Optics: measuring and testing – By shade or color – With color transmitting filter
Reexamination Certificate
2000-02-16
2002-04-09
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By shade or color
With color transmitting filter
C356S402000, C356S416000, C356S446000
Reexamination Certificate
active
06369895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of instruments used to measure the reflective color of an object, such as a reflection densitometer or a spectral reflectometer. These types of instruments are used extensively in measuring printed ink colors, paint colors, or the colors of any other object for which a numerical color value is desired. In the case of printing devices, the measured values are often used to calibrate the printing device in a feedback loop so as to reproduce a desired color. In other cases, the measured value is used to specify a desired color in a digital image or document, often for the purpose of matching the color of the measured object.
Instruments of this type are well known in the prior art and are generally comprised of one or more light sources and one or more light sensitive detectors arranged in specific geometry. Under common standards (such as ANSI/ISO May 4, 1995
Density Measurements—Part
4
: Geometric Conditions for Reflection Density
, or DIN 16536
Color Density Measurements on Prints: Requirements on Measuring Apparatus for Reflection Densitometers
), the measurement geometry is specified to consist of an annular ring of illumination projected onto the center of a sample target area at an angle of between 40 and 50 degrees. The light reflected off the sample is sensed by a detector positioned at an angle of between 85 and 90 degrees from the target sample. Alternatively, the positions of the light source and detector may be interchanged.
Detailed discussions relating to the background of color measurement instruments may be found in prior art such as U.S. Pat. Nos. 5,015,098 and 5,073,028.
Such measuring devices may also be configured as hand-held devices. Hand-held measuring devices used to measure the reflective color of an object are generally manually aimed by positioning a small (3 to 7 mm diameter) sampling aperture in contact with and over the area of the sample for which the color is to be measured. The manual aiming process can be tedious and error-prone due to the inability of the operator to accurately see where the sampling aperture of the measuring device is about to be placed on the sample. The enclosure of the measuring device is generally constrained by the measurement geometry requirements to taper away from the sampling aperture at an angle no greater than 40 degrees. Such a configuration significantly obstructs the operator's sight line during aiming and positioning of the sampling aperture over an area to be sampled.
For example, a typical prior art hand-held measuring device is illustrated in FIG.
1
.
FIG. 1
shows a prior art measuring device
100
having a sample area optical enclosure
101
. The optical enclosure
101
includes light sources
120
and
121
arranged such that light is projected towards a sampling aperture
110
at an angle of 45 degrees. The detector
130
is arranged to detect light reflected at a surface normal to the sampling aperture
110
.
FIG. 1
shows the measuring device
100
positioned over a sample area
210
of a sample
200
. The portion of the optical enclosure
101
which tapers down to form a sampling aperture
110
is formed by the optical enclosure walls
140
which narrow toward the sampling aperture in the shape of a cone. The cone shaped walls
140
are symmetrically arranged and angled at approximately 45 degrees. This angle of the walls
140
is constrained both by the placement of the light sources
120
and
121
so as to project light toward the sampling aperture
110
at an angle of 45 degrees and by the placement of the detector
130
so as to detect light reflected at a surface normal to the sampling aperture
110
.
The geometry of the prior art measuring device
100
conforms to standard measurement geometry relating to placement of the light source and detector. As can be seen from
FIG. 1
, such a configuration results in the optical enclosure obstructing the view of the area to be sampled. The operator sight line, shown in
FIG. 1
as
300
, is angled at approximately 45 degrees from the targeted sample area. Such an obstructed sight line makes it extremely difficult for an operator to accurately position the measuring device
100
over the sample area, resulting in erroneous measurements.
A slight improvement over the prior art is illustrated by
FIG. 2
, which shows a hand-held measuring device such as that disclosed in U.S. Pat. No. 5,963,333.
FIG. 2
shows the same elements as disclosed in FIG.
1
and all reference numbers correspond.
The prior art measuring device of
FIG. 2
allows for a different configuration of the light sources
120
and
121
, which results in a slightly improved operator sight line
300
. The light sources
120
and
121
are positioned such that the light is projected onto reflective surfaces
142
of walls
140
proximal to the sampling aperture, which reflective surfaces reflect the light towards the sampling aperture at an angle of approximately 45 degrees. Such a configuration maintains the standard measurement geometry, while allowing the optical enclosure walls
140
to be arranged symmetrically and angled at approximately 60 degrees. As shown in
FIG. 2
, such an arrangement of the optical enclosure walls
140
allows for a slightly improved operator sight line
300
of approximately 60 degrees.
While the sight line of the measuring device illustrated in
FIG. 2
is an improvement over that of
FIG. 1
, such a configuration still results in an obstructed view of the area to be sampled and results in difficulty in accurately positioning the sampling aperture over the sample area. The sight line of approximately 60 degrees is less than optimal.
An operator sight line approaching the optimal 90 degrees is desired and is accomplished by the present invention.
SUMMARY OF THE INVENTION
The present invention is intended to eliminate the problems associated with the restricted sight line of the prior art color measurement instruments such as reflection densitometers or spectral reflectometers. The object of the present invention is accomplished by arranging the light source and detector in a manner which allows the sample area optical enclosure walls to taper away from the sampling aperture in an asymmetrical manner. The taper angle of the optical enclosure is higher at the front of the optical enclosure where the operator requires a better sight line, while the taper angle of the optical enclosure walls at the portions towards the rear of the optical enclosure is approximately 40 degrees. Such a configuration allows for the standard measurement geometry between the detector and sample of approximately 90 degrees and between the light source and sample of approximately 45 degrees. The asymmetrical configuration of the optical enclosure allows for an operator sight line of approximately 80 degrees.
The light source can comprise, for example, one or more incandescent light sources, one or more infrared light sources, one or more light emitting diodes, or the like. Similarly, the detector can comprise, for example, one or more detectors or series of detectors, a detector with a multitude of detection elements, or the like.
In one embodiment of the present invention, the light source is positioned only towards the rear of the optical enclosure. As light is projected into the sampling aperture from only one position, such a configuration provides illumination of the sample area that is not completely in adherence with standard measurement techniques, such as the American National Standards Institute (ANSI) standard (ANSI/ISO May 4, 1995). However, the measurements achieved are sufficiently accurate for most applications. Only in the case of heavily textured sample surfaces would the orientation of illumination become significant, and only where the textured sample is significantly directional in its arrangement.
In another embodiment of the invention, a first light source is positioned towards the rear of the optical enclosure and illuminates the sampling aperture directly at an angle of projection o
Electronics for Imaging, Inc.
Evans F. L.
Lipsitz Barry R.
McAllister Douglas M.
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