses in a segment designated for printing on an intermediate color forming layer located between the first and second color forming layers.