Optics: measuring and testing – By shade or color
Reexamination Certificate
1998-12-18
2001-08-07
Evans, F L (Department: 2877)
Optics: measuring and testing
By shade or color
C356S422000, C356S423000, C356S243500
Reexamination Certificate
active
06271920
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to color measuring instruments and, in particular, to methods and apparatus for calibrating and verifying the calibration of color measuring instruments that are suitable for measuring the color of a surface, including human skin.
It is well known that color measuring instruments, such as colorimeters and spectrophotometers, can be used to measure the color of surfaces for a variety of useful applications. For example, Macfarlane et al. U.S. Pat. No. 5,313,267 describes a method and instrument for selecting personal compatible colors using a color measuring device. Also, PCT Publication No. WO 96/41140 describes methods and apparatus for determining the condition of a test subject based on color by using a color measuring instrument to detect change in a color factor indicative of a condition such as a disease, spoilage, ageing, etc. In particular, those methods and apparatus can be used to detect a medical condition known as hyperbilirubinemia by measuring skin color.
However, in order to ensure that the skin color measurements are accurate, they are usually preceded by conventional calibration and optionally conventional verification techniques. Such calibration can be performed by measuring a single color standard of predetermined coloration having premeasured color measurement value(s) and comparing the measurement value(s) with the premeasured value(s) to see that they are substantially the same. Once calibrated, the instrument is normally prepared to perform accurate color measurements producing color measurement value(s) that characterize the color of an unknown sample.
Additionally, further subsequent verification against a color standard that is different than that of the color standard used during calibration can help to ensure that the standard used to calibrate the color measuring instrument was an accurate and authorized color standard for its intended calibration and that calibration was performed according to predetermined specifications.
When color measuring instruments are used for medical applications, such as when they are used to detect abnormal medical conditions (including hyperbilirubinemia), the accuracy of the color standard used for calibration and verification is critical. However, color standards may be inaccurate because they have been inadvertently scratched and/or soiled by previous users or because they have become discolored, or faded, from atmospheric or electromagnetic radiation exposure. Furthermore, another reason for inaccuracy of the color standard includes poor quality control at the site where the color standard is manufactured. Poor quality control at the manufacturing site may yield unacceptable variability in coloration of a color standard (even though the color standard is new and unused). Moreover, color standards from unauthorized manufacturing sites may be mislabeled.
Furthermore, when a color measuring instrument is used to determine a medical condition, a portion of the instrument usually makes an optical seal on the surface of the patient's skin. In order to make the seal, however, that portion of the color measuring instrument normally makes physical contact with the skin. A disadvantage of such contact is that the contacting surface of the instrument could transfer germs between successive patients when a single color measuring instrument is used to make such measurements.
In view of the foregoing, it is an object of this invention to provide sanitary methods and apparatus for making color measurements of human skin among other uses for such an invention, such as measuring laboratory specimens.
It is yet another object of this invention to provide improved color calibration and verification methods and apparatus that can detect inaccurate or unauthorized color standards and inaccurate calibration of color measuring instruments.
It is another object of this invention to provide methods and apparatus for safely measuring medical conditions without the risk of germ transfer.
SUMMARY OF THE INVENTION
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing methods and apparatus to ensure proper calibration and verification of calibration of color measuring instruments.
As used herein, the term “calibration” includes both conventional calibration and standardization techniques as defined by
Standard Terminology of Appearance
(ASTM definitions). Conventional color calibration is the finding and elimination of systematic errors of a color measurement instrument scale or method of measurement by use of material standard and techniques traceable to an authorized national or international measurement system. Standardization is the process of adjusting the instrument output to correspond to a previously established calibration using one or more specimens or reference materials.
A method of calibrating a color measuring instrument with a color standard and verifying the color standard and the calibration according to this invention can include the following steps. First, a color standard having a surface with at least two different colors is provided. Second, the color measuring instrument is calibrated. And third, the calibration of the color measuring instrument is verified.
The color standard used in a preferred embodiment is one having at least two different colors arranged for simultaneous color measurement to sequentially calibrate a color measuring instrument with first predetermined color measurement value(s) of the color standard and verify the calibration with at least second and different predetermined color measurement value(s) of the color standard, the color calibration and verification apparatus includes variance means to provide at least such first and second different color measurement values, the variance means being selected from the group consisting of: (1) sequential inclusion and exclusion of the predetermined color measurement value(s) of the predetermined color measurement value(s) of a portion of said colors, (2) sequential exclusion and inclusion of the predetermined color measurement value(s) of the predetermined color measurement value(s) of a portion of said colors, and (3) sequential unexposure and exposure of photosensitive paper or material which provides at least one of said colors or portion of said colors.
The color standard used in another preferred embodiment of this invention has a first color that is characterized by a first predetermined coloration having premeasured color measurement value(s) and a second color that is characterized by a second predetermined coloration having premeasured color measurement value(s). The color standard used in calibrating and verifying a color measuring instrument can include: (1) a first predetermined coloration's premeasured color measurement value(s), (2) a second predetermined coloration's premeasured color measurement value(s), or (3) any combination of the first and the second predetermined coloration's premeasured color measurement value(s).
Any portion, region, or section of the color standard can be photosensitive so that its color changes in a known way when exposed to a predetermined dose of light.
The surface of the color standard can be a single surface with two colors or, in another preferred embodiment, can be two separate surfaces with two respective colors. For example, a first color which is characterized by a first predetermined coloration having premeasured color measurement value(s) can be disposed on a first surface of the color standard and a second color (which is characterized by a second predetermined coloration having premeasured color measurement value(s)) can be disposed on a second surface of the color standard. The second surface can be the opposite side of the first surface.
When two or more colors are disposed on a single surface, the colors are preferably arranged for a simultaneous color measurement. A simultaneous color measurement according to this invention includes one color measurement of
Billmeyer, Jr. Fred W.
MacFarlane Darby S.
MacFarlane David K.
Chromatics Color Sciences International Inc.
Evans F L
Fish & Neave
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