CALIBRATION OF A PRINT ENGINE

1 . A print engine controller, the controller comprising:

an image generation module to control a plurality of laser elements to produce an image by scanning the laser elements along a scan direction, the image having a calibration portion that is continuous in a direction perpendicular to the scan direction and produced by at least a group of the laser elements;

a calibration module to receive information indicative of an optical measurement of the calibration portion, determine a contribution to the optical measurement associated with each of the laser elements in the group of laser elements, and determine a calibration adjustment for the laser elements in the group of laser elements.

2 . The controller of claim 1 , wherein the image includes a registration portion, the registration portion indicative of a location of the calibration portion, and determining a contribution to the optical measurement associated with each of the laser elements in the group of laser elements includes determining a location of the calibration portion based on the registration portion.

3 . The controller of claim 1 , wherein the calibration module is to determine a contribution to the optical measurement associated with each of the laser elements in the group of laser elements by averaging the optical measurement or a property derived from the optical measurement between a plurality of calibration portions arranged along the direction perpendicular to the scan direction and mutually aligned along the scan direction.

4 . The controller of claim 1 , wherein:

the image generation module is to control a plurality of laser elements to produce the image such that the image has a plurality of calibration elements at different locations along the scan direction, and

the calibration module is to determine a plurality of sets of calibration adjustments, each set associated with a different one of the locations along the scan direction, and each set including a calibration adjustment for the laser elements in the group of laser elements.

5 . The controller of claim 1 , wherein:

the image generation module is to control a plurality of laser elements to produce the image such that the image has a plurality of calibration portions, each calibration portion having one of a plurality of different gray coverages, and

the calibration module is to determine the calibration adjustment for the laser elements in the group of laser elements based on optical measurements of two or more calibration portions, the two or more calibration portions including calibration portions having at least two different gray coverages.

6 . The controller of claim 1 , wherein:

the optical property includes a plurality of gray level values measured in the calibration portion; and

the calibration module is to determine a contribution to the optical measurement associated with each of the laser elements in the group of laser elements by:

averaging the plurality of gray level values in the scan direction to generate a gray profile,

interpolating the generated gray profile to produce an interpolated gray profile, and

assigning parts of the interpolated gray profile to respective laser elements of the group of laser elements by dividing the interpolated gray profile equally between the laser elements of the group of laser elements.

7 . A printing device comprising the print engine controller of claim 1 .

8 . A method of calibrating a print engine, the method comprising:

controlling a plurality of imaging elements of the imaging system to produce an image on a substrate by scanning the imaging elements in a scanning direction, the image including:

a calibration portion produced by a group of the imaging elements, the calibration portion being unbroken in a direction perpendicular to the scanning direction, and

a registration portion produced by one or more of the imaging elements, the registration portion indicative of a start and end of the calibration portion in the direction perpendicular to the scanning direction;

receiving a measurement of an optical property of the calibration portion of the image;

determining, by referencing the registration portion, a contribution to the received measurement due to each of the imaging elements of the group; and

determining a correction for each of the imaging elements of the group based on the determined contributions.

9 . The method of claim 8 , wherein determining a contribution of each of the imaging elements to the received measurement includes:

determining a profile of the optical property across the calibration portion in a direction non-parallel with the scan direction based on the registration portion, and

associating portions of the profile with respective imaging elements based on a number of imaging elements in the group.

10 . The method of claim 9 , wherein determining a profile of the optical property includes averaging the optical property in a direction parallel to the scan direction.

11 . The method of claim 8 , wherein the image includes a plurality of calibration portions and registration portions arranged along the scan direction, and the method comprises:

receiving a measurement for each of the calibration portions,

determining for each of the calibration portions, by referencing a corresponding registration portion, a contribution to the received measurement for that calibration portion due to each of the imaging elements of the group; and

determining for each of the calibration portions, a correction for each of the imaging elements of the group based on the determined contributions.

12 . The method of claim 8 , wherein the image includes a plurality of calibration portions and registration portions arranged along a direction perpendicular to the scan direction, and the method comprises:

receiving a measurement for each of the calibration portions,

determining for each of the calibration portions, by referencing a corresponding registration portion, a contribution to the received measurement for that calibration portion due to each of the imaging elements of the group; and

determining, for each imaging element, an average of the determined contributions associated with that imaging element among the calibration portions arranged along the direction perpendicular to the scan direction, and wherein

determining the correction for each of the imaging elements includes determining the correction based on the determined average of the contributions associated with the respective imaging element.

13 . The method of claim 8 , further comprising iterating the controlling, receiving, determining a contribution and determining a correction until a termination condition is reached.

14 . The method of claim 8 , wherein the image further includes a further calibration portion and a further registration portion, the further calibration portion having a different coverage from the calibration portion.

15 . A non-volatile computer-readable medium storing:

a control module including instructions that when executed cause a processing device to control a plurality of imaging elements to produce an image by scanning the imaging elements along a scan direction, the image having a calibration portion that is continuous in a direction perpendicular to the scan direction and produced by at least a group of the imaging elements;

a data reception module including instructions that when executed cause the processing device to receive data describing an optical measurement of the calibration portion;

a contribution determination module including instructions that when executed cause the processing device to determine a contribution to the optical measurement associated with each of the imaging elements in the group of imaging elements; and

a calibration determination module including instructions that when executed cause a processing device to determine a calibration adjustment for the imaging elements in the group of imaging elements.