Method and system for color grading of gemstones

• US 20070153256A1
• Filed: 12/30/2005
• Published: 07/05/2007
• Est. Priority Date: 12/30/2005
• Status: Active Grant

• Current Assignee: Yan Liu
• Original Assignee: Yan Liu
• Inventors: Liu, Yan
• Granted Patent: US 7,388,656 B2
• Time in Patent Office: Days
• US Class Current: 356/30
• CPC Class Codes: G01J 3/46 Measurement of colour; Colour measuring devices, e.g. colorimeters measuring colour temperature G01J5/60
• 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 3/465 taking into account the colour perception of the eye; using tristimulus detection
• CPC Class Codes: G01N 21/278 Constitution of standards
• CPC Class Codes: G01N 21/293 with colour charts, graduated scales or turrets
• CPC Class Codes: G01N 21/87 Investigating jewels G01N21/88 takes precedence

Abstract

A method and system, including a computer program product, implementing a color terminology for accurate color grading of gemstones are provided. The method includes generating a reference color to match that of a graded gemstone under the standard viewing environment, processing color data in different color spaces, assigning a color grade to specify the color of the gemstone graded. The reference color can be continuously changed by adjusting the hue, lightness and saturation values. The color grade comprises a color name and one or more corresponding color coordinates and/or one or more corresponding color notations, in the form of Color Name (Color Coordinates). The color name is used for verbal description of the color, and the color coordinate or color notation is for accurate color communication in the jewelry industry.

Claims

1. A method for color grading gemstones using a system with a computer program product, comprising:

calibrating the display element to the specifications of a white point of a CIE standard illuminant at a brightness level with a γ

correction;

observing the average color of a gemstone by the 45/0 condition under a standard CIE daylight simulator against a neutral background and surround;

adjusting hue, lightness and saturation values continuously to change the reference color by a color grader;

calculating color coordinates and color notations from the hue, lightness and saturation values;

applying γ

correction to RGB tristiumlus values;

calculating RGB digital counts;

assigning a corresponding color name from the calculated color coordinates by checking the color name look-up table;

making a logical decision;

displaying the assigned color name and color coordinates; and

displaying the reference color on the display element.

2. The method of claim 1 further comprising

printing a color grading report with the color grade for the gemstone graded, including the color name, color coordinates and/or color notations, physical and gemological properties.

3. The method of claim 1 further comprising displaying the true color of a gemstone by inputting the color coordinates of its color grade for color communication purpose.

4. The method of claim 1, wherein

the step of making a logical decision comprises if the displayed color does not match the viewed average color of the gemstone, allowing the color grader to match the viewed average color again by readjusting the hue, lightness and saturation values;

or

if the displayed color matches the viewed color, instructing a printer to print out a color grade report for the gemstone.

5. The method of claim 1, wherein

the display element is a liquid crystal display (LCD), a cathode-ray tube (CRT), a plasma display, a digital light processing (DLP) display, or a liquid crystal on silicon (LCOS) display.

6. The method of claim 1, wherein

the CIE standard illuminant is the CIE standard illuminant D50, the CIE standard illuminant D55, the CIE standard illuminant D65, the CIE standard illuminant D75, the CIE standard illuminant A, or the CIE standard illuminant C.

7. The method of claim 1, wherein

the color spaces are a CIE 1976 (L*, a* b*) color space, a CIE 1976 (L*, u*, v*) color space, a CIE 1931(XYZ) color space, a CIE 1931 (RGB) color space, a CIE 1931 γ

(RGB) color space, a CIE 1931 s(RGB) color space, a CIE 1964(XYZ) color space, a CIE 1964 (RGB) color space, a CIE 1964 γ

(RGB) color space, and/or a CIE 1964 s(RGB) color space.

8. The method of claim 1, wherein

the CIE daylight simulator has a color temperature that is the same as that of the white point for calibrating the display element.

9. The method of claim 1, wherein:

the value of γ

for the γ

correction of the RGB tristimulus values is from 1.0 to 3.0; and

the γ

value for the display element calibration matches the γ

value for the correction of the RGB tristimulus values.

10. The method of claim 1, wherein

the reference color is immediately surrounded by a large area of neutral color with a Munsell notation N6-N7;

and

the reference color can be continuously adjusted by changing the hue, lightness and saturation values by the means of changing the values of the corresponding scroll bars.

11. The method of claim 1, wherein

at least one interrelationship among the color names and the color coordinates is defined by the look-up table.

12. The method of claim 1, wherein

the color name comprises saturation intensity, lightness level, and hue term in the tripartite form.

13. The method of claim 1, wherein

the color grade of gemstone comprises of the color name and one or more color coordinates and one or more color notations in a form “

Color Name (C_ab*, L*, h_ab)”

, in a form “

Color Name (L*, a*, b*)”

, in a form “

Color Name (C_ab*, L*, h_ab) (L*, a*, b*)”

, in a form “

Color Name(H V/C)”

, in a form “

Color Name(D C H)”

, or in a form “

Color Name (Color Coordinate 1) (Color Notation 1) . . . ”

.

20. The method of claim 1, wherein

the system comprises of a display element, a data processor instructed by the computer program product, a CIE D65 daylight simulator, a neutral background and/or surround with a Munsell notation N6-N7.

14. A computer program product stored on a machine-readable medium for processing color grading of gemstone, the product comprises of instructions operable to cause a programmable data processor to:

receive inputted hue, lightness and saturation values;

calculate color coordinates from the hue, lightness and saturation values for adjusting the reference color,

apply γ

correction to the RGB tristimulus values;

calculate RGB digital counts;

assign a corresponding color name from the calculated color coordinates by checking a color name look-up table; and

instruct the data processor to drive a display element to show the reference color.

15. The product of claim 14 further comprising

causing the programmable data processor to instruct a printer to print out a color grading report with the color grade for the gemstone graded, including the color name, color coordinates, color notations, physical properties and gemological properties of the gemstone.

16. The product of claim 14, wherein

the hue, lightness and saturation value can be continuously changed by means of adjusting the values of the corresponding scroll bars, or

by means of entering the color coordinate into the corresponding text boxes.

17. The product of claim 14, wherein

the value of γ

for the γ

correction is from 1.0 to 3.0; and

the γ

value for the display element correction matches the γ

value for the γ

correction of the GRB tristimulus values.

18. The product of claim 14, wherein

the color spaces are a CIE 1976 (L*, a* b*) color space, a CIE 1976 (L*, u*, v*) color space, a CIE 1931(XYZ) color space, a CIE 1931 (RGB) color space, a CIE 1931 γ

(RGB) color space, a CIE 1931 s(RGB) color space, a CIE 1964(XYZ) color space, a CIE 1964 (RGB) color space, a CIE 1964 γ

(RGB) color space, and/or a CIE 1964 s(RGB) color space.

19. The product of claim 15, wherein

the RGB digital counts are in a format of 12 bits color (4-bits for each color channel), 15 bits color (5-bits for each color channel), 16 bits color (4 bits for each color channel and additional 4 bits for α

channel), 32-bits color (8 bits for each color channel and additional 8 bits), 64-bits color (16 bits for each color channel and additional 16 bits), 128-bits color (32 bits for each color channel and additional 32 bits), or 256-bits color (64 bits foe each color channel and addition 64 bits).