Color measurement and calibration

• US 9,794,528 B2
• Filed: 09/11/2014
• Issued: 10/17/2017
• Est. Priority Date: 09/11/2013
• Status: Expired due to Fees

• Current Assignee: Color Match, LLC
• Original Assignee: Color Match, LLC
• Inventors: Mui, Peter H.
• Primary Examiner(s): Do, Anh
• Application Number:
  US14/484,241
• Publication Number:
  US 20150070510A1
• Time in Patent Office: 1,132 Days
• Field of Search: 382165, 382164, 382162, 382167, 382128, 345109, 348187, 348E13037, 349 62, 349 96, 353 20, 35948503
• CPC Class Codes: G01J 3/462 Computing operations in or between colour spaces; Colour management systems
• CPC Class Codes: G01J 3/463 Colour matching
• CPC Class Codes: G01J 3/52 using colour charts
• CPC Class Codes: G01J 3/522 circular colour charts
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 7/90 Determination of colour characteristics
• CPC Class Codes: H04N 1/6008 with primary colour signals, e.g. RGB or CMY(K)
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 17/02 for colour television signals
• CPC Class Codes: H04N 23/10 for generating image signals from different wavelengths
• CPC Class Codes: H04N 9/01 Circuitry for demodulating colour component signals modulated spatially by colour striped filters by phase separation

Abstract

Embodiments described herein disclose a color measurement device and method for use with cameras or other imaging devices. The color measurement device may be configured to determine many different colors via a commonly owned device. Embodiments utilize sinusoidal grayscale rings to determine an exact color match of an unknown color, even if there is perspective distortion of an obtained image.

Claims

1. A system for determining a true color of an unknown color sample, the system comprising:

a template card including a cut-out and a plurality of concentric rings around the cut-out, each of the concentric rings having offset gray scales modulated as a function of an angle of a polar coordinate, wherein there is a trigonometric relationship between the gray scales of the plurality of concentric rings;

a RGB color processor configured to determine, in an image of the template card over the unknown color sample, a first radial cross-section of one of the concentric rings having an intensity that matches a determined average red color value of the image of the unknown color sample and to determine a true average red color value of the unknown color sample based on an intensity profile of the one of the concentric rings and a polar angle of the first radial cross-section; and

an angular processor configured to determine the polar angle of the first radial cross-section.

2. The system of claim 1, wherein the angular processor is configured to determine the polar angle of the first radial cross-section by comparing the intensity in the image of the first radial cross-section with an intensity in the image of a radial cross-section of another of the concentric rings along a same radial segment and utilizing the trigonometric relationship between the gray scales of the concentric rings.

3. The system of claim 1, wherein the RGB color processor is further configured to determine, in the image of the template card over the unknown color sample, a second radial cross-section of a second one of the concentric rings having an intensity that matches a determined average green color value of the image of the unknown color sample and to determine a true average green color value of the unknown color sample based on a ring intensity profile of the second one of the concentric rings and a polar angle of the second radial cross-section, and to determine, in the image of the template card over the unknown color sample, a third radial cross-section of a third one of the concentric rings having an intensity that matches a determined average blue color value of the image of the unknown color sample and to determine a true average blue color value of the unknown color sample based on a ring intensity profile of the third one of the concentric rings and a polar angle of the third radial cross-section, and wherein the angular processor is configured to determine the polar angle of the second and third radial cross-sections.

4. The system of claim 3, further comprising an exact color processor configured to determine the true color of the unknown color sample based on the true average red color value, the true average green color value, and the true average blue color value.

5. The system of claim 1, wherein each concentric ring is phase shifted a given angle from each other concentric ring.

6. The system of claim 5, wherein the plurality of concentric rings comprise three concentric rings, the second concentric ring being phase shifted a first given angle from the first concentric ring and the third concentric ring being phase shifted a second given angle from the second concentric ring.

7. The system of claim 1, further comprising an image capturing device configured to obtain an image of the template card over the unknown color sample.

8. The system of claim 1, wherein the template card further comprises distinctive markings at known locations and wherein the center of the concentric rings can be determined from an image of the template card using geometric relationships between the distinctive markings and the center.

9. The system of claim 8, wherein the template card is rectangular, the distinctive markings comprise corner markings, and the center of the concentric rings is at the center of the template card, wherein the center of the concentric rings in the image can be determined based on an intersection of a first line from a first of the corner markings diagonally to a third of the corner markings and a second line from a second of the corner markings diagonally to a fourth of the corner markings, wherein the center of the concentric rings is then used to determine a radial segment on which a radial cross-section lies.

10. The system of claim 1, wherein the RGB processor is further configured to determine, in the image of the template card over the unknown color sample, another radial cross-section of another of the concentric rings having an intensity that matches the determined average red color value of the image of the unknown color sample and to determine a second true average red color value of the unknown color sample based on an intensity profile of the another of the concentric rings and a different polar angle of the another radial cross-section, and to determine a final true average red color value of the unknown color sample by calculating a weighted average of the true average red color value and the second true average red color value.

11. A method for determining a true color of an unknown color sample, the method comprising:

obtaining an image wherein the image includes the unknown color sample and a template comprising a cut-out and a plurality of concentric rings around the cut-out, each of the plurality of concentric rings having offset gray scales modulated as a function of an angle of a polar coordinate and a trigonometric relationship existing between the gray scales of the plurality of concentric rings;

determining a first radial cross-section of one of the concentric rings that matches a determined average red color value of the unknown color sample in the image;

determining a polar angle of the first radial cross-section; and

determining a true average red color value of the unknown color sample based on an intensity profile of the one of the concentric rings and the polar angle of the first radial cross-section;

wherein the method is performed utilizing a camera.

12. The method of claim 11, further comprising positioning the cut-out of the template over the unknown color sample, wherein obtaining the image comprises actuating an image-capturing device.

13. The method of claim 11, wherein the polar angle of the first radial cross-section is determined by comparing the intensity in the image of the first radial cross-section with an intensity in the image of a radial cross-section of another of the concentric rings along a same radial segment as the first radial cross-section and utilizing the trigonometric relationship between the gray scales of the concentric rings.

14. The method of claim 11, further comprising determining, in the image, a second radial cross-section of a second one of the concentric rings having an intensity that matches a determined average green color value of the image of the unknown color sample and determining a true average green color value of the unknown color sample based on an intensity profile of the second one of the concentric rings and a polar angle of the second radial cross-section, and determining, in the image, a third radial cross-section of a third one of the concentric rings having an intensity that matches a determined average blue color value of the image of the unknown color sample and determining a true average blue color value of the unknown color sample based on an intensity profile of the third one of the concentric rings and a polar angle of the third radial cross-section, and determining the polar angle of the second and third radial cross-sections.

15. The method of claim 13, further comprising determining the true color of the unknown color sample based on the true average red color value, a true average green color value, and a true average blue color value.

16. The method of claim 11, wherein the template further comprises distinctive markings at known locations and further comprising determining the center of the concentric rings from the image using geometric relationships between the distinctive markings and the center, and using the center of the concentric rings to determine a radial segment on which a radial cross-section lies.

17. The method of claim 11, further comprising determining, in the image, another radial cross-section of another of the concentric rings having an intensity that matches the determined average red color value of the image of the unknown color sample and determining a second true average red color value of the unknown color sample based on a ring intensity profile of the another of the concentric rings and a polar angle of the another radial cross-section, and determining a final true average red color value of the unknown color sample by calculating a weighted average of the true average red color value and the second true average red color value.

18. A color identification system, comprising:

a template card comprising one or more full gray scale continuums, wherein a true color intensity along each continuum is a function of geometric position on the template card;

an image obtaining device configured to obtain an image of an unknown color sample adjacent to the template card; and

color identification processors configured to determine geometric positions on the gray scale continuums in the image where their intensities match determined red, green, and blue color values of the image of the unknown color sample, and to use the determined geometric positions to determine the true color intensity of the gray scale continuum at each geometric position, and to use these true color intensities to determine the color of the unknown color sample.

19. A color identification method, comprising:

obtaining an image of an unknown color sample adjacent to a template comprising one or more full gray scale continuums, wherein a true intensity along each continuum is a function of geometric position on the template;

determining geometric positions on the gray scale continuums in the image where intensity matches determined red, green, and blue color values of the image of the unknown color sample;

determining the true intensity of the gray scale continuums at each geometric position based on the determined geometric positions; and

determining the color of the unknown color sample based on these true intensities;

wherein the method is performed utilizing a camera.