`US006522432B1
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`(0) Patent No:
`US 6,522,432 B1
`a2) United States Patent
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`(45) Date of Patent:
`Feb. 18, 2003
`Lin
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`IMAGE SCANNER WITH AUTOMATIC
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`SIGNAL COMPENSATION
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`Inventor: Chien-Chih Lin, Hsien (TW)
`(75)
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`(73) Assignee: Primax Electronics Ltd., Taipei (TW)
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`(*) Notice:
`Subject to anydisclaimer, the term ofthis
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`patent is extended or adjusted under 35
`US.C. 154(b) by 1049 days.
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`1/1994 Webb et al.
`5,278,674 A *
`......ceeee 358/475
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`3/1994 Suzukiet al.
`5,296,944 A *
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`5,587,746 A * 12/1996 Nakakuki
`..........020+ 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 Hsu
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`67)
`ABSTRACT
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`The present invention relates to an image scanner with
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`(21) Appl. No.: 08/633,389
`automatic signal compensation function for compensating
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`oa.
`the instability of a light source of the image scanner. The
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`Apr. 16, 1996
`Filed:
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`image scanner comprises a test region, a light source for
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`Lente C17 icccesessseeeseseesteeneserssssssssseseee HOAN 1/04
`illuminating the document andthe test region, optical means
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`(52) US. Ch.
`ceccccccccesssssssssesseseenenenseee 358/475; 358/296
`for conveying the light reflected from the document and the
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`(58) Field of Search
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`358/206 461
`test region, a line image sensor for receiving the light from
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`358 463.465. 475.509,512 516, 484.
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`the optical means and generating an image signal corre-
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`ee OO I 348 34 500 708
`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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`References Cited
`the test region, and a signal compensation circuit for ampli-
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`fying the image signal accordingto the brightness signal to
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`compensate the instability in the brightness of the light
`U.S. PATENT DOCUMENTS
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`5,151,796 A * 9/1992 Tho cl al. reese 35g/475|SOUEEE
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`eeeneees 358/484
`§,212,376 A *
`5/1993 Liang cece
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`5,249,068 A *
`9/1993 Takase ..ccceseecees 358/475
`9 Claims, 3 Drawing Sheets
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`(56)
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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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`120~|CALCULATE BRIGHTNESS AVERAGE Y2 OF THE
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`BRIGHTNESS SIGNAL
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`(R*Yc/Y¥2, G8Yc/Y2, BeYc/¥2)
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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`SIGNAL:
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`123
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`OLYMPUS EX. 1008 - 1/7
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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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`U.S. Patent
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`Feb. 18, 2003
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`Sheet 1 of 3
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`US6,522,432 Bl
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`BRIGHTNESS
`COMPENSATION
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`CIRCUIT
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`LL 34 eee J
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`24
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`FIG. 2
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`FE 71
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`| SIGNAL
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`AMPLIFIER
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`MO~_ ee |
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`DIGITAL
`PROCESSOR
`42
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`22
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`—Vrb
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`> A/D
`40
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`FIG.
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`11
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`OLYMPUS EX. 1008 - 2/7
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`OLYMPUS EX. 1008 - 2/7
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`

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`U.S. Patent
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`Feb. 18, 2003
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`Sheet 2 of 3
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`US 6,522,432 B1
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`44
`42
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`OLR BIA
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`CL PRB LLG HOAPEERREREL
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`FIG. 7
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`F | G10
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`OLYMPUS EX.1008 - 3/7
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`OLYMPUS EX. 1008 - 3/7
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`U.S. Patent
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`Feb. 18, 2003
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`Sheet 3 of 3
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`US 6,522,432 B1
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`120~
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`130~
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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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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`SIGNAL:
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`(R*Yc/Y¥2, G*Yc/Y2, B¥Yc/¥2)
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`FIG 12
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`CALCULATE COLOR AVERAGE (R1. G1. B1)
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`MODIFY EACH (R.G.B) SIGNAL OF THE IMAGE
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`SIGNAL:
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`OLYMPUS EX. 1008 - 4/7
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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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`US 6,522,432 B1
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`1
`IMAGE SCANNER WITH AUTOMATIC
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`SIGNAL COMPENSATION
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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 commonlyused in color image scanner because
`of its broad spectrum coverage. One problem with such lamp
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`its brightness will gradually change to a stable
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`condition whenit 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 wail 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 scanncr’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 brightnessof the light source, but
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`it requires high precision parts and installation proccss
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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 com-
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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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`(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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`sponding to the light reflected from the document and
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`a brightness signal correspondingto the light reflected
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`from the test region; and
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`(5) a signal compensationcircuit for amplifying the image
`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 linc image scnsor comprises an array of (red, green,
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`blue) (R,G,B) sensing elements for converting the light
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`ing (R,G,B) signals wherein both the image signal and the
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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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`(R,G,B) signals of the image signal and the brightness
`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
`compensation factor calculated which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to com-
`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 advantagesof the present
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`invention will no doubt become obviousto 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 whichisillustrated
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`in the various figures and drawings.
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`BRIEF DESCRIPTION OF ‘THE DRAWINGS
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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 showsthe 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 showsa process for compensating the brightness
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`of the image signal.
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`FIG. 13 showsanother 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 retcr 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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`undemeath, 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 mcans which comprisesa 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 lest region 12, a line image
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`sensor 22 which is a CCD (charge couple device) for
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`OLYMPUS EX. 1008 - 5/7
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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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`3
`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
`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 throughthe transparent
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`window26 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
`after it is powered on and three sampling pointstl, t2 and t3.
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`It shows that
`the brightness of the light source 14 is
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`increasing at both point tl and point (2, and it reaches a
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`stable level at point t3. FIGS. 5 to 7 showsthe 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 t3. FIG. 5 showsa brightness
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`signal 52 whichis generated fromthelight reflected fromthe
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`test region 12 and an image signal 54 venerated 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 shownin 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 shownin 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 tl, t2 and 3.
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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
`brightness signal accordingto a fixed reference voltage Vib,
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`and a digital processor 42 for adjusting the digitized image
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`10
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`5a
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`4
`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 arrayofred, green,
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`blue (R,G,B) sensing elements (not shown) for converting
`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
`the brightness signals generated bythe 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
`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
`to
`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
`in the cquation listed below:
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`Yea"R+b"G+e"B
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`where the a, b, and ¢ 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
`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
`Yc is approximately equal to the average brightness of the
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`test region 12 whenthe 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 obtainedat 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.
`The process 120 comprises the following steps:
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`step 121 calculate a brightness Y1 for each (R,G,B)signal
`of the brightness signal by using the cquation:
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`Yl=a*R+b*G+c*B
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`step 122 obtain a brightness average Y2 fromthe bright-
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`ness Y1 of all the (R,G,B) signals of the brightness
`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 (Yc/Y¥2): (R* Yc/Y2,
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`G*Yc/Y¥2, B*Yc/Y2).
`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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`14is initially powered on,it usually showsa 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
`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,B])fromall the
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`(R,G,B) signals (R,G,B) of the brightness signal
`scanned from the test region 12;
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`OLYMPUS EX. 1008 - 6/7
`
`HUAWEI EX. 1008 - 6/7
`
`OLYMPUS EX. 1008 - 6/7
`
`

`

`
`
`US 6,522,432 B1
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`5
`step 132 multiply each (R,G,B) signal of the image signal
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`scanned from the document 16 bya color compensation
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`factor (Re/R1, Ge/G1, Be/BL): (R*Re/R1, G*Ge/G1,
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`B*Be/B1).
`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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`metes and bounds of the appendedclaims.
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`Whatis claimedis:
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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
`test region;
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`(3) optical means for conveying the light reflected from
`the document and the test region;
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`(4) a line image sensor for receiving the light from the
`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 lightreflected
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`fromthe test region; the line image sensor comprising
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`an arrayof(red, green, blue)(R,G,B) sensing elements
`for converting the light received from the optical means
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`into an array of corresponding (R,G,B) signals wherein
`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 compensationcircuit for amplifying the image
`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-
`ness signal.
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`2. The scannerof claim 1 further comprising a transparent
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`windowfor scanning the document wherein the test region
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`is installed next to the window.
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`6
`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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`collimating 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 cach of the
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`digitized (R,G,B) signals of the image signal is multiplied by
`a brightness compensation factor which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to com-
`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/Y¥2 over which Ycis the
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`brightness average of the test region obtained whenthelight
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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 brightnessofall the digitized (R,G,B)signals
`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
`according to the following equation:
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`Yea"R+b"G+c"B
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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
`compensation factor calculated which is obtained from the
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`digitized (R,G,B) signals of the brightness signal to com-
`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 (Re/R1,Gc/G1,Be/B1) over
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`which the color reference (Rc,Gc,Bc) is the color average of
`the test region obtained when the light source is in a stable
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`condition and the color average (R1,G1,B1)is the average of
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`all the digitized (R,G,B) signals of the brightness signal.
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`10
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`20
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`40
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`OLYMPUS EX. 1008 - 7/7
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`HUAWEI EX. 1008 - 7/7
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`OLYMPUS EX. 1008 - 7/7
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