Printer with in-track position error correction

1. A digital printing system incorporating in-track position corrections, comprising:

one or more printing subsystems, each printing subsystem including a linear printhead extending in a cross-track direction including an array of light sources for exposing a photosensitive medium;

a data processing system;

a digital memory for storing an in-track position correction function; and

a program memory communicatively connected to the data processing system and storing instructions configured to cause the data processing system to implement a method for determining an in-track position correction function for at least one printing subsystem, wherein the method includes:

a) providing digital image data for a test target including a plurality of alignment marks positioned at predefined cross-track positions;

b) printing the test target using the digital printing system to provide a printed test target;

c) using a digital image capture system to capture an image of the printed test target;

d) automatically analyzing the captured image to determine a measured in-track position for each of the alignment marks;

e) comparing the measured in-track positions for the alignment marks to reference in-track positions to determine measured in-track position errors;

f) determining the in-track position correction function responsive to the measured in-track position errors, wherein the in-track position correction function specifies in-track position corrections to be applied as a function of cross-track position; and

g) storing a representation of the in-track position correction function in the digital memory;

wherein the digital printing system is adapted to print digital images using a printing process that includes:

i) receiving digital image data for a digital image to be printed by the digital imaging system, wherein the digital image includes a plurality of image lines extending in the cross-track direction;

ii) determining corrected image lines by resampling the digital image data responsive to the stored representation of the in-track position correction function; and

iii) printing the corrected image lines using the one or more printing subsystems to provide a printed image with reduced in-track position errors;

wherein the linear printhead includes a plurality of individual light source chips, each including a plurality of light sources, and wherein alignment marks are positioned in proximity to boundaries between adjacent light source chips; and

wherein the representation of the in-track position correction function stored in the digital memory includes the cross-track positions and transition direction of transitions in the in-track position correction function.

2. A digital printing system incorporating in-track position corrections, comprising:

one or more printing subsystems, each printing subsystem including a linear printhead extending in a cross-track direction including an array of light sources for exposing a photosensitive medium;

a data processing system;

a digital memory for storing an in-track position correction function; and

a program memory communicatively connected to the data processing system and storing instructions configured to cause the data processing system to implement a method for determining an in-track position correction function for at least one printing subsystem, wherein the method includes:

a) providing digital image data for a test target including a plurality of alignment marks positioned at predefined cross-track positions;

b) printing the test target using the digital printing system to provide a printed test target;

c) using a digital image capture system to capture an image of the printed test target;

d) automatically analyzing the captured image to determine a measured in-track position for each of the alignment marks;

e) comparing the measured in-track positions for the alignment marks to reference in-track positions to determine measured in-track position errors;

f) determining the in-track position correction function responsive to the measured in-track position errors, wherein the in-track position correction function specifies in-track position corrections to be applied as a function of cross-track position; and

g) storing a representation of the in-track position correction function in the digital memory;

wherein the digital printing system is adapted to print digital images using a printing process that includes:

i) receiving digital image data for a digital image to be printed by the digital imaging system, wherein the digital image includes a plurality of image lines extending in the cross-track direction;

ii) determining corrected image lines by resampling the digital image data responsive to the stored representation of the in-track position correction function; and

iii) printing the corrected image lines using the one or more printing subsystems to provide a printed image with reduced in-track position errors;

wherein the in-track position correction function is quantized to integer in-track position corrections; and

wherein the representation of the in-track position correction function stored in the digital memory includes the cross-track positions and transition direction of transitions in the quantized in-track position correction function.

3. The digital printing system of claim 2 , wherein the digital printing system includes a plurality of printing subsystems for printing a corresponding plurality of color channels, wherein one of the color channels is designated to be a reference color channel and the other color channels are designated to be non-reference color channels, and wherein the reference positions for the alignment marks for the non-reference color channels are determined responsive to the measured positions of one or more alignment marks printed with the reference color channel.

4. The digital printing system of claim 3 , wherein a predefined color channel is designated to be the reference color channel.

5. The digital printing system of claim 2 , wherein the reference positions correspond to ideal positions of the alignment marks.

6. The digital printing system of claim 2 , wherein the printed test target is on a print medium, and wherein the digital image capture system captures an image of the printed test target on the print medium.

7. The digital printing system of claim 2 , wherein the printed test target is on an imaging surface, the imaging surface being a surface of a photoconductor, a surface of an intermediate transfer member or a surface of a transport web, and wherein the digital image capture system captures an image of the printed test target on the imaging surface.

8. The digital printing system of claim 2 , wherein the plurality of alignment marks includes at least ten alignment marks.

9. The digital printing system of claim 2 , wherein the light sources of the linear printhead are LED light sources.

10. The digital printing system of claim 2 , wherein the resampling of the digital image data is also responsive to a resize factor.

11. The digital printing system of claim 2 , wherein the digital image capture system is a component of the digital printing system.