Method for deriving consistent, repeatable color measurements from data provided by a digital imaging device

1. A method for obtaining a target color measurement using an electronic image capturing device having a plurality of reference colors and light and dark level correction references, comprising the steps of:

as a set up step, before measuring a target color:

determining a field correction array by placing an identical color reference in each of a plurality of locations in the field of the image capturing device and computing a field correction array; and

determining a level correction vector using the light and dark level correction references wherein the level correction vector is determined based upon a predicted value of red, green and blue intensities for each of the level correction references; and

each time a target color is measured using the image capturing device:

determining a color correction matrix under the conditions extant at the time that the target color is measured using the image capturing device based on the field correction array and the level correction vector; and

determining a calibration correction under the conditions extant at the time that the target color is measured by application of the field correction array and the level correction vector determined in the set up step and application of the color correction matrix to the light and dark reference colors; and

adjusting a target color measurement obtained using the electronic image capturing device based upon the color correction matrix, and the calibration correction to obtain a corrected color target measurement.

2. The method of claim 1 wherein the target color reading is made up of red, green and blue intensities.

3. The method of claim 1 wherein the electronic image-capturing device includes a plurality of color references and the color correction matrix is based upon a predicted or independently determined value of red, green and blue intensities for the color references.

4. The method of claim 1 wherein the calibration correction is obtained by measuring the red, green and blue intensities for a light color sample and a dark color sample, adjusting the measured intensities using the field correction array and the level correction vector and calculating the calibration correction based on the predicted or independently measured red, green and blue intensities for the light color sample and the dark color sample.

5. The method of claim 1 wherein the field correction array is calculated based upon the formula:

x

i

=

m

i

c

wherein x i is the field correction value, m i is the measured color intensity, and c is a constant.

6. The method of claim 5 wherein the uncorrected red, green and blue intensity data from the reference colors is field corrected based upon the formula: m i =x i ×r i wherein m i is the field corrected data, x i is the field correction array, and r i is the measured intensity.

7. The method of claim 1 wherein the target color measurement is field corrected to provide field corrected target reading and the field corrected target reading is level corrected based upon the equation:

x

i

=

(

m

i

-

m

D

m

L

-

m

D

)

×

(

t

L

-

t

D

)

+

t

D

where m L and m D are vectors containing the measured and field corrected red, green and blue channel values for the light and dark references and t L and t D are the predicted values of the red, green and blue channel values for the light and dark references.

8. The method of claim 7 wherein a color matrix correction B is calculated and applied to the field corrected and level corrected target reading using the equation: x=Bu where u is a vector representing the red, green and blue intensities for the target color and x is the color corrected result.

9. The method of claim 8 wherein the method includes the step of correcting the color corrected target measurement based upon the following equation:

a

=

(

x

-

x

D

x

L

-

x

D

)

×

(

c

L

-

c

D

)

+

c

D

wherein x L and x D represent vectors for the measured values for the light and dark calibration samples, c L and c D represent vectors for the color corrected target measurement and a is the calibration corrected result, and x is the vector containing the color corrected result.