Halftone calibration mechanism employing an ink model

Patent metadata

Field	Value
Publication number	US-9621762-B2
Application number	US-201213346231-A
Country	US
Kind code	B2
Filing date	Jan 9, 2012
Priority date	Jan 9, 2012
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

A printing system is disclosed. The printing system includes a halftone calibration system that receives one or more un-calibrated halftones, generates one or more calibrated halftones using an ink model from the one or more un-calibrated halftones, analyzes a printed calibration screen of the one or more calibrated halftones, and performs a halftone calibration.

First claim

What is claimed is:

1. A non-transitory machine-readable medium including data that, when accessed by a machine, cause the machine to perform operations comprising:
receiving one or more un-calibrated halftones;
generating one or more calibrated halftones from the one or more un-calibrated halftones employing an ink model by:
computing ink coverage for the one or more un-calibrated halftones;
computing ink coverage for a desired optical density; and
comparing the computed ink coverage for the one or more un-calibrated halftones with the computed ink coverage for the desired target optical density,

wherein ink coverage is defined as a total ink mass applied to a unit area;
analyzing a printed calibration screen of the one or more calibrated halftones; and
performing a halftone calibration.

2. The article of manufacture of claim 1 wherein the ink coverage for the one or more un-calibrated halftones is computed using a lookup table.

3. The article of manufacture of claim 2 wherein the ink coverage for the desired optical density is computed using a sigmoidal optical density curve.

4. The article of manufacture of claim 3 wherein comparing the computed ink coverage for the one or more un-calibrated halftones with the computed ink coverage for the desired optical density comprises determining a mapping between the one or more un-calibrated halftones and the sigmoidal optical density curve.

5. The article of manufacture of claim 4 wherein the mapping is computed using a four parameter Weibull cumulative distribution function.

6. The article of manufacture of claim 1 wherein analyzing the calibrated screen comprises calculating a mean optical density for each nozzle in a print head, deriving corresponding ink coverage per nozzle, predicting optical densities for tint values based on a sigmoidal target optical density curve using measured and predicted data.

7. The article of manufacture of claim 1 wherein performing the halftone calibration comprises generating tone reproduction curves.

8. The article of manufacture of claim 1 comprising a machine-readable medium including data that, when accessed by a machine, further causes the machine to perform operations comprising generating one or more calibration halftone files.

9. A printing system comprising:
a halftone calibration system to receive one or more un-calibrated halftones, generate one or more calibrated halftones from the one or more un-calibrated halftones by computing ink coverage for the one or more un-calibrated halftones, computing ink coverage for a desired optical density and comparing the computed ink coverage for the one or more un-calibrated halftones with the computed ink coverage for the desired target optical density, analyze a printed calibration screen of the one or more calibrated halftones, and perform a halftone calibration, wherein ink coverage is defined as a total ink mass applied to a unit area.

10. The printing system of claim 9 wherein the ink coverage for the one or more un-calibrated halftones is computed using a lookup table and the ink coverage for the desired optical density is computed using a sigmoidal optical density curve.

11. The printing system of claim 10 wherein comparing the computed ink coverage for the one or more un-calibrated halftones with the computed ink coverage for the desired optical density comprises determining a mapping between the one or more un-calibrated halftones and the sigmoidal optical density curve.

12. The printing system of claim 11 wherein the mapping is computed using a Weibull four parameter cumulative distribution function.

13. The printing system of claim 9 wherein analyzing the calibration screen comprises calculating a mean optical density for each nozzle in a print head, deriving corresponding ink coverage per nozzle, predicting optical densities for tint values employing a sigmoidal target optical density curve, based on measured and predicted data.

14. The printing system of claim 9 wherein performing the halftone calibration comprises generating tone reproduction curves.

15. The printing system of claim 14 wherein generating tone reproduction curves comprises performing single pass calibration across a medium web and performing dual pass calibration for overlap print head nozzles.

16. The printing system of claim 9 wherein the halftone calibration system generates one or more calibration halftone files.

17. The printing system of claim 9 wherein one or more un-calibrated halftones are 10 bit halftones and the one or more calibrated halftones are 8 bit halftones.

18. A method comprising:
receiving one or more un-calibrated halftones;
generating one or more calibrated halftones from the one or more un-calibrated halftones employing an ink model by:
computing ink coverage for the one or more un-calibrated halftones;
computing ink coverage for a desired optical density; and
comparing the computed ink coverage for the one or more un-calibrated halftones with the computed ink coverage for the desired target optical density,

wherein ink coverage is defined as a total ink mass applied to a unit area;
analyzing a printed calibration screen of the one or more calibrated halftones; and
performing a halftone calibration.

Assignees

• Chandu Kartheek
• Ernst Larry
• Vantaram Sreenath Rao
• Stanich Mikel J
• Wu Chai Wah
• Ricoh Co Ltd

Inventors

• Chandu Kartheek
• Ernst Larry
• Vantaram Sreenath Rao
• Stanich Mikel J
• Wu Chai Wah

Classifications

• H04N1/407

  Control or modification of tonal gradation or of extreme levels, e.g. background level · CPC title

• H04N1/405 Primary

  Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels · CPC title