JP2001217990A - Image reader and image reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide image reader that can eliminate a step difference of signals that is a defect of a linear image sensor adopting a left right split read system required to realize high-speed image reading. SOLUTION: The image reader is provided with a linear image sensor that sequentially reads an image signal of each of area divisions of light receiving pixel array from separate output terminals corresponding to the areas, a gray reference board, a CPU (20) that controls the linear image sensor to read the gray reference board while changing the exposure time, and produces LUTs (13-16) used to convert a level of an image signal outputted from each output terminal into a level of a preset reference signal and a correction means that is provided corresponding to each area and uses the LUTs to convert the image signal outputted from the output terminal.

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 a linear image sensor having a left / right separated reading structure, and more particularly to an image reading apparatus having a joint correction function.

[0002]

2. Description of the Related Art Conventionally, there is an image reading apparatus using a linear image sensor.

FIG. 10 is a diagram showing a configuration of a linear CCD image sensor used in a conventional image reading apparatus.

In FIG. 10, reference numeral 101 denotes a light-receiving pixel row of a linear CCD image sensor, and 102 and 103 separate charges accumulated in each pixel of the light-receiving pixel row into odd (ODD) pixels and even (EVEN) pixels. Analog shift registers for reading in order, 104 and 105
Is an output amplifier for converting charges read from the analog shift registers 102 and 103 into voltage signals and outputting the voltage signals.

FIG. 11 shows a configuration example of an image reading apparatus using the above-described linear CCD image sensor.

In FIG. 11, reference numeral 201 denotes a platen glass;
202 is a document, 203 is an illumination lamp for illuminating the document, 204 to 206 are first, second, and third mirrors, respectively, 207 is a lens for forming a document image on the light receiving surface of the linear image sensor 208, Reference numeral 209 denotes an image sensor driving circuit for driving the linear image sensor 208, and reference numeral 210 denotes a white plate for reading as a reference for shading correction processing.

The illumination lamp 203 and the first to third mirrors 2
Reference numerals 04 to 206 are at positions indicated by solid lines during normal document reading, but move to positions indicated by dotted lines when reading the white plate 210. When reading the original, the mirror can be two-dimensionally read by moving each mirror in the sub-scanning direction S.

[0010] In the linear CCD image sensor shown in FIG. 10, the charge stored in each pixel of the light receiving pixel row 101 is read out separately for ODD and EVEN only because of the transfer speed of the analog shift registers 102 and 103. This is necessary to achieve a reading speed higher than a predetermined speed.

However, in recent years, there has been an increasing demand for an image reading apparatus having a higher reading speed than before, and it has been required to realize a reading speed which cannot be achieved by a linear CCD image sensor of the ODD / EVEN separation reading type as shown in FIG. Have been.

Under such circumstances, as shown in FIG. 12, an ODD / EVEN linear CCD image sensor capable of realizing a reading speed twice as high as that of an ODD / EVEN separation reading type linear CCD image sensor is shown in FIG.
In addition to the above-described separation readout, a linear CCD image sensor having a structure in which charges in a light receiving pixel column are read out by dividing into left and right sides has been proposed.

In FIG. 12, reference numeral 301 denotes a light receiving pixel row of a linear CCD image sensor, and 302 to 305 divide electric charges accumulated in each pixel of the light receiving pixel row into odd (ODD) pixels and even (EVEN) pixels. Analog shift registers for sequentially reading in different directions, 306 to
An output amplifier 309 converts the charges read from the analog shift registers 302 to 305 into voltage signals and outputs the voltage signals.

[0012] The analog shift registers 302 to 305 of the linear CCD image sensor shown in FIG. 12 divide the electric charge accumulated in each pixel of the light receiving pixel array 301 into two parts at the center, and separate them into ODD / EVEN. And read.

FIG. 13 shows the driving signals and C signals of the CCD image sensor having the left-right divided readout structure shown in FIG.
4 shows a timing chart of an output signal from a CD image sensor.

In FIG. 13, "SH" is a charge shift pulse, which controls a gate for simultaneously shifting charges accumulated in the light receiving pixel column 301 to the analog shift registers 302 to 305. Therefore, as shown in FIG. 13, the time between the SH pulse and the next SH pulse is an accumulation time (Tint) for accumulating charges in the light receiving unit.

In FIG. 13, Φ1 and Φ2 are charge transfer pulses for driving the analog shift registers 302 to 305, and are shifted from the light receiving section to the analog shift registers 302 to 305 simultaneously by the SH pulse. The charge is transferred to each of the analog shift registers 302 to
The pixel is sequentially moved by one pixel in the direction of the output amplifiers 306 to 309 at the end of the pixel 305. As a result, ODD-
1, image signals such as EVEN-1, ODD-2, and EVEN-2 are output.

[0016]

However, FIG.
When the linear CCD image sensor of the left-right division reading method shown in (1) is used, a level difference occurs between the left and right reading signals due to a slight difference in linearity of each of the output signals of a total of four channels. In addition, a read signal level step occurs on the left and right.

If only ODD / EVEN divisional reading is performed as in a conventional linear CCD image sensor, O
Even if a signal level difference occurs in DD / EVEN, only a very fine repetitive pattern is slightly added to the image on the image. However, if a level difference occurs in the read signal level between the left and right division positions, Even a small signal step is very noticeable.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to eliminate a signal step which is a drawback of a left-right divided reading type linear image sensor required to realize high-speed image reading. And

[0019]

In order to achieve the above object, an image reading apparatus according to the present invention provides an image signal of each of a plurality of divided light receiving pixel rows from a separate output terminal corresponding to each area. A linear image sensor to be read, a reference density member having a predetermined density, and a level of an image signal of each area output from the output terminal based on data obtained by reading the reference density member by the linear image sensor. Adjusting means for adjusting the level of the reference signal so as to substantially match the set level of the reference signal.

Also, an image reading apparatus having a linear image sensor for reading image signals of each of a plurality of divided regions of the light receiving pixel column from separate output terminals corresponding to each region, and a reference density member having a predetermined density. According to the image reading method of the present invention, the level of an image signal output from the output terminal is made to substantially match a level of a preset reference signal based on data obtained by reading the reference density member by the linear image sensor. And an original reading step of reading an original by the linear image sensor.

According to a preferred aspect of the present invention, the adjusting means adjusts the level of the image signal of each area using an LUT, and in the adjusting step, the image signal of each area is adjusted using an LUT. Adjust the level of.

According to another preferred aspect of the present invention, the adjusting means adjusts the level of the image signal in each of the areas using an arithmetic expression, and in the adjusting step, the adjusting means uses an arithmetic expression. The level of the image signal in each area is adjusted.

Further, according to another preferred aspect of the present invention, the adjusting means adjusts an image of each area based on data obtained by reading the reference density member by the linear image sensor while changing an exposure time. The level of the signal is adjusted to substantially match the level of the preset reference signal, and in the adjusting step, each of the above-described reference density members is read by the linear image sensor while changing the exposure time. The level of the image signal in the region is adjusted so as to substantially match the level of the preset reference signal.

Preferably, when the reference density member is read while changing the exposure time, the level of the dark current output at the same exposure time as when reading the reference density member is adjusted for each of the areas output from the output terminal. The level of the image signal in each area is adjusted based on the level subtracted from the level of the image signal.In the adjusting step, when the reference density member is read while changing the exposure time, the reference density member is output with the same exposure time as when reading. The level of the image signal in each area is adjusted based on the level obtained by subtracting the level of the dark current to be output from the level of the image signal in each area output from the output terminal.

According to a preferred embodiment of the present invention, the image reading apparatus further comprises a shading correction means,
The adjusting means is arranged at a stage subsequent to the shading correcting means, and the image reading method further includes a shading correcting step, and the adjusting step is performed after the shading correcting step.

According to another preferred embodiment of the present invention, the image reading device further includes a shading correction unit, wherein the adjustment unit is disposed at a stage before the shading correction unit. And a shading correction step, wherein the adjustment step is performed before the shading correction step.

Further, according to another preferred embodiment of the present invention, the image reading apparatus switches the shading correction means and the adjustment means so as to be arranged either before or after the shading correction means. The image reading method further includes a switching unit, and the image reading method further includes a switching step of switching whether to execute the shading correction step before or after the shading correction step.

According to another preferred embodiment of the present invention, the linear image sensor is a linear image sensor having a left-right separated reading structure.

According to another aspect of the present invention, there is provided a linear image sensor for reading an image signal of each of a plurality of divided regions of a light receiving pixel row from separate output terminals corresponding to the respective regions. Shading correction means for performing shading correction on the image signal,
And adjusting means for adjusting the level of the image signal in each of the regions output from the output terminal so as to substantially match the level of a preset reference signal, which is provided in a stage preceding the shading correcting means.

Further, the image reading method of the present invention by the image reading apparatus having the linear image sensor for reading out the image signal of each of the plurality of divided regions of the light receiving pixel column from the separate output terminals corresponding to the respective regions, An adjusting step of adjusting the level of the image signal in each of the regions output from the output terminal to substantially match the level of a preset reference signal; and performing shading correction on the image signal adjusted in the adjusting step. And a shading correction step.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

(First Embodiment) FIGS. 1, 2 and 3
1 shows the configuration of the image reading device according to the first embodiment of the present invention.

In FIG. 1, reference numerals 1-4 denote amplifiers for amplifying output signals from the linear CCD image sensor having the left-right divided readout structure shown in FIG.
A / D conversion circuits for converting an output signal from the CD image sensor into a digital signal, and black offset correction processing for subtracting the black offset of the image signal of each channel and black offset for performing shading correction. -It is a shading correction circuit.

The LUT (LOOK) of the connection correction circuits 13 to 16
UP TABLE) is ODD-1, EVEN-1, ODD-
2. Adjustment of the signal level of each signal of EVEN-2 to correct connection of left and right read signals (correction of signal step)
It is for realizing.

The first memory 17 temporarily stores the output signal from the linear CCD image sensor output at the timing shown in FIG. 13, and realizes the pixel rearrangement for rearranging and outputting the correct pixel order. The scan converter and the second memory 19 store the section signal (PH) shown in FIG.
EN) is a data holding unit for temporarily holding the pixel data in the “H” section of the “EN” section so that the CPU 20 can take in the pixel data. Then, the contents to be set in the LUTs 13 to 16 for connection correction are determined from the fetched image data by arithmetic processing described later.

FIG. 2 shows the configuration of the image reading apparatus according to the present invention.

The image reading apparatus shown in FIG. 2 differs from the conventional image reading apparatus shown in FIG. 11 in that it has a gray reference plate 701.

In FIG. 2, reference numeral 201 denotes an original platen glass; 202, an original; 203, an illumination lamp for illuminating the original; 204 to 206, first, second, and third mirrors, respectively; Image sensor 208
209, an image sensor driving circuit for driving the linear image sensor 208; and 210, a white plate for reading as a reference for shading correction processing.

Illumination lamp 203 and first to third mirrors 2
Reference numerals 04 to 206 are at positions indicated by solid lines during normal document reading, but move to positions indicated by dotted lines when reading the white plate 210 and the gray reference plate 701. Also,
When reading a document, the mirror can be read two-dimensionally by moving each mirror in the sub-scanning direction S.

The gray reference plate 701 is a gray (gray between white and black) plate, and as shown in FIG.
It has the same shape as. In FIGS. 2 and 3, the gray reference plate 701 is used as the white plate 20 for shading correction.
9, the arrangement is not limited to this arrangement in the present invention.

Next, the joint correction method according to the first embodiment of the present invention will be described in detail.

FIG. 4A shows an example of the ODD-1 signal and the ODD-2 signal before the connection correction processing (before LUT conversion). In FIG. 4A, the horizontal axis represents the brightness of the document, and the vertical axis represents the read image signal level. ODD-
1 and ODD-2 are converted into digital signals through circuits different from the output stage amplifier and amplifying circuit of the linear CCD image sensor. Therefore, as shown in FIG. Read at different signal levels.
Although FIG. 4A shows an example of a signal for two channels of the ODD-1 signal and the ODD-2 signal, there is a slight difference in the linearity of each channel similarly for the four-channel signal.

As shown in FIG. 4B, the role of the LUT of the connection correction circuits 13 to 16 is to correct and convert the signal level of each channel to a predetermined linearity so that each channel has the same brightness. This is to match the signal levels. Thus, ODD-1 and ODD-
2 can be made to match, but by performing the same correction on the remaining EVEN-1 and EVEN-2 signals, it becomes possible to make the read levels of all channels match. .

In order to realize the connection correction (reading level correction) based on the above idea, the present invention performs the following operation.

First, an image is captured using the gray reference plate 701 shown in FIG. This gray reference plate 70
At the time of reading 1, the storage time of the image sensor is changed to obtain a corresponding gray reference plate reading level.

FIG. 5 shows an example of read data of a gray reference plate obtained for a certain channel.

In FIG. 5, the horizontal axis represents the accumulation time (Tin).
t), the vertical axis is the reading level of the gray reference plate. FIG.
Here, the data when the accumulation time is an integral multiple of the predetermined value T is shown, but the method of changing the accumulation time may be other methods.

Since the image data obtained by reading the gray reference plate 701 at each accumulation time is temporarily stored in the second memory 19, the CPU 20 reads the image data stored in the second memory 19 and Average value processing, etc., to obtain the signal level of each channel.
The example of the graph shown in FIG.
It is obtained repeatedly while changing int.
Therefore, FIG. 5 shows the linearity characteristics of the channel.

When the accumulation time Tint is changed,
The effect of the dark current generated in the light receiving unit changes according to the length of the accumulation time. The dark current is a charge component generated in the light receiving unit even when no light is incident. As the storage time becomes longer, the amount of charge stored due to the dark current increases. For this reason, as shown in FIG. 6, the actual read signal level of the gray reference plate 701 is different between the black level read without light incident on the image sensor and the gray reference plate read during the same accumulation time. The difference from the signal level must be treated as a gray reference plate reading.

FIG. 7 is a graph showing a conversion characteristic of the LUT for correcting the linearity characteristic of FIG. 5 to an ideal linearity characteristic, and is a characteristic obtained by performing an inverse conversion operation on the characteristic of FIG. .

By this correction, the channel having the linearity shown in FIG. 5 is corrected to an ideal linearity characteristic as shown in FIG.

In the above description, the target of the linearity correction is the ideal linearity characteristic. However, in the connection correction of the left and right divided read image sensor outputs, which is the object of the present invention, only the ideal linearity is the adjustment target. Needless to say, it is not necessary to use a predetermined linearity characteristic.

The CPU sets the contents of the correction LUT in the connection correction circuits 13 and 15 in FIG.
1. The reading level of ODD-2 is corrected. EVEN-
The other LUT circuits 14 and 16 shown in FIG.
By setting to, the reading level can be corrected.

In the description of the first embodiment of the present invention, the bridging correction circuit for performing bridging correction is arranged at the subsequent stage of the shading correction circuit. This is because the splice correction circuit not only realizes splice correction but also has the function of correcting read linearity.Therefore, by arranging the splice correction circuit after the shading correction circuit, a fixed It can provide read linearity.

(Second Embodiment) Next, a second embodiment will be described.

In the case of the first embodiment, the connection correction circuit for connection correction is arranged after the shading correction. That is, the signal from each channel is corrected so that the linearity characteristics of each channel become the same after the shading correction. For this reason, when the light amount of the illumination light source fluctuates and the gain for shading correction changes, an error may occur in the content of the linearity correction.

In order to solve this problem, the image reading apparatus according to the second embodiment of the present invention has a configuration shown in FIG.

The difference from the configuration shown in FIG. 1 described in the first embodiment is that a bridge correction circuit for performing bridge correction is arranged at a stage preceding the shading correction circuit.

However, the black offset correction circuit (a circuit for removing the black offset component by subtraction) is processed before the connection correction by the connection correction circuit. However, whether the black offset correction is located before or after the link correction circuit does not affect the content of the present invention, and may be either.

The connection correction operation is the same as in the first embodiment, and a description thereof will be omitted.

According to the second embodiment of the present invention, the linearity of each channel in the state where the shading correction is not performed can be corrected to the same characteristic by disposing the connection correction circuit before the shading correction. it can. Thereby, even if the illumination light amount of the image reading device changes, stable joint correction can be realized.

The first and second embodiments each have advantages and disadvantages, and therefore may be used properly depending on the situation.

It is also easy to use a configuration in which the connection correction circuit can be switched between the former stage and the latter stage of the shading correction circuit by the CPU.

In the first and second embodiments, the connection correction is performed by the LUT. However, the present invention is not limited to this, and instead of the LUT, an arithmetic expression for converting the linearity characteristic is used. It is also possible to generate and use this.

[0065]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. Or a CPU or MPU) reads out and executes the program code stored in the storage medium,
Needless to say, this is achieved. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
In addition, by the computer executing the readout program code, not only the functions of the above-described embodiments are realized, but also based on the instructions of the program code,
The operating system (OS) running on the computer performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

[0068]

As described above, according to the present invention,
It is possible to eliminate a step of a signal, which is a drawback of the linear image sensor of the left-right divided reading system required for realizing high-speed image reading.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a partial configuration of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an image reading device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a white reference plate and a gray reference plate according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining a joint correction method according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of read data of a gray reference plate according to the present invention.

FIG. 6 is a diagram illustrating the influence of dark current on an output signal.

FIG. 7 is a diagram showing conversion characteristics of an LUT for correcting the linearity characteristics shown in FIG. 5 to ideal linearity characteristics.

FIG. 8 is a diagram showing ideal linearity characteristics after correction.

FIG. 9 is a block diagram illustrating a partial configuration of an image reading device according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a configuration of a conventional linear CCD image sensor.

FIG. 11 is a diagram illustrating a configuration example of a conventional image reading apparatus.

FIG. 12 is a diagram showing another configuration of a conventional linear CCD image sensor.

13 is a timing chart showing driving signals of the linear CCD image sensor shown in FIG. 12 and signals output from the linear CCD image sensor.

[Explanation of symbols]

1-4 amplifier 5-8 A / D conversion circuit 9-12 black offset / shading correction circuit 13-16 LUT 17 first memory 19 second memory 20 CPU 101,301 light receiving pixel column 102,103,302-305 analog shift Registers 104, 105, 306 to 309 Output amplifier 201 Platen glass 202 Document 203 Illumination lamp 204 to 206 Mirror 207 Lens 209 Image sensor drive circuit 210 White plate 701 Gray reference plate

Claims (22)

[Claims] 1. A linear image sensor for reading image signals of each of a plurality of divided regions of a light receiving pixel column from separate output terminals corresponding to each region, a reference density member having a predetermined density, and the linear image sensor. Adjusting means for adjusting the level of the image signal of each of the regions output from the output terminal based on the data read from the reference density member so as to substantially match the level of the preset reference signal. An image reading device characterized by the above-mentioned. 2. The image reading apparatus according to claim 1, wherein the adjustment unit adjusts the level of the image signal in each of the areas using an LUT. 3. The image reading apparatus according to claim 1, wherein the adjusting unit adjusts the level of the image signal in each of the areas using an arithmetic expression. 4. The image processing apparatus according to claim 1, wherein the adjusting unit changes the level of the image signal of each area to a level of a preset reference signal based on data obtained by reading the reference density member by the linear image sensor while changing an exposure time. The image reading device according to claim 1, wherein the image reading device is adjusted so as to substantially match. 5. The image forming apparatus according to claim 1, wherein the adjusting unit is configured to read the reference density member while changing the exposure time, and to set the level of the dark current output at the same exposure time as the reading at the time of reading the image of each area output from the output terminal. The image reading apparatus according to claim 4, wherein the level of the image signal in each of the areas is adjusted based on a level subtracted from the level of the signal. 6. The image reading apparatus according to claim 1, further comprising a shading correction unit, wherein the adjustment unit is arranged at a stage subsequent to the shading correction unit. 7. The image reading apparatus according to claim 1, further comprising a shading correction unit, wherein the adjustment unit is arranged at a stage preceding the shading correction unit. 8. The method according to claim 1, further comprising: a shading correction unit; and a switching unit that switches the adjustment unit so that the adjustment unit is disposed either before or after the shading correction unit. An image reading device according to any one of the above. 9. The image reading device according to claim 1, wherein said linear image sensor is a linear image sensor having a left-right separated reading structure. 10. A linear image sensor for reading image signals of each of a plurality of divided areas of a light receiving pixel column from separate output terminals corresponding to the respective areas, and an image reading apparatus having a reference density member having a predetermined density. An image reading method, wherein a level of an image signal output from the output terminal is made to substantially match a level of a preset reference signal based on data obtained by reading the reference density member by the linear image sensor. An image reading method, comprising: an original reading step of reading an original by the linear image sensor. 11. The image reading method according to claim 10, wherein in the adjusting step, an image signal level of each of the areas is adjusted using an LUT. 12. The image reading method according to claim 10, wherein in the adjusting step, the level of the image signal in each of the areas is adjusted using an arithmetic expression. 13. In the adjusting step, based on data obtained by reading the reference density member by the linear image sensor while changing an exposure time, a level of an image signal of each area is set to a level of a preset reference signal. 2. The method according to claim 1, wherein the adjustment is performed so as to substantially match.
3. The image reading method according to any one of 2. 14. In the adjusting step, when the reference density member is read while changing the exposure time, the level of the dark current output at the same exposure time as the reading is read out from the output terminal. 14. The image reading method according to claim 13, wherein a level of the image signal in each of the areas is adjusted based on a level subtracted from a signal level. 15. The image reading method according to claim 10, further comprising a shading correction step, wherein the adjustment step is performed after the shading correction step. 16. The method according to claim 10, further comprising a shading correction step, wherein the adjustment step is performed before the shading correction step. 17. The method according to claim 10, further comprising: a shading correction step; and a switching step of switching whether to execute the adjustment step before or after the shading correction step. The image reading method according to any one of the above. 18. The image reading method according to claim 10, wherein the linear image sensor is a linear image sensor having a left-right separated reading structure. 19. A storage medium storing a program code for realizing the image reading method according to claim 10. Description: 20. A linear image sensor for reading an image signal of each of a plurality of divided regions of the light receiving pixel column from separate output terminals corresponding to the respective regions, a shading correction unit for performing shading correction on the image signal, Adjusting means disposed before the shading correction means and adjusting the level of the image signal of each area output from the output terminal so as to substantially match the level of a preset reference signal. Image reading device. 21. An image reading method by an image reading device having a linear image sensor for reading out image signals of each of a plurality of divided regions of a light receiving pixel column from separate output terminals corresponding to the respective regions, An adjusting step of adjusting the level of the image signal in each of the regions output from the terminal to substantially match a level of a preset reference signal; and shading for performing shading correction on the image signal adjusted in the adjusting step. An image reading method, comprising: a correction step. 22. A storage medium holding a program code for realizing the image reading method according to claim 21.