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`(12) United States Patent
`US 6,522,432 B1
`(10) Patent N0.:
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`Lin
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`Feb. 18, 2003
`(45) Date of Patent:
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`USOO6522432B1
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`IMAGE SCANNER WITH AUTOMATIC
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`SIGNAL COMPENSATION
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`Inventor: Chien-Chih Lin, Hsien
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`Assignee: Primax Electronics Ltd., Taipei
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`Notice:
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`Subject to any disclaimer, the term of this
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`patent is extended or adjusted under 35
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`U.S.C. 154(b) by 1049 days.
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`Appl. N0.: 08/633,389
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`Filed:
`Apr. 16, 1996
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`Int. Cl.7 ................................................ .. H04N 1/04
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`U.S. Cl.
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`Field of Search ............................... .. 358/296, 461,
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`358/463, 465, 475, 509, 512, 516, 484;
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`348/234, 500, 708
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`References Cited
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`US. PATENT DOCUMENTS
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`........... .. 358/475
`9/1992 Ito et a1.
`5,151,796 A *
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`5,212,376 A *
`. . . . .. 358/484
`5/1993 Liang . . . . .
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`9/1993 Takase ..................... .. 358/475
`5,249,068 A *
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`358/475
`1/1994 Webb et a1.
`5,278,674 A *
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`. 358/475
`3/1994 Suzuki et a1.
`5,296,944 A *
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`5,587,746 A * 12/1996 Nakakuki
`................. .. 348/708
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`* cited by examiner
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`Primary Examiner—Mark Wallerson
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`(74) Attorney, Agent, or Firm—Winston H51]
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`(57)
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`ABSTRACT
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`9 Claims, 3 Drawing Sheets
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`CALCULATE BRIGHTNESS Y1 FOR EACH (R.G.B.)
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`SIGNAL OF THE BRIGHTNESS SIGNAL
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`CALCULATE BRIGHTNESS AVERAGE Y2 OF THE
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`BR IGHTNESS SIGNAL
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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`S IGNAL=
`(R*Yc/Y2,
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`The present invention relates to an image scanner with
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`automatic signal compensation function for compensating
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`the instability of a light source of the image scanner. The
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`image scanner comprises a test region, a light source for
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`illuminating the document and the test region, optical means
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`for conveying the light reflected from the document and the
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`test region, a line image sensor for receiving the light from
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`the optical means and generating an image signal corre-
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`sponding to the light reflected from the document and a
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`brightness signal corresponding to the light reflected from
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`the test region, and a signal compensation circuit for ampli-
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`fying the image signal according to the brightness signal to
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`compensate the instability in the brightness of the light
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`source.
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`an‘Yc/YZ, B*Ye/Y2)
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`HUAWEI EX. 1008 - 1/7
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`OLYMPUS EX. 1008 - 1/7
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`

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`US. Patent
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`Feb. 18,2003
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`Sheet 1 of3
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`US 6,522,432 B1
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`%
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`! SIGNAL
`AMPLIFIER
`30
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`22
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`D MD
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`40
`““
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`l
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`DIGITAL
`PROCESSOR
`42
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`I
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`OLYMPUS EX. 1008 - 2/7
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`US. Patent
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`Feb. 18,2003
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`Sheet 2 of3
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`1.2
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`[:2
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`1111:3223
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`12
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`1.0
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`US 6,522,432 B1
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`38
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`OLYMPUS EX. 1008 - 3/7
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`US. Patent
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`Feb. 18, 2003
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`Sheet 3 013
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`US 6,522,432 B1
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`CALCULATE BRIGHTNESS Y1 FOR EACH (R.G.B.)
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`SIGNAL OF THE BRIGHTNESS SIGNAL
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`(R*Rc/R1, G*Gc/G1, B*Bc/Bl)
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`CALCULATE COLOR AVERAGE (RI. G1. BI) OF THE
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`BRIGHTNESS SIGNAL
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`CALCULATE BRIGHTNESS AVERAGE Y2 OF THE
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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`SIGNAL:
`(R*Yc/Y2. G#Yc/Y2, B$Yc/Y2)
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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`SIGNAL2
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`HUAWEI EX. 1008 - 4/7
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`OLYMPUS EX. 1008 - 4/7
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`

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`sensor 22 which is a CCD (charge couple device) for
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`brightness signals generated by the line image sensor are
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`formed by an array of (R,G,B) signals. The signal compen—
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`sation circuit comprises an A/D converter for digitizing the
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`(R,G,B) signals of the image signal and the brightness
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`signal, and a digital processor for adjusting the digitized
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`(R,G,B) signals of the image signal according to the digi-
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`tized (R,G,B) signals of the brightness signal. Each digitized
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`(R,G,B) signal of the image signal is multiplied by a color
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`compensation factor calculated which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to C011]-
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`pensate the brightness and the color of the image signal.
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`It is an advantage of the present invention that it provides
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`an image scanner which can measure the brightness of the
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`scanner’s light source by measuring the light reflected from
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`the test region instead of by using an optic fiber.
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`It is another advantage of the present invention that the
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`image scanner can measure color variations of the scanner’s
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`light source by measuring the light reflected from the test
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`region to compensate the digitized RGB signals of the image
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`signal.
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`These and other objects and the advantages of the present
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`invention will no doubt become obvious to those of ordinary
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`skill in the art after having read the following detailed
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`description of the preferred embodiment which is illustrated
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`in the various figures and drawings.
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`BRIEF DESCRll’l‘lON OF THE DRAWlN GS
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`FIG. 1 is a perspective View of a hand-held image
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`scanner’s optical components according to the present
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`invention.
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`FIG. 2 is a hardware block diagram of the signal com-
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`pensation circuit of the scanner according to the present
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`invention.
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`FIG. 3 shows the test region and a document viewed
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`through a transparent window of the scanner.
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`FIG. 4 shows a curve of the brightness of the scanner’s
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`light source after it is powered on.
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`FIGS. 5 to 7 shows the brightness and image signals
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`generated by the signal amplifier of the scanner.
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`FIGS. 8 to 10 shown each of the resulting reference
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`voltages Vrb generated by the brightness compensation
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`circuit of the scanner.
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`FIG. 11 is an alternative hardware block diagram of the
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`signal compensation circuit.
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`FIG. 12 shows a process for compensating the brightness
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`of the image signal.
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`FIG. 13 shows another process for compensating both the
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`brightness and the color of the image signal.
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`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENT
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`Please refer to FIGS. 1 and 2. FIG. 1 is a perspective View
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`of a hand-held image scanner’s optical components accord-
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`ing to the present invention and FIG. 2 is a hardware block
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`diagram of the signal compensation circuit 24 attached to the
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`CCD 22 shown in FIG. 1. The scanner 10 comprises a
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`transparent window 26 for scanning a document 16 lying
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`underneath, a rectangular glass 28 installed inside the win-
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`dow 26, a test region 12 installed on the glass 28 next to one
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`side of the window 26, a light source 14 above the window
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`26 for illuminating a document 16 under the window 26 and
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`the test region 12, an optical means which comprises a reflex
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`mirror 18 and a lens 20 for conveying the light reflected
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`from the document 16 and the test region 12, a line image
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`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
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`The present invention relates to an image scanner, and
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`signal compensation function for compensating the instabil-
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`ity of a light source of the image scanner.
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`2. Description of the Prior Art
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`Fluorescent lamp such as cold cathode fluorescent tube
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`(CCFT) is commonly used in color image scanner because
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`of its broad spectrum coverage. One problem with such lamp
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`is that
`its brightness will gradually change to a stable
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`condition when it is powered on. Such period usually takes
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`three to five minutes. In order to get a stable image output
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`by using such a lamp, a user usually has to wait until the
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`lamp is completely warmed up.
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`US. Pat. No. 5,212,376, which is assigned to the same
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`assignee of the present invention, discloses an image scan-
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`ner with an optic fiber connected to a line image sensor for
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`measuring the brightness of the image scanner’s light source
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`and a signal compensation circuit for adjusting the bright-
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`ness of the scanned image according to the measured
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`brightness of the light source. The optic fiber method is very
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`effective in measuring the brightness of the light source, but
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`it requires high precision parts and installation process
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`which is very expensive and time consuming. Besides, the
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`brightness of the light measured by the optic fiber is very
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`sensitive to the distance between the input end of the optic
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`fiber and the light source. Any shock or vibration over the
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`scanner may change this distance or move the input end of
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`the optic fiber which may have great consequence over the
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`output of the signal compensation circuit.
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`SUMMARY OF THE INVENTION
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`It is therefore a primary objective of the present invention
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`to provide an image scanner which can measure the bright-
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`ness of the scanner’s light source to compensate a scanned
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`image and avoid the above mentioned problem.
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`It is another objective of the present invention to provide
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`an image scanner which can measure color variations of the
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`scanner’s light source to compensate the scanned image
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`accordingly.
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`Briefly, in a preferred embodiment, the present invention
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`includes an image scanner for scanning a document C0111-
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`prising:
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`(1) a test region;
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`(2) a light source for illuminating the document and the
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`test region;
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`(3) optical means for conveying the light reflected from
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`the document and the test region;
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`(4) a line image sensor for receiving the light from the
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`optical means and generating an image signal corre-
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`sponding to the light reflected from the document and
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`a brightness signal corresponding to the light reflected
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`from the test region; and
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`(5) a signal compensation circuit for amplifying the image
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`signal according to the brightness signal to compensate
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`the instability in the brightness of the light source.
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`The line image sensor comprises an array of (red, green,
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`blue) (R,G,B) sensing elements for converting the light
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`received from the optical means into an array of correspond-
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`ing (R,G,B) signals wherein both the image signal and the
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`1
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`IMAGE SCANNER WITH AUTOMATIC
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`SIGNAL COMPENSATION
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`US 6,522,432 B1
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`HUAWEI EX. 1008 - 5/7
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`OLYMPUS EX. 1008 - 5/7
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`

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`US 6,522,432 B1
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`4
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`signal according to the digitized brightness signal to com-
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`pensate the instability in the brightness of the light source
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`14.
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`The line image sensor 22 comprises an array of red, green,
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`blue (R,G,B) sensing elements (not shown) for converting
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`the light received from the lens 20 into an array of corre-
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`sponding (R,G,B) signals wherein both the image signal and
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`the brightness signals generated by the line image sensor 22
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`are formed by an array of (R,G,B) signals. The A/D con—
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`verter 40 digitizes the (R,G,B) signals of the image signal
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`and the brightness signal according to the fixed reference
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`voltage Vrb, and then the digital processor 42 adjusts the
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`digitized (R,G,B) signals of the image signal according to
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`the digitized (R,G,B) signals of the brightness signal
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`compensate the instability in the color of the light source.
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`The brightness (Y) of a (R,G,B) signal can be represented
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`in the equation listed below:
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`Y=a ’“R+h"‘G+C "‘B
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`scanned from the test region 12;
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`3
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`receiving the light from the lens 20 and generating an image
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`signal corresponding to the light reflected from the docu-
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`ment 16 and a brightness signal corresponding to the light
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`reflected from the test region 12, and a signal compensation
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`circuit 24 for processing the brightness signal and amplify—
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`ing the image signal according to the brightness signal to
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`compensate the instability in the brightness of the light
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`source 14. The test region 12 is of white color for measuring
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`the brightness of the light source. The reflex mirror 18 is
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`used for reflecting the light from the document 16 and the
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`test region 12 and then the lens 20 will collimate the light
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`reflected from the reflex mirror 18 to the line image sensor
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`22.
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`The signal compensation circuit 24 comprises a signal
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`amplifier 30 for amplifying the image signal and brightness
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`signal from the line image sensor 22 to an appropriate
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`voltage level. an A/D (analog—to—digital) converter 32 for
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`digitizing the amplified image signal according to an adapt-
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`able reference voltage Vrb, a sampling circuit 34 for sam-
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`pling the brightness signal and generating a sample voltage
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`Vs, and a brightness compensation circuit 36 for adjusting
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`the reference voltage Vrb of the A/D converter 32 according
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`to the sample voltage Vs to compensate the instability in the
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`brightness of the light source 14.
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`FIGS. 3 to 10 show an example which teaches how the
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`test region 12 is used to compensate the instability in the
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`brightness of the light source 14. FIG. 3 shows the test
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`region 12 and a document 38 viewed through the transparent
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`window 26 which comprises three different sections: white
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`section 40, grey section 42 and black section 44. FIG. 4
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`shows a curve of the brightness (Y) of the light source 14
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`after it is powered on and three sampling points t1, t2 and 13.
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`It shows that
`the brightness of the light source 14 is
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`increasing at both point t1 and point t2, and it reaches a
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`stable level at point t3. FIGS. 5 to 7 shows the brightness and
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`image signals generated by the signal amplifier 30 at the
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`three sampling points t1, t2 and 13. FIG. 5 shows a brightness
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`signal 52 which is generated from the light reflected from the
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`test region 12 and an image signal 54 generated from the
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`light reflected from the document 38. The image signal 54
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`comprises three voltage levels 56, 58 and 60 which are
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`corresponding to the three sections of the document 38:
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`white section 40, grey section 42 and black section 44. The
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`voltage level Vrb shown in FIGS. 5 to 7 is equal to the
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`voltage level of the brightness signal 53 in FIG. 7 which is
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`obtained when the brightness of the light source 14 reaches
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`a stable condition.
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`The A/D converter 32 shown in FIG. 2 digitizes the image
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`signal 54 according to the reference voltage Vrb. If the Vrb
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`is fixed at a constant level just like the one shown in FIGS.
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`5 to 7, the image signals shown in these three figures will be
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`digitized into three different signal sets but in fact the only
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`difference between these three signal sets is the brightness
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`which is caused by the light source 14. In order to compen—
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`sate such difference, the brightness signal 52 is fed into the
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`brightness compensation circuit 36 to generate the reference
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`voltage Vrb so that the digitized image signals generated by
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`the A/D converter 32 at two different times will be the same
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`if the images scanned at these two different times are the
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`same. FIGS. 8 to 10 shown each of the resulting reference
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`voltages Vrb generated by the brightness compensation
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`circuit 36 at the three different points t1, t2 and t3,
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`FIG. 11 is an alternative block diagram of the signal
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`compensation circuit 110. It comprises an A/D (analog-to-
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`digital) converter 40 for digitizing the image signal and the
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`brightness signal according to a fixed reference voltage Vrb,
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`and a digital processor 42 for adjusting the digitized image
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`where the a, b, and c are three predetermined constants.
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`From this equation the brightness and color of the image
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`signal’s (R,G,B) signals can be compensated by using the
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`digital processor 42. FIG. 12 shows a process for compen-
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`sating the brightness of the image signal and FIG. 13 shows
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`another process for compensating both the color and bright-
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`ness of the image signal. In compensating the brightness or
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`color of the image signal, a brightness reference Yc and a
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`color reference (Rc,Gc,Bc) are used for adjusting each
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`(R,G,B) signal of the image signal. The brightness reference
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`Yc is approximately equal to the average brightness of the
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`test region 12 when the light source is in a stable condition
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`such as at the point t3 shown in FIG. 4, and the color
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`reference (Rc,Gc,Bc) is the color average of the test region
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`12 obtained at the same time point.
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`FIG. 12 shows a process 120 which compensates the
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`brightness of all the (R,G,B) signals of the image signal
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`according to the (R,G,B) signals of the brightness signal.
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`The process 120 comprises the following steps:
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`step 121 calculate a brightness Y1 for each (R,G,B) signal
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`of the brightness signal by using the equation:
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`Y1=a *R+b *G+c *3
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`step 122 obtain a brightness average Y2 from the bright-
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`ness Y1 of all the (R,G,B) signals of the brightness
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`signal;
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`step 123 modify the brightness of the image signal by
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`multiplying each (R,G,B) signal of the image signal by
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`a brightness compensation factor (Ye/Y2): (R*Yc/Y2,
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`G*Yc/Y2, B*YC/Y2).
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`The process 120 can compensate the variations over the
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`brightness of the light source 14 but can not compensate
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`color variations over the light source. When the light source
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`14 is initially powered on, it usually shows a light blue color
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`instead of a pure white color. Such color temperature change
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`will affect the (R,G,B) signals of the image signal scanned
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`from the document 16. By using the (R,G,B) signals of the
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`brightness signal scanned from the test region 12 to measure
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`the color of the light source, both the color and the bright—
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`ness of the image signal can be compensated. FIG. 13 shows
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`the process 130 which is used to compensate both the
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`brightness and the color of the image signal. Process 130
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`comprises the following steps:
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`step 131 calculate a color average (R1,G1,B1) from all the
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`(R,G,B) signals (R,G,B) of the brightness signal
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`HUAWEI EX. 1008 - 6/7
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`OLYMPUS EX. 1008 - 6/7
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`

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`6
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`3. The scanner of claim 1 wherein the test region is of
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`white color for measuring the brightness of the light source.
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`4. The scanner of claim 1 wherein the optical means
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`comprises a reflex mirror for reflecting the light reflected
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`from the document and the test region and a lens for
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`colliniating the light reflected from the reflex mirror to the
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`line image sensor.
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`5. The image scanner of claim 1 wherein each of the
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`digitized (R,G,B) signals of the image signal is multiplied by
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`a brightness compensation factor which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to com-
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`pensate the brightness of the image signal.
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`6. The image scanner of claim 5 wherein the brightness
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`compensation factor is equal to Yc/Y2 over which Yc is the
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`brightness average of the test region obtained when the light
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`source is in a stable condition and Y2 is the brightness
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`average of the brightness signal which is obtained by
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`averaging the brightness of all the digitized (R,G,B) signals
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`of the brightness signal.
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`7. The image scanner of claim 6 wherein the brightness Y
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`of each (R,G,B) signal of the brightness signal is calculated
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`according to the following equation:
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`Y=a *R+b*G+c *3
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`over which a, b, and c are three predetermined constants.
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`8. The image scanner of claim 1 wherein each digitized
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`(R,G,B) signal of the image signal is multiplied by a color
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`compensation factor calculated which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to com-
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`pensate the brightness and the color of the image signal.
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`9. The image scanner of claim 8 wherein the color
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`compensation factor is equal to (Rc/RLGc/GLBc/Bl) over
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`which the color reference (Rc,Gc,Bc) is the color average of
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`the test region obtained when the light source is in a stable
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`condition and the color average (R1,G1,Bl) is the average of
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`US 6,522,432 B1
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`5
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`step 132 multiply each (R,G,B) signal of the image signal
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`scanned from the document 16 by a color compensation
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`factor (RC/R1, GC/Gl, Bc/Bl): (R*RC/R1, G*GC/G1,
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`B*Rc/Rl).
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`The above disclosure is not intended as limiting Those
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`skilled in the art will readily observe that numerous modi-
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`fications and alterations of the device may be made while
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`retaining the teachings of the invention. Accordingly,
`the
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`above disclosure should be construed as limited only by the
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`nietes and bounds of the appended claims.
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`What is claimed is:
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`1. An image scanner for scanning a document comprising:
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`(1) a test region;
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`(2) a light source for illuminating the document and the
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`test region;
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`(3) optical means for conveying the light reflected from
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`the document and the test region;
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`(4) a line image sensor for receiving the light from the
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`optical means and generating an image signal corre-
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`sponding to the light reflected from the document and
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`a brightness signal corresponding to the light reflected
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`from the test region; the line image sensor comprising
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`an array of (red, green, blue)(R,G,B) sensing elements
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`for converting the light received from the optical means
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`into an array of corresponding (R,G,B) signals wherein
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`both the image signal and the brightness signals gen-
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`erated by the line image sensor are formed by an array
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`of (R,G,B) signals; and
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`(5) a signal compensation circuit for amplifying the image
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`signal according to the brightness signal to compensate
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`the instability of the light source; the signal compen—
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`sation circuit comprising an A/D converter for digitiz—
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`ing the (R,G,B) signals of the image signal and the
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`brightness signal, and a digital processor for adjusting
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`the digitized (R,G,B) signals of the image signal
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`according to the digitized (R,G,B) signals of the bright—
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`ness signal.
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`2. The scanner of claim 1 further comprising a transparent
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`window for scanning the document wherein the test region
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`is installed next to the window.
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`all the digitized (R,G,B) signals of the brightness signal.
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`HUAWEI EX. 1008 - 7/7
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`OLYMPUS EX. 1008 - 7/7
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