JPH07184006A - Image reader - Google Patents

Abstract

PURPOSE:To perform the read processing of high quality with a simple constitution by providing a monitor sensor means, which detects the quantity of light of a light source, and a correcting means which corrects the level value of the reference object used for correction of the level value of image information. CONSTITUTION:In a step 1, the level value of a reference white sheet is read by an optical unit 17. The read processing is executed by sensor elements in a part B of a CCD line image sensor. In a step 2, the white level value detected by reflection monitor sensor elements (part (b)) is read synchronously with the read processing of the level value of this reference sheet. Next, movement of the optical unit 17 is started for the purpose of reading a reflection document, and simultaneously, the read processing of picture information by the CCD line image sensor is started, and shading correction is executed with the level value of the reference white sheet read in the step 1 to read the reflection document. Thus, the level value of the reference wite sheet is updated in real time in accordance with the variance of a reflection light source 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having a structure for reading image information of an original using a line image sensor, and more particularly to an image reading apparatus which realizes a high quality reading process in accordance with a simpler structure than ever before. Regarding the device.

An image reading device has a function of reading image information of an original using a line image sensor. In such an image reading apparatus, it is necessary to construct a structure that realizes high-quality reading processing according to a simple structure.

[0003]

2. Description of the Related Art In a reflection type image reading apparatus for reading an opaque reflective original, a reference white sheet attached to the apparatus is read at the start of reading the original, and shading is performed by using the detected value of the reference white sheet. By correcting the error, the configuration is adopted to realize accurate reading of the original.

Further, in a transmissive image reading apparatus for reading a transparent transparent original, the light amount distribution of the light source is read at the start of reading the original, and the shading is corrected using the detected value of the light source light amount distribution. Therefore, the configuration that realizes accurate reading of the original is adopted.

If such a configuration is adopted and the level value of the read reference object for shading correction varies, accurate reading of the original cannot be realized. Therefore, in the past, as shown in FIG. 10, a transmissive light source 100 (which may include a lighting circuit) for illuminating a transmissive original,
A reflection light source 200 (which may include a lighting circuit) for illuminating a reflection original is configured to emit light in an amount corresponding to the amount of power supply, and a power supply unit for supplying power to these transmission light source 100 and reflection light source 200 is provided. The configuration is such that the power supply amount is variable, and the phototransistor 300 that monitors the light amount of the transmissive light source 100 and the phototransistor 400 that monitors the light amount of the reflective light source 200 are provided, and the light source state is the standard. Processing for adjusting the amount of power supplied by the power supply means so that the detection values of the phototransistors 300 and 400 match those at the time of reading the reference object in order to maintain the values when the object is read. Was running.

In FIG. 10, reference numeral 500 is a transparent document table on which a document is placed, 600 is a line image sensor for reading the image information of the document, and 700 is a diffusion plate for diffusing the light of the transmissive light source 100.

[0007]

However, according to such a conventional technique, the transmissive light source 100 and the reflective light source 200 must be configured to emit the light amount according to the power supply amount, and further, The power supply means for supplying power to the transmissive light source 100 and the reflective light source 200 must be configured with variable power supply amount.
00 and the phototransistors 300 and 400 for monitoring the light quantity of the reflected light source 200 must be provided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a new image reading apparatus that realizes high-quality reading processing in accordance with a simpler configuration than in the past.

[0009]

To achieve this object, a light source and a line image sensor are provided, and according to the line image sensor, the image information of the document illuminated by the light source is read and the reading of the document is started. At this time, the line image sensor reads the level value of the reference object (the light amount distribution of the light source when the transparent original is the reading object, the level value of the reference white sheet when the reflective original is the reading object), and the read reference value In an image reading apparatus having a configuration in which the level value of image information to be read is corrected according to a target level value, in the first aspect of the present invention, the image reading apparatus is provided in the vicinity of the light source and detects the light amount of the light source. A monitor sensor means and a correction means for correcting the level value of the reference object used for correcting the level value of the image information are provided. To configure.

Further, in the second aspect of the present invention, when the image reading device adopts a configuration of reading a transparent original, the light source (which may include a lighting circuit) emits a light amount corresponding to the power supply amount. In addition to the above configuration, the power supply means for supplying power to the light source is configured to have a variable power supply amount. Further, even when the original is being read, one or a plurality of sensor elements at the end portion of the line image sensor are constantly illuminated by the light source, and the sensor element at this end portion is provided. Is set as the monitor sensor means, and is provided with an adjusting means for adjusting the amount of power supplied by the power supply means.

Further, in the third aspect of the present invention, when the image reading device adopts a configuration of reading a transparent original, and even when the original is being read, one or a plurality of end portions of the line image sensor are provided. The sensor element is constantly illuminated by the light source, and the sensor element at this end is set as the monitor sensor means, and the light source light quantity used for correcting the level value of the image information is adopted. It is configured to include a correction unit that corrects the distribution.

Further, in the fourth aspect of the present invention, when the image reading device adopts a configuration of reading a reflective original, the light source (which may include a lighting circuit) emits a light amount according to the power supply amount. In addition to the above configuration, the power supply means for supplying power to the light source is configured to have a variable power supply amount. Further, even when the document is being read, a configuration is adopted in which white-level image information is constantly input to one or a plurality of sensor elements at the end of the line image sensor. The configuration is such that the sensor element is set as the monitor sensor means, and the adjusting means for adjusting the amount of power supplied by the power supply means is provided.

According to the fifth aspect of the present invention, when the image reading device adopts a configuration of reading a reflective original, and even when the original is being read, one or a plurality of end portions of the line image sensor are used. A configuration is adopted in which white-level image information is constantly input to the sensor element, and the sensor element at this end is set as monitor sensor means, and is used to correct the level value of the image information. It is configured to include a correction unit that corrects the level value of the reference white sheet.

[0014]

According to the first aspect of the present invention, the correcting means determines the former detected value from the detected value of the monitor sensor means when reading the original and the detected value of the monitor sensor means when reading the reference object. When it becomes larger than the detection value of, the corresponding level value of the reference object used for the correction of the level value of the image information is corrected accordingly, and the detection value of the former becomes smaller than the detection value of the latter. In some cases, the entire level value of the reference object used for correcting the level value of the image information is corrected accordingly.

According to this configuration, in the first invention of the present invention, a high-quality original reading process can be performed without the need for a light source with a variable light quantity and a power supply means with a variable power supply, which are required in the prior art. To be realized.

Further, in the second aspect of the present invention, when the image reading apparatus adopts the configuration of reading the transparent original, the monitor sensor means for detecting the light source light amount required by the prior art is not provided specially. Thus, by adopting a configuration in which the sensor element at the end portion of the line image sensor is constantly illuminated by the light source, and using the sensor element at this end portion as the monitor sensor means, the conventional technique is performed. Adjust the light source.

According to this structure, in the second aspect of the present invention, a high quality original reading process is realized without the need for special monitor sensor means for detecting the light source light amount, which is required in the prior art.

Further, in the third aspect of the present invention, when the image reading apparatus adopts the configuration of reading the transparent original, the monitor sensor means for detecting the light source light amount required by the prior art is not provided specially. Thus, the sensor element at the end of the line image sensor is constantly illuminated by the light source, and the sensor element at this end is used as the monitor sensor means, and the correction means according to the first aspect of the invention. According to the correction process of the correction unit that exhibits the same function as the above, the high-quality document reading process is realized.

According to this structure, the third invention of the present invention requires a light source with variable light quantity, a power source means with variable power supply, and a special monitor sensor means for detecting the light quantity of the light source, which are required in the prior art. Realizes high-quality document reading processing.

Further, according to the fourth aspect of the present invention, when the image reading apparatus adopts a configuration of reading a reflection original, the monitor sensor means for detecting the light source light amount required by the prior art is not provided specially. Thus, by adopting a configuration in which image information of white level is constantly input to the sensor element at the end of the line image sensor and the sensor element at this end is used as the monitor sensor means, Perform the light source adjustment that the technology was performing.

According to this configuration, in the fourth aspect of the present invention, a high-quality original reading process is realized without the need for a special monitor sensor for detecting the light source light amount, which is required in the prior art.

Further, in the fifth aspect of the present invention, when the image reading apparatus adopts a configuration of reading a reflection original, the monitor sensor means for detecting the light source light amount required by the prior art is not provided specially. Then, the sensor element at the end portion of the line image sensor is always input with the image information of the white level, and the sensor element at the end portion is used as the monitor sensor means.
According to the correction process of the correction unit that exhibits the same function as the correction unit of the first aspect of the invention, the reading process of the high quality original is realized.

According to this configuration, the fifth invention of the present invention requires the light source with variable light amount, the power source means with variable power supply, and the special monitor sensor means for detecting the light amount of the light source, which are required in the prior art. Realizes high-quality document reading processing.

Thus, by using the present invention,
The image information of the original can be read using the line image sensor according to a simpler configuration than the conventional one.

[0025]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 illustrates an external configuration of an image reading apparatus equipped with the present invention that enables reading of both a transparent original and a reflective original.

In the figure, 10 is a housing, 11 is an original table made of transparent glass, which is provided on the upper surface of the housing 10 and on which an original to be read is placed, 12 is an original table 1
A document pressing cover that opens and closes about a rotation fulcrum axis that is parallel to 1 for accommodating a transmissive light source 13 for a transmissive document and fixing a document placed on a document table 11, and 14 is a document. A diffusing plate provided on the surface of the pressing cover 12 that comes into contact with the document table 11 for diffusing the light emitted from the transmissive light source 13, and 15 is a slit formed on the upper surface of the housing 10 for pressing the document. A member that is formed in parallel with the rotation fulcrum axis of the cover 12 and cuts out the upper surface of the housing 10.
Reference numeral 16 is a slit blinding portion for hiding the slit 15.

FIG. 2 shows an embodiment of the internal structure of the image reading apparatus. In the figure, 17 is an optical unit that moves in the sub-scanning direction, and is a CCD line image sensor 18 that reads image information of an original placed on the original table 11.
And a reflection light source 19 for illuminating a document placed on the document table 11.
And a power inverter 20 for supplying power to the reflected light source 19.
And a lens / reflection mirror for forming an image of the document surface on the CCD line image sensor 18.

Reference numeral 21 denotes a carrier shaft provided in the sub-scanning direction for guiding the movement of the optical unit 17,
Reference numeral 22 is a driven rail provided in the sub-scanning direction, which guides the movement of the optical unit 17, and 23 is a belt having a tooth groove, which engages with the optical unit 17 and is sub-scanned by a motor (not shown). By reciprocating in the direction, the movement of the optical unit 17 is controlled.

Reference numeral 24 is an adapter unit base body for accommodating the transmitted light source 13, and 25 is a projection receiving portion formed on the adapter unit base body 24 for processing mechanical connection with the optical unit 17. 26 is a connector that is connected to the transmissive light source 13 by flexible wiring, and that handles electrical connection with the optical unit 17, 27 is a connector that is provided in the optical unit 17, Reference numeral 28 denotes a member for processing electrical connection with the adapter unit base 24, and reference numeral 28 denotes a protrusion provided on the optical unit 17 for processing mechanical connection with the adapter unit base 24.

Here, the above-mentioned slit 15 provided on the upper surface of the housing 10 is cut out so as to have a width that allows the housing portion of the protrusion 28 to reciprocate.

At this time, the protrusion 28 of the optical unit 17 is inserted into the protrusion receiving portion 25 of the adapter unit base 24, and the connector 26 of the adapter unit base 24 and the optical unit 17 are inserted. When the connector unit 27 is connected to the connector 27, the adapter unit base body 24 is mechanically / electrically detachably connected to the optical unit 17 while using the protrusion 28 of the optical unit 17 as a rotation fulcrum shaft. . The adapter unit base 24, as shown in FIG.
Will be implemented inside. Here, 29 in FIG.
Is a drive motor for executing the movement processing of the optical unit 17,
Reference numeral 30 is a driven rail that guides the movement of the adapter unit base body 24, and 31 is a slit blinding portion that blinds the slit 14.

According to this structure, the adapter unit base 2
4 is the above-mentioned slit 15 provided on the upper surface of the housing 10.
Through the operation of the optical unit 17, the optical unit 17 is moved so as to move on the document table 11, and the transmissive light source 13 is turned on by receiving power supply from the power inverter 20.

With such a configuration, the image reading apparatus having the configuration shown in FIGS. 1 to 3 turns on the transmissive light source 13 when reading a transmissive original, and
The transparent light source 19 is turned off and the optical unit 17 is moved in the sub-scanning direction to read the transparent original. When the reflective original is read, the reflective light source 19 is turned on and the transparent light source 13 is turned off. By reading the reflective original by moving the optical unit 17 in the sub-scanning direction, both the transparent original and the reflective original are read.

In reading the reflective original, the optical unit 17 reads the reference white sheet 32 provided at the specified position, as shown in FIG. 4A, before reading the image information of the reflective original. By using the read level value of the reference white sheet 32, shading correction is performed on the level value of the image information of the reflective original that is subsequently read.

Further, in reading the transparent original, the optical unit 17 sets the transparent light source at a position where the original is not placed, as shown in FIG. 4B, before reading the image information of the transparent original. 13 is read, and by using the read light source light amount distribution of the transmissive light source 13, the shading correction is performed on the level value of the image information of the transparent original to be subsequently read.

FIG. 5 illustrates an embodiment of an optical system configured to implement the present invention. As shown in this figure,
In order to realize the present invention, the CCD line image sensor 18 of the optical unit 17 executes the reading of the reflection original by the sensor element in the central portion indicated by the portion B in the drawing when the reflection original is to be read. With
A sensor element at an end portion indicated by a portion b in the drawing (hereinafter, may be referred to as a reflection monitor sensor element)
On the other hand, by adopting a configuration in which the white information possessed by the correction white sheet (provided long on both sides of the document table 11 in the sub-scanning direction) indicated by 33 in FIG. The element is configured to constantly detect white level image information.

Further, in order to realize the present invention, the CCD line image sensor 18 of the optical unit 17 is a sensor element at the central portion indicated by A in the figure when a transparent original is to be read, and the transparent original is read. By performing reading of the above, and by adopting a configuration in which the transparent original is not placed on the sensor element at the end portion indicated by a portion in the drawing (hereinafter, also referred to as a transmission monitor sensor element), With the sensor element at the end,
The configuration is such that the amount of light emitted from the transmissive light source 13 is constantly detected.

6 to 9 show processing flows executed by the control mechanism of the image reading apparatus having the present invention.
Next, the operation processing of the present invention will be described in detail according to these processing flows.

The control mechanism of the image reading apparatus equipped with the present invention, when the user requests the reading of the reflection original, as shown in the processing flow of FIG. 6, first, in step 1, in FIG. As described above, the optical unit 17 is moved to the arrangement position of the reference white sheet 32, and the level value of the reference white sheet 32 is read. This reading process is shown in FIG.
The CCD line image sensor 18 shown in FIG. Next, in step 2, the white level value detected by the reflection monitor sensor element is read in synchronization with the reading process of the level value of the reference white sheet 32.

Subsequently, in step 3, the optical unit 17 is moved to read the reflection original, and the image information is read by the CCD line image sensor 18, and the reference white read in step 1 is read. Using the level value of the sheet 32, the reflection original is read while performing the shading correction.

During execution of this reading process, the following step 4
Then, when it is determined that the prescribed update cycle is reached,
Proceeding to step 5, the white level value detected by the above-mentioned reflection monitor sensor element is read, and the following step 6
Then, the rate of change between the detection value of the reflection monitor sensor element at the start of reading read in step 2 and the detection value of the reflection monitor sensor element read in step 5 is obtained.

Then, in step 7, a multiplication value of the rate of change obtained in step 6 and the level value of the reference white sheet 32 obtained in step 1 is calculated, and this multiplication value is newly used for shading correction. It is set as the level value of the reference white sheet 32. When the rate of change obtained in step 6 shows a value of "1" or more, that is, the detected value in step 5 is larger than the detected value in step 2, the reflected light source 19
When the increase in the light amount of the light source is indicated, the entire level value of the reference white sheet 32 used for shading correction is updated to a value indicating a large value, and the change rate obtained in step 6 is “1”.
When the following values are indicated, that is, when the detection value in step 5 is smaller than the detection value in step 2 and thus the light source light amount of the reflected light source 19 decreases, the level of the reference white sheet 32 used for shading correction is indicated. The whole value is updated to indicate a small value.

Subsequently, in step 8, it is judged whether or not the reading of the original is finished. When it is judged that the reading is not finished, the process returns to step 3 and the newly set reference white sheet 32 for shading correction is read. The reflection original is read by performing shading correction using the level value.

As described above, according to the present invention, the level value of the reference white sheet 32 used for shading correction is read by using the detection value of the reflection monitor sensor element when reading the reflection original according to the processing flow of FIG. By following the changes in 19 and updating in real time,
This makes it possible to accurately read the reflection original.

On the other hand, the control mechanism of the image reading apparatus according to the present invention, when a user requests the reading of a transparent original, as shown in the processing flow of FIG.
Then, as described with reference to FIG. 4B, the optical unit 17 is moved to a position where the transparent original is not placed, and the transparent light source 13 is moved.
The light source light intensity distribution of is read. This reading process is performed by A of the CCD line image sensor 18 shown in FIG.
It is executed by a part of the sensor element. Next, step 2
Then, the light source light amount of the transmissive light source 13 detected by the transmissive monitor sensor element is read in synchronization with the reading process of the light source light amount distribution of the transmissive light source 13.

Subsequently, in step 3, the optical unit 17 is moved to execute the reading of the transparent original, the image information is read by the CCD line image sensor 18, and the transparent light source read in step 1 is entered. 1
Using the light source light amount distribution of 3, the transparent original is read while performing the shading correction.

During the execution of this reading process, the following step 4
Then, when it is determined that the prescribed update cycle is reached,
Proceeding to step 5, the light source light amount of the transmissive light source 13 detected by the transmission monitor sensor element described above is read, and in the following step 6, the detection value of the transmission monitor sensor element at the start of reading read in step 2 and step 5 The rate of change from the read detection value of the transmission monitor sensor element is obtained.

Subsequently, in step 7, a multiplication value of the rate of change obtained in step 6 and the light source light amount distribution of the transmissive light source 13 obtained in step 1 is calculated, and this multiplication value is newly used for shading correction. It is set as the light source light amount distribution of the transmissive light source 13. When the rate of change obtained in step 6 shows a value of "1" or more, that is, when the detected value in step 5 is larger than the detected value in step 2, the transmitted light source 13
When the increase in the light source light amount of is indicated, the entire light source light amount distribution of the transmissive light source 13 used for shading correction is updated to a large value, and the change rate obtained in step 6 is “1”.
When the following values are shown, that is, when the detection value in step 5 is smaller than the detection value in step 2 and the light source light amount of the transmission light source 13 decreases, the light source light amount of the transmission light source 13 used for shading correction is shown. The whole distribution is updated to show a small value.

Subsequently, in step 8, it is judged whether or not the reading of the original is finished. When it is judged that the reading is not finished, the process returns to step 3, and the light source of the newly set transmission light source 13 for shading correction is returned. The transparent original is read by performing shading correction using the light amount distribution.

As described above, according to the present invention, the light source light amount distribution of the transmissive light source 13 used for shading correction is read by using the detection value of the transmissive monitor sensor element when reading the transmissive original according to the processing flow of FIG. By following the fluctuations of 13 and updating in real time,
This realizes accurate reading of transparent originals.

The processing flow shown in FIG. 6 discloses a configuration in which the level value of the reference white sheet 32 used for shading correction is corrected by using the rate of change of the detection value detected by the reflection monitor sensor element. Instead of configuration,
As shown in step 7 of the processing flow of FIG. 8, the detection value of the reflection monitor sensor element read in step 5 matches the detection value of the reflection monitor sensor element at the start of reading read in step 2. In addition, it is also possible to adopt a method of adjusting the amount of power supplied to the reflection light source 19.

When this method is adopted, the light source state is similar to that of the conventional technique, and the reference white sheet 3 used for shading correction is used.
By maintaining the level value of 2 at the time of reading, high quality reading becomes possible.

The processing flow shown in FIG. 7 discloses a configuration in which the light source light amount distribution of the transmissive light source 13 used for shading correction is corrected by using the rate of change of the detection value detected by the transmission monitor sensor element. Instead of this configuration, as shown in step 7 of the process flow of FIG. 9, the detection value of the transmission monitor sensor element read in step 5 is the detection value of the transmission monitor sensor element read in step 2 at the start of reading. It is also possible to adopt a method of adjusting the amount of power supplied to the transmissive light source 13 so as to match the above.

If this method is adopted, the state of the light source is maintained as it was when the light source light amount distribution of the transmissive light source 13 used for shading correction was read, as in the prior art, so that the same high quality reading can be performed. It will be possible.

Although the illustrated embodiment has been disclosed, the invention is not limited thereto. For example, in the example,
Although the document to be placed is targeted for reading, the present invention can be applied as it is to an image reading apparatus having a configuration in which the optical unit is fixed and the document is moved.

[0056]

As described above, according to the present invention,
The image information of the original can be read by using the line image sensor while following the simpler configuration than the conventional one.

[Brief description of drawings]

FIG. 1 is an external configuration diagram of an image reading apparatus including the present invention.

FIG. 2 is an internal configuration diagram of an image reading apparatus including the present invention.

FIG. 3 is an internal configuration diagram of an image reading apparatus including the present invention.

FIG. 4 is an explanatory diagram of shading correction.

FIG. 5 is an example of an optical system for realizing the present invention.

FIG. 6 is an example of a processing flow executed by the present invention.

FIG. 7 is an example of a processing flow executed by the present invention.

FIG. 8 is an example of a processing flow executed by the present invention.

FIG. 9 is an example of a processing flow executed by the present invention.

FIG. 10 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Housing 11 Original platen 12 Original document cover 13 Transmitted light source 14 Diffuser 15 Slit 16 Slit blind part

Claims (5)

[Claims] 1. A light source and a line image sensor are provided, and according to the line image sensor, image information of a document illuminated by the light source is read, and at the start of reading the document, the line image sensor serves as a reference object. An image reading apparatus configured to read a level value and correct the level value of image information to be read according to the read level value of a reference object, is provided in the vicinity of the light source, and detects the light amount of the light source. The level value of the reference target used to correct the level value of the image information based on the monitor sensor unit, the detection value of the monitor sensor unit when reading the document, and the detection value of the monitor sensor unit when reading the reference target. An image reading apparatus comprising: a correction unit that corrects 2. A light source which emits a light amount according to a power supply amount, and a line image sensor, which reads image information of a document which is transmitted and illuminated by the light source according to the line image sensor, and reads the document. At the start, in the transmission type image reading apparatus having a configuration in which the light amount distribution of the light source is read by the line image sensor and the level value of the image information to be read is corrected according to the read light source light amount distribution, Even when reading, one or more sensor elements at the end of the line image sensor are constantly illuminated by a light source, and the sensor element at the end is set as monitor sensor means. And the detection value of the monitor sensor means at the time of reading the original is the light source. And to match the detection value of the monitoring sensor means when reading the amount of distribution, in that it comprises adjusting means for adjusting the power amount supplied to the light source, the image reading apparatus according to claim. 3. A light source and a line image sensor are provided, and according to the line image sensor, image information of an original document that is transmitted and illuminated by the light source is read, and at the start of reading the original document, the line image sensor detects the light source of the light source. In a transmissive image reading apparatus having a configuration in which the light amount distribution is read and the level value of image information to be read is corrected according to the read light source light amount distribution, even when reading a document, the line image sensor A configuration is adopted in which one or a plurality of sensor elements at the end portions are constantly illuminated by a light source, and the sensor elements at the end portions are set as monitor sensor means, and a document is read. The detection value of the monitor sensor means at the time From the detected value of Nitasensa means, further comprising a correcting means to continue to correct the light source light quantity distribution to be used for correction of the level value of the image information, the image reading apparatus according to claim. 4. A light source which emits a light amount according to a power supply amount, and a line image sensor, which reads image information of a document reflected and illuminated by the light source according to the line image sensor, and reads the document. At the start, the level image sensor reads the level value of the reference white sheet, and the level value of the image information to be read is corrected according to the read level value of the reference white sheet. In the apparatus, even when a document is being read, white line image information is always input to one or more sensor elements at the end of the line image sensor, and the sensor at the end is used. The configuration is such that the element is set as the monitor sensor means, and the above-mentioned monitor set at the time of reading the document is adopted. The image reading device is provided with an adjusting unit that adjusts the amount of power supplied to the light source so that the detection value of the sensor unit matches the detection value of the monitor sensor unit when the reference white sheet is read. apparatus. 5. A light source and a line image sensor are provided, and according to the line image sensor, image information of an original document reflected and illuminated by the light source is read, and when the reading of the original document is started, a reference white image is read by the line image sensor. In a reflection-type image reading device having a configuration in which the level value of a sheet is read and the level value of the image information to be read is corrected according to the read level value of the reference white sheet, even when reading a document. A configuration is adopted in which white level image information is constantly input to one or a plurality of sensor elements at the end portion of the line image sensor, and the sensor element at the end portion is set as monitor sensor means. The reference white sheet and the detection value of the monitor sensor means when the original is read Image reading apparatus for and a detection value of the monitoring sensor means at the time of reading, further comprising a correcting means to continue to correct the level value of the reference white sheet used for the correction of the level value of the image information, characterized.