JPH05207232A - Picture reader - Google Patents

Abstract

PURPOSE:To attain high speed processing by attaining high speed reading with high precision. CONSTITUTION:A signal charge subjected to photoelectric conversion and storage by photodiode arrays 7a, 7b in CCD line sensors 6a, 6b is fed to CCD shift registers 8a, 8b and each picture element signal is sequentially fed to output sections 9a, 9b to read a picture element signal by one line (sensor). The CCD line sensors 6a, 6b are independently and simultaneously driven by a drive section 10 respectively, their output signals are subject to sample-and-hold processing, A/D conversion, dark state output correction by a signal processing section 11. in which two data strings outputted in parallel in opposite directions from the center of the original picture are rearranged so as to be outputted as one serial data string arranged in order from data at the end of the original picture and processing such as shading correction is implemented.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an image reading device, and more particularly to an image reading device using a CCD line sensor, and more particularly to an image reading device capable of high-speed and high-definition reading. For example, it is applied to image input of a scanner, a copying machine, a facsimile, and the like.

[0002]

2. Description of the Related Art In an image reading apparatus using a CCD line sensor, an image reading apparatus has been proposed in which an original is divided into a plurality of areas and a plurality of line sensors corresponding to the respective areas are arranged in the main scanning direction to read an original image. There is. For example, Japanese Patent Publication No. 1-53538 discloses an attempt to increase the reading speed and reading density of image reading. Further, in recent years, a scanner capable of high-speed and high-definition reading has been desired. Further, CCD line sensors capable of high-speed operation and high-density CCD line sensors have appeared due to advances in fine processing technology. However, a conventional image reading apparatus using one CCD line sensor is still insufficient in terms of high speed and high definition. In order to forcibly achieve high-speed and high-definition reading, it is required that the CCD drive circuit and the output signal processing circuit can operate at high speed, which is not only disadvantageous in terms of cost but also the accuracy of the pixel information to be read becomes poor. Is expected.

Further, in the conventional example, when reading an original smaller than the maximum readable original size, the CCD is used.
Since all the pixel information including unnecessary pixel information among the pixel information of the line sensor is read and processed, the reading efficiency is poor.

[0004]

[Object] The present invention has been made in view of the above circumstances, and enables high-speed and high-definition reading even when the CCD line sensor, CCD drive circuit, and output signal processing circuit operate at low speeds, and small originals. It is possible to read only the necessary pixels when reading
Also, by using two CCD line sensors,
High-speed and high-definition reading is possible, especially when reading small documents
The dark output can be accurately corrected even when the number of pixels smaller than that of the D line sensor is read, and the dark output can be corrected with higher accuracy, and the shading with higher accuracy can be performed. The object of the present invention is to provide an image reading apparatus that enables higher-definition reading by performing correction, and that has an output format similar to that of a single CCD line sensor.

[0005]

In order to achieve the above object, the present invention provides (1)
In an image reading apparatus that obtains an electric signal according to the density of an original by a photoelectric conversion element, the photoelectric conversion elements (6a, 6b) are associated with the original area so that the original area is divided into two and read in the main scanning direction. Of the two photoelectric conversion elements, the document position corresponding to the read pixel read first of the two photoelectric conversion elements is substantially at the center in the main scanning direction of the document area, and the document position corresponding to the read pixel read subsequently is read. Installed so that the directions are opposite to each other, only the light blocking plates (29a, 29b) that block the reflected light from other than the original and the pixels of the photoelectric conversion element corresponding to the size of the original are output, and the photosensitive section is First holding means (52a, 52b) for holding the output part of the pixel only in the transfer part and the output of the pixel in which the light shield is provided on the photosensitive part (the non-reading image before the reading line). Second holding means for holding the sum of the outputs) dark generated in pixels where light shielding is made by in generated dark output and the read lines (53a, 5
3b) and the first holding means (52a, 52b)
And a first normalizing means (56) for normalizing the dark-time output signal actually output from each pixel over one line with the output of the second holding means (53a, 53b) as a reference.
a, 56b) and a first storage means (58a, 5) for storing the dark output signal normalized by the first normalization means.
8b) and third holding means (59a, 59) for holding the output of the pixel having the light shield on the photosensitive portion.
b), multiplication means (60a, 60b) for multiplying the output of the third holding means and the output of reading the contents of the first storage means over one line, and the output of the multiplication means for reading an image. Subtraction means (6
3a, 63b), and (2) the accumulation time for reading the dark output signal over one line from the photoelectric conversion element is set longer than the accumulation time for each line when reading an image. In addition, (3) In the above (1) or (2), the first holding means (5) for holding the output portion of the pixel having no photosensitive portion and only the transfer portion.
2a, 52b), peak hold means (90a, 90b) for holding the peak value of the output signal when the white reference plate is read over one line, and the output values of the first hold means and the peak hold means. First normalizing means (56a, 5a) for normalizing the white reference plate read signal and the image read signal over one line as a reference.
6b), second storage means (65a, 65b) for storing the normalized white reference plate read signal output from the first normalizing means over one line, and the first normalizing means. Second normalizing means (66a, 66b) for normalizing the output when the image is read by the output of reading the contents over one line, and further (4)
In the above (1), (2) or (3), two data strings output in parallel in opposite directions from the central portion of the original image are serial data strings arranged in order from the end data of the original image. It is characterized in that a rearrangement circuit (67) for outputting is output. Hereinafter, description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining an embodiment of an image reading apparatus according to the present invention. In the figure, 1 is a document, 2 is a contact glass, 3 is an illumination light source, and 6a and 6b are CCDs.
Line sensors, 24a, 24b are lenses, 29a, 29
b is a light-shielding plate.

The original 1 on the contact glass 2 is linearly illuminated by an illumination light source 3. Of the reflected light from the original 1,
The reflected light from the center of the original 1 to the left is imaged on the left CCD line sensor 6a, and the reflected light from the center of the original 1 to the right is imaged on the right CCD line sensor 6b by lenses 24a and 24b. In addition, two CCD line sensors 6a,
The output portion 6b is arranged outward so that the image signal of the central portion of the linearly illuminated image is first output. The optical system shown in FIG. 1 is an example, and if the optical system can divide an original image into two in the main scanning direction (x direction), for example, a method using a mirror, a half mirror, or a roof mirror, etc. Any method may be used. The light blocking plates 29a and 29b block the reflected light reflected from other than the reading area.

FIG. 2 is a diagram showing a photoelectric conversion system, a drive system and a signal processing system. In the figure, 7a and 7b are CCD shift registers, 8a and 8b are photodiode arrays, and 9a and 9b.
Is an output unit, 10 is a CCD drive unit, 11 is a signal processing unit, 3
Reference numeral 0 is a light shielding plate control unit, 31 is a document size detection unit, 32 is an illumination light source control unit, and 33 is a sub-scanning speed control unit.

The CCD line sensors 6a, 6b photoelectrically convert incident light by the photodiode arrays 7a, 7b and receive the accumulated signal charges from the CCD driving unit 10 and send them to the CCD shift registers 8a, 8b in parallel. Next, each pixel signal is converted into C by the CCD shift registers 8a and 8b.
Receiving the transfer pulse of the CD drive unit 10, the output units 9a, 9 sequentially
b, then the signal for one pixel is sent, then the CCD
By repeating the clearing of the electric charge by the reset pulse RS of the drive unit 10 by the number of pixels for one sensor line, it is possible to read out pixel signals for one sensor line. The CCD line sensors 6a and 6b are independently and simultaneously driven by the driving unit 10, and the output signal is sampled and held by the signal processing unit 11, A / D conversion,
Dark output correction, rearranged so that two data strings output in parallel in opposite directions from the central portion of the original image are output as one serial data string arranged in order from the edge data of the original image, and shading is performed. Processing such as correction is performed. The processing of the signal processing unit 11 will be described later.
The illumination light source 3, the CCD line sensors 6a and 6b, and the lenses 24a and 24b are integrated and installed on a carriage (not shown), and when the reading of one line is completed, it moves to the next reading position. FIG. 3 shows a timing diagram of the shift pulse SH, the clock pulses φ1 and φ2, and the reset pulse RS output from the CCD drive unit.

In the embodiment of the present invention, when the original 1 smaller than the maximum readable original size is read, the light shielding plates 29a and 29b shield light other than the reflected light having image information from the original, and the light shielding plates 29a and 29b. The pixels of the CCD line sensors 6a and 6b corresponding to the shaded portions are not read. That is, in the case of the embodiment of the present invention, the output signals of the CCD line sensors 6a and 6b are, for example, as shown in FIG.
As shown in (A), the output DS (E) of the pixel having only the transfer part without the photosensitive part, the output DS (S) of the pixel having the light-shielded photosensitive part, and the output of the pixel corresponding to the reading area are output in this order. However, even if the CCD line sensor has n pixels, the next line reading is started when only m (m <n) pixels are read. For this reason, the document size detection unit 31 automatically detects the document size (main scanning direction) or the document size specified by a person (main scanning direction).
Of the CCD line sensor 6a, 6
The required number of pixels m for b is set. Information on the set number of pixels is sent to the CCD drive unit 10, the signal processing unit 11, the illumination light source control unit 32, the sub-scanning speed control unit 33, and the light shielding plate control unit 30.

The light-shielding plate control unit 30 moves the light-shielding plates 29a and 29b so as to shield the pixel portions of the pixels of the CCD line sensors 6a and 6b that do not contribute to image reading, in accordance with the sent pixel number information. CCD drive unit 10
Outputs m and outputs φ1 and φ2 so that only m pixels of the CCD line sensor are read out according to the transmitted information on the number of pixels, and then outputs the shift pulse SH. The signal processing unit 11 performs signal processing assuming that the number of pixels in one line is 2 m. The sub-scanning speed control unit 33 determines the sub-scanning speed in accordance with the sent information on the number of pixels and performs sub-scanning. In this case, since the reading time for one line is m / n times, the sub-scanning speed is increased by n / m times as compared with the case of reading all pixels n. The illumination light source control unit 32 drives the illumination light source 3 by determining the intensity of the illumination light source 3 according to the sent information on the number of pixels. In this case, since the reading time for one line is m / n times, the exposure amount of the CCD line sensor is also reduced to m / n times as it is. Therefore, the illumination light source 3 is controlled so that the illuminance becomes n / m times as compared with the case of reading all the pixels n.

According to the embodiment of the present invention, two CCD line sensors are used, and the CCD line sensors are driven independently and simultaneously.
When the driving frequency of the D line sensor is the same and the reading density is the same, one line can be read at twice the speed. Further, when the driving frequency of the CCD line sensor is the same and the reading speed of one line is the same, the reading density can be doubled. By rearranging the data output from the central portion of the document image in order from the edge of the document image, output data can be obtained in the same output format as when one CCD line sensor is used. Further, since the light shielding plate is used to prevent the pixels that do not contribute to reading from being read out, the reading speed can be increased when reading a small document.

In this case, the brightness of the illumination and the sub-scanning speed are not changed, and the clock speed of the CCD line sensor is multiplied by m / n to reduce the power consumption for driving the photoelectric conversion element. You can In addition, the brightness of the illumination, the sub-scanning speed, and the clock speed of the CCD line sensor are not changed at all, and only the pixels related to the image reading are read out, and the pixels not related to the image reading are not sent by sending the clock. By doing so, the total amount of data can be reduced.

In the image reading apparatus as described above, by reading out only the pixels relating to the image reading among the pixels of the CCD line sensor, the photoelectric conversion output corresponding to the exposure amount is generated at that pixel. It appears in the form of the sum of the dark output and the dark output generated in the non-read pixels at the time of reading before the previous line. FIG. 5 shows how the dark outputs overlap when 25% of the pixels of the CCD line sensor are read. As shown in FIG. 5, CC
It can be seen that, after outputting the output signals by the number of CCD shift registers included in the D line sensor, the dark output output from each pixel is the sum of the dark output generated in the same pixel. Therefore, even if only m pixels are output, if the dark output level does not change with time, once the number n of pixels possessed by the CCD line sensor is output once, it is included in the output signal of each pixel in the subsequent reading. The dark output is constant for each line reading.

An embodiment of the signal processing unit of the embodiment of the present invention when the dark output variation and the light source intensity variation are extremely small during one original image reading period will be described below. CCD with CCD shift register for n pixels
When only m pixels are read from the line sensor, the j-th pixel output d _out (i, j) on the i-th line is as follows. d _out (i, j) = d _mo (i, j) + Σ {d _BK (j + m (h-1))} (1) where d _mo (i, j): i-th line, j-th Th image signal d _BK (k): dark output generated at the k th pixel of the sensor, and d _BK (k) = 0 when k> n

Therefore, in order to accurately convert the information contained in the document into an electric signal, some kind of correction for reducing the dark output with respect to the output signal of the photoelectric conversion element, sensitivity variation between pixels of the CCD line sensor, and light source. Shading correction is necessary to correct the non-uniformity of the intensity distribution of the. Further, in the present invention, the processing of rearranging the output data is required together with the dark output correction and the shading correction. For this reason, the signal processing unit 11 according to the embodiment of the present invention has a configuration described below. In the embodiment of the present invention, it is assumed that the intensity variation of the light source is small and the temperature change of the CCD line sensor is very small and the dark output can be regarded as constant in one image reading.

FIG. 6 is a diagram showing an embodiment of the signal processing section.
In the figure, 51a, 51b, 52a, 52b, 53a, 53
b is a sample hold (S / H) circuit, 54a, 54b
Is an amplifier, 55 is a switch circuit, and 56a and 56b are A /
D converters, 57a and 57b are switching circuits, 58a and 58b
Is a dark output memory, 59a and 59b are averaging circuits, 63
a and 63b are subtraction circuits, 64a and 64b are switching circuits, and 6
5a and 65b are white reference memories, 66a and 66b are division circuits, 67 is a rearrangement circuit, 90a and 90b are peak hold circuits 91a and 91b are switching circuits.

One line of the output of the CCD line sensor has a waveform as shown in FIG. 4 (A), for example.
These 1-line waveforms are guided to the S / H circuits 51a and 51b, and the transfer clock waveform of the CCD line sensor is removed, resulting in the waveform of FIG. 4 (B). In this embodiment, the write address and read address of each memory are reset before all signal processing. Next, a dark output for one line is generated and stored. First, all pixel signals are output so that there is no dark output remaining in each pixel of the CCD line sensor. Next, the switch circuit 91a,
91b is set to a switching position opposite to that shown in the figure, and the outputs of the S / H circuits 51a and 51b are S / H circuits 52a, 52b and S.
/ H circuits 53a and 53b, peak hold circuit 90a,
90b and A / D conversion circuits 56a and 56b. Assuming that the exposure amount of the CCD line sensor is zero over one line, the output for that one line is the S / H circuit 51.
After passing through a and 51b, the waveform becomes as shown in FIG.

That is, the DS (S) and the reading area are all at the dark output level, and the values vary from pixel to pixel. This is led to S / H circuits 52a and 52b, and DS
The value of (E) is sampled and held, and the A / D conversion circuit 56
The upper limit reference V _refH of a and 56b is used. The next dark output is output until it becomes constant and is led to the S / H circuits 53a and 53b, sampled and held by the average value or representative value of DS (S), and the amplifier circuits 54a and 54b.
Amplification is performed to obtain the lower limit reference value V _{refL of} the A / D conversion circuits 56a and 56b.

As a result, A / D conversion is performed, and the outputs thereof are respectively set to 1 in dark output memories 58a and 58b (having a memory area for one line or more of the CCD line sensor) with the switching circuits 57a and 57b as the lower switching positions. Lines (m pixels) are stored. The average value of the dark output that is actually output from the pixel DS (S) of the light-shielded photosensitive portion after the dark output that is output by this is constant,
Alternatively, the acquisition of the actual dark output pattern for one line based on the representative value is completed. This dark output pattern is D _BK (j) / (V _refH −V _refL ) = D _BK (j) / D _BK (2) where D _BK (j) is the dark accumulated on the j-th pixel over several lines. Time output D _BK : Representative value or average value of the dark output accumulated in several lines in DS (S), and the accumulated dark output level output from each pixel is output from the light shielded photosensitive section. It is a value that indicates how many times the dark output is. After this, the dark output memory 5
The write address and read address of 8a and 58b are reset.

Next, the white reference of one line is taken in. In the case of the embodiment of the present invention, the reference value of the A / D converter is first generated in order to capture the white reference. Therefore, the switching positions of the switching circuits 91a and 91b are set to the illustrated positions, and the peak value of one line when the white reference plate is read is set to the lower limit reference value V _refL . As the upper limit reference value, V _refH used for capturing the dark output pattern is used. This reference V _refH , V
_refL is used as it is when reading an image. As a result, the reference V of the A / D conversion circuits 56a and 56b
_refH , V _refL and signal input (= S / H circuits 51a, 51b
Output) is as shown in FIG. 7 (B).
At this time, the data output from the A / D converter is (d _wo (j) + D _BK (j)) / (d _wpeek + D _Bpeek ) (3) where d _wo (j): white reference Photoelectric conversion output at the j-th pixel for reading d _wpeek : Photoelectric conversion output for a pixel having an output value of one line for white reference reading D _Bpeek : Number of pixels having an output peak value for one line for white reference reading It becomes a dark output when accumulated over the line, and this output has the switching circuits 57a and 57b at positions shown in the figure, and the averaging circuits 59a and 59b and the subtraction circuit 6
3a, 63b.

On the other hand, simultaneously with this operation, the following is performed. The dark output memories 58a and 58b are sequentially read from the dark output corresponding to the first pixel. This output is input to the multiplication circuits 60a and 60b. The averaging circuit 59 is connected to the other inputs of the multiplication circuits 60a and 60b.
The outputs of a and 59b are input. Addition / averaging circuit 59
a and 59b have a function of sequentially adding input pixel outputs to obtain an average value when the input control signal is ON, and retain the value as they are after obtaining the average value.
In this case, a control signal that is turned ON when the value of DS (S) at the time of reading the first line is input. During this period d _wo
Since (j) is zero, the averaging circuits 59a and 59b are added.
Is the average value of DS (S) or D which is a representative value.
_BK / (d _wpeek + D _Bpeek ) As a result, the multiplication circuit 6
The outputs of 0a and 60b are {D _BK / (d _wpeek + D _Bpeek )} ・ (D _BK (j) / D _BK ) = D _BK (j) / (d _wpeek + D _Bpeek ) (4) and the subtraction circuit It is led to the negative side inputs of 63a and 63b.

On the other hand, since the equation (3) is input to the positive side inputs of the subtraction circuits 63a and 63b, the subtraction circuits 63a and 63b.
The output of b is d _wo (j) / (d _wpeek + D _Bpeek ) (5). Each calculation of the white reference reading is performed by the number of read pixels (m pixels by each sensor). This output (equation (5)) is stored in the white reference memory as the switching positions of the switching circuits 64a and 64b opposite to those shown in the drawing. This completes the capture of the white reference for one line (m pixels in each sensor). After that, the write addresses and read addresses of the dark output memories 58a and 58b and the white reference memories 65a and 65b are reset.

The image input is performed up to the subtraction circuits 63a and 63b in the same manner as the white reference fetch. Less than,
The difference between white reference input and image input will be described. Subtraction circuit 63
The data output from a and 63b is d _mo (i, j) / (d _wpeek + D _Bpeek ) (6). This output is input to the division circuits 66a and 66b with the switching circuits 64a and 64b at the positions shown in the figure, and division is performed by the output read from the white reference memories 65a and 65b for each line.

As a result, the outputs of the division circuits 66a and 66b are calculated from (Equation (6)) / (Equation (5)) as {d _mo (i, j) / (d _wpeek + D _Bpeek )} / {d _wo (j ) / (d _wpeek + D _Bpeek )} = {d _mo (i, j) / d _wo (j)} (7), and the data subjected to the dark output correction and the shading correction are output. The two pieces of data output in parallel in the opposite direction from the center of the original image are input to the rearrangement circuit 67 and arranged in order from the data at the edge of the original 1
It is output as one serial data string. That is, the data sequence before the rearrangement is two parallel data sequences arranged as shown in FIGS. 10A and 10B, but the rearrangement circuit 6
7 is converted and output as shown in FIG.
As described above, according to the embodiment of the present invention, when the dark output before the previous line reading remains when the intensity of the dark output variation and the intensity variation of the light source during one reading period is sufficiently small. However, there is an effect that quantization and shading correction can be performed without being affected by dark output and light source fluctuation, and by rearranging, output data in the same output format as when one CCD line sensor is used. Is obtained.

FIG. 8 is a diagram showing another embodiment of the signal processing section. In the signal processing unit 11 shown in FIG.
Up to 3a and 63b, the signal processing unit has the same configuration as that of FIG. The difference from the signal processing unit shown in FIG.
The outputs of a and 63b are input to the rearrangement circuit 67, and the two parallel data strings are rearranged as one serial data string arranged from the end data of the original image. Therefore, the switching circuit 64, the white reference memory 65, the division circuit 6
6 is one at a time. In the signal processing unit in FIG. 8, the shading correction is performed after the rearrangement circuit 67. Other than that, it is the same as the signal processing unit shown in FIG. The signal processing unit of FIG. 8 has the same effect as the signal processing unit of FIG. 6, and moreover, the circuit configuration for shading correction is simplified.

FIG. 9 is a diagram showing still another embodiment of the signal processing section. In the signal processing unit 11 shown in FIG.
The conversion circuits 56a and 56b are the same as the signal processing unit of FIG. The difference from the signal processing unit shown in FIG.
The outputs of the conversion circuits 56a and 56b are output by the switching circuit 68.
rearrangement circuit 67 and memory 69 via a and 68b.
a, 69b, and two parallel data are rearranged as one serial data string arranged from the data string at the end of the original image. At this time, if the data is directly input to the rearrangement circuit 67, the information of DS (S) will be destroyed as shown in FIG. Therefore DS
In order not to destroy the information of (S), the information of DS (S) output from each sensor is stored in the memories 69a and 69b, the data is rearranged, and then the selection circuit 70
In, two DS (S) are inserted, converted into data as shown in FIG. 10 (D), and output. In the signal processing unit shown in FIG. 9, dark output correction and shading correction are performed after the rearrangement circuit. Other than that, it is the same as the signal processing unit shown in FIG. The signal processing circuit of FIG. 9 has the same effect as the signal processing circuit of FIG. 6, and moreover, the circuit configuration for dark output correction and shading correction is simple.

[0028]

As is apparent from the above description, the present invention has the following effects. (1) According to the first aspect of the invention, in the image reading apparatus for obtaining the electric signal according to the density of the original by the photoelectric conversion element, the photoelectric conversion element is used so that the original area is divided into two in the main scanning direction and is read. Two pieces are provided corresponding to the areas, and the document position corresponding to the read pixel to be read first of the two photoelectric conversion elements is at the substantially center of the document area in the main scanning direction, and to the read pixel to be read subsequently. Installed so that the directions of the corresponding document positions are opposite to each other, and output only the light shielding plate that shields the reflected light from other than the document, and the pixels of the photoelectric conversion element corresponding to the document size,
First holding means for holding an output portion of a pixel having only a transfer portion without a photosensitive portion, and output of a pixel having a light shield on the photosensitive portion (a dark output and a reading which occur in a non-read pixel before a reading line) Second holding means for holding the sum of the dark output generated in the pixels where the light is shielded by the line, and actually for one line based on the outputs of the first holding means and the second holding means. First normalizing means for normalizing the dark output signal output from each pixel, and first storing means for storing the dark output signal normalized by the first normalizing means,
Third holding means for holding the output of the pixel having the light shield on the photosensitive section, and the output of the third holding procedure and the output of reading the contents of the first storage means over one line are multiplied. Since the multiplying means and the subtracting means for subtracting the output of the multiplying means from the output when the image is read are provided, high-speed and high-definition reading is possible, and when reading a small document, it is possible to read at higher speed. When there is no change in the dark output by one reading, even if the number of pixels smaller than the number of pixels of the photoelectric conversion element is read, accurate dark output correction can be performed with a simple circuit configuration. .. (2) In the invention described in claim 2, in the invention described in claim 1, the accumulation time when the dark output signal over one line is read from the photoelectric conversion element is set longer than the accumulation time when the image is read. Since this is done, it is possible to more accurately correct the dark output. (3) In the invention according to claim 3, in the invention according to claim 1, the first holding means for holding the output part of the pixel having only the transfer part without the photosensitive part and the white reference plate are read over one line. A peak hold means for holding the peak value of the output signal at this time, the first hold means, and a first normalization means for normalizing the white reference plate read signal and the image read signal over one line with the output value of the peak hold means as a reference. 1 normalizing means, 2nd storing means for storing the normalized white reference plate read signal output from the 1st normalizing means over one line, and the contents of the 1st normalizing means. Since the second normalizing means for normalizing the output read out over one line is provided, accurate shading correction is possible when there is no intensity fluctuation of the light source. A. (4) In the invention described in claim 4, since the rearrangement circuit is provided in the inventions of claims 1 to 3, it is possible to obtain output data of the same output format as one photoelectric conversion element.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an image reading apparatus according to the present invention.

FIG. 2 is a diagram showing a photoelectric conversion system, a drive system, and a signal processing system.

FIG. 3 is a timing diagram showing output pulses of a CCD driving unit.

FIG. 4 is a diagram showing an output signal of a CCD line sensor.

FIG. 5 is a diagram showing how dark outputs of CCD line sensors overlap.

FIG. 6 is a diagram illustrating an example of a signal processing unit.

FIG. 7 is a diagram showing an output for one line of a CCD line sensor.

FIG. 8 is a diagram showing another embodiment of the signal processing unit.

FIG. 9 is a diagram showing still another embodiment of the signal processing unit.

FIG. 10 is a diagram showing an input data string and an output data string of a rearrangement circuit.

[Explanation of symbols]

7a, 7b ... CCD shift register, 8a, 8b ... Photodiode array, 9a, 9b ... Output section, 10 ... CCD
Drive unit, 11 ... Signal processing unit, 30 ... Light shielding plate control unit, 31
Document size detector 32, illumination light source controller 33, sub-scanning speed controller.

Claims (4)

[Claims] 1. An image reading apparatus for obtaining an electric signal according to the density of a document by a photoelectric conversion element, wherein the photoelectric conversion element corresponds to the document area so that the document area is divided into two in the main scanning direction and is read. Of the two photoelectric conversion elements, the document position corresponding to the read pixel read first of the two photoelectric conversion elements is substantially at the center in the main scanning direction of the document area, and the document position corresponding to the read pixel read subsequently is read. Installed so that the directions are opposite to each other, a light-shielding plate that shields reflected light from other than the original, and outputs only the pixels of the photoelectric conversion element corresponding to the size of the original, without the photosensitive section and only the transfer section. First holding means for holding the output portion of the pixel, second holding means for holding the output of the pixel having a light shield on the photosensitive portion, the first holding means and the second holding means. 1 based on the output of the holding means
First normalizing means for normalizing the dark output signal actually output from each pixel over the line, and first storing means for storing the dark output signal normalized by the first normalizing means. And third holding means for holding the output of the pixel having the light shield on the photosensitive portion, the output of the third holding means and the output of reading the contents of the first storage means over one line. An image reading apparatus comprising: multiplying means for multiplying; and subtracting means for subtracting an output of the multiplying means from an output when an image is read. 2. The image according to claim 1, wherein the accumulation time for reading the dark output signal over one line from the photoelectric conversion element is set longer than the accumulation time for each line when reading the image. Reader. 3. A first holding means for holding an output portion of a pixel having only a transfer portion without a photosensitive portion, and a peak hold means for holding a peak value of an output signal when the white reference plate is read over one line. First normalizing means for normalizing the white reference plate read signal and the image read signal over one line with reference to the output values of the first hold means and the peak hold means;
Second storage means for storing the normalized white reference plate read signal which is the output of the normalization means of 1 line,
3. The second normalizing means for normalizing the output when an image is read by the output of reading the content of the first normalizing means over one line. Image reading device. 4. A rearrangement circuit is provided which outputs two data strings output in parallel in opposite directions from the central portion of the original image as one serial data string arranged in order from the end data of the original image. The image reading apparatus according to claim 1, 2, or 3, wherein.