Color measurement and calibration
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.
1. A system for determining a color match, comprising:
a database storing color definitions, each having a unique RGB value;
a template card comprising at least one reference scale;
a memory for storing pre-determined calibration RGB values corresponding to the at least one reference scale; and
a processor configured to:
receive a first image of the template card and color sample,
process the first image and output a sample RGB value corresponding to the color sample and at least one reference scale RGB value,
apply color correction to the sample RGB value based on a difference between the at least one reference scale RGB value and a corresponding calibration RGB value of the at least one reference scale to produce a color corrected sample RGB value, and
compare the color corrected sample RGB value with the RGB values of the color definitions stored within the database to determine a color match.
2. The system of claim 1 , wherein the processor is further configured to apply a predetermined least squares fitting function to the color corrected RGB value prior to comparing the color corrected sample RGB value with the RGB values of the color definitions stored within the database.
3. The system of claim 1 , further comprising a camera configured to capture the first image.
4. The system of claim 1 , wherein the template card comprises a substrate and a cut-out, wherein the color sample portion of the image is in the cut-out.
5. The system of claim 4 , wherein the at least one reference scale comprises a modulated gray scale arranged on the substrate.
6. The system of claim 4 , wherein the at least one reference scale comprises a plurality of gray scales arranged on the substrate.
7. The system of claim 4 , wherein the at least one reference scale comprises a plurality of gray scales arranged on the substrate and modulated as a function of an angle of a polar coordinate.
8. The system of claim 4 , wherein the at least one reference scale comprises three gray scales arranged on the substrate and modulated as a function of an angle of a polar coordinate, each of the gray scales being offset by 120 degrees with respect to each of the other two gray scales.
9. The system of claim 4 , wherein the at least one reference scale comprises a plurality of concentric rings arranged on the substrate 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.
10. The system of claim 9 , wherein the at least one reference scale comprises one or more reference colors arranged around the plurality of concentric rings.
11. The system of claim 10 , wherein the one or more reference colors comprises a series of reference colors surrounding the plurality of concentric rings.
12. The system of claim 4 , wherein the template card further comprises a plurality of distinctive markings readable by the processor as part of the first image; and the processor is further configured to correct perspective distortion of the first image using the distinctive markings.
13. The system of claim 3 , wherein the camera is part of a smartphone.
14. The system of claim 1 , wherein the processor is part of a smartphone.
15. The system of claim 1 , wherein the color definitions correspond to paint colors.
16. The system of claim 1 , wherein the color definitions correspond to shades of skintone for matching cosmetic makeups to skintones.
17. The system of claim 1 , wherein each of the color definitions corresponds to a color within the RGB color spectrum.
18. The system of claim 1 , wherein intensity on the at least one reference scale is a function of geometric position on the template card.
19. The system of claim 2 , wherein the template card further comprises a machine-readable code configured to provide the pre-determined calibration RGB values and the predetermined least squares fitting function.
20. The system of claim 19 , wherein the machine-readable code is a bar code.
21. A method for matching colors, comprising:
arranging a template card comprising at least one reference scale adjacent to a color sample of unknown color;
obtaining a first image of the template card and the color sample;
determining a sample RGB value of the color sample and at least one reference RGB value from the first image to produce a determined sample RGB value;
applying color correction to the determined sample RGB value based on a difference between the at least one reference RGB value and corresponding calibration RGB values of the at least one reference scale to produce a color corrected sample RGB value, and
comparing the color corrected sample RGB value with RGB values of a plurality of color definitions stored within a database to determine a color match.
22. The method of claim 21 , further comprising applying a predetermined least squares fitting function to the color corrected RGB value prior to comparing the color corrected sample RGB value with the RGB values of the color definitions stored within the database.
23. The method of claim 21 , wherein obtaining the first image comprises actuating a camera.
24. The method of claim 21 , wherein the template card comprises a substrate and a cut-out, and wherein the arranging a template card comprises positioning the cut-out over the color sample.
25. The method of claim 24 , wherein the reference scale comprises a modulated gray scale arranged on the substrate.
26. The method of claim 24 , wherein the reference scale comprises a plurality of gray scales arranged on the substrate.
27. The method of claim 24 , wherein the reference scale comprises a plurality of gray scales arranged on the substrate and modulated as a function of an angle of a polar coordinate.
28. The method of claim 24 , wherein the reference scale comprises three gray scales arranged on the substrate and modulated as a function of an angle of a polar coordinate, and each of the gray scales being offset by 120 degrees with respect to each of the other two gray scales.
29. The method of claim 24 , wherein the reference scale comprises a plurality of concentric rings arranged on the substrate 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.
30. The method of claim 29 , wherein the reference scale further comprises at least one reference color arranged around the plurality of concentric rings.
31. The method of claim 30 , wherein the at least one reference color comprises a series of reference colors surrounding the plurality of concentric rings.
32. The method of claim 24 , wherein the template card further comprises a plurality of distinctive markings; and the method further comprising correcting a perspective distortion of the first image using the distinctive markings.
33. The method of claim 23 , wherein the camera is part of a smartphone.
34. The method of claim 21 , wherein the processor is part of a smartphone.
35. The method of claim 21 , wherein the color definitions correspond to paint colors.
36. The method of claim 21 , wherein the color definitions correspond to shades of skintone for matching cosmetic makeups to skintones.
37. The method of claim 21 , wherein each of the color definitions corresponds to a color within the RGB color spectrum.
38. The method of claim 21 , wherein intensity on the reference scale is a function of geometric position on the template card.
39. The method of claim 38 , wherein determining a sample RGB value of the color sample from the first image comprises determining measured red, green and blue color values of the color sample and determining geometric positions on the template card where intensity on the reference scale matches each of the measured red, green and blue color values.
40. The method of claim 22 , further comprising using a machine-readable code on the template card to obtain the calibration RGB values and the predetermined least squares fitting function.
41. The method of claim 40 , wherein the machine-readable code is a bar code.
42. A system for color determination, comprising:
a database storing color definitions, each having a unique RGB value;
one or more template cards, each comprising at least one reference scale and at least one reference color; and
a processor configured to:
receive one or more images of the template cards and one or more known color samples,
process the images,
output known sample RGB values and at least one reference color RGB value,
store the at least one reference color RGB value as a calibration RGB value matrix for color correction,
compare the output known sample RGB values with the RGB values of corresponding color definitions stored within the database; and
perform a least squares fit of the output known sample RGB values to the corresponding color definition RGB values to generate coefficients of a transform function for transforming output RGB values into corresponding color definition RGB values.
43. The system of claim 42 , wherein the processor is further configured to associate the calibration RGB value matrix and transform function coefficients with a machine-readable code on the template cards.
44. The system of claim 42 , further comprising an image capturing device configured to capture the images.
45. A method for color determination, comprising:
obtaining one or more images of template cards and one or more known color samples,
outputting known sample RGB values and at least one reference color RGB value,
storing the at least one reference color RGB value as a calibration RGB value matrix for color correction,
comparing the output known sample RGB values with RGB values of corresponding color definitions stored within a database; and
performing a least squares fit of the output known sample RGB values to the corresponding color definition RGB values to generate coefficients of a transform function for transforming output RGB values into corresponding color definition RGB values.
46. The method of claim 45 , further comprising associating the calibration RGB value matrix and transform function coefficients with a machine-readable code on the template cards.
47. The method of claim 45 , wherein obtaining the images comprises actuating an image capturing device.