JP2007208939A - Image reader, image reading method, and image reading program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader, an image reading method and an image reading program which can maintain a stable reading level. <P>SOLUTION: The image reader has an analog processing circuit having an amplifier for causing an exposure device to expose an original placed on an original platen, and amplifying the level of an analog electric signal output from a photoelectric conversion element for converting a reflection light of the original into the analog electric signal; and an A/D converter for converting the analog electric signal output from the amplifier into a digital signal. The image reader has the photoelectric conversion element for reading a white reference plate equipped on the image reader and the original, and the analog processing circuit has a gain calculating means for calculating a gain value of the amplifier from a digital signal of the white reference plate output from the A/D converter. The amplifier amplifies the level of the analog electric signal on the basis of the gain value calculated by the gain calculating means. Thus, a time required for gain adjustment in an image reading operation process can be shortened. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image reading apparatus, an image reading method, and an image reading program, and in particular, an image reading apparatus, an image reading method, and an image reading capable of maintaining a stable reading level even when a light amount variation such as a lamp occurs. Regarding the program.

  The system configuration of the conventional image reading apparatus includes a photoelectric conversion element 201, an analog buffer 202, an AC coupling 203, a line clamp 204, an S & H 205, a VGA 206, an A / D converter 207, an averaging circuit 208, a Peak detection circuit 209, and a CPU 210. (Shown in FIG. 2).

  The photoelectric conversion element 201 converts the reflected light of the document image into an analog electric signal by photoelectric conversion. The analog buffer 202 buffers an analog electric signal output from the photoelectric conversion element 201.

  An analog electrical signal obtained in the photoelectric conversion element CCD 201 is input to an analog processing IC that performs analog processing via an analog buffer 202 and an AC coupling 203.

  In the analog processing IC, first, the line clamp circuit 204 performs clamping in the black pixel output period in one CCD output line so as to keep the potential between one line constant. During this black pixel output period, the photoelectric conversion element 20 is shielded from light, and the level does not fluctuate even when light (document reflected light) enters. Therefore, the output of the photoelectric conversion element 201 during this black pixel output period is referred to as “black level” with the absolute black reference of the image data. That is, there is no signal at a level lower than this.

  The S & H unit 205 converts the image signal into a continuous analog signal by sampling and holding the image signal with a sample pulse. VGA (a variable gain amplifier 206 amplifies the image signal sampled and held in the S & H unit 205 with a gain value.

  The A / D conversion circuit 207 converts to a digital signal based on a reference level generated from a reference voltage, and outputs digital data of image data.

  Digital data output from the analog processing IC is input to the averaging circuit 208. The averaging circuit 208 calculates the average of the image signal levels of the pixels constituting each block included in the digital data of the white reference plate 105, and outputs the average value of the image signal levels of each block to the Peak detection circuit 209.

  The Peak detection circuit 209 detects a block having the highest average image signal level and outputs the average image signal level of the block to the CPU 210. The CPU 210 calculates a difference between the average value input from the peak detection circuit 209 and a preset value, and calculates a gain value. The gain value calculated by the CPU 210 is input to the VGA 206, and the image signal is amplified using the gain value.

In Patent Document 1, an image reading apparatus that exposes a document placed on a document placement table by an exposure device and reads the document using a photoelectric conversion element that converts reflected light of the document into an electric signal, Thereafter, before the image reading, the white reference plate is read by the photoelectric conversion element, the gain of the amplifier is adjusted so that the level of the read image signal becomes a predetermined level, and the level of the read image signal after the adjustment is held. An image reading apparatus having a storage device has been proposed.
Japanese Patent Laid-Open No. 2003-324587

  However, the above invention has the following problems.

  As described above, the conventional image reading apparatus calculates the gain value based on the digital data of the white reference plate 105 outside the analog processing IC, and inputs the calculated value to the analog processing IC again. For this reason, gain adjustment in the VGA 206 takes time due to communication or the like, and it is impossible to quickly cope with fluctuations in the amount of light such as a lamp.

  Conventionally, it is performed separately from the document scanning operation only when the power is turned on. The gain value adjusted when the power is turned on is used in subsequent scans. Therefore, when a short-term fluctuation of the lamp occurs, the digital data can be used only within a narrow range of the dynamic range of the A / D converter when it is amplified and converted into digital data with the gain value at power-on, and the final reading The gradation of the value is deteriorated, and the image processing in the subsequent image processing circuit is hindered.

  Therefore, the present invention exposes a document placed on a document placement table with an exposure device, and converts the level of the analog electrical signal output from the photoelectric conversion element that converts the reflected light of the document into an analog electrical signal at a predetermined level. An image reading apparatus having an analog processing circuit having an amplifier that amplifies the analog electric signal and an A / D converter that converts an analog electric signal output from the amplifier into a digital signal. The analog processing circuit has a gain calculating means for calculating the gain value of the amplifier from the digital signal of the white reference plate output from the A / D converter. , An image reading apparatus, an image reading method, and an image reading program for amplifying the level of the analog electric signal based on the gain value calculated by the gain calculating means It is intended to propose the ram.

  According to the first aspect of the present invention, the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table by the exposure device and converts the reflected light of the document into an analog electrical signal is predetermined. An image reading apparatus having an analog processing circuit including an amplifier that amplifies the signal to an analog level and an A / D converter that converts an analog electric signal output from the amplifier into a digital signal. The image reading apparatus includes: A white reference plate provided in the apparatus and the photoelectric conversion element for reading an original; and the analog processing circuit calculates a gain value of the amplifier from a digital signal of the white reference plate output from the A / D converter. And a gain calculating means.

  According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the photoelectric conversion element reads the white reference plate before the image reading after the power is turned on. The gain value is calculated based on a digital signal of the white reference plate read by a conversion element.

  According to a third aspect of the present invention, in the image reading device according to the first or second aspect, when the image reading is performed in the book read mode, the photoelectric conversion element moves the white reference while returning to the home position after reading the document. The gain is calculated by reading the plate, and the gain calculating means calculates the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element.

  According to a fourth aspect of the present invention, in the image reading apparatus according to the first or second aspect, when the image reading is performed in the sheet through mode, the photoelectric conversion element is located between the white reference plate and the reading position between the documents. The white reference plate is read twice, and the gain calculating means calculates the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element at the time of return. It is characterized by doing.

  According to a fifth aspect of the present invention, in the image reading apparatus according to any one of the first to fourth aspects, when the image reading apparatus is in a standby state, the photoelectric conversion element is configured to cause the white reference plate to be removed every predetermined time. And the gain calculating means calculates the gain value based on the digital signal of the white reference plate read by the photoelectric conversion element.

  According to a sixth aspect of the present invention, in the image reading apparatus according to any one of the first to fifth aspects, the analog processing circuit includes a gain value Gn used for the previous amplification of the analog signal and the gain calculation. Calculation means for calculating a difference from the new gain value Gn + 1 calculated by the means, and storage means for storing the threshold value Gth of the difference, wherein the amplifier calculates the difference calculated by the calculation means. When the difference is smaller than the threshold Gth, the analog electric signal is amplified by the gain value Gn + 1. When the difference calculated by the calculating means is equal to or larger than the threshold Gth, the analog electric signal is again inputted by the gain value Gn. Amplifying.

  According to the seventh aspect of the present invention, the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table by the exposure device and converts the reflected light of the document into an analog electrical signal is predetermined. An amplifier that amplifies the analog electrical signal output from the amplifier to a digital signal, and the amplifier from the white reference plate digital signal output from the A / D converter An image reading method of an image reading apparatus having an analog processing circuit having a gain calculation means for calculating a gain value of the image, a white reference plate and the photoelectric conversion element for reading an original, and reading the image after turning on the power Before, the step of reading the white reference plate by the photoelectric conversion element, the digital of the white reference plate read by the photoelectric conversion element by the gain calculation means Characterized by a step of calculating the gain value based on the signal.

  According to an eighth aspect of the present invention, in the image reading method according to the seventh aspect, when the image reading is performed in the book read mode, the white reference plate is placed on the way to return to the home position after the original is read by the photoelectric conversion element. And a step of calculating the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element. .

  According to a ninth aspect of the present invention, in the image reading method according to the seventh or eighth aspect, when the image reading is performed in the sheet through mode, the photoelectric conversion element is used to provide a gap between the white reference plate and the reading position. The gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element at the time of return by the step of reciprocatingly reading the white reference plate twice. And a step of calculating.

  According to the tenth aspect of the present invention, the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table by the exposure device and converts the reflected light of the document into an analog electrical signal is predetermined. An amplifier for amplifying the analog electrical signal output from the amplifier to a digital signal, and the amplifier from the digital signal of the white reference plate output from the A / D converter An image reading program of an image reading apparatus having an analog processing circuit having a gain calculation means for calculating a gain value of the image, a white reference plate and the photoelectric conversion element for reading an original, and reads an image after power is turned on Before, the white reference plate read by the photoelectric conversion element by the gain calculation means and the process of reading the white reference plate by the photoelectric conversion element And having a process for calculating the gain value based on the digital signal.

  According to an eleventh aspect of the invention, in the image reading program according to the tenth aspect, when the image reading is performed in the book read mode, the photoelectric conversion element causes the white reference plate to be moved in the middle of returning to the home position after reading the document. The processing for reading and the gain calculation means include processing for calculating the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element. .

  According to a twelfth aspect of the present invention, in the image reading program according to the tenth or eleventh aspect, when the image reading is performed in the sheet through mode, the photoelectric conversion element causes the gap between the white reference plate and the reading position between the documents. The gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element at the time of return by the process of reciprocatingly reading the white reference plate twice. And a process of calculating.

  The present invention exposes a document placed on a document table with an exposure device, and amplifies the level of an analog electrical signal output from a photoelectric conversion element that converts reflected light of the document into an analog electrical signal to a predetermined level. And an analog processing circuit having an A / D converter for converting an analog electric signal output from the amplifier into a digital signal. The image reading apparatus includes a white reference plate provided in the image reading apparatus. And an analog processing circuit having a gain calculating means for calculating a gain value of the amplifier from the digital signal of the white reference plate output from the A / D converter. It is necessary for gain adjustment in the image reading operation process by amplifying the level of the analog electric signal based on the gain value calculated by the calculating means. It is possible to shorten the time.

  The configuration and operation of the image reading apparatus according to an embodiment of the present invention will be described below.

  First, the configuration of the image reading apparatus according to the present embodiment will be described with reference to FIG.

  The image reading apparatus according to this embodiment includes a traveling body 101, a lens 103, a photoelectric conversion element 104, a white reference plate 105, and a contact glass 106.

  The scanning operation of the original 102 is performed by reading the original 102 from the original 102 as original information while moving the original 102 on the contact glass 106 in the sub-scanning direction at the time of reading the pressure plate and moving the original 102 at the time of sheet-through reading. Read the reflected light. Reflected light from the original 102 is imaged on the photoelectric conversion element CCD 104 via the lens 103, and is converted into an analog electric signal by photoelectric conversion in the photoelectric conversion element CCD 104. The image reading apparatus performs analog processing and digital processing on the obtained analog electric signal and reads image information as digital data. Further, shading correction is performed in order to make the main scanning distribution of the document uniform. Note that the read data of the white reference plate 105 for shading correction is acquired before the original is scanned.

  Next, the system configuration of the image reading apparatus according to the present embodiment will be described with reference to FIG.

  The system configuration of the image reading apparatus includes a photoelectric conversion element 201, an analog buffer 202, an AC coupling 203, a line clamp 204, an S & H 205, a VGA 206, an A / D converter 207, and a gain adjustment circuit 301 (FIG. 2). To show).

  The photoelectric conversion element 201 converts the reflected light of the document image into an analog electric signal by photoelectric conversion. The analog buffer 202 buffers an analog electric signal output from the photoelectric conversion element 201.

  An analog electrical signal obtained in the photoelectric conversion element CCD 201 is input to an analog processing IC that performs analog processing via an analog buffer 202 and an AC coupling 203.

  In the analog processing IC, first, the line clamp circuit 204 performs clamping in the black pixel output period in one CCD output line so as to keep the potential between one line constant. During this black pixel output period, the photoelectric conversion element 20 is shielded from light, and the level does not fluctuate even when light (document reflected light) enters. Therefore, the output of the photoelectric conversion element 201 during this black pixel output period is referred to as “black level” with the absolute black reference of the image data. That is, there is no signal at a level lower than this.

  The S & H unit 205 converts the image signal into a continuous analog signal by sampling and holding the image signal with a sample pulse. VGA (a variable gain amplifier 206 amplifies the image signal sampled and held in the S & H unit 205 with a gain value.

  The A / D conversion circuit 207 converts to a digital signal based on a reference level generated from a reference voltage, and outputs digital data of image data.

  The gain adjustment circuit 301 calculates a gain value based on the digital data of the white reference plate 105 output from the A / D conversion circuit 207 and inputs the gain value to the VGA 206.

  The gain adjustment circuit 301 includes an averaging circuit 208, a peak detection circuit 209, and a gain value calculation circuit 211. The digital data of the white reference plate 105 output from the A / D conversion circuit 207 is input to the averaging circuit 208. The averaging circuit 208 calculates the average of the image signal levels of the pixels constituting each block included in the digital data of the white reference plate 105, and outputs the average value of the image signal levels of each block to the Peak detection circuit 209.

  The Peak detection circuit 209 detects a block having the highest average image signal level and outputs the average image signal level of the block to the gain value calculation circuit 211. The gain value calculation circuit 211 calculates a difference between the average value input from the peak detection circuit 209 and a preset value, and calculates a gain value. The gain value calculated in the gain value calculation circuit 211 is input to the VGA 206, and the image signal is amplified using the gain value.

  Next, a timing chart of operation control signals of the image reading apparatus according to the present embodiment will be described with reference to FIGS.

  FIG. 4 shows a timing chart of operation control signals in the conventional image reading apparatus. In a reading operation in a conventional image reading apparatus, first, a sub-scanning white reference plate area signal (hereinafter referred to as a SLEAD signal) is asserted to acquire data of the white reference plate 105. Thereafter, the original area is read by a sub-scan original area signal (hereinafter referred to as FGATE signal), and when the forward operation is completed, the traveling body is returned to the home position. Here, the SLEAD signal assertion period for reading the white reference plate 105 first is used as white reference data for shading correction. For this reason, after the traveling body 101 returns to the home position, the white reference plate 105 is read again by the traveling body 101 to acquire an image signal for gain adjustment.

  On the other hand, in the reading operation in the image reading apparatus according to the present embodiment (shown in FIGS. 6 and 7), the SLEAD signal is first asserted to acquire the data of the white reference plate 105. Thereafter, the document area is read by the FGATE signal, and when the forward operation is completed, the SLEAD signal is asserted again, and the data of the white reference plate 105 is acquired in the process in which the traveling body 101 returns to the home position. According to this process, it is not necessary to operate the traveling body again for gain adjustment by reading the white reference plate 105 while the traveling body returns to the home position. Therefore, the time required for gain adjustment in the image reading operation process. Can be shortened.

  Further, when reading images of a plurality of documents in the sheet-through mode, as shown in FIG. 8, the traveling body is reciprocated under the white reference plate 105 at the time of paper separation, the gain is adjusted, and the next scan is performed at the time of return. The white reference plate 105 is read for the shading correction.

  Next, the operation of the image reading apparatus according to this embodiment will be specifically described.

  First, the operation when image reading is performed in the book read mode will be described with reference to FIG.

  When the power of the image reading apparatus is turned on, the traveling body 101 is moved below the white reference plate 105 to read the white reference plate 105, and the analog processing IC calculates a gain value in the gain adjustment circuit 301, and outputs it to the VGA 206. A gain value is set (step S501). Then, it waits for an instruction to start the image reading operation (step S502). When the image reading operation is requested (step S502 / YES), the movement of the traveling body 101 is started and reading of the white reference plate 105 and the original is started based on the timing chart shown in FIG. 6 (step S503).

  When the traveling body 101 starts to move, the photoelectric conversion element 201 reads the white reference plate 105 and the original according to the timing chart shown in FIG. First, it waits for the SLEAD signal to go low (step S504). When the SLEAD signal becomes low (step S504 / YES), the photoelectric conversion element 201 performs reading of the white reference plate 105 (step S505), and when the SLEAD signal becomes high, the reading of the white reference plate 105 ends. Note that the image data of the white reference plate 105 read in step S505 is used as data for shading correction.

  Next, it waits for the FGATE signal to go low (step S506). When the FGATE signal becomes low (step S506 / YES), the photoelectric conversion element 201 reads the original (step S507), and when the FGATE signal becomes high, the reading of the original ends.

  When the FGATE signal becomes High and the reading of the document is completed, the traveling body 101 starts returning to the home position (step S508). Then, in the process of returning to the home position, it waits for the SLEAD signal to go low (step S509). When the SLEAD signal becomes low again (step S509 / YES), the photoelectric conversion element 201 reads the white reference plate 105 in order to obtain a gain value used for amplification of the image signal in the VGA 206 in the next image reading operation. The gain value is calculated (step S510). Then, when the SLEAD signal becomes High, reading of the white reference plate 105 is finished. When all the reading operations by the photoelectric conversion element 201 are completed (step S511), the gain value calculated in step S510 is reflected in the VGA 206 and used in the next image reading operation (step S512).

  Next, FIG. 9 is used to describe the operation in which the gain value is reset regardless of whether or not the image reading operation is requested when a preset time has elapsed since the gain value was reflected on the VGA 206. I will explain.

  When the power of the image reading apparatus is turned on, the traveling body 101 is moved below the white reference plate 105 to read the white reference plate 105, and the analog processing IC calculates a gain value in the gain adjustment circuit 301, and outputs it to the VGA 206. A gain value is set (step S901). Then, it waits for an instruction to start the image reading operation. When a certain time has elapsed since the last gain value was set (step S902 / YES), the traveling body 101 is moved below the white reference plate 105 to read the white reference plate 105, and the analog processing IC performs a gain adjustment circuit. In 301, the gain value is calculated, and the gain value is reset in the VGA 206 (step S901).

  When an image reading operation is requested (step S903 / YES), movement of the traveling body 101 is started and reading of the white reference plate 105 and the original is started based on the timing chart shown in FIG. 6 (step S904). .

  When the traveling body 101 starts to move, the photoelectric conversion element 201 reads the white reference plate 105 and the original according to the timing chart shown in FIG. First, it waits for the SLEAD signal to go low (step S905). When the SLEAD signal becomes low (step S905 / YES), the photoelectric conversion element 201 performs reading of the white reference plate 105 (step S906), and when the SLEAD signal becomes high, the reading of the white reference plate 105 ends. Note that the image data of the white reference plate 105 read in step S906 is used as data for shading correction.

  Next, it waits for the FGATE signal to go low (step S907). When the FGATE signal becomes low (step S907 / YES), the photoelectric conversion element 201 reads the original (step S908), and when the FGATE signal becomes high, the reading of the original ends.

  When the FGATE signal becomes High and the reading of the document is completed, the traveling body 101 starts to return to the home position (Step S909). Then, in the process of returning to the home position, it waits for the SLEAD signal to go low (step S910). When the SLEAD signal becomes low again (step S910 / YES), the photoelectric conversion element 201 reads the white reference plate 105 in order to acquire a gain value used for amplification of the image signal in the VGA 206 in the next image reading operation. The gain value is calculated (step S911). Then, when the SLEAD signal becomes High, reading of the white reference plate 105 is finished. When all the reading operations by the photoelectric conversion element 201 are completed (step S912), the gain value calculated in step S911 is reflected in the VGA 206 and used in the next image reading operation (step S913).

  According to the above operation, when waiting for a scan operation including the energy saving mode, the next scan operation is not performed from the previous scan operation, and when a certain period of time elapses, the white reference plate is read again and the gain adjustment is performed. By updating the value, it is not necessary to adjust the gain when returning to the energy saving mode, and the energy saving mode return time can be shortened.

  Next, when the difference between the gain value Gn set in the VGA 206 and the gain value Gn + 1 newly calculated by the gain adjustment circuit 301 is calculated, and the difference is lower than the threshold value Gth set in the register in advance Next, an operation procedure for resetting the gain value Gn + 1 to the VGA 206 will be described with reference to FIG.

  The system configuration of the image reading apparatus according to the present embodiment is shown in FIG. The image reading apparatus according to the present embodiment includes a determination calculation unit 1101 that performs a gain value update determination in the analog processing IC. In addition, the determination calculation unit 1101 calculates the difference between the gain value Gn and the gain value Gn + 1 by the memory 1102 that stores the gain value Gn and the threshold value Gth, and determines whether the difference is lower than the threshold value Gth. A determination unit 1103 is included. According to this configuration, it is possible to prevent the circuit and the system from becoming complicated by determining whether or not the gain adjustment result is reflected in the next scan in the analog processing IC.

  When the power of the image reading apparatus is turned on, the traveling body 101 is moved below the white reference plate 105 to read the white reference plate 105, and the analog processing IC calculates the gain value Gn in the gain adjustment circuit 301, and the VGA 206 The gain value Gn is set to (step S1001). Then, it waits for an instruction to start the image reading operation. When a predetermined time has elapsed since the last gain value Gn was set (step S1002 / YES), the traveling body 101 is moved under the white reference plate 105 to read the white reference plate 105, and the analog processing IC performs gain adjustment. The circuit 301 calculates the gain value Gn + 1 and determines whether or not the difference between the gain value Gn and the gain value Gn + 1 is lower than the threshold value Gth (step S1013). If the difference is lower than the threshold value Gth (step S1013 / YES), the gain value Gn + 1 is reset to the VGA 206 (step S1001). On the other hand, if the difference is greater than or equal to the threshold Gth (step S1013 / NO), the gain value Gn is reset in the VGA 206 (step S1014).

  When an image reading operation is requested (step S1003 / YES), the movement of the traveling body 101 is started and reading of the white reference plate 105 and the original is started based on the timing chart shown in FIG. 6 (step S1004). .

  When the traveling body 101 starts to move, the photoelectric conversion element 201 reads the white reference plate 105 and the original according to the timing chart shown in FIG. First, it waits for the SLEAD signal to go low (step S1005). When the SLEAD signal becomes low (step S1005 / YES), the photoelectric conversion element 201 performs reading of the white reference plate 105 (step S1006), and when the SLEAD signal becomes high, the reading of the white reference plate 105 ends. Note that the image data of the white reference plate 105 read in step S1006 is used as data for shading correction.

  Next, it waits for the FGATE signal to go low (step S1007). When the FGATE signal becomes low (step S1007 / YES), the photoelectric conversion element 201 reads the original (step S1008), and when the FGATE signal becomes high, the reading of the original ends.

  When the FGATE signal becomes High and the reading of the document is finished, the traveling body 101 starts returning to the home position (step S1009). Then, in the process of returning to the home position, it waits for the SLEAD signal to go low (step S1010). When the SLEAD signal becomes low again (step S1010 / YES), the photoelectric conversion element 201 reads the white reference plate 105 in order to acquire a gain value used for amplification of the image signal in the VGA 206 in the next image reading operation. The gain value Gn + 1 is calculated (step S1011). When the SLEAD signal becomes High, reading of the white reference plate 105 is finished. When all the reading operations by the photoelectric conversion element 201 are completed (step S1012), it is determined whether or not the difference between the gain value Gn and the gain value Gn + 1 is lower than the threshold value Gth (step S1013). When the difference is lower than the threshold value Gth (step S1013 / YES), the gain value Gn + 1 is reset to the VGA 206. On the other hand, if the difference is greater than or equal to the threshold Gth (step S1013 / NO), the gain value Gn is reset in the VGA 206 (step S1014).

  According to the above-described operation, after the gain value Gn + 1 is calculated by the n-th gain adjustment, the difference from the previously calculated gain value Gn is taken, and this difference value is obtained from the threshold value Gth previously set in the register. If the value is low, the image signal is amplified by this gain value Gn + 1 at the next scan, and conversely if it is greater than or equal to the threshold value Gth, the gain value has changed significantly, so this gain value Gn + 1 is not reflected. In addition, by continuously using the gain value Gn during the next scan, it is possible to prevent an inaccurate update to the gain value Gn + 1.

1 is a schematic diagram of an image reading apparatus according to an embodiment. It is a block diagram which shows the system configuration | structure of the conventional image reading apparatus. 1 is a block diagram illustrating a system configuration of an image reading apparatus according to an embodiment. 6 is a timing chart of an image reading operation of a conventional image reading apparatus. It is a flowchart of the operation | movement which sets a gain value. 6 is a timing chart of an image reading operation of the image reading apparatus according to the present embodiment. It is a figure which shows operation | movement of the traveling body at the time of image reading operation in book read mode. It is a figure which shows operation | movement of the traveling body at the time of image reading operation | movement in sheet | seat through mode. It is a flowchart of the operation | movement which sets a gain value. It is a flowchart of the operation | movement which sets a gain value. 1 is a block diagram illustrating a system configuration of an image reading apparatus according to an embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Traveling body 102 Document 103 Lens 104, 201 Photoelectric conversion element 105 White reference plate 202 Analog buffer 203 AC coupling 204 Line clamp 205 S & H
206 VGA
207 A / DC
208 Averaging circuit 209 Peak detection circuit 210 CPU
301 Gain adjustment

Claims (12)

An amplifier that amplifies the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table with an exposure device and converts the reflected light of the document into an analog electrical signal; and In an image reading apparatus having an analog processing circuit having an A / D converter that converts an analog electric signal output from the amplifier into a digital signal,
The image reading device has a white reference plate provided in the image reading device and the photoelectric conversion element for reading a document,
The image reading apparatus according to claim 1, wherein the analog processing circuit includes a gain calculating unit that calculates a gain value of the amplifier from a digital signal of the white reference plate output from the A / D converter. After turning on the power and before reading the image,
The photoelectric conversion element reads the white reference plate,
The image reading apparatus according to claim 1, wherein the gain calculating unit calculates the gain value based on a digital signal of the white reference plate read by the photoelectric conversion element. When reading an image in book read mode,
The photoelectric conversion element reads the white reference plate in the middle of returning to the home position after reading the document,
3. The image according to claim 1, wherein the gain calculating unit calculates the gain value used in a next image reading operation based on digital data of the white reference plate read by the photoelectric conversion element. Reader. When scanning images in sheet-through mode,
The photoelectric conversion element reciprocates between the white reference plate and a reading position between documents, and reads the white reference plate twice.
The gain calculation means calculates the gain value used in the next image reading operation based on digital data of the white reference plate read by the photoelectric conversion element at the time of return. Image reading apparatus. When the image reading apparatus is in a standby state,
The photoelectric conversion element reads the white reference plate every predetermined time,
5. The image reading apparatus according to claim 1, wherein the gain calculating unit calculates the gain value based on a digital signal of the white reference plate read by the photoelectric conversion element. The analog processing circuit includes:
Calculating means for calculating a difference between the gain value Gn used for the previous amplification of the analog signal and the new gain value Gn + 1 calculated by the gain calculating means;
Storage means for storing the threshold Gth of the difference,
The amplifier is
When the difference calculated by the calculation means is smaller than the threshold Gth, the analog electric signal is amplified by the gain value Gn + 1,
6. The image reading apparatus according to claim 1, wherein when the difference calculated by the calculating unit is equal to or greater than the threshold value Gth, the analog electric signal is amplified again by the gain value Gn. . An amplifier that amplifies the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table with an exposure device and converts the reflected light of the document into an analog electrical signal; and An A / D converter that converts an analog electrical signal output from the amplifier into a digital signal, and a gain calculation that calculates a gain value of the amplifier from the digital signal of the white reference plate output from the A / D converter An image reading method of an image reading apparatus comprising: an analog processing circuit having a means; and a white reference plate and the photoelectric conversion element for reading an original,
After turning on the power and before reading the image,
Reading the white reference plate with the photoelectric conversion element;
And a step of calculating the gain value based on a digital signal of the white reference plate read by the photoelectric conversion element by the gain calculating means. When reading an image in book read mode,
The photoelectric conversion element reads the white reference plate in the middle of returning to the home position after reading the document;
The gain calculating means includes a step of calculating the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element. Image reading method. When scanning images in sheet-through mode,
A step of reading the white reference plate twice by reciprocating between the white reference plate and a reading position between documents by the photoelectric conversion element;
The gain calculating means includes a step of calculating the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element at the time of return. 9. The image reading method according to 7 or 8. An amplifier that amplifies the level of the analog electrical signal output from the photoelectric conversion element that exposes the document placed on the document placement table with an exposure device and converts the reflected light of the document into an analog electrical signal; and An A / D converter that converts an analog electrical signal output from the amplifier into a digital signal, and a gain calculation that calculates a gain value of the amplifier from the digital signal of the white reference plate output from the A / D converter An image reading program of an image reading apparatus comprising: an analog processing circuit having a means; and a white reference plate and the photoelectric conversion element for reading an original,
After turning on the power and before reading the image,
A process of reading the white reference plate by the photoelectric conversion element;
An image reading program comprising: calculating the gain value based on a digital signal of the white reference plate read by the photoelectric conversion element by the gain calculating means. When reading an image in book read mode,
The photoelectric conversion element reads the white reference plate in the middle of returning to the home position after reading the document;
11. The gain calculating means includes processing for calculating the gain value used in the next image reading operation based on digital data of the white reference plate read by the photoelectric conversion element. Image reading program. When scanning images in sheet-through mode,
A process of reading the white reference plate twice by reciprocating between the white reference plate and a reading position between documents by the photoelectric conversion element;
The gain calculation unit includes a process of calculating the gain value used in the next image reading operation based on the digital data of the white reference plate read by the photoelectric conversion element at the time of return. The image reading program according to 10 or 11.

Images