Fluid ejection printing with automatic print mode switching

1. A method of printing a document using a fluid-ejection printing device, the method comprising:

receiving gray scale image data for the document;

identifying at least one area fill feature of the image data;

determining whether the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect if printed in an N-pass bidirectional print mode, where N is an integer;

printing non-fill regions of the image data using the N-pass bidirectional print mode; and

automatically switching to an M-pass bidirectional print mode for printing the at least one area fill feature when it is determined that the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect, where M is an integer greater than N.

2. The method of claim 1 , wherein N is one and M is two.

3. The method of claim 1 , wherein the at least one area fill feature represents a plurality of contiguous pixels that all have a common gray scale value.

4. The method of claim 1 , and further comprising:

automatically switching back to the N-pass bidirectional print mode after printing the at least one area fill feature.

5. The method of claim 1 , wherein the fluid-ejection printing device is an inkjet printing device.

6. The method of claim 1 , wherein the fluid-ejection printing device is a monochrome inkjet printing device that is configured to exclusively print with black inks.

7. A fluid-ejection printing device, comprising:

a fluid-ejection printing mechanism configured to eject droplets of fluid on media in correspondence with image data;

a data processing mechanism configured to identify at least one area fill feature of the image data that will be printed with a combination of different black inks and that is likely to produce a visible image defect if printed in a one-pass bidirectional print mode; and

wherein the fluid-ejection printing mechanism is configured to print non-fill regions of the image data using the one-pass bidirectional print mode, and is configured to automatically switch to a multi-pass bidirectional print mode for printing the at least one area fill feature.

8. The fluid-ejection printing device of claim 7 , wherein the at least one area fill feature represents a plurality of contiguous pixels that all have a common gray scale value.

9. The fluid-ejection printing device of claim 7 , wherein the fluid-ejection printing mechanism is configured to automatically switch back to the one-pass bidirectional print mode after printing the at least one area fill feature.

10. A printing system, comprising:

a fluid-ejection printing mechanism configured to eject droplets of fluid on media in correspondence with image data;

a controller configured to identify at least one area fill feature of the image data that will be printed with a combination of different black inks and that is likely to produce a visible image defect if printed in a one-pass bidirectional print mode; and

wherein the controller is configured to cause the fluid-ejection printing mechanism to print non-fill regions of the image data using the one-pass bidirectional print mode and automatically switch to a multi-pass bidirectional print mode for printing the identified at least one area fill feature.

11. A method of printing a document using a fluid-ejection printing device, the method comprising:

receiving gray scale image data for the document;

identifying at least one area fill feature of the image data;

determining whether the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect if printed in an N-pass bidirectional print mode, where N is an integer;

printing non-fill regions of the image data using the N-pass bidirectional print mode; and

automatically switching to an M-pass bidirectional print mode for printing the at least one area fill feature when it is determined that the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect, where M is an integer greater than N;

wherein the determining whether the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect if printed in the N-pass bidirectional print mode comprises:

identifying whether an ink density of the at least one area fill feature is greater than a minimum threshold density at which gray scale shift banding becomes visible to the human eye.

12. The method of claim 11 , wherein the minimum threshold density is about 70%.

13. The method of claim 11 , wherein the minimum threshold density is about 85%.

14. The method of claim 11 , wherein the determining whether the at least one area fill feature will be printed with a combination of different black inks and is likely to produce a visible image defect if printed in the N-pass bidirectional print mode comprises:

identifying whether the ink density of the at least one area fill feature is less than a maximum threshold density at which only a single black ink is used to print the at least one area fill feature.

15. The method of claim 14 , wherein the maximum threshold density is about 99%.

16. A fluid-ejection printing device, comprising:

a fluid-ejection printing mechanism configured to eject droplets of fluid on media in correspondence with image data;

a data processing mechanism configured to identify at least one area fill feature of the image data that will be printed with a combination of different black inks and that is likely to produce a visible image defect if printed in a one-pass bidirectional print mode; and

wherein the fluid-ejection printing mechanism is configured to print non-fill regions of the image data using the one-pass bidirectional print mode, and is configured to automatically switch to a multi-pass bidirectional print mode for printing the at least one area fill feature; and

wherein the data processing unit is configured to identify whether an ink density of the at least one area fill feature is greater than a minimum threshold density at which gray scale shift banding becomes visible to the human eye.

17. The fluid-ejection printing device of claim 16 , wherein the minimum threshold density is about 70%.

18. The fluid-ejection printing device of claim 16 , wherein the minimum threshold density is about 85%.

19. The fluid-ejection printing device of claim 16 , wherein the data processing unit is configured to identify whether the ink density of the at least one area fill feature is less than a maximum threshold density at which only a single black ink is used to print the at least one area fill feature.

20. The fluid-ejection printing device of claim 19 , wherein the maximum threshold density is about 99%.