Print engine with print-mode-dependent pulse timing functions

A print engine adapted to print image data, comprising:

• a printer module for printing image data in a plurality of different print modes, the printer module including a printhead having a plurality of light sources for exposing a photosensitive medium, wherein each print mode has an associated line print time, the line print time being the amount of time that the printhead takes to print a line of image data;
• a data interface that receives image data and associated metadata for a print job from a pre-processing system, wherein the metadata includes print mode metadata that provides an indication of the print mode that is to be used to print the image data;
• a digital memory that stores a plurality of pulse timing functions, each pulse timing function defining an exposure time as a function of an integer pulse count, wherein each pulse timing function corresponds to one of the line print times associated with the plurality of print modes;
• a metadata interpreter that interprets the metadata and determines the print mode to be used to print the image data;
• and
• a printer module controller that controls the printer module to print the image data responsive to the determined print mode, wherein the printer module controller controls the printhead using the pulse timing function corresponding to the line print time associated with the print mode, each light source being activated for a pulse count corresponding to a pixel code value of an associated image pixel of the image data;
• wherein the pulse timing functions associated with each of the line print times are determined to provide an aim exposure function, the aim exposure function defining an aim exposure to be provided by the light sources as a function of the pulse count, and wherein the pulse timing functions are determined by a process including:
• a) providing an initial pulse timing function for a particular line print time which defines an exposure time as a function of pulse count;
• b) determining a light output function for the light sources responsive to the pulse timing function, wherein the light output function gives a light output of the light sources as a function of exposure time;
• c) updating the pulse timing function responsive to the light output function and the aim exposure function;
• d) repeating steps b)-c) until a predefined iteration termination criterion is satisfied;
• and
• e) storing the pulse timing function in the digital memory for use with the particular line print time.