Calibration techniques for imaging devices

• US 20040218233A1
• Filed: 05/26/2004
• Published: 11/04/2004
• Est. Priority Date: 12/31/2001
• Status: Active Grant

• Current Assignee: Christopher J. Edge
• Original Assignee: Christopher J. Edge
• Inventors: Edge, Christopher J.
• Granted Patent: US 7,509,222 B2
• Time in Patent Office: Days
• US Class Current: 358/504
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence
• CPC Class Codes: H04N 17/02 for colour television signals
• CPC Class Codes: H04N 17/04 for receivers

Abstract

The invention is directed to various calibration techniques for calibrating an imagining device such as a display device, a printer, or a scanner. The techniques may involve characterizing the imaging device with a device model such that an average error between expected outputs determined from the device model and measured outputs of the imaging device is on the order of an expected error, and adjusting image rendering on the imaging device to achieve a target behavior. The invention can achieve a balance between analytical behavior of the imaging device and measured output. In this manner, adjustments to image rendering may be more likely to improve color accuracy and less likely to overcompensate for errors that are expected.

Claims

1. A method of calibrating a cathode ray tube comprising:

measuring outputs of the cathode ray tube for a subset of device values of the cathode ray tube;

choosing one or more adjustable parameter values of a device model for the cathode ray tube such that an average error between expected outputs determined from the device model and measured outputs of the cathode ray tube is on the order of an expected error, wherein a number of the adjustable parameters is less than a number of measured outputs of the imaging device; and

adjusting image data according to the device model to achieve a target behavior for the cathode ray tube.

2. The method of claim 1, wherein the subset of device values substantially correspond to neutral colors having values of red, green and blue on the order of one another.

3. The method of claim 1, wherein adjusting image data further includes creating a lookup table (LUT) based on the device model.

4. The method of claim 1, wherein adjusting image data further includes creating a color profile for the imaging device based on the device model.

5. The method of claim 1, wherein the parameters comprise a gamma value and a black onset value.

6. The method of claim 1, wherein the target behavior corresponds to a defined gamma value.

7. A method of calibrating a cathode ray tube comprising:

initializing a lookup table (LUT);

adjusting settings of the cathode ray tube to substantially achieve a defined output;

measuring output for a number of color values;

choosing adjustable parameter values for a device model, wherein a number of adjustable parameters is less than a number of measured outputs; and

generating entries for the LUT based on the device model.

8. The method of claim 7, wherein adjustable parameters of the device model include a gamma value and an onset value.

9. The method of claim 7, wherein measuring output includes displaying a substantially white trace during measurement to bias an output measurement.

10. The method of claim 9, wherein the trace has a halo shape.

11. The method of claim 7, wherein the LUT resides in a video card.

12. A method comprising:

measuring output of a display device; and

displaying a substantially white trace during measurement to bias an output measurement.

13. The method of claim 12, wherein the trace has a halo shape.

14. The method of claim 12, further comprising displaying the substantially white trace during measurement to bias output measurements by approximately 0.5 to 1.0 percent.

15. The method of claim 12, further comprising displaying the substantially white trace during measurement to bias an output measurement by an amount sufficient to ensure that the output measurement is within a dynamic range of a measurement device.

16. A cathode ray tube calibrated such that:

an average color error is approximately less than (0.75 delta e) from an analytical expected color output; and

a maximum color error is approximately less than (1.5 delta e) from the analytical expected color output.

17. The cathode ray tube of claim 16, wherein:

the average color error is approximately between (0.3 delta e) and (0.75 delta e) from the analytical expected color output; and

the maximum color error is approximately between (0.6 delta e) and (1.1 delta e) from the analytical expected color output.

18. The cathode ray tube of claim 17, wherein the average color error is approximately between (0.3 delta e) and (0.4 delta e) from the analytical expected color output;

and

the maximum color error is approximately between (0.6 delta e) and (0.8 delta e) from the analytical expected color output.

19. A set of cathode ray tubes, wherein each cathode ray tube in the set is calibrated such that:

an average color error is approximately less than (0.75 delta e) from an analytical expected color output; and

a maximum color error is approximately less than (1.5 delta e) from the analytical expected output.

20. The set of cathode ray tubes of claim 19, wherein each cathode ray tube in the set is calibrated such that:

the average color error is approximately between (0.3 delta e) and (0.75 delta e) from the analytical expected color output; and

the maximum color error is approximately between (0.6 delta e) and (1.1 delta e) from the analytical expected color output.

21. The set of cathode ray tubes of claim 20, wherein each cathode ray tube in the set is calibrated such that:

the average color error is approximately between (0.3 delta e) and (0.4 delta e) from the analytical expected color output; and

the maximum color error is approximately between (0.6 delta e) and (0.8 delta e) from the analytical expected color output.

22. A computer readable medium storing program code that when executed calibrates a cathode ray tube by:

measuring outputs of the cathode ray tube for a subset of device values of the cathode ray tube;

choosing one or more adjustable parameter values of a device model for the cathode ray tube such that an average error between expected outputs determined from the device model and measured outputs of the cathode ray tube is on the order of an expected error, wherein a number of the adjustable parameters is less than a number of measured outputs of the imaging device; and

adjusting image data according to the device model to achieve a target behavior for the cathode ray tube.

23. The computer readable medium of claim 22, wherein the subset of device values substantially correspond to neutral colors having values of red, green and blue on the order of one another.

24. The computer readable medium of claim 22, wherein adjusting image data further includes creating a lookup table (LUT) based on the device model.

25. The computer readable medium of claim 22, wherein adjusting image data further includes creating a color profile for the imaging device based on the device model.

26. The computer readable medium of claim 22, wherein the parameters comprise a gamma value and a black onset value.

27. The computer readable medium of claim 22, wherein the target behavior corresponds to a defined gamma value.

28. A computer readable medium storing program code that when executed calibrates a cathode ray tube by:

initializing a lookup table (LUT);

adjusting settings of the cathode ray tube to substantially achieve a defined output;

measuring output for a number of color values;

choosing adjustable parameter values for a device model, wherein a number of adjustable parameters is less than a number of measured outputs; and

generating entries for the LUT based on the device model.

29. The computer readable medium of claim 28, wherein adjustable parameters of the device model include a gamma value and an onset value.

30. The computer readable medium of claim 28, wherein measuring output includes displaying a substantially white trace during measurement to bias an output measurement.

31. The computer readable medium of claim 30, wherein the trace has a halo shape.

32. The computer readable medium of claim 28, wherein the LUT resides in a video card.

33. A computer readable medium storing program code that when executed:

measures output of a display device; and

displays a substantially white trace during measurement to bias an output measurement.

34. The computer readable medium of claim 33, wherein the trace has a halo shape.

35. The computer readable medium of claim 33, wherein the program code when executed displays the substantially white trace during measurement to bias output measurements by approximately 0.5 to 1.0 percent.

36. The computer readable medium of claim 33, wherein the program code when executed displays the substantially white trace during measurement to bias an output measurement by an amount sufficient to ensure that the output measurement is within a dynamic range of a measurement device.