(12) United States Patent
`Lin
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US006522432Bl
`US 6,522,432 Bl
`Feb.18,2003
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54)
`
`IMAGE SCANNER WITH AUTOMATIC
`SIGNAL COMPENSATION
`
`(75)
`
`Inventor: Chien-Chih Lin, Hsien (TW)
`
`(73) Assignee: Primax Electronics Ltd., Taipei (TW)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 1049 days.
`
`(21) Appl. No.: 08/633,389
`
`(22) Filed:
`
`Apr. 16, 1996
`
`Int. Cl.7 .................................................. H04N 1/04
`(51)
`(52) U.S. Cl. ........................................ 358/475; 358/296
`(58) Field of Search ................................. 358/296, 461,
`358/463, 465, 475, 509, 512, 516, 484;
`348/234, 500, 708
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,151,796 A * 9/1992 Ito et al. ..................... 358/475
`5,212,376 A * 5/1993 Liang ......................... 358/484
`5,249,068 A * 9/1993 Takase ....................... 358/475
`
`5,278,674 A * 1/1994 Webb et al.
`................ 358/475
`5,296,944 A * 3/1994 Suzuki et al. ............... 358/475
`5,587,746 A * 12/1996 Nakakuki ................... 348/708
`
`* cited by examiner
`
`Primary Examiner-Mark Wallerson
`(74) Attorney, Agent, or Firm-Winston Hsu
`
`(57)
`
`ABSTRACT
`
`The present invention relates to an image scanner with
`automatic signal compensation function for compensating
`the instability of a light source of the image scanner. The
`image scanner comprises a test region, a light source for
`illuminating the document and the test region, optical means
`for conveying the light reflected from the document and the
`test region, a line image sensor for receiving the light from
`the optical means and generating an image signal corre(cid:173)
`sponding to the light reflected from the document and a
`brightness signal corresponding to the light reflected from
`the test region, and a signal compensation circuit for ampli(cid:173)
`fying the image signal according to the brightness signal to
`compensate the instability in the brightness of the light
`source.
`
`9 Claims, 3 Drawing Sheets
`
`CALCULATE BRIGHTNESS Yl FOR EACH
`SIGNAL OF THE BRIGHTNESS SIGNAL
`
`(R.G.B.)
`
`12 o-..,, CALCULATE BRIGHTNESS AVERAGE Y2 OF THE
`BRIGHTNESS SIGNAL
`
`(R.G.B) SIGNAL OF THE
`IMAGE
`MODIFY EACH
`(R:'.:Yc/Y2. G:t.:Yc/Y2, B*Yc/Y2)
`SIGNAL:
`
`I
`
`1~1
`
`,
`122
`
`,
`123
`
`)
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`OLYMPUS et al. EX. 1007 - 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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`US 6,522,432 Bl
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`/
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`/~-...../
`10
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`28
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`26
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`16
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`12
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`FI G. 1
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`I
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`SIGNAL
`AMPLIFIER
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`SAMPLING
`CIRCUIT
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`24 ---r
`L
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`CCD
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`22
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`CCD
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`22
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`32
`AID
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`1
`I
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`I
`
`Vrb
`vs .---__ .......__ __ _
`f----=;.J BRIGHTNESS
`COMPENSATION
`36 CIRCUIT
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`F ! G. 2
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`34
`______________ _J
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`, - - - - - - - - - - - - - - 1
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`1-----+:.>1
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`AID
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`40
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`DIGITAL
`PROCESSOR
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`42
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`-
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`FI G. 11
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`I
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`U.S. Patent
`
`Feb.18,2003
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`Sheet 2 of 3
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`US 6,522,432 Bl
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`12
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`D
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`,;
`26
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`42
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`44
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`40
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`\ -
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`FIG. 3
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`38
`
`y
`
`FIG. 4
`
`y
`
`52
`- - - -
`
`56
`- - -
`
`---......._
`
`58
`- - - - __ Vrb
`60
`
`--5'
`
`y
`
`- - Vrb
`-
`---- - - - - -
`........... ..._ ___ ..........__..T
`
`Fl G. 5
`
`F ! G. 8
`
`yr---------------Wb n~ •T
`
`FIG. 6
`
`ylff~---Vrb
`
`..... __ ....._._ ____ ---Jio_,. T
`FIG. 9
`
`y153 n-r==-s-Vrb
`
`....._ __ ..-........ _ __ _ ----l~,r
`
`FIG. 7
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`FI G. 10
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`

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`U.S. Patent
`
`Feb.18,2003
`
`Sheet 3 of 3
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`US 6,522,432 Bl
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`CALCULATE BRIGHTNESS Yl FOR EACH
`SIGNAL OF THE BRIGHTNESS SIGNAL
`
`(R.G.B.)
`
`120.._ CALCULATE BRIGHTNESS AVERAGE Y2 OF THE
`BRIGHTNESS SIGNAL
`
`I
`
`I
`
`MODIFY EACH (R.G.B) SIGNAL OF THE
`IMAGE
`(R:'.:Yc/Y2, G:'.:Yc/Y2, B*Yc/Y2)
`SIGNAL:
`
`F l G. 12
`
`I
`
`1~1
`
`I
`)
`122
`
`,
`123
`
`J
`
`CALCULATE COLOR AVERAGE ( R 1. G 1 . Bl) OF THE
`130- BRIGHTNESS SIGNAL
`I
`IMAGE
`MODIFY EACH (R.G.B) SIGH AL OF THE
`SIGNAL:
`(R*Rc/Rl, G*Gc/Gl, B*Bc/Bl)
`
`I
`I
`
`131
`
`I
`>
`132
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`F I G. 13
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`US 6,522,432 Bl
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`2
`brightness signals generated by the line image sensor are
`formed by an array of (R,G,B) signals. The signal compen(cid:173)
`sation circuit comprises an AID converter for digitizing the
`(R,G,B) signals of the image signal and the brightness
`5 signal, and a digital processor for adjusting the digitized
`(R,G,B) signals of the image signal according to the digi(cid:173)
`tized (R,G,B) signals of the brightness signal. Each digitized
`(R,G,B) signal of the image signal is multiplied by a color
`compensation factor calculated which is obtained from the
`10 digitized (R,G,B) signals of the brightness signal to com(cid:173)
`pensate the brightness and the color of the image signal.
`It is an advantage of the present invention that it provides
`an image scanner which can measure the brightness of the
`scanner's light source by measuring the light reflected from
`15 the test region instead of by using an optic fiber.
`It is another advantage of the present invention that the
`image scanner can measure color variations of the scanner's
`light source by measuring the light reflected from the test
`region to compensate the digitized RGB signals of the image
`20 signal.
`These and other objects and the advantages of the present
`invention will no doubt become obvious to those of ordinary
`skill in the art after having read the following detailed
`description of the preferred embodiment which is illustrated
`25 in the various figures and drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`1
`IMAGE SCANNER WITH AUTOMATIC
`SIGNAL COMPENSATION
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to an image scanner, and
`signal compensation function for compensating the instabil(cid:173)
`ity of a light source of the image scanner.
`2. Description of the Prior Art
`Fluorescent lamp such as cold cathode fluorescent tube
`(CCFT) is commonly used in color image scanner because
`of its broad spectrum coverage. One problem with such lamp
`is that its brightness will gradually change to a stable
`condition when it is powered on. Such period usually takes
`three to five minutes. In order to get a stable image output
`by using such a lamp, a user usually has to wait until the
`lamp is completely warmed up.
`U.S. Pat. No. 5,212,376, which is assigned to the same
`assignee of the present invention, discloses an image scan(cid:173)
`ner with an optic fiber connected to a line image sensor for
`measuring the brightness of the image scanner's light source
`and a signal compensation circuit for adjusting the bright(cid:173)
`ness of the scanned image according to the measured
`brightness of the light source. The optic fiber method is very
`effective in measuring the brightness of the light source, but
`it requires high precision parts and installation process
`which is very expensive and time consuming. Besides, the
`brightness of the light measured by the optic fiber is very
`sensitive to the distance between the input end of the optic
`fiber and the light source. Any shock or vibration over the
`scanner may change this distance or move the input end of
`the optic fiber which may have great consequence over the
`output of the signal compensation circuit.
`
`SUMMARY OF THE INVENTION
`
`It is therefore a primary objective of the present invention
`to provide an image scanner which can measure the bright(cid:173)
`ness of the scanner's light source to compensate a scanned
`image and avoid the above mentioned problem.
`It is another objective of the present invention to provide
`an image scanner which can measure color variations of the
`scanner's light source to compensate the scanned image
`accordingly.
`Briefly, in a preferred embodiment, the present invention
`includes an image scanner for scanning a document com(cid:173)
`prising:
`(1) a test region;
`(2) a light source for illuminating the document and the
`test region;
`(3) optical means for conveying the light reflected from
`the document and the test region;
`( 4) a line image sensor for receiving the light from the
`optical means and generating an image signal corre(cid:173)
`sponding to the light reflected from the document and
`a brightness signal corresponding to the light reflected
`from the test region; and
`(5) a signal compensation circuit for amplifying the image
`signal according to the brightness signal to compensate
`the instability in the brightness of the light source.
`The line image sensor comprises an array of (red, green,
`blue) (R,G,B) sensing elements for converting the light 65
`received from the optical means into an array of correspond(cid:173)
`ing (R,G,B) signals wherein both the image signal and the
`
`35
`
`FIG. 1 is a perspective view of a hand-held image
`scanner's optical components according to the present
`30 invention.
`FIG. 2 is a hardware block diagram of the signal com(cid:173)
`pensation circuit of the scanner according to the present
`invention.
`FIG. 3 shows the test region and a document viewed
`through a transparent window of the scanner.
`FIG. 4 shows a curve of the brightness of the scanner's
`light source after it is powered on.
`FIGS. 5 to 7 shows the brightness and image signals
`40 generated by the signal amplifier of the scanner.
`FIGS. 8 to 10 shown each of the resulting reference
`voltages Vrb generated by the brightness compensation
`circuit of the scanner.
`FIG. 11 is an alternative hardware block diagram of the
`signal compensation circuit.
`FIG. 12 shows a process for compensating the brightness
`of the image signal.
`FIG. 13 shows another process for compensating both the
`50 brightness and the color of the image signal.
`
`45
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Please refer to FIGS. 1and2. FIG. 1 is a perspective view
`55 of a hand-held image scanner's optical components accord(cid:173)
`ing to the present invention and FIG. 2 is a hardware block
`diagram of the signal compensation circuit 24 attached to the
`CCD 22 shown in FIG. 1. The scanner 10 comprises a
`transparent window 26 for scanning a document 16 lying
`60 underneath, a rectangular glass 28 installed inside the win(cid:173)
`dow 26, a test region 12 installed on the glass 28 next to one
`side of the window 26, a light source 14 above the window
`26 for illuminating a document 16 under the window 26 and
`the test region 12, an optical means which comprises a reflex
`mirror 18 and a lens 20 for conveying the light reflected
`from the document 16 and the test region 12, a line image
`sensor 22 which is a CCD (charge couple device) for
`
`OLYMPUS et al. EX. 1007 - 5/7
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`US 6,522,432 Bl
`
`5
`
`3
`receiving the light from the lens 20 and generating an image
`signal corresponding to the light reflected from the docu(cid:173)
`ment 16 and a brightness signal corresponding to the light
`reflected from the test region 12, and a signal compensation
`circuit 24 for processing the brightness signal and amplify-
`ing the image signal according to the brightness signal to
`compensate the instability in the brightness of the light
`source 14. The test region 12 is of white color for measuring
`the brightness of the light source. The reflex mirror 18 is
`used for reflecting the light from the document 16 and the
`test region 12 and then the lens 20 will collimate the light
`reflected from the reflex mirror 18 to the line image sensor
`22.
`The signal compensation circuit 24 comprises a signal
`amplifier 30 for amplifying the image signal and brightness
`signal from the line image sensor 22 to an appropriate
`voltage level, an ND (analog-to-digital) converter 32 for
`digitizing the amplified image signal according to an adapt(cid:173)
`able reference voltage Vrb, a sampling circuit 34 for sam(cid:173)
`pling the brightness signal and generating a sample voltage 20
`Vs, and a brightness compensation circuit 36 for adjusting
`the reference voltage Vrb of the ND converter 32 according
`to the sample voltage Vs to compensate the instability in the
`brightness of the light source 14.
`FIGS. 3 to 10 show an example which teaches how the 25
`test region 12 is used to compensate the instability in the
`brightness of the light source 14. FIG. 3 shows the test
`region 12 and a document 38 viewed through the transparent
`window 26 which comprises three different sections: white
`section 40, grey section 42 and black section 44. FIG. 4 30
`shows a curve of the brightness (Y) of the light source 14
`after it is powered on and three sampling points tl, t2 and t3.
`It shows that the brightness of the light source 14 is
`increasing at both point tl and point t2, and it reaches a
`stable level at point t3. FIGS. 5 to 7 shows the brightness and 35
`image signals generated by the signal amplifier 30 at the
`three sampling points tl, t2 and t3. FIG. 5 shows a brightness
`signal 52 which is generated from the light reflected from the
`test region 12 and an image signal 54 generated from the
`light reflected from the document 38. The image signal 54 40
`comprises three voltage levels 56, 58 and 60 which are
`corresponding to the three sections of the document 38:
`white section 40, grey section 42 and black section 44. The
`voltage level Vrb shown in FIGS. 5 to 7 is equal to the
`voltage level of the brightness signal 53 in FIG. 7 which is 45
`obtained when the brightness of the light source 14 reaches
`a stable condition.
`The ND converter 32 shown in FIG. 2 digitizes the image
`signal 54 according to the reference voltage Vrb. If the Vrb
`is fixed at a constant level just like the one shown in FIGS. 50
`5 to 7, the image signals shown in these three figures will be
`digitized into three different signal sets but in fact the only
`difference between these three signal sets is the brightness
`which is caused by the light source 14. In order to compen(cid:173)
`sate such difference, the brightness signal 52 is fed into the 55
`brightness compensation circuit 36 to generate the reference
`voltage Vrb so that the digitized image signals generated by
`the ND converter 32 at two different times will be the same
`if the images scanned at these two different times are the
`same. FIGS. 8 to 10 shown each of the resulting reference 60
`voltages Vrb generated by the brightness compensation
`circuit 36 at the three different points tl, t2 and t3.
`FIG. 11 is an alternative block diagram of the signal
`compensation circuit 110. It comprises an ND (analog-to(cid:173)
`digital) converter 40 for digitizing the image signal and the 65
`brightness signal according to a fixed reference voltage Vrb,
`and a digital processor 42 for adjusting the digitized image
`
`4
`signal according to the digitized brightness signal to com(cid:173)
`pensate the instability in the brightness of the light source
`14.
`The line image sensor 22 comprises an array of red, green,
`blue (R,G,B) sensing elements (not shown) for converting
`the light received from the lens 20 into an array of corre(cid:173)
`sponding (R,G,B) signals wherein both the image signal and
`the brightness signals generated by the line image sensor 22
`are formed by an array of (R,G,B) signals. The ND con(cid:173)
`verter 40 digitizes the (R,G,B) signals of the image signal
`and the brightness signal according to the fixed reference
`voltage Vrb, and then the digital processor 42 adjusts the
`digitized (R,G,B) signals of the image signal according to
`the digitized (R,G,B) signals of the brightness signal to
`15 compensate the instability in the color of the light source.
`The brightness (Y) of a (R,G,B) signal can be represented
`in the equation listed below:
`
`10
`
`Y~a*R+b*G+c*B
`
`where the a, b, and c are three predetermined constants.
`From this equation the brightness and color of the image
`signal's (R,G,B) signals can be compensated by using the
`digital processor 42. FIG. 12 shows a process for compen(cid:173)
`sating the brightness of the image signal and FIG. 13 shows
`another process for compensating both the color and bright(cid:173)
`ness of the image signal. In compensating the brightness or
`color of the image signal, a brightness reference Y c and a
`color reference (Rc,Gc,Bc) are used for adjusting each
`(R,G,B) signal of the image signal. The brightness reference
`Ye is approximately equal to the average brightness of the
`test region 12 when the light source is in a stable condition
`such as at the point t3 shown in FIG. 4, and the color
`reference (Rc,Gc,Bc) is the color average of the test region
`12 obtained at the same time point.
`FIG. 12 shows a process 120 which compensates the
`brightness of all the (R,G,B) signals of the image signal
`according to the (R,G,B) signals of the brightness signal.
`The process 120 comprises the following steps:
`step 121 calculate a brightness Yl for each (R,G,B) signal
`of the brightness signal by using the equation:
`
`Y1~a*R+b*G+c*B
`
`step 122 obtain a brightness average Y2 from the bright(cid:173)
`ness Yl of all the (R,G,B) signals of the brightness
`signal;
`step 123 modify the brightness of the image signal by
`multiplying each (R,G,B) signal of the image signal by
`a brightness compensation factor (Y c/Y2): (R *Y c/Y2,
`G*Yc/Y2, B*Yc/Y2).
`The process 120 can compensate the variations over the
`brightness of the light source 14 but can not compensate
`color variations over the light source. When the light source
`14 is initially powered on, it usually shows a light blue color
`instead of a pure white color. Such color temperature change
`will affect the (R,G,B) signals of the image signal scanned
`from the document 16. By using the (R,G,B) signals of the
`brightness signal scanned from the test region 12 to measure
`the color of the light source, both the color and the bright(cid:173)
`ness of the image signal can be compensated. FIG. 13 shows
`the process 130 which is used to compensate both the
`brightness and the color of the image signal. Process 130
`comprises the following steps:
`step 131 calculate a color average (Rl,Gl,Bl) from all the
`(R,G,B) signals (R,G,B) of the brightness signal
`scanned from the test region 12;
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`OLYMPUS et al. EX. 1007 - 6/7
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`US 6,522,432 Bl
`
`5
`step 132 multiply each (R,G,B) signal of the image signal
`scanned from the document 16 by a color compensation
`factor (Rc/Rl, Gc/Gl, Be/Bl): (R*Rc/Rl, G*Gc/Gl,
`B*Bc/Bl).
`The above disclosure is not intended as limiting. Those
`skilled in the art will readily observe that numerous modi(cid:173)
`fications and alterations of the device may be made while
`retaining the teachings of the invention. Accordingly, the
`above disclosure should be construed as limited only by the
`metes and bounds of the appended claims.
`What is claimed is:
`1. An image scanner for scanning a document comprising:
`(1) a test region;
`(2) a light source for illuminating the document and the
`test region;
`(3) optical means for conveying the light reflected from
`the document and the test region;
`( 4) a line image sensor for receiving the light from the
`optical means and generating an image signal corre(cid:173)
`sponding to the light reflected from the document and
`a brightness signal corresponding to the light reflected
`from the test region; the line image sensor comprising
`an array of (red, green, blue)(R,G,B) sensing elements
`for converting the light received from the optical means 25
`into an array of corresponding (R,G,B) signals wherein
`both the image signal and the brightness signals gen(cid:173)
`erated by the line image sensor are formed by an array
`of (R,G,B) signals; and
`(5) a signal compensation circuit for amplifying the image 30
`signal according to the brightness signal to compensate
`the instability of the light source; the signal compen(cid:173)
`sation circuit comprising an AID converter for digitiz(cid:173)
`ing the (R,G,B) signals of the image signal and the
`brightness signal, and a digital processor for adjusting 35
`the digitized (R,G,B) signals of the image signal
`according to the digitized (R,G,B) signals of the bright(cid:173)
`ness signal.
`2. The scanner of claim 1 further comprising a transparent
`window for scanning the document wherein the test region 40
`is installed next to the window.
`
`6
`3. The scanner of claim 1 wherein the test region is of
`white color for measuring the brightness of the light source.
`4. The scanner of claim 1 wherein the optical means
`comprises a reflex mirror for reflecting the light reflected
`5 from the document and the test region and a lens for
`collimating the light reflected from the reflex mirror to the
`line image sensor.
`5. The image scanner of claim 1 wherein each of the
`digitized (R,G,B) signals of the image signal is multiplied by
`10 a brightness compensation factor which is obtained from the
`digitized (R,G,B) signals of the brightness signal to com(cid:173)
`pensate the brightness of the image signal.
`6. The image scanner of claim 5 wherein the brightness
`15 compensation factor is equal to Y c/Y2 over which Y c is the
`brightness average of the test region obtained when the light
`source is in a stable condition and Y2 is the brightness
`average of the brightness signal which is obtained by
`averaging the brightness of all the digitized (R,G,B) signals
`20 of the brightness signal.
`7. The image scanner of claim 6 wherein the brightness Y
`of each (R,G,B) signal of the brightness signal is calculated
`according to the following equation:
`
`Y~a*R+b*G+c*B
`
`over which a, b, and c are three predetermined constants.
`8. The image scanner of claim 1 wherein each digitized
`(R,G,B) signal of the image signal is multiplied by a color
`compensation factor calculated which is obtained from the
`digitized (R,G,B) signals of the brightness signal to com(cid:173)
`pensate the brightness and the color of the image signal.
`9. The image scanner of claim 8 wherein the color
`compensation factor is equal to (Rc/Rl,Gc/Gl,Bc/Bl) over
`which the color reference (Rc,Gc,Bc) is the color average of
`the test region obtained when the light source is in a stable
`condition and the color average (Rl,Gl,Bl) is the average of
`all the digitized (R,G,B) signals of the brightness signal.
`
`* * * * *
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`OLYMPUS et al. EX. 1007 - 7/7
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