JP2014060564A - Image reader, image reading method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide image data of high quality by effectively utilizing a dynamic range during A/D conversion at the maximum while color balance between light sources is kept.SOLUTION: An image reader includes: a light volume level calculation section 165 which subtracts a black level in a state where incident light is zero from an output level of entire main scanning direction valid pixels, which is obtained by reading a reference white board by allowing individual light emitting elements of light sources to have prescribed light volumes, to calculate a light volume level; a light volume peak value detection section 166 which detects a peak value in the entire main scanning valid pixels in the light volume level; an initial light volume adjusting value calculation section 167 which calculates an initial light volume adjusting value of the individual light emitting elements from a ratio between the peak value and a target value; an output level peak value detection section 168 which simultaneously lights the light sources in a state where the initial light volume adjusting value is set and detects the peak value of the output level, which is obtained by reading a reference white board; and a light volume adjusting value calculation section 169 which considers the black level so that it is adjusted to a white level target value in response to the peak value and calculates the ratio by which the initial light volume adjusting value is multiplied.

Description

  The present invention relates to an image reading apparatus, an image reading method, and a program.

  2. Description of the Related Art Conventionally, an image reading apparatus that reads image data by irradiating light on a document and taking in light from the document generally uses a photoelectric conversion element array, which is called an image sensor, in which photoelectric conversion elements are arranged in one line in the main scanning direction. ing. A document image is read by moving the document relative to the image sensor in the sub-scanning direction or by transporting the document.

  Inexpensive readers use one or more light sources consisting of three colors of LEDs (Light Emitting Diodes) of red (RED), green (GREEN), and blue (BLUE), and a single line image sensor is used in combination. It is done. When reading a color image, the image reading is performed by sequentially switching the LEDs of the respective colors at a predetermined lighting duty. When reading a monochrome image, it is necessary to turn on only a single color (for example, GREEN), and the amount of light is insufficient to support high-speed reading. Is called.

  However, when all the LEDs are turned on at the same time in order to increase the amount of light, there is a concern that the reproducibility of the color document may be deteriorated due to an increase in the amount of light only for a specific color or a loss of color balance between the LEDs. For this reason, in the prior art, a method of adjusting the light quantity of each LED in order to balance the color of the light source is known. Specifically, the light amount level (sensor output corresponding to the result obtained by integrating the light emission amount of the LED with the light emission time) read by lighting each of the R, G, and B LEDs in each of the plurality of light sources is a certain predetermined value. A method of adjusting the amount of light so as to obtain the target value is disclosed (for example, see Patent Document 1).

  On the other hand, there are variations in illuminance such as individual differences of light sources, temperature dependence, changes with time, etc., and there are also differences in optical system components between apparatuses. There are also individual sensitivity differences in photoelectric conversion elements. For this reason, in order to absorb those variations and perform A / D conversion of the photoelectric conversion element output with a large dynamic range most efficiently, the output level when reading the reference white plate is adjusted to a predetermined target value. It is necessary to adjust the white level by adjusting the gain inside the AFE or adjusting the amount of light. Since this output level includes a dark output: black level read when the incident light is zero, the output level is generally adjusted to the target value in a blackened state.

  As described above, the white level adjustment is intended to use a wide dynamic range (to increase the resolution) as much as possible so that the A / D conversion circuit does not overflow, that is, the output of the converted digital data is not saturated. It is. Therefore, even in the case of light amount adjustment at the time of simultaneous lighting, the A / D converter circuit does not fall within the range where the converted digital data output is saturated, and the dynamic range is used as much as possible (increasing resolution) Need to be adjusted).

  In Patent Document 1, the sensor output corresponding to the result obtained by integrating the light emission amount of the LED with the light emission time, that is, the output data after subtraction of the dark output level read in the state of zero incident light (hereinafter referred to as the light amount level) Is used to calculate and set the light amount adjustment value for each light source so that the light amount level becomes a predetermined target value. Since the light level at the time of simultaneous lighting is the total value of the light level of each light source, if the light level is set so that the light level at the time of lighting of each light source becomes a predetermined target level, The document can be read in a state in which is maintained.

  As for the black level, for example, a technique disclosed in Patent Document 2 is known. Here, in a reduction optical system image reading apparatus, for example, an image sensor using a CCD is used. Since this CCD has the number of pixels that can ensure an effective reading width with one sensor chip, it is output to each pixel in the sensor chip in a state where no light is incident: the dark output becomes the same value, and a certain target The black level is adjusted to be a value. For this reason, the black level does not vary so much in the main scanning.

  However, it is known that a CIS (Contact Image Sensor) frequently used in an image reading apparatus of an equal magnification optical system has a configuration in which a plurality of sensor IC chips composed of a plurality of pixels are arranged at the same sub-scanning position. The final stage output buffer in the sensor IC chip has a slight individual difference, and the dark output level in a state where no light is incident is different for each chip due to a variation factor for each chip. Therefore, in the case of CIS, the dark output level as shown in FIG. 11 is obtained due to the arrangement of a plurality of sensor IC chips. Hereinafter, it is described as dark output or black output.

  Further, in the case of the CIS in which the sensor IC is a CMOS sensor, the CMOS sensor has a buffer 303 and a shift register 304 for outputting in units of pixels (effective pixels 301) (see FIG. 12), so that the final output for each pixel. Due to the individual difference of the buffer 305, the black output level is different for each pixel even in the sensor IC chip (see FIG. 13).

  Further, in the prior art, a method for changing the color balance of the light source is considered. When the characteristic color of a color original is emphasized and reproduced as a monochrome image, the light quantity level of the LED of a specific color is lowered. Generally, it is only necessary to reduce the light intensity of the light emitting element corresponding to the color component whose density is to be increased as the color balance of each color of the white light source. It has been.

  However, the conventional techniques as described above have the following problems. In Patent Document 1, since an actual read image includes a black level, it is necessary to perform white level adjustment in consideration of the black level. If the target level of the light level of each color is set without considering the black level, the upper limit of the dynamic range of the A / D conversion circuit may be exceeded.

  In addition, the amount obtained by subtracting the black level from the target value may be set as the target value of the light amount level. However, when there are a plurality of sensor chips such as a contact image sensor, the black level varies within the main scanning range. It is difficult to optimally set the target value of the light level. For this reason, there is a problem that it is difficult to carry out accurate white level adjustment while maintaining color balance during simultaneous lighting.

  Further, in the conventional technology, the target level of each color is not set in consideration of the black level, and further, if the light amount of a specific LED is reduced too much, the total light amount may decrease, and the noise component In addition, the dynamic range cannot be effectively utilized. Therefore, there is a problem that high quality image data cannot be obtained.

  As described above with reference to FIGS. 11 to 13, a means for determining the amplification factor by assuming the maximum black level that can be generated is also conceivable. In this method, although output saturation can be avoided 100%, most of them can be avoided. Cannot effectively use the dynamic range of the A / D conversion circuit. As a result, the number of effective gradations is reduced, and the SN (Signal / Noise) performance of the image data is deteriorated. On the other hand, in the method of determining the amplification factor of the light amount by considering the black level as a value smaller than the true value, output saturation is likely to occur when a highly reflective document is scanned, and reflection of the scanned document is difficult. There is a problem that image data faithful to the rate cannot be obtained.

  The present invention has been made in view of the above, and at the time of adjusting the amount of light when simultaneously turning on a light source having a plurality of light emitting elements, photoelectric conversion without maintaining output color saturation while maintaining the color balance between the light sources. An object of the present invention is to obtain high-quality image data by making effective use of the dynamic range at the time of A / D conversion of image data later.

  In order to solve the above-described problems and achieve the object, the present invention includes a light source including a plurality of light emitting elements having different emission colors, photoelectric conversion unit that photoelectrically converts reflected light from a document, and the photoelectric conversion unit. An image reading apparatus having a reference white plate read by a conversion unit, wherein each light emitting element of the light source has a predetermined light amount, and the output level of effective pixels in all main scanning directions obtained by reading the reference white plate A light amount level calculation unit that calculates a light amount level by subtracting a black level read in a state where incident light is zero, and a maximum value in all main scanning effective pixels of the light amount level calculated by the light amount level calculation unit. An initial light amount adjustment value calculating unit that calculates an initial light amount adjustment value of each light emitting element of the light source from a ratio between the maximum value of the light amount level detected by the maximum value detecting unit and a predetermined target value; The first With the initial light amount adjustment value calculated by the light amount adjustment value calculation unit set, an output level maximum value detection unit that detects the maximum value of the output level when the reference white plate is read by simultaneously turning on the light sources, and Based on the maximum value detected by the output level maximum value detection unit, a ratio for multiplying the initial light amount adjustment value in consideration of the black level is calculated so that the white level target value is adjusted, and the light amount of the light source is calculated. A light amount adjustment value calculation unit for adjustment.

  The present invention adjusts the light amount of the light source by calculating the ratio by which the initial light amount adjustment value is multiplied in consideration of the black level when adjusting the light amount when simultaneously turning on light sources having light emitting elements of a plurality of colors. Therefore, it is possible to maximize the dynamic range at the time of A / D conversion of the image data after photoelectric conversion without saturating the output while maintaining the color balance between the light sources. There is an effect that it can be acquired.

FIG. 1 is a configuration diagram illustrating a schematic configuration of a copier according to an embodiment. FIG. 2 is a configuration diagram showing a detailed configuration of the ADF provided in the copying machine. FIG. 3 is a block diagram of an ADF control system. FIG. 4 is a diagram illustrating a main part of an electric circuit in the second image reading unit of the ADF. FIG. 5 is a block diagram illustrating a functional configuration of a CPU included in the controller. FIG. 6 is an explanatory diagram showing light amount adjustment when the light source unit is an LED. FIG. 7 is a timing chart showing light amount adjustment when reading a color image (A) and reading a monochrome image (B). FIG. 8 is a flowchart showing an operation example (1) at the time of white level adjustment. FIG. 9 is an explanatory diagram showing a case where the target value of the total R, G, B initial light quantity is calculated. FIG. 9A shows a case where black is the minimum, and FIG. 9B shows a case where black is the maximum. FIG. 10 is a flowchart showing an operation example (2) during white level adjustment. FIG. 11 is an explanatory diagram showing the dark output level of the CIS in which a plurality of sensor IC chips are arranged. FIG. 12 is an explanatory diagram illustrating an example in which an output buffer is provided for each pixel in a CIS in which the sensor IC is a CMOS sensor. FIG. 13 is an explanatory diagram showing an example of black level output of the CIS in which the sensor IC is a CMOS sensor.

  Exemplary embodiments of an image reading apparatus, an image reading method, and a program according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment)
FIG. 1 is a configuration diagram showing a schematic configuration of a copying machine 1 according to the present embodiment. As shown in FIG. 1, the copier 1 includes an automatic document feeder (ADF) 100 having a function as an image reading device, a paper feeding unit 2, and an image forming unit 3.

  The paper feeding unit 2 includes paper feeding cassettes 21 and 22 that store recording papers having different paper sizes, and various rollers that transport the recording papers stored in the paper feeding cassettes 21 and 22 to the image forming position of the image forming unit 3. The sheet feeding means 23 is provided.

  The image forming unit 3 includes an exposure device 31, a photosensitive drum 32, a developing device 33, a transfer belt 34, and a fixing device 35. The image forming unit 3 exposes the photosensitive drum 32 by the exposure device 31 based on the image data of the original read by the image reading unit inside the ADF 100 to form a latent image on the photosensitive drum 32, and the developing device 33. Thus, different color toner is supplied to the photosensitive drum 32 for development. The image forming unit 3 transfers the image developed on the photosensitive drum 32 by the transfer belt 34 onto the recording paper supplied from the paper feeding unit 2, and then transfers the toner image transferred to the recording paper by the fixing device 35. The toner is melted to fix the color image on the recording paper.

  FIG. 2 is a configuration diagram showing a detailed configuration of the ADF 100, and FIG. 3 is a block diagram of a control system of the ADF 100. As shown in FIG. 2, the ADF 100 is fed with a document setting unit A on which a document bundle is set, and a separation feeding unit B that separates and feeds the documents one by one from the set document bundle. The original document is firstly abutted and aligned, the registration unit C that pulls out and conveys the aligned document, and the conveyed document is turned so that the document surface faces the reading side (downward in the drawing) of the first document reading unit 131. A turn part D for conveying the paper, a first reading / conveying part E for reading the front surface image of the original document from below the contact glass by the first image reading part 131, and a second image for the back side of the original after the front side image is read. A second reading conveyance unit F that is read by the image reading unit 135, a paper discharge unit G that discharges a document whose front and back images have been read out, and a stack unit H that stacks and holds the discharged document. Further, as shown in FIG. 3, the ADF 100 includes motors 101 to 105 that drive the respective units and a controller 150 that controls a series of operations. The controller 150 is connected to the main body control unit 10 that performs overall control of the copying machine 1 via the I / F 107. The main body control unit 10 is connected to an operation unit 11 through which the user performs various operations via the I / F 108. The first image reading unit 131 and the second image reading unit 135 use CIS as will be described later, and are hereinafter also referred to as CIS 131 and CIS 135 as appropriate.

  A document bundle 110 to be read is set in the document setting section A. The document bundle 110 is set on the document table 112 including the movable document table 111. A document bundle 110 is set on the document table 112 with the document surface facing upward. At this time, the width direction of the document bundle 110 is positioned in a direction orthogonal to the conveyance direction by a side guide (not shown). Further, the setting of the document bundle 110 is detected by the set filler 113 and the set sensor 114, and information indicating that the document bundle 110 is set is transmitted from the controller 150 to the main body control unit 10 via the I / F 107. .

  Further, an outline of the length of the original bundle 110 in the transport direction is determined by original length detection sensors 115 and 116 provided on the original table surface. As the document length detection sensors 115 and 116, for example, a reflection type sensor or an actuator type sensor capable of detecting even one document is used. Further, the document length detection sensors 115 and 116 need to be arranged so that at least whether the document size is vertical or horizontal can be determined.

  The movable document table 111 can be moved up and down in the directions a and b in FIG. When the document bundle 110 is not set on the document table 112, the movable document table 111 is in a lowered state, and this state is detected by the bottom plate HP sensor 117. When the controller 150 detects that the document bundle 110 is set on the document table 112 by the set filler 113 and the set sensor 114, the controller 150 rotates the bottom plate raising motor 105 in the normal direction so that the top surface of the document bundle 110 is separated and fed. The movable document table 111 is raised so as to come into contact with the pickup roller 118 of the feeding unit B. The pickup roller 118 is moved in the c and d directions in FIG. 2 by the action of the cam mechanism by the pickup motor 101, and the movable document table 111 is raised and pushed by the upper surface of the document bundle 110 on the movable document table 111. 2, the upper limit can be detected by the proper paper feed position sensor 119.

  When the user presses the print key of the operation unit 11 and a document feed signal is transmitted from the main body control unit 10 to the controller 150 via the I / F 107, the pickup roller 118 is rotated by the forward rotation of the feed motor 102. Rotation is driven to pick up several (ideally one) originals on the original table 112. The rotation direction is a direction in which the uppermost document is conveyed to the sheet feeding port.

  The paper feed belt 120 is driven in the paper feed direction by the normal rotation of the paper feed motor 102. Further, the reverse roller 121 is rotationally driven in the reverse direction to the paper feed by the forward rotation of the paper feed motor 102. As a result, the top document and the document below it are separated, and only the top document can be fed. More specifically, the reverse roller 121 is in contact with the paper feed belt 120 at a predetermined pressure. When the reverse roller 121 is in contact with the paper feed belt 120 directly or via one original, the reverse roller 121 is counterclockwise as the paper feed belt 120 rotates. Rotate in the direction. On the other hand, when two or more originals enter between the paper feeding belt 120 and the reverse roller 121, the follower force is set to be lower than the torque of the torque limiter, and the reverse roller 121 is driven in the original driving direction. Rotate clockwise to push back excess manuscript. As a result, double feeding of documents is prevented.

  The original separated into one sheet by the action of the paper feeding belt 120 and the reverse roller 121 is sent to the registration portion C side by the paper feeding belt 120, and further advances after the leading edge is detected by the abutting sensor 122. It strikes against the pull-out roller 123 that has stopped. Thereafter, the document is fed by a predetermined distance from the detection of the abutting sensor 122, and the paper feeding motor 102 is stopped in a state where it is pressed against the pull-out roller 123 with a predetermined amount of bending, thereby feeding the paper belt. The driving of 120 stops. At this time, by rotating the pickup motor 101, the pickup roller 118 is retracted from the upper surface of the document, and the document is fed only by the conveying force of the paper feed belt 120, so that the leading edge of the document is in the nip of the upper and lower rollers of the pull-out roller 123. Entry and tip alignment (skew correction) are performed.

  The pull-out roller 123 has a skew correction function and is a roller for conveying the skew-corrected document after separation to the intermediate roller 124, and is driven by reverse rotation of the paper feed motor 102. In addition, when the paper feed motor 102 rotates in the reverse direction, the pull-out roller 123 and the intermediate roller 124 are driven, but the pickup roller 118 and the paper feed belt 120 are not driven.

  A plurality of document width sensors 125 are provided side by side in the depth direction of FIG. 2 and detect the size in the width direction orthogonal to the transport direction of the document transported by the pull-out roller 123. Further, the length of the document in the conveyance direction is detected from the motor pulse by reading the leading edge and the trailing edge of the document with the abutment sensor 122.

  When the document is conveyed from the registration unit C to the turn unit D by driving the pull-out roller 123 and the intermediate roller 124, the conveyance speed at the registration unit C is set higher than the conveyance speed at the first reading conveyance unit E. Thus, the processing time for sending the document to the image reading unit is shortened. When the leading edge of the document is detected by the reading entrance sensor 126, before the leading edge of the document enters the nip between the pair of upper and lower rollers of the reading entrance roller 127, the document is decelerated to make the document transportation speed the same as the reading transportation speed. Simultaneously with the start, the reading motor 103 is driven forward to drive the reading inlet roller 127, the reading outlet roller 128, and the CIS outlet roller 129. When the registration sensor 130 detects the leading edge of the document, the controller 150 decelerates the document conveyance speed over a predetermined conveyance distance, temporarily stops the document in front of the first image reading unit 131, and controls the main body control unit. A registration stop signal is transmitted to 10 via the I / F 107.

  Subsequently, when a reading start signal is transmitted from the main body control unit 10 to the controller 150 via the I / F 107, the controller 150 moves the registration stopped document to the position of the first image reading unit 131. It is transported at an increased speed so as to rise to a predetermined transport speed before reaching. At this time, the position of the leading edge of the document is detected based on the pulse count of the reading motor 103, and at the timing when the leading edge of the document reaches the first image reading unit 131, the sub-scanning direction (the document A gate signal indicating an effective image area in the same direction as the conveyance direction) is transmitted. This gate signal is continuously transmitted until the trailing edge of the document leaves the first image reading unit 131. Then, while the original is conveyed by the driving of the reading entrance roller 127 and the reading exit roller 128, the first image reading unit 131 reads the surface image of the original.

  In the case of single-sided original reading, the original whose surface image has been read by the first image reading unit 131 of the first reading conveyance unit E passes through the second reading conveyance unit F as it is and is conveyed to the paper discharge unit G. Is done. At this time, when the paper discharge sensor 132 detects the leading edge of the document, the controller 150 drives the paper discharge motor 104 to rotate forward to rotate the paper discharge roller 133 counterclockwise. Further, the controller 150 detects the discharge motor driving speed immediately before the trailing edge of the document comes out of the nip of the upper and lower roller pairs of the discharge roller 133 based on the pulse count of the discharge motor 104 from the detection of the leading edge of the document by the discharge sensor 132. Is controlled so that the document discharged onto the sheet discharge tray 134 of the stack portion H does not jump out.

  On the other hand, in the case of double-sided original reading, the position of the leading edge of the document being conveyed is detected by the pulse count of the reading motor 103 after the leading edge of the document is detected by the paper discharge sensor 132, and the second reading conveyance unit F 2nd. At the timing when the leading edge of the document reaches the position of the image reading unit 135, a gate signal indicating an effective image area in the sub-scanning direction on the back side of the document is transmitted from the controller 150 to the second image reading unit 135. This gate signal is continuously transmitted until the trailing edge of the document leaves the second image reading unit 135. Then, while the original is conveyed by driving the reading exit roller 128 and the CIS exit roller 129, the second image reading unit 135 reads the back side image of the original by the original flow reading method (sheet through reading). The second reading roller 136 disposed opposite to the second image reading unit 135 suppresses the floating of the original in the second image reading unit 135 and at the same time, a reference for acquiring shading data in the second image reading unit 135. It also serves as a white part. In addition, the roller facing the first reading unit 131 also serves as a reference white portion for acquiring shading data in the first image reading unit 131 while suppressing the floating of the document.

  In the copying machine 1 according to the present embodiment, the second image reading unit 135 of the ADF 100 described above is configured as a CIS image reading apparatus. Hereinafter, the second image reading unit 135 will be described in more detail.

  FIG. 4 is a diagram for explaining a main part of the electric circuit 210 in the second image reading unit 135. As shown in the figure, the second image reading unit 135 is individually connected to the light source unit 200 including an LED array, the linear image sensor 201 having two sensor chip groups, and each sensor chip of the sensor chip group. A plurality of amplifier circuits 202, and a plurality of A / D conversion circuits 203 connected to each amplifier circuit 202. The second image reading unit 135 includes a black correction unit (not shown) that removes a black level offset other than signal components included in the output signal of the A / D conversion circuit 203, and a document read by the linear image sensor 201. An image processing unit 205 that generates the image data, a frame memory 206 that holds the image data generated by the image processing unit 205 in units of frames, an output control circuit 207 that controls output of the image data, and an I / F circuit 208 With.

  Each of the sensor chip groups 300A and 300B included in the linear image sensor 201 has a configuration in which a plurality of sensor chips are arranged at the same position in the sub-scanning direction (direction corresponding to the document conveying direction), that is, the main scanning direction (document width). This is a configuration having a plurality of sensor chips arranged along a direction corresponding to the direction. Each sensor chip constituting the sensor chip group 300A, 300B is a sensor chip referred to as an equal magnification contact image sensor, and a plurality of photoelectric conversion elements arranged in a straight line in the main scanning direction corresponding to the pixels. And an optical lens. As will be described in detail later, the linear image sensor 201 used in the second image reading unit 135 includes two sensor chip groups 300A and 300B arranged in parallel to each other at different positions in the sub-scanning direction, and the sensor chip group 300A. The boundary position between the sensor chips in FIG. 5 and the boundary position between the sensor chips in the sensor chip group 300B are arranged so as to be different in the main scanning direction.

  In the ADF 100, a lighting ON signal is sent from the controller 150 to the light source unit 200 before the document enters the reading position by the second image reading unit 135. As a result, the light source unit 200 is turned on, and the light is irradiated toward the document that has entered the reading position of the second document reading unit 135. The reflected light reflected from the document is condensed on the photoelectric conversion element by the condenser lens and read as image information in each sensor chip of the sensor chip groups 300A and 300B included in the linear image sensor 201. Image signals read by the sensor chips of the sensor chip groups 300A and 300B are amplified by the amplifier circuit 202 and then converted to digital data by the A / D conversion circuit 203.

  Each digital data output from the A / D conversion circuit 203 is input to the image processing unit 205 after the offset component is removed by the black correction unit 204. The image processing unit 205 performs shading correction and the like on the input digital data, and then generates image data of a document using these data and temporarily stores it in the frame memory 206.

  Thereafter, the image data of the document stored in the frame memory 206 is converted into a data format that can be received by the main body control unit 10 by the output control circuit 207, and is then sent to the main body control unit 10 via the I / F circuit 208. Is output. The controller 150 notifies the second image reading unit 135 of the timing at which the leading edge of the document reaches the reading position by the second image reading unit 135 (image data after that timing is treated as valid data). The timing signal, the lighting signal of the light source unit 200, the power source for driving the sensor chip groups 300A and 300B of the light source unit 200 and the linear image sensor 201, the A / D conversion circuit 203, and the like are output. Yes.

  FIG. 5 is a block diagram illustrating a functional configuration of the CPU 160 included in the controller 150. As shown in FIG. 5, the controller 150 includes a CPU 160, a ROM 161, and a RAM 162. The CPU 160 has functions of a light amount level calculation unit 165, a light amount peak value detection unit 166, an initial light amount adjustment value calculation unit 167, an output level peak value detection unit 168, and a light amount adjustment value calculation unit 169 described later.

  The light amount level calculation unit 165 sets each light emitting element of the light source unit 200 to a predetermined light amount, and subtracts the black level read with the incident light being zero from the output level obtained by reading the reference white plate. Calculate the level. The light amount peak value detection unit 166 calculates a peak value in all main scanning effective pixels of the light amount level calculated by the light amount level calculation unit 165. The initial light amount adjustment value calculation unit 167 calculates an initial light amount adjustment value from the ratio between the peak value of the light amount level calculated by the light amount peak value detection unit 166 and a predetermined target value. The output level peak value detection unit 168 sets the peak value of the output level when the light source unit 200 is simultaneously turned on and the reference white plate is read with the initial light amount adjustment value calculated by the initial light amount adjustment value calculation unit 167 set. To detect. The light amount adjustment value calculation unit 169 sets a ratio K by which the initial light amount adjustment value is multiplied in consideration of the black level so that the white level target value is adjusted based on the peak value detected by the output level peak value detection unit 168. The light quantity of the light source unit 200 is adjusted by calculating.

  Next, light amount adjustment when the light source unit 200 is an LED (Light Emitting Diode) will be described below. FIG. 6 is an explanatory diagram showing light amount adjustment when the light source unit 200 is an LED. In FIG. 6, XLSYNC is a signal of one line, and is a signal which becomes “L” (low level) for a period corresponding to several pixels at the head of the line. LED_ON is a signal that is in the lighting period “H” (high level) in synchronization with the rise of the XLSYNC period.

  The adjustment of the light amount is realized by adjusting the assertion period of the LED_ON signal. The LED_ON signal is a signal generated based on a reference clock inside the controller 150, and for adjusting the assertion period, for example, a register for setting the number of clocks is provided inside the controller 150, and the clock signal set in each register The configuration is such that the number is counted and a signal is output. Note that the LED_ON signal is asserted for R, G, and B separately, and the light amount can be adjusted individually for R, G, and B.

  FIG. 7 is a timing chart showing light amount adjustment when reading a color image (A) and reading a monochrome image (B). As shown in FIG. 7A, in the color reading mode, the R, G, and B LEDs are sequentially lit while the LED_ON signal assert period is set for each of R, G, and B. In this case, the image data at the RED LED is RED (red) data, the GREEN LED data is GREEN (green) data, and the BLUE LED data is It is acquired as BLUE (blue) data.

  On the other hand, in the monochrome reading mode as shown in FIG. 7B, the R, G, and B LEDs are turned on at the same time with the LED_ON signal assertion period set for each of R, G, and B. At this time, the image data is acquired as monochrome data in the image processing unit 205. Since the output level of each sensor chip of the sensor chip group 300A, 300B is an integral value of the light amount, in the monochrome reading mode, the R, G, B LEDs are simultaneously turned on so that a sufficient amount of light can be obtained even at high speed reading. The image can be read.

  FIG. 8 is a flowchart showing an operation example (1) at the time of white level adjustment. This operation is executed by each functional configuration of the CPU 160. When the white level adjustment is started, in order to obtain the light amount level when the LED (light source unit 200) is turned on individually for R, G, and B, first, the color reading mode (the light source unit 200 (LED) is sequentially set). (Lighting) is set (step S1). Subsequently, the lighting time of the LED is set so that a predetermined light amount is obtained, the light source unit 200 is turned on (step S2), the reference white plate is read, and the output converted into digital data by the A / D conversion circuit 203 Data (referred to as white level data) is acquired (step S3).

  The LED lighting time at this time may be set so that the white level data does not saturate so that the output level (white level data) at the time of reading the reference white plate can be accurately measured. For example, if white level data is saturated when scanned at a lighting time of 100%, it is reduced to 50%, the reference white plate is read again, and white level data is acquired repeatedly until the white level data is not saturated. To do.

  Next, the light quantity level calculation unit 165 calculates the light quantity level for each of R, G, and B (steps S4 to S6). The light level is a sensor output corresponding to a result obtained by integrating the black level read with the incident light being zero from the output level at the time of reading the reference white plate with the difference amount and the light emission amount of the LED with the light emission time. is there.

  First, the light source unit 200 is turned off (step S4), and black level data is acquired (step S5). The linear image sensor 201 has a subtractor for black level data (not shown), and subtracts the black level acquired in step S5 from the white level data acquired in step S3 to calculate the light amount level (step S6).

  Next, an initial light amount adjustment (initial lighting time of the LED light source) is calculated (steps S7 to S8). The light quantity peak value detection unit 166 has a peak detection means from all effective main scanning pixels (not shown) in the linear image sensor 201 based on the R, G, B light quantity levels acquired in step S6, and the peak detection means acquires in step S6. The peak values of all the main scanning effective pixels at the R, G, B light quantity levels are detected (step S7). Note that if the peak value in all effective pixels is matched to the target level, the light amount level does not exceed the target level.

  The peak values are R: Wpk_r, G: Wpk_g, and B: Wpk_b, respectively. The initial light amount adjustment values are set so that Wpk_r, Wpk_g, and Wpk_b are the respective predetermined target levels T1r, T1g, and T1b. Since the light amount and the light amount level are proportional, the initial light amount adjustment value calculation unit 167 includes the following: R, G, and B initial light quantity adjustment values are calculated from the equation (step S8).

Initial light intensity adjustment value (R) = (R lighting time when reading white level data) × T1r / Wpk_r
Initial light intensity adjustment value (G) = (G lighting time when reading white level data) × T1 g / Wpk_g
Initial light intensity adjustment value (B) = (B lighting time when reading white level data) × T1 g / Wpk_b

  Here, a method for setting the target levels T1r, T1g, and T1b will be described. First, the initial light intensity when simultaneously lighting must be set to a value that does not cause the white level at the initial light intensity to exceed the dynamic range (do not saturate), so the total target level of each color = white level target Value-Set to the maximum black level.

  The reason for the above setting will be described below. FIG. 9A is an explanatory diagram showing a case where the target value of the total R, G, and B initial light amounts is calculated as the black minimum. FIG. 9B is an explanatory diagram showing a case where the target value of the total R, G, and B initial light amounts is calculated as black maximum.

  Since the white level at the time of reading the reference white plate when the light source unit 200 is simultaneously turned on is the total value of each light amount level and black level when R, G, and B are individually turned on, R, G, B The target value of each color may be set so that the total value of the light amount levels of the respective colors becomes (target value) − (black level). However, since the black level varies in the linear image sensor 201 or the like, if the black level is set to be the minimum, the white level target value may be exceeded and saturated if the actual black level is the maximum. Yes (see FIG. 9A).

If the output is saturated, the peak value of the white level cannot be detected accurately. Therefore,
(Total value of target levels for each color) = (White level target value)-(Black level maximum value)
As a result, even when the black level varies, the white level at the initial light amount adjustment value does not exceed the dynamic range (see FIGS. 9 and 9B).

  Further, the ratio of the target levels T1r, T1g, and T1b of each color is finally set so as to be the color balance of R, G, and B when the light source unit 200 is simultaneously turned on. For example, when the color balance of R, G, and B is desired to be 1: 1: 1, T1r: T1g: T1b = 1: 1: 1 is set.

  In this way, the total of the target values of the LEDs of the respective colors at the time of calculating the initial light amount adjustment value is set to be a difference between the white level target value and the maximum black level that can be assumed. If saturated, the exact proportional relationship between the light quantity and the light quantity level cannot be obtained, and the ratio K for multiplying the initial light quantity at the time of simultaneous lighting cannot be accurately calculated. It is necessary to set the white level with the amount of light so that it does not saturate without exceeding the dynamic range. The white level at the time of simultaneous lighting is a value obtained by adding the black value to the total value of the light amount level (the black level is subtracted from the data at the time of reading the white plate) when each color is lighted independently. Therefore, if the initial light amount is set so that the total light amount level of each color = white level target value−black level max, the value is not necessarily saturated at the time of simultaneous lighting, and the ratio K can be accurately obtained.

  Further, in the case where the characteristic color of a color original is emphasized and reproduced as a monochrome image, the ratio may be set such that the light amount level of the LED of the specific color is lowered. Generally, since it is only necessary to reduce the light amount of the light emitting element corresponding to the color component whose density is to be increased as the color balance of each color of the white light source, when it is desired to emphasize G, T1r: T1g: T1b = 2: 1: 2 You can make it.

  Next, white level adjustment is performed in consideration of the black level when the light source unit 200 is simultaneously turned on (steps S9 to S16).

  With the light amount adjustment value calculated in step S8, the balance of the light amount of each color can be adjusted, but the dynamic range cannot be effectively used because it is adjusted below the variation of the black level from the white level target value. . Therefore, since the dynamic range can be effectively utilized by amplifying the amount of light corresponding to the variation in the black level, a white level adjustment method considering the black level is performed. Hereinafter, an example of white level adjustment in consideration of the black level will be described.

  Since the linear image sensor 201 has a plurality of sensor chips, the black level of each sensor chip is different. Therefore, it is difficult to predict the black level at the white level peak level. Therefore, the black level is estimated using the following method, and the amplification factor K for amplifying the initial light amount adjustment value is calculated.

  In FIG. 8, first, the initial light amount adjustment value calculated in steps S7 to S8 is set for each color LED (step S9), and the setting for switching to the monochrome reading mode is performed (step S10), and the light sources are turned on simultaneously (step S10). S11), the white level data when the reference white plate is read is acquired, and the peak value in all the main scanning effective pixels is detected and set as the first white level peak value Pk1 (step S12).

  Next, a lighting time that is ½ of the initial light amount adjustment value is set for each light source (step S13), white level data obtained when the reference white plate is read in a state in which the light sources are simultaneously turned on is acquired, and all the main scanning effective pixels are obtained. The peak value in the middle is detected and set as the second white level peak value Pk2 (step S14). In this example, the light amount adjustment value at the time of detecting Pk2 is ½ of the initial light amount adjustment value, but the second white level peak value Pk2 of another light amount is maintained in a state where the color balance of R, G, B is maintained. As long as it can be detected, each initial light amount adjustment value may be a value that is decreased at the same rate. Subsequently, the amplification factor K is calculated from Pk1 and Pk2 as follows (step S15).

Initial light intensity adjustment (lighting time) R, G, B total value ... a
R, G, B total value of initial light intensity adjustment (lighting time) ... b (= a / 2)
White level target value TR, G, B
Then, the amount of light change ΔW per lighting time unit is
ΔW = (Pk1−Pk2) / (ab)
Accordingly, since the lighting time required to match the white level target value is ((TR, G, B−Pk1) / ΔW) + a, the amplification factor K can be obtained from the following equation.
K = ((TR, G, B−Pk1) / ΔW) + a) / a
Each light intensity adjustment value (lighting time)
Light intensity adjustment value (R) = Initial light intensity adjustment value (R) × K
Light intensity adjustment value (G) = Initial light intensity adjustment value (G) x K
Light intensity adjustment value (B) = Initial light intensity adjustment value (B) × K
(Step S16).

  In the case of the above equation, the light intensity adjustment values of R, G, and B are multiplied by a constant amplification factor, so that the white level can be adjusted to the white level target value while the light intensity balance of each color is kept constant. This completes the white level adjustment.

  In the above-described embodiment, when light sources having light emitting elements of different colors are turned on simultaneously, output in the dark: even when the black level is different for each pixel or chip, the light quantity is maintained while maintaining the color balance of each color. It is possible to obtain a light amount amplification factor that can accurately match the peak value to the white level adjustment target value. Accordingly, the reading value of the reference white plate can be accurately adjusted to the white level target value, and as a result, the dynamic range of the A / D conversion circuit 203 is effectively used as compared with the case where the light amount adjustment of the embodiment is not performed. It will be possible.

  As described above, the ratio of multiplying the initial light amount adjustment value for reaching the white level adjustment target value when the light source is simultaneously turned on is determined based on the output data obtained by reading the reference white plate with the initial light amount adjustment value and the initial light amount adjustment value of each color. This is calculated from the output data obtained by reading the reference white plate at a reduced ratio. As a result, in an image sensor such as the linear image sensor 201 in which the black level varies, it is difficult to accurately obtain the light amount adjustment. Therefore, even when the black level varies by the above method, the amplification factor K can be accurately calculated. Therefore, the white level can be adjusted with high accuracy.

  FIG. 10 is a flowchart showing an operation example (2) during white level adjustment. Up to the initial light amount adjustment value setting (steps S21 to S30) in this operation, the same operations as in steps S1 to S10 described in FIG. 8 are executed. After setting the initial light amount adjustment value, the light source unit 200 is turned on (step S31), and the white level data peak value Pk in the main scanning all effective image at the time of reading the reference white plate is acquired (step S32).

  Next, it is determined whether or not the white level data peak value Pk is within a range (for example, 190 <Pk <210) in which the white level target value has an adjustment tolerance (step S33). Here, if it is within the tolerance range of the white level target value (determination Yes), the white level adjustment is terminated.

  On the other hand, the case where the white level target value is not within the tolerance range in Step S33 (determination No) will be described below. The amplification factor K is calculated so that the amplification amount is amplified at a constant level in each light quantity adjustment value (step S34).

For example, the amplification factor K is calculated by the following equation so that the amplification amount is about 10.
K = 1 + 10 / (Pk−Bk)
Here, Bk represents a black level, and an average value of all the main scanning effective pixels of the black level acquired in step S34 may be used, or a black level value obtained in advance by design calculation may be used. Actually, since the black level amount of the Pk value is unknown, when the above amplification factor is set, the amplification amount is not exactly 10, but an amplification amount close to 10 is obtained.

  Next, the light amount adjustment value = previous light amount adjustment value × K is set for each color (step S35). When the reference white plate is read again in this state, a Pk value increased by about 10 from the previously read Pk value can be obtained.

  Then, it is confirmed again whether the Pk value is within the tolerance range of the white level target value. If not, the operation of step S34 → step S35 → step S31 → step S32 → step S33 is repeated, Can adjust the white level within the tolerance range of the white level target value. In this case, since the white level is gradually brought closer to the target value, the upper limit of the tolerance range of the white level adjustment target value is not exceeded. Therefore, even when the black level varies, the white level can be adjusted while maintaining the color balance of R, G, and B.

  That is, the ratio of multiplying the initial light amount adjustment value for accurately adjusting the white level target value at the time of simultaneous lighting of the light source is gradually increased at a constant rate, as described above, as in the linear image sensor 201. In an image sensor with a black level variation, it is difficult to accurately calculate the light amount. Therefore, even when the black level varies with the above method, the amplification factor K can be accurately calculated. Can be adjusted.

  Further, the linear image sensor 201 in which the light amount adjustment is performed in this embodiment is arranged with a plurality of sensor chips that perform photoelectric conversion as described above. Since there are a plurality of sensor chips, the dark output level varies from chip to chip, but the dynamic range of the A / D conversion circuit can be effectively utilized by using the light amount adjustment in this embodiment.

  In addition, in the light source of the LED, the light amount integrated by the light source lighting time is the light amount level. Therefore, the light amount of the LED light source can be easily adjusted by ON / OFF control of the light source.

  In addition, as shown in FIG. 2, the image reading apparatus is provided with a front-side CIS 131 and a back-side CIS 135, and targets for calculating initial light amount adjustment values of light-emitting elements of the same color as the light sources of the respective image-reading apparatuses. Same value. As a result, the CIS 131 for reading the front surface and the CIS 135 for reading the back surface in the double-sided simultaneous reading apparatus can make the ratio of each color the same at all output levels and the color balance is the same, so there is no difference in image quality between the front surface reading and the back surface reading. .

  By the way, the program executed in the present embodiment is provided by being incorporated in the ROM 161 in advance, but is not limited to this. The program executed in the present embodiment can be read by a computer such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk), etc. in an installable or executable file. It may be recorded on a recording medium and provided as a computer program product.

  Further, the program executed in the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. In addition, the program executed in the present embodiment may be configured to be provided or distributed via a network such as the Internet.

  The program executed in the present embodiment includes the above-described light amount level calculation unit 165, light amount peak value detection unit 166, initial light amount adjustment value calculation unit 167, output level peak value detection unit 168, and light amount adjustment value calculation unit 169. The module has a module configuration. As actual hardware, the CPU 160 (processor) reads the program from the recording medium and executes the program, so that each unit is loaded on the main storage device such as the RAM 162, and the light amount level calculation unit 165, A light amount peak value detection unit 166, an initial light amount adjustment value calculation unit 167, an output level peak value detection unit 168, and a light amount adjustment value calculation unit 169 are generated on the main storage device.

1 Copier 131 First Reading Unit (CIS)
135 Second reading unit (CIS)
150 controller 160 CPU
161 ROM
162 RAM
165 Light quantity level calculation part 166 Light quantity peak value detection part 167 Initial light quantity adjustment value calculation part 168 Output level peak value detection part 169 Light quantity adjustment value calculation part 200 Light source part 201 Linear image sensor

JP 2006-2111175 A JP 2005-295158 A

Claims (9)

An image reading apparatus having a light source composed of a plurality of light emitting elements having different emission colors, a photoelectric conversion unit that photoelectrically converts reflected light from a document, and a reference white plate that is read by the photoelectric conversion unit,
A light amount level obtained by subtracting a black level read in a state where incident light is zero from an output level of effective pixels in all main scanning directions obtained by reading the reference white plate with each light emitting element of the light source having a predetermined light amount. A light level calculation unit for calculating
A maximum value detecting unit for detecting a maximum value in all main scanning effective pixels of the light amount level calculated by the light amount level calculating unit;
An initial light amount adjustment value calculating unit that calculates an initial light amount adjustment value of each light emitting element of the light source from a ratio between the maximum value of the light amount level detected by the maximum value detecting unit and a predetermined target value;
An output level maximum value detection unit that detects the maximum value of the output level when the reference white plate is read by simultaneously turning on the light source in a state where the initial light amount adjustment value calculated by the initial light amount adjustment value calculation unit is set; ,
Based on the maximum value detected by the output level maximum value detection unit, a ratio for multiplying the initial light amount adjustment value in consideration of the black level so as to be adjusted to the white level target value is calculated, and the light amount of the light source A light amount adjustment value calculation unit for adjusting
An image reading apparatus comprising:   The initial light amount adjustment value calculating unit adjusts the initial light amount so that the total of the target values of the light emitting elements of the respective colors at the time of calculating the initial light amount adjustment value is a difference between the white level target value and the maximum expected black level. The image reading apparatus according to claim 1, wherein a value is calculated.   The initial light amount adjustment value calculation unit is configured to multiply the initial light amount adjustment value for reaching the white level adjustment target value at the time of simultaneous lighting of the light source, output data obtained by reading the reference white plate with the initial light amount adjustment value, and 3. The image reading apparatus according to claim 1, wherein the image reading device is calculated from output data obtained by reading the reference white plate while reducing an initial light amount adjustment value of each color by a predetermined ratio.   The initial light amount adjustment value calculating unit gradually increases a ratio of multiplying the initial light amount adjustment value for adjusting to the white level target value when the light sources are simultaneously turned on at a constant rate. The image reading apparatus according to claim 1, 2, or 3.   The image reading apparatus according to claim 1, wherein the photoelectric conversion unit includes a plurality of sensor chips that perform photoelectric conversion.   The image reading apparatus according to claim 1, wherein the light source is an LED light source, and the light amount adjustment value calculation unit controls a lighting time of the light source.   The photoelectric conversion unit and the light source are respectively arranged at positions to read images on the front and back sides of the document to be read, and the initial light amount adjustment value calculation unit has the same color in each light source corresponding to the front and back sides of the document. The image reading apparatus according to claim 1, wherein the target value of the initial light amount adjustment value of the light emitting element is calculated as the same value for both the front surface and the back surface of the document. Executed by an image reading apparatus having a light source composed of a plurality of light emitting elements having different emission colors, and having a photoelectric conversion unit that photoelectrically converts reflected light from a document, and a reference white plate that is read by the photoelectric conversion unit. An image reading method comprising:
A light amount level obtained by subtracting a black level read in a state where incident light is zero from an output level of effective pixels in all main scanning directions obtained by reading the reference white plate with each light emitting element of the light source having a predetermined light amount. A light level calculation process for calculating
A maximum value detecting step for detecting a maximum value in all main scanning effective pixels of the light amount level calculated by the light amount level calculating step;
An initial light amount adjustment value calculating step of calculating an initial light amount adjustment value of each light emitting element of the light source from a ratio between the maximum value of the light amount level detected in the maximum value detecting step and a predetermined target value;
An output level maximum value detecting step for detecting a maximum value of an output level when the reference white plate is read by simultaneously turning on the light sources in a state where the initial light amount adjustment value calculated in the initial light amount adjustment value calculating step is set; ,
Based on the maximum value detected in the output level maximum value detection step, a ratio for multiplying the initial light amount adjustment value in consideration of the black level so as to be adjusted to the white level target value is calculated, and the light amount of the light source A light amount adjustment value calculating step for adjusting
An image reading method comprising: A program for causing a computer to execute a computer having a light source composed of a plurality of light emitting elements having different light emission colors and photoelectrically converting reflected light from a document and a reference white plate read by the photoelectric conversion unit Because
A light amount level obtained by subtracting a black level read in a state where incident light is zero from an output level of effective pixels in all main scanning directions obtained by reading the reference white plate with each light emitting element of the light source having a predetermined light amount. A light level calculation step for calculating
A maximum value detecting step for detecting a maximum value in all main scanning effective pixels of the light amount level calculated by the light amount level calculating step;
An initial light amount adjustment value calculating step for calculating an initial light amount adjustment value of each light emitting element of the light source from a ratio between the maximum value of the light amount level detected in the maximum value detecting step and a predetermined target value;
An output level maximum value detecting step for detecting a maximum value of an output level when the reference white plate is read by simultaneously turning on the light sources in a state where the initial light amount adjustment value calculated in the initial light amount adjustment value calculating step is set; ,
Based on the maximum value detected in the output level maximum value detection step, a ratio for multiplying the initial light amount adjustment value in consideration of the black level so as to be adjusted to the white level target value is calculated, and the light amount of the light source A light amount adjustment value calculating step for adjusting
For causing the computer to execute.

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