United States Patent 19
`Beretta
`
`(54)
`
`CORRELATED COLOR TEMPERATURE
`DETECTOR
`
`(T5)
`
`(73)
`
`(21)
`22)
`(51)
`52)
`
`58)
`
`Inventor: Giordano B. Beretta, Palo Alto, Calif.
`Assignee: Canon Information & Systems, Inc.,
`Costa Mesa, Calif.
`
`Appl. No.: 981,396
`Filed:
`Nov. 25, 1992
`Int. Cl. ......................... G01 3/46; H05B 37/02
`U.S. Cl. .......................... 356/402; 356/407; 356/419;
`315/151
`Field of Search ..................................... 356/402,407,
`356/414, 416, 418, 4.19; 355/38; 315/151,
`293, 149; 358/504
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,315,029 4/1967 Suhrmann ................................ 178/5.4
`4,335,943
`6/1982 Numata ..........
`... 354f60 R
`4,726,676 2/1988 Maslaney et al.
`... 356,731
`4,764,670 8/1988 Pace et al. ......
`... 250/226
`4,773,761
`9/1988 Sugiyama et al.
`356,405
`4,876,166 10/1989 Wake et al. .........
`... 430/7
`4,894,683
`1/1990 McGuire et al. ...
`... 355/71
`4,922,089 5/1990 McGuire et al. ...
`250/205
`4,979,803 12/1990 McGuckin et al. .
`... 350/37
`5,004,349 4/1991 Sato et al............
`356,402
`5,008,739 4/1991 D'Luna et al. .
`... 358/21
`5,021,875 6/1991 Iida et al.........
`... 358/29
`5,037,201
`8/1991 Smith, III et al.
`... 356/326
`5,048,955 9/1991 Bernhard ............
`356/213
`5,053,299 10/1991 Hanrahan et al. .......................... 430/7
`5,087,808 2/1992 Reed ..............
`250/24 R
`5,087,937 2/1992 Fricket al. ................................. 355/1
`5,099,313 3/1992 Suemoto et al.
`... 358/29
`5,137,364 8/1992 McCarthy ......
`356/402
`5,172,146 12/1992 Wooldridge
`... 354/21
`5,241,374 8/1993 Yang et al. ............................... 358/29
`
`
`
`III IIII
`USOO5521708A
`11) Patent Number:
`5,521,708
`45 Date of Patent:
`May 28, 1996
`
`FOREIGN PATENT DOCUMENTS
`0444689 9/1991 European Pat. Off..
`454479 10/1991 European Pat. Off..
`0491131
`6/1992 European Pat. Off..
`3642922 6/1987 Germany.
`3622043 1/1988 Germany.
`60-244178 12/1985 Japan.
`62-22036
`1/1987 Japan.
`OTHER PUBLICATIONS
`"Color Equalization', by J. Schwartz, Journal Of Imaging
`Science And Technology, vol. 36, No. 4, Jul/Aug. 1992, pp.
`328-334.
`Color Measurement Theme And Variations, by D. L. Mac
`Adam, pp. 94-101.
`Primary Examiner-Vincent P. McGraw
`Assistant Examiner-K. P. Hantis
`Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper &
`Scinto
`ABSTRACT
`57
`A correlated color temperature measuring device for mea
`suring the color temperature of light includes a sensor which
`individually senses plural light components of light incident
`thereon and for providing plural corresponding digital color
`component signals representative thereof, a memory which
`stores correction data for correcting the plural digital color
`temperature component signals, and a processor which
`receives the plural digital color component signals from the
`sensor. The processor accesses the correction data in the
`memory, corrects the plural color component signals from
`the sensor based on the correction data and derives a digital
`signal representative of the color temperature of the incident
`light. The derived digital signal may be displayed on a
`digital display or may be outputted on a digital I/O interface
`in response to a request for digital color temperature infor
`mation.
`
`59 Claims, 14 Drawing Sheets
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 1 of 14
`
`5,521,708
`
`0.9
`
`0.8
`
`O.7
`
`0.6
`
`O.5
`
`
`
`0.4
`
`0.3
`
`O.2
`
`O.
`
`2856 2360 1900
`3500
`
`600
`
`O.
`
`0.2
`
`O.3
`
`0.4
`
`0.5
`
`0.6
`
`0.7
`
`0.8
`
`FIG.1
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`US. Patent
`
`May 28, 1996
`May 28, 1996
`
`Sheet 2 of 14
`Sheet 2 of 14
`
`5,521,708
`5,521,708
`
`
`
`1.9.
`
` .
`
`FIG.2
`
`HTC, Exhibit 1021
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 3 of 14
`
`5,521,708
`
`| | | | | |
`
`
`
`TENNWHO
`
`62
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`US. Patent
`
`May 28, 1996
`May 28, 1996
`
`Sheet 4 of 14
`Sheet 4 of 14
`
`5,521,708
`5,521,708
`
`
`
`FIG.3A
`
`HTC, Exhibit, 1021
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 5 of 14
`
`5,521,708
`
`
`
`FIG.4
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 6 of 14
`
`5,521,708
`
`2
`
`AVD
`
`AVD
`
`
`
`2 32 2
`
`31
`
`MEMORY
`
`30
`
`-
`
`
`
`FIG.5
`
`40
`
`42
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`KS 45 Š 40
`
`
`
`
`
`
`
`
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 7 of 14
`
`5,521,708
`
`NITATE LINE MONITOR LOOP
`
`S701
`
`S703
`
`RE-NITATE
`LNE
`
`S702
`
`
`
`NEW START
`CHARACTER ON
`LINE
`
`
`
`S704
`READ RECIPIENT ADDRESS
`
`
`
`
`
`S705
`
`
`
`COLOR
`SENSOR
`ADDRESSED
`
`S706
`
`YE S
`
`STORE SENDER ADDRESS
`
`S707
`
`EXTRACT COMMAND
`
`S708
`
`
`
`
`
`TEMPERATURE
`QUERY
`
`YES
`
`SEND COLOR
`TEMPERATURE
`
`S709
`
`NO
`
`FIG.7(a)
`
`F1G.7(b)
`
`F. G.7
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 8 of 14
`
`5,521,708
`
`GE)
`
`S71 O
`DSTANCE
`QUERY
`
`
`
`NO
`
`S712
`
`FIG.7(b)
`
`S711
`
`YES
`
`SEND DISTANCE FROM CE
`DAYLIGHT LOCUS
`
`()
`
`S713
`
`UMINANCE
`
`QUERY
`
`YES
`
`SENDUMINANCE
`
`()
`
`
`
`
`
`
`
`
`
`
`
`
`
`NO
`
`S714
`
`S715
`
`TRISTIMULUS
`QUERY
`
`YES
`
`SEND CORRECTED COLOR
`COMPONENTS
`
`NO
`
`S76
`
`S717
`
`CALEBRATE
`MODE
`
`YES
`
`LUMINATE
`LED
`
`S718
`
`SEND
`UNCORRECTED
`COLOR
`COMPONENTS
`
`NO
`
`S79
`
`NEW
`CABRATION
`TALE
`
`NO
`
`S721
`
`S720
`
`YES
`
`STORE NEW CALIBRATION
`TABLE
`
`S722
`
`NEW
`DEVICE ADDRESS
`
`
`
`YES
`
`STORE NEWADDRESS
`
`
`
`NO
`
`S723
`
`SEND ERROR MESSAGE
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 9 of 14
`
`5,521,708
`
`
`
`51
`
`COLOR
`MONITOR
`
`53
`
`COLOR
`PRINTER
`
`HOST CPU
`
`
`
`52
`
`FIG.8
`
`ADJUST
`MONITOR
`WHITE POINT
`
`
`
`S901
`
`READ VEWING LIGHT COLOR
`TEMPERATURE
`
`
`
`S902
`
`S
`MONITOR WHITE
`POINT ECUAL TO VIEWING
`LIGHT COLOR
`TEMPERATURE
`
`
`
`
`
`
`
`
`
`
`
`
`
`S904
`
`PRINT
`COMMAND
`
`ECRUALIZE PRINTED COLORS BASED ON
`VIEWENG LIGHT COLOR TEMPERATURE
`
`FIG.9
`
`
`
`
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`US. Patent
`
`May 28, 1996
`May 28, 1996 '
`
`Sheet 10 of 14
`Sheet 10 of 14
`
`5,521,708
`5,521,708
`
`HTC, Exhibit 1021
`
`50
`
`to
`DO
`
`CD O
`gr,
`O :
`2
`E9
`!
`-
`z“-
`
`0
`
`
`
` E
`
`3.
`
`O
`.-
`
`E
`g
`0
`O
`
`
`
`EOO
`
`D:
`UJ
`I-
`an
`I)
`O
`D.
`Ol
`O
`O
`
`PRINTER
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 11 of 14
`
`5,521,708
`
`6
`
`FLOURESCENT
`SOURCE
`
`64
`
`NTENSTY
`CONTROL
`
`60
`
`NCANDESCENT
`SOURCE
`
`62
`
`NTENSITY
`CONTROL
`
`sy % 59
`57 O
`56 ?
`VIEWING
`LIGHT
`TEMPERATURE
`
`51
`
`COLOR
`MONITOR
`
`2 OCss
`5|\
`
`MONITOR
`TEMPERATURE
`
`50
`
`53
`
`HOST CPU
`
`COLOR
`PRINTER
`
`KEYBOARD
`
`52
`
`FIG.11
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 12 of 14
`
`5,521,708
`
`S12O1
`
`S12O2
`
`READ VIEWING LIGHTTEMPERATURE
`
`COMPARE VIEWING LIGHT TEMPERATURE TO
`DESERED COLOR TEMPERATURE
`
`S1203
`
`WITHIN
`TOLEANCE
`
`YES
`
`END
`
`NO
`
`S1204
`
`
`
`
`
`
`
`EWING
`TEMPERATURE
`LOW
`
`YES
`
`S12O7
`
`NO
`
`Si2O5
`
`NCREASE INCANDESCENT
`INTENSTY
`
`DECREASE
`INCANDESCENT ENTENSITY
`
`S208
`
`Si2O6
`
`DECREASE FLUORESCENT
`INTENSTY
`
`NCREASE FLUORESCENT
`NTENSITY
`
`F.G. 12
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 13 of 14
`
`5,521,708
`
`READ VIEWING LIGHT
`TEMPERATURE
`
`S1301
`
`S1302
`
`DETERMINE MONITOR WHITE
`POINT
`
`S1303
`
`
`
`WITHEN
`
`TOLEANCE
`
`YES
`
`END
`
`NO
`
`
`
`S1304
`MONITOR
`WHITE POINT
`L9W
`
`
`
`
`
`
`
`
`
`S1305
`
`YES
`
`INCREASE MONITOR
`WHITE POINT
`
`NO
`
`S1306
`
`()
`
`DECREASE MONTOR
`WHITE POINT
`
`F.G. 13
`
`HTC, Exhibit 1021
`
`

`

`U.S. Patent
`
`May 28, 1996
`
`Sheet 14 of 14
`
`5,521,708
`
`S1401
`
`()
`
`READ VIEWING LIGHTTEMPERATURE
`
`S1402
`
`READ MONITOR WHITE POINT
`
`S1403
`
`
`
`WITHIN
`TOLERANCE
`
`YES C END
`
`NO
`
`S1404
`
`
`
`MONTOR
`WHITE PgiNT LOW
`
`YES
`
`
`
`S4O7
`
`NO
`
`DECREASE INCANDESCENT
`INTENSITY
`
`S1408
`
`NCREASE FLUORESCENT
`INTENSITY
`
`S1405
`
`ENCREASE INCANDESCENT
`NTENSITY
`
`S1406
`
`DECREASE FLUORESCENT
`INTENSTY
`
`F.G. 14
`
`HTC, Exhibit 1021
`
`

`

`1.
`CORRELATED COLOR TEMPERATURE
`DETECTOR
`
`5,521,708
`
`2
`Heretofore, however, it has not been possible to measure
`the white color temperature of viewing light simply and
`effectively. Instead, white color temperatures have been
`estimated, or complicated measuring devices have been used
`to measure red, green and blue tristimulus values of the
`viewing light in order to find the corresponding white color
`temperature. Such measuring devices, however, are not
`ordinarily designed to serve the single use of measuring the
`white color temperature. To the contrary, such devices are
`designed to serve many different purposes besides white
`color temperature calculation. Consequently, such conven
`tional devices are large, expensive, and complicated, and
`typically require trained technical personnel for operation.
`SUMMARY OF THE INVENTION
`It is an object of the present invention to address the
`foregoing difficulties.
`The invention provides a digital color temperature sensor
`which provides a digital signal of white color temperature in
`response to a digital request to provide the white color
`temperature. The color temperature sensor device includes
`calibratable color sensors, and is most preferably fabricated
`on a single substrate or on a single VLSI chip.
`According to this aspect of the invention, a color tem
`perature measuring device for measuring the color tempera
`ture of light comprises a substrate, a sensor fixed to the
`substrate for individually sensing the plural color compo
`nents of light incident on the sensor and for providing plural
`corresponding digital color component signal representative
`of the color components, a memory fixed to the substrate for
`storing correction data for correcting the digital color com
`ponent signals from the sensor, and a processor also fixed to
`the substrate and including a digital interface. The processor
`receives the plural digital color component signals from the
`sensor, accesses the correction data in the memory to correct
`the plural digital signals in accordance with that correction
`data, derives a white color temperature from the corrected
`color component signals, and in response to a request to
`provide a white color temperature, outputs the white color
`temperature on the digital interface. The digital interface
`may be provided by an input/output (I/O) interface which
`may also receive the request. The interface may be addres
`sable, thereby allowing the device to be connected to a serial
`line and monitor the serial line for requests that are specifi
`cally addressed to it. An alarm may also be provided to
`indicate that the sensed digital color component signals
`pertain to a light source whose chromaticity is outside the
`range of the white line.
`In addition to the foregoing sensing mode, the device may
`also be operable in a calibration mode, and in this case may
`be provided with an internal light source such as an LED by
`which new correction data for the sensors may be derived.
`In response to a command for entering the calibration mode,
`the device sequences the light source through a series of
`different light levels, and rather than providing white color
`temperature on the digital interface, the device provides the
`plural digital color component signals. Based on those
`signals, new correction data is derived, and the correction
`data is written, via the interface, back to the memory.
`This brief summary of the invention is provided so that
`the nature of the invention may be understood quickly. A
`fuller understanding may be obtained by reference to the
`following detailed description of the invention in connection
`with the appended drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a chromaticity diagram showing the Planckian
`locus (or hereinafter "white line') in CIE space.
`
`10
`
`15
`
`20
`
`35
`
`25
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to correlated color tempera
`ture detection of ambient or projected light, and, in particu
`lar, to a digital color temperature detector fabricated on an
`integrated chip.
`2. Description of the Related Art
`In color reproduction fields such as commercial printing
`and photography, it is known that the correlated color
`temperature of the viewing light affects the way in which an
`observer perceives a color image. More particularly, an
`observer will perceive the same color image differently
`when viewed under lights having different correlated color
`temperatures. For example, a color image which looks
`normal when viewed in early morning daylight will look
`bluish and washed out when viewed under overcast midday
`skies.
`Correlated color temperature is characterized in color
`reproduction fields according to the temperature in degrees
`Kelvin (K.) of a black body radiator which radiates the
`same color light as the light in question. FIG. 1 is a
`chromaticity diagram in which Planckian locus (or herein
`after "white line") 1 gives the temperatures of whites from
`30
`about 1500 K. to about 10,000 K. The white color tem
`perature of viewing light depends on the color content of the
`viewing light as shown by line 1. Thus, the aforementioned
`early morning daylight has a white color temperature of
`about 3,000 K. (hereinafter "D30”) while overcast midday
`skies has a white color temperature of about 10,000 K.
`(hereinafter "D100"). A color image viewed at D60 will
`have a relatively reddish tone, whereas the same color image
`viewed at D100 will have a relatively bluish tone.
`Because of these perceptual differences, conventional
`color reproduction practice accepts 5,000 K. (hereinafter
`"D50") as a standard white color temperature. In accordance
`with this convention, commercial color reproduction facili
`ties ordinarily evaluate color images for color fidelity in a
`room whose light is controlled to a white color temperature
`of D50.
`Recently, however, low-cost high-quality color reproduc
`tion equipment has become available to individual users.
`Such users are not ordinarily in a position to provide a room
`having ambient light controlled to D50. And, even if such
`rooms are available, the color image is not ordinarily dis
`played in a room whose ambient light is D50. Rather, such
`color images are more likely to be displayed in rooms not
`having a white color temperature of D50 and may, for
`example, be used in an office building as part of a business
`presentation where the viewing light is far different from
`D50.
`Since the white color temperature affects the perception of
`color, it has been proposed to modify the colors in a color
`image based on a measurement of white color temperature
`of the viewing light. For example, "Color Equalization" by
`J. Schwartz, Journal Of Image Science And Technology, Vol.
`36, No. 4, July/August, 1992, suggests to equalize a color
`image based on the white color temperature of viewing light
`by adjusting the amount of individual inks used during a
`printing process based on the color temperature of the
`viewing light.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`HTC, Exhibit 1021
`
`

`

`5,521,708
`
`3
`FIG. 2 is a perspective view of a color sensing device
`according to the present invention.
`FIG. 3 is a functional block diagram of a color sensing
`device according to the invention.
`FIG. 3A is a calibration device for calibrating the color
`sensing device.
`FIG. 4 is a CIE chromaticity diagram showing isotem
`perature lines which give correlated color temperatures for
`illumanants which do not fall directly on the white line of
`FIG. 1.
`FIG. 5 is an elevational view of the physical arrangement
`of the components shown in the FIG. 3 block diagram, and
`FIG. 6 is a cross-sectional view along the line 6-6 in FIG.
`S
`FIG. 7, comprised by FIGS. 7(a) and 7(b), is a flow
`diagram showing process steps by which the FIG.3 embodi
`ment interacts with requests on a serial line.
`FIG. 8 is a block diagram showing an arrangement by
`which the colors in a color monitor and a color printer may
`be adjusted in accordance with the color temperature of
`viewing light, and FIG. 9 is a flow diagram showing the
`process steps for such an adjustment.
`FIG. 10 is a block diagram view showing the arrangement
`of plural color temperature sensors in different physical
`locations.
`FIG. 11 is a block diagram view showing an arrangement
`by which viewing light temperature and another color tem
`perature may be matched to each other, and FIGS. 12
`through 14 are flow diagrams showing methods for match
`ing the viewing light temperature, in which FIG. 12 is a flow
`diagram for adjusting the viewing light temperature to match
`a desired color temperature such as D65, FIG. 13 is a flow
`diagram by which a monitor temperature is adjusted to the
`viewing light temperature, and FIG. 14 is a flow diagram by
`which viewing light temperature is matched to that of a
`monitor.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`4
`FIG. 3 is a block diagram showing the functional con
`struction of a correlated color temperature sensor according
`to the invention. The correlated color temperature sensor
`includes three photosensors 21, 22 and 23, each for sensing
`a separate color component of ambient light 24 and for
`providing an analog signal representative thereof. In the
`present case, sensor 21 senses the red color component and
`provides an analog signal therefor, sensor 22 senses the
`green color component of light 24 and provides an analog
`signal therefor, and sensor 23 senses the blue color compo
`nent of light 24 and provides an analog signal therefor. In
`addition, there may be an optional sensor 21a for measuring
`the blue contribution R1 to the red signal R. In this fashion,
`detection accuracy would improve. Each of the analog
`signals is converted by respective analog to digital (AWD)
`converters 25, 26 and 27 and the converted digital signals
`are led to multiplexer 29.
`In response to channel information from microprocessor
`30, multiplexer 29 provides a selective one of the digital
`signals from A/D converter 25, 26 or 27 via a data line to the
`microprocessor 30. Microprocessor 30 may be implemented
`as a logical gate array, but more preferably it is a program
`mable microprocessor such as NEC V53. For each digital
`color component signal, microprocessor 30 accesses
`memory 31 for correction data to correct the digital signal
`for non-linearities, inconsistencies and other errors in sen
`sors 21, 22 and 23. Specifically, memory 31 includes areas
`31a, 31b and 31c for storing correction data for the red
`channel, the green channel and the blue channel. The cor
`rection data may be in the form of a simple bias and gain
`adjustment, but preferably the correction data is in the form
`of a look-up table by which the digital data from one of the
`A/D converters is used to look-up a corrected value for that
`data.
`It is also possible to provide measuring head 11 with a
`temperature sensor which is sampled by multiplexor 29 and
`an associated A/D converter to provide microprocessor 30
`with the temperature of the sensors 21, 22 and 23 in the
`sensor head. In this case, the correction data also includes
`corrections based on temperature so as to allow micropro
`cessor 30 to calculate temperature-compensated R, G, and B
`light quantities.
`After correcting each of the R, G and B components for
`ambient light 24, microprocessor 30 refers to a correlated
`color temperature table 31d stored in memory 31.
`Correlated color temperature table 31d provides a corre
`lated color temperature based on the corrected R, G and B
`digital signals. Correlated color temperature refers to a
`situation in which the color content of ambient light 24 is not
`exactly equal to any of the white colors indicated on line 1
`of FIG. 1. The correlated color temperature is defined as the
`temperature of the black body radiator whose perceived
`color most closely resembles that of the given black body
`radiator at the same brightness and under the same viewing
`conditions.
`FIG. 4 shows isotemperature lines in CIE 1931 (x, y)
`space. Line 1 is the same white line shown in FIG. 1. The
`additional lines which are approximately perpendicular to
`line 1 are isotemperature lines. The values stored in the
`correlated color temperature table 31d are such that colors
`falling on one of the isotemperature lines are followed back
`along that line until it meets white line 1. The correlated
`color temperature is considered to be the temperature at
`which white line 1 is met. Thus, for example, ambient light
`whose color is such that its RGB values place it at the point
`indicated by reference numeral 2, then the correlated color
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODMENT
`FIG. 2 is a perspective view of a correlated color tem
`perature sensing device 10 according to the invention. The
`color sensing device includes a measuring head 11 com
`45
`prised of an integrating sphere or a diffusing hemisphere by
`which ambient light such as light by which color images are
`viewed is collected and presented uniformly to a light
`sensor. In the case where the light sensing elements are
`integrated in a single substrate as described below., measur
`ing head 11 contains that substrate. Measuring head 11 is
`mounted on base 12 which provides support for optional
`display 14 and alarm indicator 15. Display 14 displays a
`correlated color temperature of the light striking measuring
`head 11; in FIG. 2 the numerals "65' are displayed indicat
`ing a correlated color temperature of 6,500 K. or "D65";
`and alarm indicator 15 visually warns when the light inci
`dent on measuring head 11 is so highly hued that it cannot
`be considered to be a white light and correspondingly does
`not have a correlated color temperature. The operation of
`indicator 15 is described in more detail below in connection
`with FIG. 4.
`Serial cable 17 provides a digital I/O interface by which
`the sensor receives requests and/or commands for operation
`and by which the sensor provides a digital output of corre
`lated color temperature. A suitable serial convention such as
`RS-232 may be used.
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`50
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`55
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`60
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`65
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`HTC, Exhibit 1021
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`

`

`5,521,708
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`temperature of the ambient light is 6,500 K. or D65. In this
`situation, even though the ambient light departs from a pure
`white color, its departure is not so great as to consider it
`non-white, even though points above the white line 2 appear
`slightly greenish while points below the white line 1 appear
`slightly pinkish.
`On the other hand, light whose color components place it
`approximately outside the areas indicated by dashed lines 3
`are so hued that they can no longer be considered white. For
`light whose colors are outside the dashed region 3, such as
`light indicated by point 4, microprocessor 30 uses correlated
`color temperature table 31d to generate a non-white indica
`tor which is used to illuminate out of range indicator 15.
`The correlated color temperature derived from correlated
`color temperature table 31d is utilized to generate a signal to
`illuminate indicator 14. Thus, in the case of light whose
`color places it at point 2, a signal "65” is generated corre
`sponding to the 6,500 K. color temperature of that light.
`Reverting to FIG. 3, microprocessor 30 is preferably
`provided with a serial interface by which it may provide a
`digital signal representative of the correlated color tempera
`ture not only to indicator 14 but also onto a serial line for
`communication to other digital equipment such as a personal
`computer. Interface 32 shown in FIG.3 may be constructed
`of a conventional universal asynchronous receiver/transmit
`ter (“UART") by which serial requests received on serial line
`17 may be processed and, if appropriate, a digital signal
`representative of the correlated color temperature may be
`provided.
`In addition to the color sensing mode described above,
`microprocessor 30 may also be programmed to provide a
`calibration mode. In such a calibration mode, microproces
`sor 30 does not output correlated color temperatures, but
`rather outputs uncorrected digital R, G and B signals. More
`particularly, in response to a command to enter a calibrate
`mode, which is illustrated schematically as a command from
`the serial line but which may also be a command formed
`from a simple push-button switch operation, microprocessor
`30 enters a calibration mode by which uncorrected R, G and
`B values are output. The output values are compared with
`expected RGB output values. Thus, for example, those
`values are compared with calibrated values which are
`expected by exposing the sensor to calibrated light. The
`expected values for each of the R, G and B components,
`45
`together with the actual, uncorrected values for each of the
`R, G and B components are assembled into the R, G and B
`correction tables 31a, 31b and 31c. The new correction data
`are provided to microprocessor 30, for example, over the
`serial interface, where they are stored in memory 31.
`In connection with the calibrate mode, the sensor may be
`provided with a self contained light emitting device such as
`LED 34. In response to a command to enter the calibration
`mode, microprocessor 30 controls LED 34 to illuminate at
`various pre-designated intensity levels. Since LEDs have
`stable color temperature values over their lifetimes, the
`uncorrected R, G and B output values may be compared
`readily to those that are expected from the pre-designated
`levels to which the LED is illuminated, thereby forming
`correction data for tables 31a, 31b and 31c.
`While LED 34 is illustrated as a single, whitish-output,
`LED, it is also possible to provide separate LEDs, such as a
`red, green and blue LED, whose combined light provides a
`whitish light. In this case, the LEDs should be arranged so
`as to project light into measuring head 11 so as to allow the
`light to mix before illuminating the color sensors, thereby to
`minimize color crosstalk.
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`6
`It is also possible to provide calibration LEDs in a
`separate calibration device. For example, FIG. 3A illustrates
`a perspective view with a cut-out section of the calibration
`device which could be used to calibrate the color tempera
`ture sensing device of the present invention. Calibration
`device 70 consists of hollow cylinder 71 having opening 72
`at one end. Opening 72 is large enough to allow the color
`temperature sensing device to enter in the direction of Arrow
`A.
`Cylinder 71 has approximately the same diameter opening
`72 as the measuring head 11 of the color temperature sensing
`device so that cylinder 71 fits snugly over measuring head 11
`in order to prevent stray light from entering the tube. To this
`end, the walls of bottom portion 73 of cylinder 71 are
`painted black so as to form a light adsorbing surface. The
`remaining interior 74 is coated with a white lining consisting
`of any substance normally used for perfect white diffusers,
`such as polished opal glass, ceramics, and fluorinated poly
`mer. At the opposing end of opening 72 of cylinder 71, there
`is disposed three light emitting diodes (LEDs) 75, 76 and 77.
`Each LED is mounted for good heat dissipation on the top
`portion of cylinder 71.
`LEDs 75, 76 and 77 are each of a different color and
`preferably, red, green and blue. In this manner, when LEDs
`75, 76 and 77 emitlight simultaneously, the combined colors
`mix to white. Any number of LEDs may be used in any
`proportion to obtain a predetermined correlated color tem
`perature. For example, blue LEDs often emit less light than
`red LEDs so that in order to obtain white, blue LEDs should
`be present in a larger proportion. Moreover, the individual
`LEDs may be illuminated independently in order to obtain
`the same effect.
`Power is supplied to calibration device 70 through cable
`78 from plug 79. Plug 79 is a feed through RS-232C
`connector and a Data Terminal Ready Line may be used to
`branch off the required energy to calibrating device 70.
`An optional LED 80 may be mounted to the extension of
`cylinder 11 to indicate to an operation that calibration device
`11 is operational.
`The calibration device is illustrated in FIG. 3A as a
`cylinder, but other configurations are possible, such as an
`integrating sphere having an entrance aperture for receiving
`light from the LEDs and an exit aperture for emitted mixed
`LED illumination light. An internal baffle may be provided
`to ensure light from the LEDs is shielded from direct
`emission through the exit aperture.
`To use, the calibration device 70 is placed over color
`temperature sensor 10 which is operated in the calibration
`mode. The calibration device 70 exposes the color sensors to
`whitish light and the microprocessor 30 returns uncorrected
`RGB values as described above. The uncorrected RGB
`values are compared with expected RGB values and cali
`bration tables are derived therefrom.
`FIG. 5 is an elevational view of the structure of the sensor
`shown in the FIG. 3 block diagram.
`As shown in FIG. 5, the color temperature sensor is
`fabricated on a substrate 40, which is shown as a dotted line
`in FIG. 3, in which are integrated or fixed the color com
`ponent sensors 21, 22 and 23, the A/D converters 25, 26 and
`27, microprocessor 30, memory 31, and interface 32. The
`device shown in FIG. 5 is also provided with an additional
`color sensor 21a and corresponding A/D converter 25a
`which is designed to sense the blue contribution of the red
`signal and which may provide more accurate tristimulus R,
`G and B values. Substrate 40 may be a non-conductive
`substrate to which the individual components shown in FIG.
`
`HTC, Exhibit 1021
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`

`

`7
`5 are mounted, but more preferably substrate 40 is a VLSI
`chip on which the components shown in FIG. 5 are fabri
`cated in accordance with known VLSI techniques. Not
`shown in FIG. 5 are connectors for interconnecting between
`the individual elements on substrate 40 and for providing
`external access to the color temperature sensor.
`Sensors 21, 22 and 23 (and, if provided, sensor 21a) are
`not pre-sensitized to a particular color matching function.
`Rather, those sensors are conventional photosensitive
`devices which are covered by a filter or other device for
`separating ambient light into red, green and blue tristimulus
`values. Thus, as shown in FIG. 6 which is a cross-section
`taken along line 6-6 of FIG. 5, red sensor 21 and green
`sensor 22 are each comprised by a conventional photosens
`ing element 41 covered by a filter 42 of appropriate color.
`Superimposed on each color filter 42 is a lenslet 44 which
`collect ambient light and inhibit light scattering in the
`assembly. In this regard, further improvements in sensitivity
`are obtained if areas away from the photosensing elements
`are shielded by an opaque layer of material such as the layer
`indicated illustratively at 45.
`In operation, power from an unshown source is provided
`to the color temperature sensing device, and the correlated
`color temperature sensing device is placed in position to
`collect ambient light such as viewing light for viewing a
`color printout. A user reads the correlated color temperature
`of the viewing light from indicator 14 and verifies that
`indicator 15 is not illuminated which would indicate that the
`viewing light is too hued to be considered white. The user
`utilizes the correlated color temperature to ensure that color
`images are viewed under the proper conditions. Thus, in one
`situation, a user may change the color temperature of the
`viewing light, for example, by opening shades to outside
`windows so as to increase the color temperature or by
`illuminating incandescent bulbs so as to decrease the color
`temperature. Alternatively, a user may adjust the white point
`of a color monitor, which is the temperature of the color
`produced by a color monitor when its red, green and blue
`guns are generating their maximum signals so that it
`matches the color temperature of the illuminating ambient
`light. As yet another example, a user may enter the color
`temperature into color printing software which operates on
`the color temperature so as to equalize the colors printed by
`a color printer to the viewing conditions.
`In the case where the color temperature sensor 10 is
`provided with a serial interface which allows access to other
`digital equipment, that digital equipment may use the color
`sensor in accordance with the flow diagram illustrated in
`FIG. 7.
`In step S701, microprocessor 30 initiates its line monitor
`loop. The line monitor loop monitors the status of serial line
`17 until a new start character is detected on the serial line.
`Until a new start character is detected on the serial line in
`step S702, microprocessor 30 simply reinitiates its line
`monitoring operations (step S703) and remains in the line
`monitor loop until a new start charact