JPH06164921A - Picture signal correction device - Google Patents

Abstract

PURPOSE:To obtain the picture signal correction device executing stable and sure dark state output offset correction or shading correction in a short time. CONSTITUTION:When a dark state output reference signal is to be acquired, contacts b, c of a changeover switch 5 are closed and a memory 1, a subtractor 3 and an adder 4 implement processing based on a recurrence formula of Dbn= Xbn-Db(n-1)/4+Db(n-1) with respect to a dark state reference signal inputted from an external line image sensor. The Dbn obtained by the processing is stored in the memory 1 as the dark state reference signal in place of the data Db(n-1) stored therein before. After the processing as above is repeated for plural number of times, contacts a, c of the changeover switch 5 are closed and a picture signal Xp inputted externally is given to the subtractor 2, in which Db/4 is subtracted and the result is outputted as a picture signal Yp subject to dark state output offset correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for correcting an image signal, and more particularly to a dark output offset correction or a shutter for an image signal from a so-called line image sensor.
The present invention relates to an image signal correction device that performs ding correction.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus having a so-called line image sensor in which a plurality of light receiving elements are arranged on a straight line, non-uniformity of dark output between respective elements of the line image sensor, that is, respective pixels, and There are so-called dark output offset correction and so-called shading correction as techniques for compensating the nonuniformity of the sensitivity of each light receiving element forming the line image sensor.

FIG. 9 shows the dark output offset correction and shutter.
A schematic configuration of an image signal correction apparatus for performing the Ding correction is shown, and these two corrections will be schematically described below with reference to FIG. The image signal correction apparatus shown in the figure is configured by connecting a dark output offset correction unit 20 and a shrouding correction unit 21 in series. First, the dark output offset correction unit 20 outputs the dark output It is composed of a memory 22 and a subtractor 23. The dark output memory 22 stores the dark reference output of the line image sensor when light is not incident on the line image sensor (not shown). The subtractor 23 subtracts the dark reference output stored in the dark output memory 22 from the image signal input from the line image sensor (not shown), and the dark output offset correction is performed by this processing. Become.

On the other hand, the shading correction section 21 comprises a white reference memory 24 and a divider 25, and the white reference memory 24 is a white reference plate (not shown) by a line image sensor (not shown). The output of the line image sensor at the time of photographing (No.) is stored. And
In the divider 25, the dark output offset correction unit 20
By dividing the image signal input from the white reference signal stored in the white reference memory 24, the shading correction is performed.

When the dark reference signal or the white reference signal of the line image sensor is stored in the memory, external noise such as thermal noise may be mixed and stored in the memory at the same time. For this reason, in the finally obtained image, streaky lines appear in the sub-scanning direction of the image capture. As a technique for removing the image disturbance caused by noise mixed when storing the dark reference signal or the white reference signal, the dark reference signal or the white reference signal is acquired for several lines and the average thereof is obtained. There is a method in which the influence of mixed noise is minimized.

[0006]

However, in the so-called averaging process as described above, it is necessary to increase the number of times of averaging in order to increase the calculation accuracy, but it is not possible to increase the number of times of averaging. Inevitably, the processing time is long, and there is a problem that a high-quality image signal cannot be obtained within a short time. Further, there is a problem that the storage capacity of the memory is required to be large in proportion to the number of times of averaging, resulting in an increase in cost of the device. Further, there is a problem that the image cannot be read while the averaging process is being executed, and the image cannot be read at an arbitrary time.

The present invention has been made in view of the above circumstances, and provides an image signal correction apparatus capable of removing the influence of noise mixed in the dark output and the white reference output with a short processing time and a simple configuration. To do.

[0008]

According to a first aspect of the present invention, there is provided an image signal correction apparatus, which comprises a dark reference signal storage means for storing a dark reference signal of a line image sensor, and a dark reference signal storage means for reading the dark reference signal. And a subtraction means for subtracting the output value of the data compression means from the input image signal, the dark reference signal storage means being a line image. The dark reference signal of the line image sensor in a state where the incident light to the image sensor is blocked is cyclically input, and the dark reference signal that has already been input is subjected to coefficient processing. This is done by adding and updating the data already stored as a new dark reference signal. In the image signal correction apparatus according to the second aspect of the present invention, the white reference signal storage means for storing the white reference signal of the line image sensor and the white reference signal read from the white reference signal storage means are divided by a constant. Data compression means and division means for dividing the input image signal by the output value of the data compression means are provided, and the white reference signal storage means is a white plate received by a line image sensor. The white reference signal that is the output of the line image sensor for the reflected light is cyclically input, and the white reference signal that has already been input is subjected to coefficient processing and added to the input white reference signal, and a new white reference signal is added. The data stored as the white reference signal is updated.

[0009]

In the image signal correcting apparatus according to the first aspect of the present invention, the dark reference signal is repeatedly input from the line image sensor, and each time the dark reference signal is added to the dark reference signal stored in the dark reference signal storage means. The processing is performed, and the result of the processing is used as update data of the dark reference signal already stored in the dark reference signal storage means. Therefore, the dark reference signal in the dark reference signal storage means has been subjected to processing based on the so-called cut-down equation, a convergent value can be obtained relatively quickly compared to the averaging processing, and the input value suddenly changes. Even if the value becomes abnormal, its effect is smaller than that of the averaging process, and therefore, an image signal correction apparatus that performs stable and reliable dark output offset correction is provided. In the image signal correction apparatus according to the second aspect of the present invention, the white reference signal is repeatedly input from the line image sensor, and each time the addition processing is performed with the white reference signal stored in the white reference signal storage means. That is, the result of the processing is used as update data of the white reference signal already stored in the white reference signal storage means. Therefore, the white reference signal in the white reference signal storage means has been subjected to the processing based on the so-called cut-down equation, a convergent value can be obtained relatively quickly compared to the averaging processing, and the input value suddenly changes. Even if it becomes an abnormal value, its influence is smaller than that of the averaging process, and therefore stable and reliable so-called shading correction is performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image signal correcting apparatus according to the present invention will be described below with reference to FIGS. Here, FIG. 1 is a circuit diagram showing a first embodiment of an image signal correction circuit according to the invention described in claim 1, and FIG. 2 is a second embodiment of the image signal correction circuit according to the invention described in claim 1. FIG. 3 is a circuit diagram showing a third embodiment of the image signal correction circuit according to the invention described in claim 1, and FIG. 4 is a line scan in the embodiment shown in FIG. FIG. 5 is a characteristic diagram showing a relationship with the level of dark output data to be generated, FIG. 5 is a characteristic diagram showing how the output signal of the line image sensor fluctuates, and FIG. 6 is an image signal according to the invention of claim 2. FIG. 7 is a circuit diagram showing a first embodiment of the correction circuit, and FIG. 7 is a circuit diagram showing a second embodiment of the image signal correction circuit according to the present invention.

First, the image signal correction apparatus shown in FIG. 1 has a memory 1, a first subtractor 2 and a second subtractor 3.
And an adder 4, and an image signal of 8 bits per pixel is input from an image sensor (not shown). The memory 1 in this embodiment is a so-called FIFO (First-In First).
-Out) structure of 10 bits, the contact point c of the changeover switch 5 is connected to the input side thereof, and the output end thereof is the first subtractor 2, the second subtractor 3, the adder 4 and the It is connected to one contact a of the changeover switch 5, respectively.
Here, although the data length per pixel in this embodiment is 8 bits as described, the arithmetic processing of dividing the dark reference signal of 8 bits by 4 as described later is performed by dividing the dividend by lower bits. The size of one data of the memory 1 is set to 10 bits in order to realize by shifting by 2 bits in the direction.

The first subtractor 2 receives the image signal Xp from an image sensor (not shown) as input, and the upper 8 bits of the 10-bit output data output from the memory 1 above. Bits are fetched, and division processing is performed on the image signal Xp using the upper 8 bit data as a divisor. Here, taking in the upper 8 bits of the 10-bit length data output from the memory 1 is equivalent to dividing the 8-bit length input data Db by exactly 4. Similarly to the first subtractor 2, the second subtractor 3 inputs the image signal Xp at the same time as capturing the upper 8 bits of the output data of the memory 1 described above, and inputs the image signal Xp from the image signal Xp. 8 bits of the output data Db of
b / 4 is subtracted, and its output end is connected to the adder 4. The adder 4 outputs the output data D of the memory 1.
b and the output signal of the second subtractor 3 are input, they are added, and they are connected to the contact b of the changeover switch 5.

Next, the operation of the present apparatus having the above configuration will be described. First, it is necessary to store a dark reference signal from a line image sensor (not shown) in the memory 1. At the storage operation of this dark reference signal, the changeover switch 5 switches so that the contact b and the contact c are closed. . The line image sensor connected to this apparatus is a so-called line image sensor in which a plurality of light receiving elements are linearly arranged (not shown).

Under such a setting, the line image sensor (not shown) is prevented from entering the light, and the line image sensor is set.
The dark reference signal Xb is input to the apparatus for each pixel (each light receiving element forming the line image sensor) with the image sensor in a dark output state. Then, the dark reference signal Xb is input to the second subtractor 3, but at the start of the operation of this circuit, since no data is stored in the memory 1, the output data from the memory 1 is not stored. The data is zero, and the input data from the memory 1 to the second subtractor 3 is zero. Therefore, the dark reference signal Xb is directly output from the second subtractor 3 and is input to the adder 4. In the adder 4 as well, since the input data to the input terminal connected to the memory 1 is still zero, the output from the adder 4 is also the dark reference signal Xb itself. After all, the first dark reference signal Xb is
It is stored in the memory 1 as it is.

From the line image sensor (not shown), the dark reference signal in the next pixel is supplied to the second subtractor 3
Is input to the second subtractor 3, the following arithmetic processing is performed. That is, if the previous data already stored in the memory 1 is Db _(n-1), and the dark reference signal currently input is Xbn, the second subtractor 3 outputs Xbn. -Db _(n-1) / 4 will be output. Then, the operation result of the second subtractor 3 is input to the adder 4, and the adder 4 adds the 10-bit length data from the memory 1 to the operation result of the second subtractor 3. To be done. Here, 1 output from the memory 1
0 bit de - data is reality With 8-bit length with 8 bits of the upper dark reference signal 10 bit length stored previously _{Db (n-1), Db} (n-1) / 4 data is obtained. Eventually, the adder 4 outputs data of 10-bit length as the operation result, which is input to the memory 1 via the changeover switch 5. Therefore, the storage data of the memory 1 is from Db _{(n -1)} to Xbn-Db _(n-1).
It will be updated to / 4 + Db _(n-1) .

Therefore, in the dark reference signal input state in which the contact b and the contact c of the changeover switch 5 are closed, the memory 1, the second subtractor 3 and the adder 4 cause Dbn
= Xbn-Db _(n-1) / 4 + Db _(n-1) (hereinafter, this formula is referred to as Formula 1), and the stored data in the memory 1 is stored as a result of the calculation. It will be updated. That is, if the dark reference signal is input at a certain time, the data Db input and stored from the memory 1 at the operation timing immediately before that.
n is read out, and the above-mentioned arithmetic processing is performed. Then, the reading of the dark reference signal by the above line image sensor is performed again after the number of pixels of the line image sensor has been read. This repetition is called a line scan here, and the value of the data stored in the memory 1 converges to a substantially constant value as the number of line scans increases, as described later.

FIG. 4 is a characteristic diagram showing the result of simulating how the dark output level stored in the memory 1 changes depending on the number of line scans, and FIG.
For comparison, a characteristic diagram showing how the dark reference signal level from the line image sensor changes with the passage of time, that is, the number of line scans, is shown for comparison. According to the simulation result of FIG. 4, the level fluctuations are substantially converged after the 8 line scan. The standard deviation σ after the 8-line scan is 1.2, which is much smaller than the conventional one. on the other hand,
The output signal of the line image sensor before the correction by the present apparatus fluctuates considerably as shown in FIG. 5, and the standard deviation σ is 3.1, which is the signal corrected by the previous apparatus. It turns out that it is quite large.

Further, comparing the above result in this embodiment with a conventional one, for example, FIG. 7 shows a circuit diagram for averaging the dark output of the image sensor for four line scans. FIG. 8 is a characteristic diagram for explaining how the averaging data varies in the circuit shown in FIG. First, the circuit shown in FIG. 7 includes an average value memory 10, a changeover switch 11, a subtractor 12,
An adder 13 is provided, and a signal from a line image sensor is input as in the case of the embodiment of the present invention shown in FIG. 1, and the data length per pixel is 8 bits. .
On the other hand, the dark reference signal Db stored in the averaging memory 10
Is required to be divided by 4, and in order to realize this division processing by bit shifting, the average value memory-10 is shown in FIG.
A 10-bit so-called FIFO memory is used, like the memory 1 in the circuit shown in FIG. 1 is different from the circuit shown in FIG. 1 in that the second subtractor 3 in FIG. 1 is not provided and the image signal is input to the adder 13 in addition to the subtractor 12. It is a point. Then, when averaging the input dark reference signals, the changeover switch 11 is set to the state of being switched to the contact b. FIG. 8 shows a characteristic diagram showing the relationship between the line scan and the averaging level in this circuit, and its standard deviation σ is 1.9, which is based on the standard deviation in the characteristic diagram shown in FIG. It is getting bigger.

By the way, as described above, in the circuit of FIG. 1, after the dark reference signal is acquired, the contact a and the contact c of the changeover switch 5 are closed so that
Dark output offset correction is performed on the image signal. That is, a line image sensor (not shown)
Shifts from the dark output state to the image reading state, and the read image signal is input pixel by pixel as in the acquisition of the dark reference signal. The image signal Xp is input to the subtractor 2, where the data Db / 4 obtained by dividing the dark base signal Db read from the memory 1 by a coefficient 4 is subtracted, and so-called dark output offset correction is performed. The image signal Yp is output.

Next, a second embodiment will be described with reference to FIG. The same components as those in the first embodiment described with reference to FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In the following description, different points will be mainly described. The second embodiment is different from the first embodiment in that the value of the constant A for dividing the dark reference signal Db is set to 2. That is, the bit length per pixel of the image signal is 8 bits as in the first embodiment described with reference to FIG.
Then, it is necessary for the first subtractor 2 to divide the dark reference signal Db by a constant 2. On the other hand, 2 bits of 8-bit data
The operation of dividing by 8 can be executed by shifting the 8-bit data by 1 bit to the lower bit. Therefore, a 9-bit FIFO is used for the memory 1a.
By inputting the upper 8 bits of the data input to the IFO to the first subtractor 2, the above-mentioned 1-bit shift is realized. Here, by substituting 2 into the constant A of the equation 1 described in the first embodiment and rearranging the equation 1,
Dbn = Xbn + Db _(n-1) / 2. That is, by setting the constant A to 2, the addition process may be performed once in the calculation process for the dark reference signal process. Therefore, in the circuit shown in FIG. 2, only the adder 4 is provided in the portion that processes the dark reference signal, and the second subtractor 3 in the circuit shown in FIG. It is not needed in the example circuit. Since the operation of this circuit is basically the same as that of the first embodiment described with reference to FIG. 1, its description is omitted here.

Next, a third embodiment will be described below with reference to FIG. The same components as those of the embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. Hereinafter, different points will be mainly described. The embodiment shown in FIG. 3 is an example in which dark output offset correction is performed on an analog image signal. The same components as those in the embodiment shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In the following description, different points will be mainly described. In the third embodiment, the upper 8 bits of the stored data are read from the memory 1 as in the first embodiment described with reference to FIG. 1, but this read data is D / It is adapted to be input to the A converter 14, where the digital signal is converted into an analog signal.
The second selector switch 15 is provided on the output side of the D / A converter 14.
Are connected. That is, the second changeover switch 15
, The contact a is connected to the D / A converter 14 and the contact b is connected to the ground, and the contact c is connected to the inverting input terminal of the analog adder 16 including an operational amplifier. An analog image signal is input to the non-inverting input terminal of the analog adder 16. An A / D converter 17 is connected to the output side of the analog adder 16 so that the analog image signal subjected to the dark output offset correction is finally output as a digital signal. .

In this circuit, the second changeover switch 1
Reference numeral 5 is set to the contact b when the dark output data is acquired, and is set to the contact a when the image signal is corrected. In this circuit, since the image signal input to the A / D converter 17 is a signal from which the dark output offset has been removed, there is an advantage that the dynamic range of the A / D converter 17 can be set large. The basic operation of the dark output offset correction in this embodiment is shown in FIG.
Since it is the same as the embodiment described above, detailed description thereof is omitted here.

Next, an embodiment of an image signal correction apparatus for shading correction will be described with reference to FIGS. 6 and 7. First, the embodiment shown in FIG. 6 will be described. The image correction device includes a memory 1, a divider 18,
The second subtractor 3, the adder 4, and the changeover switch 5 are included. The difference from the circuit of FIG. 1 is that the first subtractor 2 in FIG. 1 is changed to a divider 18,
The connection with the surroundings is basically the same as the circuit of FIG.

To explain the operation in such a configuration, first, it is assumed that the bit length per pixel of the input image signal is 8 bits, as in the previous embodiment. Then, the contact b and the contact c of the changeover switch 5 are closed, and the white reference output from the line image sensor (not shown) is input to the memory 1
Is stored as white reference data Dw. This white reference data Dw is, like the dark reference signal Db, input data during several line scans. For example, a white reference signal of the n-th line scan is input as an X
wn, when this white reference signal Xwn is input,
The white reference data Dw _(n-1) stored in the memory 1 in the previous (n-1) scan divided by a constant 4 is the white reference data input to the second subtractor 3. Is subtracted from the data Dw. Here, for the operation of Dw _(n-1) / 4, a 10-bit FIFO is actually used in the memory 1, and the upper 8-bit data is extracted from this (the input 8-bit data is converted into the lower-order data). Equivalent to shifting to 2 bits).

The operation result of the second subtractor 3 is input to the adder 4, and the data Dw read from the memory 1 is read there.
Is added to the memory 1 and is input to the memory 1 as new data. After all, Dwn = Xwn−Dw _(n−1) / A + Dw by the memory 1, the second subtractor 3, and the adder 4.
The arithmetic processing of _(n-1) (hereinafter, referred to as Expression 2) is performed, and Dwn is stored in the memory 1. Then, an appropriate number of line scans and a white reference data based on the above equation 2 are used.
When the data is stored, the contact a and the contact c of the changeover switch 5 are closed to enter the correction state of the image signal. That is, the line image sensor (not shown) changes from the output state of the white reference signal to the output state of the original image, and the image signal Xp is input to the divider 18. Then, in the divider 18, the image signal Xp is divided by Dw / 4 obtained by dividing the white reference data Dw read from the memory 1 by 4, so that so-called shading correction is performed on the image signal. Since it has been applied, it is output as the image signal Yp.

Next, another embodiment will be described with reference to FIG. The same components as those in the embodiment shown in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted. Hereinafter, different points will be mainly described. In the embodiment shown in FIG. 7, the constant A is set to 2 in the equation 2 described above. That is, Dwn = Xwn
In Expression 2 expressed as −Dw _(n-1) / A + Dw _(n-1) , if 2 is substituted for A, the same expression becomes Dwn = Xwn + D
It is organized as w _{(n -1)} / 2. Here, the processing of Dwn / 2 can be realized by shifting the 8-bit white reference data by 1 bit in the lower bit direction.
By using a 9-bit FIFO for inputting, 8-bit white reference data is input to this 9-bit FIFO from the lower bit, and the upper 8 bits are output to the adder 4 to obtain the 8-bit white reference data. It realizes a process of shifting 1 bit to a lower bit. Therefore, in the white reference data processing, the subtractor is not required as shown in FIG. 7, and the memory 1 and the adder 4 are connected in a loop shape via the switching switch 5. Then, the divider 18 divides the image signal Xp by Dw / 2 and outputs the image signal Yp which has been subjected to the shading correction.

In each of the image signal correction device for performing the dark output offset correction shown in FIGS. 1 to 3 and the image signal correction device for performing the shading correction shown in FIG. 6 and FIG. Since the dark reference signal or the white reference signal is updated based on the cutting equation, the value of the dark reference signal or the white reference signal reaches a converged value in a relatively short time compared to the conventional averaging process. Moreover, even if the input value of the dark reference signal or the white reference signal suddenly becomes an abnormal value due to external noise, etc., it returns to the original converged value within a short time compared to the conventional average value calculation processing. Therefore, the influence of an abnormal input value is relatively small, and stable and reliable dark output offset correction or shading correction can be performed.

[0028]

As described above, according to the present invention,
While repeatedly inputting the dark reference signal or the white reference signal from the line image sensor, the dark reference signal or the white reference signal previously input and the processing based on the cutting equation are applied, and the processing result is a new dark reference signal or By storing as a white reference signal, the value of the dark reference signal or the white reference signal converges within a short time compared to the conventional method of obtaining the average value of the dark reference signal or the white reference signal. An image signal correction device with a short processing time can be provided. In addition, even if these values become abnormal due to external noise when inputting the dark reference signal or white reference signal, the effect is less than that of the conventional averaging process, so it is stable. In addition, it is possible to provide a reliable image signal correction device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an image signal correction circuit according to the invention of claim 1.

FIG. 2 is a circuit diagram showing a second embodiment of the image signal correction circuit according to the invention described in claim 1.

FIG. 3 is a circuit diagram showing a third embodiment of the image signal correction circuit according to the invention of claim 1.

FIG. 4 is a characteristic diagram showing the relationship between the line scan and the level of dark output data stored in the memory in the embodiment shown in FIG.

FIG. 5 is a characteristic diagram showing how the output signal of the line image sensor fluctuates.

FIG. 6 is a circuit diagram showing a first embodiment of an image signal correction circuit according to the invention of claim 2;

FIG. 7 is a circuit diagram showing a second embodiment of the image signal correction circuit according to the second aspect of the invention.

FIG. 8 is a circuit diagram showing an example of a conventional averaging circuit.

9 is a characteristic diagram showing how the dark output data fluctuates in the conventional circuit shown in FIG.

FIG. 10 is a configuration diagram showing a configuration example of a conventional image signal correction circuit.

[Explanation of symbols]

1 ... Memory, 2 ... First subtractor, 3 ... Second subtractor, 16 ... Analog adder

Claims (2)

[Claims] 1. A dark reference signal storage means for storing a dark reference signal of a line image sensor, and a data compression means for dividing the dark reference signal read from the dark reference signal storage means by a constant. Subtracting means for subtracting the output value of the data compressing means from the image signal, and the dark reference signal storing means is the dark reference of the line image sensor in a state where the incident light to the line image sensor is blocked. A signal is cyclically input, and the dark reference signal that has already been input is subjected to coefficient processing and added to the input dark reference signal to update the data already stored as a new dark reference signal. An image signal correction apparatus characterized by: 2. A white reference signal storage means for storing the white reference signal of the line image sensor, and a data compression means for dividing the white reference signal read from the white reference signal storage means by a constant. And a dividing means for dividing the image signal by the output value of the data compressing means, and the white reference signal storing means outputs the output of the line image sensor with respect to the reflected light from the white plate received by the line image sensor. In addition to cyclically inputting the white reference signal, the already-input white reference signal subjected to coefficient processing is added to the input white reference signal to obtain a new white reference signal that has already been stored. An image signal correction device characterized by updating the data.