Multilevel screening mapping tone values to control signal values for greater color or shade fidelity and reduced print aberrations

• US 7,969,617 B2
• Filed: 06/04/2008
• Issued: 06/28/2011
• Est. Priority Date: 06/12/2007
• Status: Active Grant

• Current Assignee: FFEI Limited (XAAR, PLC)
• Original Assignee: FFEI Limited (XAAR, PLC)
• Inventors: Rughani, Daxa Neykumar
• Primary Examiner(s): Rogers; Scott A
• Application Number:
  US12/133,186
• Publication Number:
  US 20090046118A1
• Time in Patent Office: 1,119 Days
• Field of Search: 358/1.9, 358/3.06, 358/3.13, 358/3.14, 358/3.21, 358/3.22, 358/3.23, 358/3.26, 358/502, 358/504, 358534-536, 358/406, 358/465, 358/466, 347 10- 15, 347/19, 347/40, 347/42, 347/43
• US Class Current: 358/3.13
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

Abstract

A method of producing a printed output on a substrate is provided using a drop emitting device which is adapted to emit a plurality of ink quantities in response to a control signal. The method comprises the steps of receiving image data corresponding to a pixel of an image to be printed, the received image data comprising a tone value; generating a threshold value for use in a screening operation based on the location of the pixel within the image to be printed; mapping the received tone value to a mapped tone value using a first tone mapping, the mapped tone value being generated based on the received tone value; performing the screening operation by comparing the mapped tone value with the threshold value; mapping the received tone value to a control signal value using a first control mapping if the output of the comparison performed in the previous step indicates a first relationship, the control signal value being generated based on the received tone value; and repeating the previous three steps if the output of the comparison performed in the previous step indicates a second relationship, wherein the first mapping step comprises using an alternate tone mapping and the second mapping step comprises using an alternate control mapping.

Claims

1. A method of producing a printed output on a substrate using a drop emitting device adapted to emit a plurality of ink quantities in response to a control signal, the method comprising the steps of:

a. receiving image data corresponding to a pixel of an image to be printed, the received image data comprising a tone value;

b. generating a threshold value for use in a screening operation based on the location of the pixel within the image to be printed;

c. mapping the received tone value to a mapped tone value using a first tone mapping, the mapped tone value being generated based on the received tone value;

d. performing the screening operation by comparing the mapped tone value with the threshold value;

e. mapping the received tone value to a control signal value using a first control mapping if the output of the comparison performed in previous step (d) indicates a first relationship, the control signal value being generated based on the received tone value; and

f. repeating steps (c) to (f) if the output of the comparison performed in previous step (d) indicates a second relationship, wherein step (c) comprises using an alternate tone mapping and step (e) comprises using an alternate control mapping.

2. The method of claim 1, wherein the control signal value controls the number of drops of ink emitted from the drop emitting device and step (e) further comprises generating a control signal value inversely proportional to the number of iterations of steps (c) to (f) using the one or more control mappings.

3. The method of claim 1, wherein using one of the tone mappings comprises using a corresponding look-up table, each look-up table being indexed by the received tone value.

4. The method of claim 1, wherein using one of the tone mappings comprises using a two dimensional array indexed by the received tone value and the number of repetitions of steps (c) to (f).

5. The method of claim 1, wherein using one of the control mappings comprises using a corresponding control look-up table, each look-up table being indexed by the received tone value.

6. The method of claim 1, wherein using one of the control mappings comprises using a two dimensional array indexed by the received tone value and the number of repetitions of steps (c) to (f).

7. The method of claim 4, wherein:

before step (c) the method further comprises setting an iteration counter to an initial value;

step (f) further comprises, if the output of the comparison indicates the second relationship, incrementing the iteration counter; and

each mapping comprises looking up a mapped output in one of the two-dimensional arrays using the received tone value and the iteration counter as indices.

11. The method of claim 1, wherein the method further comprises:

g. measuring the characteristics of a test printed output;

h. generating a measured dot gain characteristic curve based on the measured characteristics; and

i. calibrating one or more tone mappings and/or one or more control mappings so as to minimise the difference between the measured dot gain characteristic curve and a reference dot gain characteristic curve.

12. The method of claim 1, wherein the method further comprises configuring one or more tone mappings and/or one or more control mappings so as to limit the maximum quantity of ink emitted from the drop emitting device.

13. The method of claim 1, wherein the tone mapping is calibrated so as to vary the dot percentage range for a plurality of tone values.

8. A method of producing a printed output on a substrate using a drop emitting device adapted to emit a plurality of ink quantities in response to a control signal, the method comprising the steps of:

a. receiving image data corresponding to a pixel of an image to be printed, the received image data comprising a tone value;

b. generating a threshold value for use in a screening operation based on the location of the pixel within the image to be printed;

c. mapping the received tone value to a plurality of mapped tone values using a corresponding plurality of tone mappings, the plurality of mapped tone values being generated based on the received tone value;

d. performing the screening operation by comparing each of the plurality of mapped tone values with the threshold value; and

e. mapping the received tone value to a control signal value using a control mapping, the control mapping being selected from a plurality of control mappings based on the output of step (d), the control signal value being generated based on the received tone value.

9. The method of claim 8, wherein the control mapping selects a control signal value from a group of two or more control signal values representative of two or more ink quantities.

10. The method of claim 9, wherein the group of two or more control signal values representative of two or more ink quantities is a non-sequential group of control signal values.

14. A system for producing a printed output upon a substrate the system comprising:

a drop emitting device for emitting a plurality of ink quantities in response to a control signal;

an image receiver for receiving image data corresponding to a pixel of an image to be printed, the received image data comprising a tone value;

a threshold generator for producing a threshold value for use in a screening operation;

a mapping generator for generating a mapped tone value based on one of a plurality of tone mappings, each tone mapping operating on the received tone value;

a comparator for performing a screening operation, wherein the comparator is adapted to compare the mapped tone value with the threshold value; and

a controller for processing the comparator output and generating a control signal value based on one of a plurality of control mappings, each control mapping operating on the received tone value,

wherein;

if the output of the comparator indicates a first relationship, the controller is adapted to select one of the plurality of control mappings to generate control signal value;

if the output of the comparator indicates a second relationship the controller is further adapted to instruct the mapping generator to produce a mapping tone value using an alternate one of the plurality of tone mappings and to select an alternate one of the plurality of control mappings with which to generate the control signal value.

15. The system of claim 14, wherein:

the mapping generator comprises a first two-dimensional mapping array for providing a mapped tone value based on the received tone value and an iteration counter;

the threshold generator comprises a second two-dimensional threshold array for providing a threshold value based on the location of the pixel within the image to be printed;

the controller comprises a third two-dimensional control array for generating a control signal value based on the received tone value and the iteration counter; and

the controller is further adapted to perform the following steps in response to receiving a tone value;

i. generating a threshold value using the second two-dimensional threshold array;

ii. resetting the iteration counter;

iii. generating a mapped tone value using the first two dimensional mapping array; and

iv. generating an output using the comparator,

wherein, if the output of the comparison indicates a first relationship, the controller is adapted to generate a control signal value using the third two-dimensional control array, and, if the output of the comparison indicates a second relationship, the controller is adapted to increment the iteration counter and repeat steps (iii) and (iv).

16. The system of claim 14, wherein the comparator is further adapted to generate a binary output based on the comparison of each mapped tone value and the threshold value.

17. The system of claim 14, wherein:

the mapping generator comprises a first two dimensional mapping array for providing a plurality of mapped tone values based on the received tone value and an ink quantity index;

the threshold generator comprises a second two-dimensional threshold array for providing a threshold value based on the location of the pixel within the image to be printed;

the comparator is adapted to produce a plurality of outputs based on a comparison of a plurality of mapped tone values and the threshold value; and

the controller comprises a third two dimensional control array for generating a control signal value based on the received tone value and the ink quantity index,

wherein the controller is further adapted to perform the following steps in response to receiving a tone value;

i. generating a threshold value using the second two-dimensional threshold array;

iii. generating a plurality of mapped tone values using the first two dimensional mapping array and a range of ink quantity indices; and

iv. generating a plurality of outputs using the comparator,

wherein the controller is adapted to select an ink quality index based on the plurality of outputs and to generate a control signal value using the third two dimensional control array and the selected ink quality index.

18. The system of claim 15, wherein the size of each the first and third two-dimensional arrays in one dimension is determined by the maximum number of ink quantities that can be emitted by the drop emitting device.

19. The system of claim 14, wherein a control mapping selects the control signal value from a group of two or more control signal values representative of two or more ink quantities.

20. The system of claim 19, wherein the group of two or more control signal values representative of two or more ink quantities is a non-sequential group.

21. The system of claim 14, wherein the drop emitting device is adapted to output zero or more of drops of ink when emitting a given quantity of ink.

22. The system of claim 14, wherein the system further comprises:

a sensor for measuring a printed output upon a substrate, the printed output comprising a test pattern; and

a calibration module for calibrating one or more tone mappings and/or one or more control mappings based on one or more measurements received from the sensor.

23. The system of claim 22, wherein the calibration module is adapted to generate a measured dot gain characteristic curve based on the one or more measurements received from the sensor and to calibrate the one or more tone mappings and/or one or more control mappings based on a comparison of the measured dot gain characteristic curve and a reference dot gain characteristic curve.

24. The system of claim 14, wherein the screening system is adapted to configure one or more tone mappings and/or one or more control mappings so as to limit the maximum quantity of ink emitted from the drop emitting device.

25. The system of claim 24, wherein the screening system is adapted to configure the one or more tone mappings and/or one or more control mappings based on the type of substrate to be printed upon.

26. The system of claim 14, wherein the mapping generator is calibrated so as to vary the dot percentage range for a plurality of tone values.

27. A colour printing apparatus for producing a colour printed output on a substrate, the printing apparatus comprising:

a plurality of systems according to claim 14, wherein each system is adapted to produce a printed output of a different colour component on the substrate.