Optics: measuring and testing – By shade or color – Trichromatic examination
Reexamination Certificate
1999-11-09
2002-08-13
Evans, F L (Department: 2877)
Optics: measuring and testing
By shade or color
Trichromatic examination
C356S407000, C356S419000, C250S226000
Reexamination Certificate
active
06433873
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88114801, filed Aug. 30, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a color meter. More particularly, this invention relates to an imaging-splitting color meter at an optical entrance pupil.
2. Description of the Related Art
To inspect the quality of color, a color meter has been broadly applied to various industries as an instrument for quality inspection and management of color. Referring to
FIG. 1
, a conventional color meter is schematically illustrated. An observing object
10
reflects a light beam after being incident with a light source, for example, a light emitting diode (LED) or a television screen. This incident light source is converged by a converging lens
20
and restricted by an entrance pupil
30
, and then forms an image on a photodetective plane
40
. The observing object
10
and the photodetective plane
40
are conjugate image points, that is, the observing object
10
is an object plane of the optical system, while the photodetective plane
40
is the image plane of the optical system.
After the photodetective plane
40
, multiple photosensors
50
are disposed. As shown in
FIG. 1
, color filtering devices
80
(color filters in general) are used to filter red light (R), green light (G), and blue light (B). Being filtered, these lights are then received by the photosensors
50
which can also detect the light intensity of these lights. Therefore, different signals are generated according to various colors with different light intensities. These signals are then transmitted from an amplifier
60
to an electronic system
70
, the color of the observing object
10
can thus be measured and calculated.
The chromaticity of three colors R, G and B are calculated by the electronic system
70
according to the intensities of the light signals thereof. Different methods of color filtering have been developed currently, for example, {overscore (x
a
+L )}, {overscore (x
b
+L )}, {overscore (y)} and {overscore (z)} coloring filters of human vision; red (R), yellow (Y), green (G), cyan (C) and blue (B) color filtering method; and visible range multi-wavelength color filtering method. These above functions can be achieved using photosensors of different observing objects.
In
FIG. 2
, assuming that the observing object A is partitioned into three portions a
1
, a
2
and a
3
, and an image of the object A is formed onto the photodetective plane
40
, that is, on B. The photodetective plane B is also partitioned into three portions b
1
, b
2
and b
3
to dispose photosensors for R, G and B lights, respectively. If the colors are uniformly distribute over the object A, the distribution of lights on the photodetective plane B is substantially uniform as well. Under this circumstance, the arrangement of the photosensors of various colors would not be affected. However, if the color distribution in the portions a
1
, a
2
and a
3
of the object A is non-uniform, and consequently the color distribution of the portions b
1
, b
2
and b
3
is non-uniform, the arrangement of the photosensors is then impacted.
For example, human eyes are synthetically uniform against color. Therefore, the color of the object A observed by the human eyes is an average of the colors in A, that is, an average a
ave
of a
1
, a
2
and a
3
. In the photodetective plane B, b
1
receives the light from a
1
, b
2
receives the light from a
2
and b
3
receives the light from a
3
. When the position of the photosensors is out of place, the color calculated is not equal to an average value b
ave
of b
1
, b
2
and b
3
. Thus, the color detected by the photosensors is not real.
Referring to
FIG. 3
, a non-uniform color distribution of an object is illustrated. Assuming that the signals R=B=G, that is, a
1
=a
3
=a
3
, the color a
ave
that the observer sees is white.
FIG.
4
and
FIG. 5
illustrate a result of a poor arrangement of photosensors in the photodetective plane. The red dash line circles the location of a red color filtering device and a red photosensor. The green dash line circles the location of a green color filtering device and a green photosensor, and the blue dash line circles the location of blue color filtering device and a blue photosensor.
In
FIG. 4
, only blue light can transmit through the blue color filtering device to be received by the blue photosensor. The green light can not pass through the red color filtering device, so that the red photosensor can not receive any signal. The red light cannot pass through the green color filtering device, so that there is nothing received by the green photosensor. As a result, being analyzed by the electronic system, the light of the object is blue instead of white.
In
FIG. 5
, the photosensors are turned with an angle. A small portion of the blue light can pass through the blue color filtering device and received by the blue photosensor. An even smaller portion of the red light can pass through the red color filtering device to be received by the red photosensor. However, both of the blue light and the red light can not transmit through the green color filtering device, so that the green photosensor can not detect any signal. Being analyzed by the electronic system, the object is in purple color instead of being white.
Therefore, when the color distribution of an object to be observed is non-uniform, the arrangement of photosensors greatly affects the analysis of the electronic system. The above problems happen to the color inspection of textile, fabric, ceramic tiles with uneven surface or metal.
To resolve the above problems, methods have been proposed such as:
(a) Using a diffuser:
Referring to
FIG. 6
, a diffuser is used between the entrance pupil
30
and the photodetective plane
40
to mitigate the effect caused by non-uniform color distribution. The diffuser, though improves the uniformity, reduces the efficiency of light due to the diffusion.
(b) Using a photoconductive optic fiber:
Referring to
FIG. 7
, photoconductive optic fiber is disposed on the photodetective plane
40
. The light focused onto the photodetective plane
40
is coupled into the photoconductive optic fiber to be conducted into various color filtering device
80
to the corresponding sensors
50
. Again, this method greatly enhances the uniformity but reduces the efficiency of light.
(c) Using an integrating sphere:
Referring to
FIG. 8
, an integrator sphere is installed on the photodetective plane
40
. The light converged at the photodetective plane
40
is conducted into the integrator sphere
110
, and passes through the color filtering device
80
to reach the photosensors
50
. This method uses scattering of light to improve the uniformity. Though the improvement of uniformity is the best among these methods, the efficiency is poor, and the cost is high, the volume is large.
SUMMARY OF THE INVENTION
The invention provides an image-splitting color meter. An image splitting device is disposed at an entrance pupil to improve the uniformity of light with a high efficiency.
The image-splitting color meter provided by the invention comprises a light converging device, an image-splitting device, multiple color filtering devices and a photosensor including multiple color sense devices. The light converging device is used to restrict an incoming light beam from an observing object. The image-splitting device is disposed at an entrance pupil to split the incoming light beam into multiple split light beams. The color filtering devices are used to receive the split light beams, so as to convert these split light beams into corresponding color light beams. The color sensors receive the corresponding color light beams and transform these color light beams into electrical signals.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 61
Evans F L
J. C. Patents
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