JPH10257313A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct shadings due to the light quantity change or the color change of a light source by detecting light source changes from the output of a photodiode(PD) for reading a white plate and correcting the outputs of a PD group for reading an original. SOLUTION: A color CCD linear image sensor 101 is provided with PDs 104, 106 and 108 having the filters of respective colors RGB and PD 102, where the RGB filters are arrayed in order. An RGB comparing circuit 132 compares light source reference data stored in a memory 131 with the present light source for every color. In a shading correcting circuit 133, for example, data by which the white plate is read is stored in a line memory 136, and the ratio of the level of the data with a prescribed level is calculated. The multiplication of data obtained by PD 104 by the ratio is executed in a multiplier 137, and sensitivity correction at every image element in PD 104 is executed. Multiplication with ratio data which is calculated by the RGB comparing circuit 132 is executed, and correction for changes with passage of time the light source is executed at the same time.

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 using an image sensor, and more particularly, to performing real-time correction of shading due to a change in light amount of a light source or a change in color during continuous reading of a document. The present invention relates to a characteristic image reading apparatus.

[0002]

2. Description of the Related Art In recent years, an image reading apparatus is incorporated in a copying machine, a facsimile, an OCR, or the like, and reads an original image and outputs it to a transmission system, or exposes and transfers a photosensitive member according to a read signal. Used.

[0003] In an image reading apparatus, a halogen lamp is mainly used as a light source for irradiating a document because the light amount and the color temperature are stable. However, the power consumption of halogen lamps tends to increase in order to increase the amount of light as the copying speed increases and the resolution increases,
Heat generation of halogen lamps has become a major problem.

[0004] Therefore, fluorescent lamps have attracted much attention as light sources replacing halogen lamps.

[0005] Fluorescent lamps are expected to generate less heat than halogen lamps, and to be relatively freely mixed in color by selecting a fluorescent paint or the like, so that great expectations are placed on them.

[0006]

However, when a fluorescent lamp is used as a light source, the amount of light and the color of the light source change greatly with time. It is necessary to take measures to correct the change over time, such as increasing the power supplied to the fluorescent lamp, and a specific method has not yet been clarified.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention irradiates a white plate provided adjacent to a reading position for continuously reading a document, and irradiates the document including the white plate. Image sensor having a light source for reading, a first photodiode group consisting of a photodiode array of three colors of RGB for reading the original, and a second photodiode in which filters of three colors of RGB for reading the white plate are arranged for each pixel. An optical system that forms an image of reflected light of the original including the white plate on the image sensor, a detector that detects a change in the parameter of the light source from the output of the second photodiode, and A correction circuit for correcting the output of the first photodiode group;
Is provided.

In an image reading apparatus for reading a document and converting it into an image signal, a first memory for storing reference data obtained by reading a white plate at the time of reference, and a shading correction circuit for performing shading correction on the read data of the document. , The reference data and the second read as needed
Detecting means for detecting the degree of change of the document reading system with time from the second reference data at the time of reference, and performing shading correction on the read data in accordance with the degree of change. . In the above image reading apparatus, the shading correction circuit includes a second memory for storing the read data and a multiplier for multiplying the read data by a signal corresponding to the degree of change. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a configuration diagram of a scanner equipped with a color CCD linear image sensor 101.

The scanner 200 is a scanner body 200
a and a document feeder 200b.

The scanner body 200a is configured as follows. Reference numeral 210 denotes a platen glass on which a document is mounted. Reference numeral 212 denotes a first mirror unit, which includes a light source 205 such as a fluorescent lamp for exposing a document and a first reflection mirror 202. 213 is a second mirror unit,
, And a third reflecting mirror 204. Reference numeral 201 denotes a lens unit for reducing and forming an image of the original reflected light on the color CCD linear image sensor 101. Reference numeral 209 denotes a platen glass for drift reading when drift reading (continuous reading) of a document is performed using the document feeder 200b.

The document feeder 200b is composed of the following. Reference numeral 206 denotes a document input tray. Reference numeral 207 denotes a document pickup roller. 20
Reference numeral 8 denotes a feed roller for feeding a document. 211 is a paper discharge tray.

In the above configuration, the platen glass 210
When reading a document image mounted thereon, document reading scanning is performed by the following operation.

First, it is assumed that an original is mounted on the platen glass 210 with the original surface facing down. The first mirror unit 212 and the second mirror unit 213 are moved and scanned in the direction of arrow A (sub-scanning direction) at a scanning speed of 2: 1 by the stepping motor 214 with the start point as the position indicated by the dotted line in the drawing. During this time, the original is read while the optical path length from the reflection surface of the original to the CCD linear image sensor 101 is kept constant.

Further, in the above configuration, when reading the original loaded on the input tray 206, the original reading scanning is performed by the following operation.

First, it is assumed that a document is mounted on the input tray 206 with the document surface facing upward.

In the case of reading a single-sided document, the document is read while being conveyed in the direction of the dashed arrow. That is, the original is fed by the pickup roller 207 to the feed roller 2.
08, and according to the document reading timing,
The paper is fed by the feed roller 208, conveyed in the direction of the dashed arrow, passes over the platen glass 209, and is discharged to the discharge tray 211.

In the case of reading a double-sided document, the document is read while being conveyed in the direction of the solid arrow. That is, first, the document fed by the feed roller 208 is transported in the direction of the solid arrow. Next, the surface (omotenmen)
After passing through the reading position of the platen glass plate 209 and being read, the sheet is reversed according to the transport path (solid line arrow), the back side is read in the direction opposite to the direction of the front side reading, and finally, the paper discharge path (solid line). Arrow)
The paper is discharged to the paper discharge tray 211.

The first mirror unit 212 and the second mirror unit 213 are arranged at predetermined positions for moving reading in both the case of reading a single-sided original and the case of reading a double-sided original. The irradiation light from the light source 205 is reflected by the original and the white plate at the position of the platen glass 209 for the flow reading, passes through the reflection mirror group (202 to 204) and the lens unit 201, and forms a reduced image on the color CCD linear image sensor 101. Is done. Color CCD linear image sensor 1
Reference numeral 01 reads an image while scanning the image in the main scanning direction (the direction running through the figure).

At this time, the sub-scanning direction of the formed image on the color CCD linear image sensor 101 is indicated by an arrow B when reading the front side and an arrow C when reading the back side. On the other hand, the main scanning direction is the same in both cases.

FIG. 2 is a circuit block diagram in an embodiment according to the present invention. In FIG. 2, a color CCD linear image sensor 101 includes photodiodes 104, 106, and 108 (hereinafter, referred to as filters) having filters of RGB colors.
"R.PD104", "G.PD106",
The photodiode 102 (hereinafter referred to as “B. PD 108”) in which transfer registers 105, 107, 109 for transferring respective charges, output amplifiers 111, 112, 113, and RGB filters are sequentially arranged.
PD 102), a transfer register 103 for transferring the charge, and an output amplifier 110.

Color CCD linear image sensor 10
1 are output from sample hold circuits 114 and 1 respectively.
15, 116, 117 (hereinafter, “SH circuits 114, 11
5, 116, 117 ") and the range is adjusted by the amplifiers 118, 119, 120, 121 and the clamp circuits 122, 123, 124, 125, and then the AD converters 126, 127, 128, At 129, it is converted to digital data.

[0023] The RGB. The output of the PD 102 is an RGB separation circuit 130
In the reference data memory 13
1 and the RGB comparison circuit 132.

In the reference data memory 131,
Reference data storage time immediately before reading the first document to monitor changes over time in the light source (shown in FIG. 4)
And stores the data of each color of RGB separated for each color.

The RGB comparison circuit 132 compares the reference data of the light source stored in the reference data memory 131 with the current light source for each color, and obtains the ratio between them. The RGB comparison circuit 132 outputs ratio data of the change over time of the light source of each color of RGB.

The R.R. signals converted into digital data by the AD converters 127, 128 and 129 are used. PD 104, G.P. PD10
6, B. The output of the PD 108 is input to the shading correction circuits 133, 134, and 135, respectively. Here, the shading correction circuits 133, 134, and 135 have the same configuration although they handle different colors.

The red signal of the original will be described. In the shading correction circuit 133, digital data obtained by reading the reference white plate 303 is stored in the line memory 136 while being averaged, and the level of the data stored in the line memory 136 is obtained. And the ratio between the predetermined level and a predetermined level is calculated. The multiplier 137 multiplies the digital data by this ratio for each pixel obtained by the PD 104, and distributes the light of the light source and the R.D. of the CCD linear image sensor 101. The sensitivity of each pixel of the PD 104 is corrected. This corrected result is described in R.E. The sensitivity difference of each pixel in the PD 104 is corrected, and the output of each pixel becomes a constant value when the target image is the same target.

In the present embodiment, the multiplier 137 uses not only the ratio calculated by the line memory 136 but also
The multiplication with the ratio data for correcting the temporal change of the light source calculated by the RGB comparison circuit 132 is performed at the same time, and the temporal change correction of the light source and the like are performed at the same time.

G. PD106 and B.I. The correction of the sensitivity difference between the pixels in P108 and the correction over time of the light source and the like are also performed by the shading correction circuits 134 and 135 in the same manner as described above.

The shading correction circuits 133, 134,
The output data of 135 is output to the image processing circuit 138 by γ
Various image processing such as correction is performed.

FIG. 3 is a view showing a state in which the color CCD linear image sensor 10 is mounted on the platen glass 209 for reading in FIG.
1 shows an optical path up to 1.

The platen glass 209 comprises a slit 301 for actually reading the original and a white plate 302 for correcting the change of the light source 205 with time. Reference numeral 303 denotes a reference white plate for performing shading correction, and density management is previously performed on white of the document.

The reflected light from the platen glass 209 is the first
The light passes through the reflection lens 202, the second reflection lens 203, the third reflection lens 204, and the lens unit 201 and is reduced and image-formed on the color CCD linear image sensor 101.

The broken line in FIG. 3 shows the optical path of the light reflected by the original and reduced and formed on the CCD linear image sensor 104 for R. The thin solid line indicates the CCD linear image sensor 106 for G reflected by the original.
Is the optical path of the light that is reduced and imaged. The dashed line indicates the optical path of the light reflected from the original and reduced and imaged on the CCD linear image sensor 108 for B. The bold solid line shows the optical path of the light reflected by the white plate 302 for performing shading correction due to the temporal change of the light source and formed on the CCD linear image sensor 102 used for performing the shading correction. .

FIG. 4 is a timing chart showing the change over time of the light source, the reading timing of the original, and the change of the correction coefficient for the change over time during the flow reading.

In the above arrangement, continuous reading of the conveyed document is performed by the following operation.

When a document reading instruction is given, the light source 205
The first mirror unit 212 including the first mirror and the second mirror unit 213 including the second reflection mirror and the third reflection mirror move below the reference white plate 303 to read the reference white plate 303.

In this state, the red photodiode R.R. PD104
The R signal of the reference white plate read in is converted into digital data and stored in the line memory 136 while being averaged by the shading correction circuit 133. Also,
Green photodiode G. PD106, blue photodiode B. The read output of the PD 108 is similarly processed.

Next, the mirror units 212 and 213 move below the platen glass 209 for moving reading, and continuous reading of the original conveyed by the document feeder 200b is started.

The reflected light from the white plate 302 is the RGB. An image is formed on the PD 102 (shown by a thick solid line in FIG. 3).

By the time the first original document is carried to the platen glass 209 for moving reading, the RGB. The output data of the PD 102 is separated for each color by the RGB separation circuit 130 and stored in the reference data memory 131.

At this time, the reference data memory 1
The data stored in 31 serves as reference data for correcting a temporal change of the light source. However, the setting of this reference data is
For the sake of explanation, it is assumed that the reading is performed at the time of starting the reading, but this may be performed at the time of manufacture and shipment, at the start of setting of the apparatus, at the time of reading a certain number of sheets, or the like.

At this time, as shown by the correction coefficient in FIG. 4C, all the outputs of the RGB comparison circuit 132 become 1 during the reference data accumulation time or when reading the first original.
It is.

Each output of the RGB comparison circuit 132 is supplied to the corresponding color shading correction circuit 133 to 135, and the time-dependent change correction coefficient in all the multipliers 137 is set to 1.

Next, the first document arrives at the platen glass 209 for drift reading, and the first document is read. Until the reading of the first document is completed, the value of each output of the RGB comparison circuit 132 is held at 1.

After reading of the first document is completed,
In the period until the reading of the first document starts (the time-varying data accumulation time 1 in FIG. 4B), the RGB. PD102
4A, the light amount of the light source is increased as shown in the temporal change of the light source shown in FIG. 4A. The value of the correction coefficient which is the output of the RGB comparison circuit 132 is 0.83 of the reciprocal thereof.
And this value is the value of each of the shading correction circuits 133-1
It is set as a correction coefficient input for each of the 35 multipliers.

In the period from the end of reading the second sheet to the start of reading the third sheet (time-dependent data accumulation time 2 in FIG. 4B), RGB. The data of the white plate 302 for temporal change correction read by the PD 102 is 0.97 times the reference data because the light amount of the light source is reduced as shown by the temporal change of the light source shown in FIG. The correction coefficients output from the RGB comparison circuit 132 are all 1.03, and this value is set as a correction coefficient input to each multiplier of each of the shading correction circuits 133 to 135.

In the same manner, the data for time-dependent change correction is updated in the non-reading time of the document, and the time-dependent change correction of the light source is performed.

In the present embodiment, for the sake of easy understanding, the same correction coefficient is used for each of RGB. However, by performing correction for each color, it is possible to correct even a temporal change of the light source color. Becomes Therefore, in this embodiment,
The change has been described with the light amount of the light source as one parameter.
The sensitivity change of the photoelectric conversion of 01 may be a correction target as another parameter, and if there is a factor having a change in particular, it may be a target of shading correction including the factor. It should be noted that these aging changes are caused by the light source,
There are various types such as a reflection mirror, a lens unit, and a color CCD linear image sensor, and these are called a document reading system.

Further, the light source is not limited to the fluorescent lamp, but can be applied to the case where a halogen lamp or the like is used.

Further, RGB. PD102 is R.P. PD10
4, G. PD 106, B.I. It has the same number of pixels as the PD 108, and the RGB filters are arranged in groups of three, so that the RGB separation circuit 130, the reference data memory 131, and the RGB comparison circuit 132 handle data for every three pixels, 3 against time-dependent changes in light distribution
It is also possible to perform correction for each pixel.

In the above embodiment, when the flow reading is started, the reference data is stored in the reference data memory 131.
However, the present invention is not limited to this. For example, this may be performed at the time of shipment from a factory or periodically.

In the above-described embodiment, the correction means for the time-dependent change especially when the original is scanned and read is described. However, when the original is placed on a normal platen glass and read, the original is read in a predetermined state. Of course, the correction may be made based on the reference data described above, or may be corrected with respect to a long-term temporal change due to deterioration of the light source or the like.

In the above description, a CCD image sensor has been described as an example. However, the present invention can be applied to a MOS type or other type of photoelectric conversion device.

[0055]

As described above, by practicing the present invention, it is possible to correct the temporal change of the original reading system including the light source light amount and the light source color when performing the flow reading.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a scanner according to the present invention and a conventional example.

FIG. 2 is a circuit block diagram of the image reading device according to the present invention.

FIG. 3 is an explanatory diagram of an optical path in the present invention.

FIG. 4 is a timing chart according to the present invention.

[Explanation of symbols]

Reference Signs List 101 color CCD linear image sensor 102 photodiode in which RGB filters are sequentially arranged for every three pixels 104 photodiode having an R filter 106 photodiode having a G filter 108 photodiode having a B filter 103, 105, 107 , 109 Transfer register 110-113 Output amplifier 114-117 Sample hold circuit 118-121 Amplifier 122-125 Clamp circuit 126-129 A / D converter 130 RGB separation circuit 131 Reference data memory 132 RGB comparison circuit 133-135 Shading correction circuit 136 line Memory 137 Multiplier 138 Image processing circuit 200 Scanner 200a Scanner body 200b Document feeder 201 Lens Unit 202 First reflection mirror 203 Second reflection mirror 204 Third reflection mirror 205 Fluorescent lamp 206 Input tray 207 Pickup roller 208 Feed roller 209 Flowing platen glass 210 Platen glass 211 Discharge roller 212 First mirror unit 213 Second mirror Unit 214 Stepping motor 301 Slit for reading original 302 White plate for performing shading correction due to aging of light source 303 Reference white plate

Claims (7)

[Claims] 1. A white plate provided adjacent to a reading position for continuously reading a document, a light source for irradiating the document including the white plate, and a photodiode array of three RGB colors for reading the document. An image sensor having a combination of one photodiode group and a second photodiode in which RGB three-color filters for reading the white plate are arranged for each pixel; and reflecting the reflected light of the original including the white plate to the image sensor. An optical system that forms an image, a detector that detects a change in the parameter of the light source from the output of the second photodiode, and a correction circuit that corrects the output of the first photodiode group from the output of the detector. Characteristic image reading device. 2. The image reading apparatus according to claim 1, wherein the parameters are a light amount of the light source and a light source color. 3. The image reading apparatus according to claim 1, wherein the detector uses the output of the second photodiode immediately before reading the first document as reference data when performing continuous document reading, wherein An image reading apparatus for outputting a ratio between the output of the second photodiode immediately before reading a document and the reference data. 4. The image reading device according to claim 1, wherein the detector outputs correction ratio data of three colors of RGB. 5. The image reading apparatus according to claim 1, wherein the detector fixes and holds an output when reading the document. 6. An image reading apparatus for converting a document into a read image signal, a first memory for storing reference data obtained by reading the reference document at the time of reference, and a shading correction circuit for performing shading correction on the read data of the document. Detecting means for detecting the degree of change of the document reading system with time based on the reference data and the second reference data at the time of the second reference which has been read as needed, and according to the degree of change with respect to the read data. An image reading device for performing shading correction. 7. The image reading apparatus according to claim 6, wherein the reference data is data obtained by reading a white plate with an image sensor, and the shading correction circuit includes a second memory storing the read data and the change data. An image reading apparatus comprising a multiplier for multiplying a signal corresponding to a degree and the read data.