JPH06253143A - Image sensor - Google Patents

Abstract

PURPOSE:To generate accurate picture information by using newest reference data at all times to execute accurate shading correction without deteriorating handling performance. CONSTITUTION:A sensor 1, a driver 2, a clamp circuit 4, an amplifier circuit 5 and an A/D converter circuit 6 generate a digital picture signal ND corresponding to an incident optical image. A command generating circuit 11, a decoder 12 and a timing generating circuit 3 make reading in the state of stopped lighting over a predetermined period and the state of lighted white reference board in response to the start of reading and then read an original. Then the timing generating circuit 3 stores the digital picture signal ND generated for a predetermined period to a memory 10 as reference data RD. A shading correction circuit 9 executes shading correction to the digital picture signal generated by reading the original based on the reference data RD stored in the memory 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for reading an image formed on a document and generating corresponding image information, and more particularly to an image sensor having a shading correction function.

[0002]

2. Description of the Related Art An image sensor obtains an image signal by converting light reflected from a document into an electric signal by a sensor such as a CCD line sensor. In general, the analog signal output from the sensor is subjected to very simple processing such as amplification and sample hold, and then output, or further subjected to analog / digital conversion and output as digital data.

However, in recent years, there is an increasing demand for higher performance of image sensors, and image sensors having an image processing function have also appeared. There are various types of image processing to be performed when generating image information, and a typical example is shading correction. This shading correction is
This is to correct the unevenness of the reading density due to the unevenness of the sensitivity of the sensor and the unevenness of the light amount of the light source.

In general, in shading correction, the white reference level RD _W and the black reference level RD _B are preset for each line based on the sensitivity characteristic of the sensor and the light amount distribution of the light source. Then, the level ND of the signal obtained by actually reading the original is compared with the reference level for each pixel, and the following expression is calculated to obtain the level SD of the corrected image signal. SD = (ND−RD _B ) / (RD _W −RD _B ) × constant Note that the constant is “255” when the gray level of the image signal is represented by 8 bits, for example.

By the way, reference data (white reference level RD
The memory for storing _W and black reference levels RD _B) semiconductor memory is used, but the case which is fixedly stored, and if you want to be updated as needed.

When the reference data is fixedly stored,
Since the user does not need to manage the reference data at all, it is easy to handle. However, since the sensitivity characteristic of the sensor and the light amount distribution of the light source change over time due to deterioration of the sensor and the light source, the reference data is not always based on the actual sensitivity characteristic of the sensor and the actual light amount distribution of the light source. , It is difficult to make accurate shading correction.

On the other hand, when the reference data is stored so that it can be updated, if the sensitivity characteristic of the sensor and the light amount distribution of the light source change, the optimum reference data can be set based on the changed characteristic. It is possible to perform more accurate shading correction. However, since the user has to perform a complicated operation and management of the reference data to set the reference data, the operability is deteriorated.

[0008]

As described above, in the conventional image sensor, if the reference data for shading correction is fixedly stored, accurate shading correction cannot be performed, and if the reference data can be updated, There was a problem that the handleability deteriorated.

The present invention has been made in consideration of such circumstances, and an object thereof is to always perform accurate shading correction using the latest reference data without deteriorating the handling property. An object is to provide an image sensor that can generate accurate image information.

[0010]

To achieve the above objects, the present invention provides image information such as a digital image signal according to an incident light image, for example, a sensor, a driver,
In response to an instruction to start the reading operation and a reading unit including a clamp circuit, an amplifier circuit, and an A / D circuit, the reading unit is instructed to display, for example, a state in which illumination is stopped and a white reference surface. In order to store the predetermined reference information and the reading control means including, for example, a command generation circuit, a decoder and a timing generation circuit that causes the document to be read after the reading is performed under a predetermined reference condition such as an illuminated state. Storage means such as a memory, reference information generation means such as a timing generation circuit for storing image information generated by the reading means in the storage means as reference information in the predetermined period, and the reading means stores the document. Shading correction is performed on image information generated by reading based on the reference information stored in the storage unit, for example, shading. And and a correction means such as positive circuit.

[0011]

When the start of the reading operation is instructed by taking such means, the reading means is controlled by the reading control means for a predetermined period before reading the original document. Therefore, the reading is performed under a predetermined reference condition. At this time, the image information generated by the reading means is
The reference information generation means stores the reference information in the storage means. After that, the reading unit reads the document under the control of the reading control unit. At this time, the correction unit performs shading correction on the image information generated by the reading unit reading the document based on the reference information stored in the storage unit.

Therefore, each time the start of the reading operation is instructed, the reference information is automatically generated and stored in the storage means, and the document is subsequently read to obtain the latest generated information. Shading correction is performed using the reference information.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing the configuration of the image sensor according to the present embodiment. In the figure, 1 is, for example, CC
A sensor such as a D line sensor. An image of a reflected light from a document (not shown) is formed on the sensor 1 by an optical system (not shown), and an electric signal (image signal) indicating the light amount of the light image, that is, the light and shade of the document is generated. To do. This sensor 1 can read one line by one reading, and repeatedly reads at a predetermined timing while being driven by the driver 2. Driver 2
Drives the sensor 1 so as to read at a predetermined timing based on the drive timing pulse TIM generated by the timing generation circuit 3. A white reference surface painted in white is formed at a position facing the sensor 1 when no document is set.

A clamp circuit 4 operates in synchronization with the clamp pulse CLMP generated by the timing generation circuit 3 and removes the offset voltage contained in the image signal from the image signal output from the sensor 1. Reference numeral 5 denotes an amplifier circuit, which amplifies the image signal output from the clamp circuit 4 into a signal having an optimum level for processing by the A / D circuit 6. The A / D circuit 6 converts the image signal (analog) output from the amplifier circuit 5 into, for example, an 8-bit digital image signal ND.

An LED array 7 illuminates the reading position of the original. The light emission of the LED array 7 is turned on / off by the ON / OFF circuit 8 based on the light emission control signal PRD generated by the timing generation circuit 3.

Reference numeral 9 is a shading correction circuit. The shading correction circuit 9 receives the digital image signal ND via the timing generation circuit 3, and uses the reference data (white reference data and black reference data) RD stored in the memory 10 for the digital image signal ND. Shading correction. Then, the shading correction circuit 9 outputs the corrected digital image signal SD. The memory 10 comprises a RAM, and stores the reference data R
It is possible to rewrite D under the control of the timing generation circuit 3.

Reference numeral 11 is a command generation circuit. The command generation circuit 11 is provided with a line start signal L supplied from the outside (for example, a device to which the image sensor is applied).
ST, reading start signal READ and investigation / inspection signal TE
Based on ST, the LED control signal LEDC and the operation form control signals S1 and S2 are generated.

Denoted at 12 is a decoder which generates mode designating signals M0, M1, M2 and M3 in accordance with the states of the operation mode control signals S1 and S2 generated by the command generation circuit 11 under the conditions shown in FIG.

The timing generation circuit 3 includes a line start signal LST, a clock signal CLK, and an LED control signal LE.
Drive timing pulse TIM, clamp pulse C based on DC and mode designation signals M0, M1, M2, M3
LMP, light emission control signal PRD, read enable signal E
R, write enable signal EW and address ADD are generated.

FIG. 3 is a block diagram showing a specific structure of the command generating circuit 11. As shown in this figure, the command generation circuit 11 includes a shift register 110 (for example, 74
HC164 equivalent) and selector 111 (eg 74
HC157 equivalent product).

A read start signal READ is input to both of the two input terminals A and B of the shift register 110. The clock input terminal of the shift register 110 is
The line start signal LST is input. Further, the clear signal input terminal CL of the shift register 110 is +5
The voltage of V is applied.

The input terminals 1A and 2A of the selector 111 are
It is connected to the output terminal Q _E of the shift register 110. The read start signal READ is input to the input terminal 1B of the selector 111. A voltage of + 5V is applied to the input terminal 2B of the selector 111. Selector 1
The input terminal 3A of 11 is connected to the output terminal Q _H of the shift register 110. Input terminal 3 of the selector 111
B and strobe terminal G are grounded. Further, the select terminal S of the selector 111 is connected to the investigation / inspection signal TE.
ST is input. The output from the output terminal 1Y of the selector 111 is given to the timing generation circuit 3 as the LED control signal LEDC. The output from the output terminal 2Y is output as the operation mode control signal S1 at the output terminal Y3.
Is supplied to the decoder 12 as the operation mode signal S2.

Next, the operation of the image sensor configured as described above will be described. First, the apparatus to which the present image sensor is applied sets the reading start signal READ to "L" in order to cause the present image sensor to perform reading (time T1 in FIG. 4). Also, the inspection / inspection signal TEST is set to "L".
In addition, the line start signal LST is set to "L" at a predetermined cycle.

Here, the command generation circuit 11 operates as follows. That is, the shift register 110 converts the input read start signal READ into the line start signal L.
It shifts sequentially at the rising edge of ST, and outputs from the output terminal Q _E for 4 cycles of the line start signal LST and the output terminal Q _H.
Are delayed by 7 cycles and output. Thus, the output terminal Q _E is "H" from the time T1 until the fifth rising edge of the line start signal LST (time T2 in FIG. 4), and thereafter becomes "L". The output terminal Q _H is
After the time T1, it is "H" until the eighth rise of the line start signal LST (time T3 in FIG. 4), and thereafter becomes "L". And the inspection / inspection signal TEST is “L”
If so, the selector 111 selects the input terminals 1A, 2A, and 3A because the select terminal S is "L". Thus, from the selector 111, the output signal from the output terminal Q _E of the shift register 110 is the LED control signal LEDC and the operation mode control signal S1, and the output signal from the output terminal Q _H of the shift register 110 is the operation mode control signal S2. Is output as.

Now, the decoder 12 has an operation mode control signal S
Based on the states of 1 and S2, the mode designating signals M0 to M3 are generated under the conditions shown in FIG. That is, from time T1 to T
Since the operation mode control signals S1 and S2 are both “H” during the period up to the second time point, the mode designating signals are “L” for M0, “L” for M1, “L” for M2, and “H” for M3. It will be. Subsequently, in the period from the time point T2 to the time point T3, the operation form control signal S1 is "L", and the operation form control signal S
Since 2 is "H", the mode designation signal is "L" for M0, "L" for M1, "H" for M2, and "L" for M3. Further, after time T3, the operation mode control signal S
Since both 1 and S2 are "L", the mode designation signals are "H" for M0, "L" for M1, "L" for M2, and M3.
Becomes "L".

The timing generation circuit 3 has a 0th mode when M0 of the mode designation signals M0 to M3 is "H", a first mode when M1 is "H", and a M2 of "H". Second mode, and M3 is "H"
When it is, it operates as the third mode. In each mode, the 0th mode is shading correction processing, the 1st mode is investigation / inspection, and the 2nd mode is generation of white reference data.
The registration and the third mode are set to the modes for respectively performing the generation and registration of the black reference data.

During the period from the time point T1 to the time point T2, since the mode designation signal M3 is "H" as described above, the timing generation circuit 3 stores the black reference data in the memory 10.
Generate each signal to write to. That is, the timing generation circuit 3 first turns off the light emission control signal PRD according to the LED control signal LEDC, and turns off the light irradiation by the LED array 7. In this state, the driver 2 drives the sensor 1 to read. LE at this time
Since the D array 7 is OFF, there is almost no light incident on the sensor 1, and the sensor 1 is reading “black”.

The image signal generated by the sensor 1 has its offset voltage removed by the clamp circuit 4, amplified by the amplifier circuit 5, and then converted into a digital image signal ND by the A / D circuit 6. The digital image signal ND is
It is input to the shading correction circuit 9 through the timing generation circuit 3.

In the third mode, the timing generation circuit 3 sets the write enable signal EW to "H". The timing generation circuit 3 also generates an address ADD corresponding to the storage area of the black reference data in the memory 10 in synchronization with the digital image signal ND.

When the write enable signal EW is "H", the shading correction circuit 9 outputs the input digital image signal ND to the memory 10 without performing the shading correction processing. At this time, since the address ADD generated by the timing generation circuit 3 and corresponding to the storage area of the black reference data is given to the memory 10 through the shading correction circuit 9, the digital image signal ND is stored in the memory 10 as black reference data. I will be remembered.

This operation is repeated (here, four times) every one cycle of the line start LST in the period from the time point T1 to the time point T2. Therefore, the last written data is held in the memory 10 as the black reference data.

Subsequently, during the period from time T2 to time T3, since the mode designation signal M2 is "H", the timing generation circuit 3 generates each signal so as to write the white reference data in the memory 10. . That is, the timing generation circuit 3 first turns on the light emission control signal PRD according to the LED control signal LEDC, and turns on the light irradiation by the LED array 7. In this state, the driver 2 drives the sensor 1 to read. At this time, the LED array 7
Is ON and there is a white reference surface that is painted white facing the sensor 1, so the sensor 1 is reading “white”.

The image signal generated by the sensor 1 has its offset voltage removed by the clamp circuit 4, amplified by the amplifier circuit 5, and then converted into a digital image signal ND by the A / D circuit 6. The digital image signal ND is
It is input to the shading correction circuit 9 through the timing generation circuit 3.

Even in the second mode, the timing generation circuit 3 sets the write enable signal EW to "H". Further, the timing generation circuit 3 uses the digital image signal N
In synchronization with D, an address ADD corresponding to the storage area of the white reference data of the memory 10 is generated. Thus, the digital image signal ND is stored in the memory 10 as white reference data.

This operation is repeated (here, three times) every one cycle of the line start LST in the period from the time point T2 to the time point T3. Therefore, the last written data is held in the memory 10 as white reference data.

Since the mode designation signal M0 is "H" after the time T3, the timing generation circuit 3
Generates each signal so as to execute the shading correction processing. That is, the timing generation circuit 3 keeps the irradiation of light by the LED array 7 ON. In this state, the driver 2 drives the sensor 1 to read the document while feeding the document. At this time, the LED array 7 is ON
Since there is a document facing the sensor 1,
The sensor 1 is reading the image formed on the document.

The image signal generated by the sensor 1 has its offset voltage removed by the clamp circuit 4, amplified by the amplifier circuit 5, and then converted into a digital image signal ND by the A / D circuit 6. The digital image signal ND is
It is input to the shading correction circuit 9 through the timing generation circuit 3.

In the 0th mode, the timing generation circuit 3 sets the read enable signal ER to "H". Also, the digital signal generates an address ADD corresponding to the black reference data and the white reference data in synchronization with the signal ND.

When the read enable signal ER is "H", the memory 10 outputs the data of the address designated by the address ADD. Also, the shading correction circuit 9
Performs the shading correction process using the reference data output from the memory 10. That is, the memory 1
When the black reference data output from 0 is RD _B and the white reference data is RD _W , the calculation of SD = SD = (ND−RD _B ) / (RD _W −RD _B ) × 255 LSB is performed for each pixel.

By the way, in the apparatus to which the present image sensor is applied, when the reading of one original is completed and the reading of another original is continued, the reading start signal READ is sent as shown in FIG. After once setting to "H", it is set to "L" again. Thus, the image sensor repeats the above-mentioned operation even when reading another document.

As described above, when the reading start signal READ is set to "L" to instruct the execution of reading, "black reference data generation and registration"-"white reference data generation and registration"-"original" Reading and shading correction processing ”. That is, the black reference data and the white reference data are generated and registered prior to actually reading the document.

Therefore, the shading correction processing is extremely accurate because it is performed using the reference data generated immediately before. Further, since the reference data is automatically generated / registered based on the state of the read start signal READ, the user does not need to perform any special operation and the handling is good.

The present invention is not limited to the above embodiment. For example, in the above embodiment, generation of reference data
Although the registration is performed in the order of “black reference data” → “white reference data”, the order of “white reference data” → “black reference data” may be changed by slightly changing the configuration of the command generation circuit 11. .

FIG. 6 is a diagram showing a modified structure of the command generating circuit 11. The same parts as those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. This command generation circuit 11
Is a shift register 110, a selector 111, a NAND
Gate 112, inverter 113 and NOR gate 1
It consists of 14.

The output from the output terminal Q _A of the shift register 110 is inverted and input to one of the input terminals of the NAND gate 112. Output terminal Q of shift register 110
The output from _D is inverted and input to one of the input terminals of the NOR gate 114 via the inverter 113. The output from the output terminal Q _H of the shift register 110 is NOR
It is inverted and input to the other input terminal of the gate 114, and is also input to the input terminal 3A of the selector 111.

The output of the NOR gate 114 is inverted and input to the other input terminal of the NAND gate 112 and is also input to the input terminal 2A of the selector 111.
The output of the NAND gate 112 is input to the input terminal 1A of the selector 111.

The read start signal READ is input to the input terminal 1B of the selector 111. A voltage of + 5V is applied to the input terminal 2B of the selector 111. The input terminal 3B and the strobe terminal G of the selector 111 are grounded. Further, the select terminal S of the selector 111
A survey / inspection signal TEST is input to the. The output from the output terminal 1Y of the selector 111 is given to the timing generation circuit 3 as the LED control signal LEDC. The output from the output terminal 2Y is the operation form control signal S1, and the output from the output terminal Y3 is the operation form signal S.
2 is given to the decoder 12.

Thus, by the command generating circuit 11 configured as described above, the read start signal READ of the LED control signal LEDC and the operation mode control signal S1 is "L".
After that (at T11 in FIG. 7), the first rising edge of the line start signal LST (T12 in FIG. 7).
From the time point) to the rising time point of the fourth line start signal LST (time point T13 in FIG. 7), from the time point T13 to the rising time point of the fourth line start signal LST (time point T14 in FIG. 7). H ", and T1
After 4 becomes "L". On the other hand, the operation mode signal S2 is T1.
It becomes "H" up to the 4th time point, and "L" after the T14 time point.

Therefore, from time T12 to time T13, the second mode is set in which white reference data is generated / registered, and then, in time T14, the third mode is set in which black reference data is generated / registered. Then, after T14, the mode becomes 0, and the actual document reading is performed. In addition, various modifications can be made without departing from the scope of the present invention.

[0050]

According to the present invention, image information such as a digital image signal corresponding to an incident light image is generated, for example, L.
In response to an instruction to start the reading operation and a reading unit including an ED array, a sensor, a driver, a clamp circuit, an amplifier circuit, and an A / D circuit, the reading unit is stopped, for example, for a predetermined period of time. Read-out means including a command generation circuit, a decoder, and a timing generation circuit, which causes the original to be read after the reading is performed under a predetermined reference condition such as a state in which the white reference surface is illuminated, and a predetermined reference condition. Storage means for storing the reference information, such as a memory, and reference information generation means such as a timing generation circuit for storing image information generated by the reading means in the storage means as reference information in the storage means, Shading based on the reference information stored in the storage means for image information generated by the reading means reading the document. Since a correction means such as a shading correction circuit for performing positive correction is provided, accurate shading correction can always be performed using the latest reference data and accurate image information can be generated without deteriorating handleability. It becomes an image sensor.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a configuration of an image sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing an input / output relationship of a decoder 12.

FIG. 3 is a block diagram showing a specific configuration of a command generation circuit 11.

FIG. 4 is a timing chart showing the operation.

FIG. 5 is a timing chart showing an operation when a plurality of originals are continuously read.

FIG. 6 is a diagram showing a modified configuration of a command generation circuit 11.

7 is a timing chart showing an operation when the command generating circuit 11 shown in FIG. 6 is used.

[Explanation of symbols]

1 ... Sensor, 2 ... Driver, 3
... Timing generation circuit, 4 ... Clamp circuit,
5 ... Amplifying circuit, 6 ... A / D circuit,
7 ... LED array, 8 ... ON / OFF
Circuit, 9 ... Shading correction circuit, 10 ... Memory, 11 ... Command generation circuit, 12 ... Decoder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Kunimune 21st Toshiba Communication Technology Co., Ltd. 3-1, Asahigaoka, Hino City, Tokyo

Claims (1)

[Claims] 1. A reading unit that generates image information according to an incident light image, and a reading unit that operates under a predetermined reference condition for a predetermined period in response to a predetermined start of a reading operation. After the reading is performed, the reading control means for reading the document, the storage means for storing the predetermined reference information, and the storage means using the image information generated by the reading means in the predetermined period as the reference information. And a correction unit that performs shading correction on the image information generated by the reading unit reading the document based on the reference information stored in the storage unit. Characteristic image sensor.