JP2001268364A - Image signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image signal processing circuit capable of improving the gradation of an image, and obtaining an image with high quality regardless of the fluctuation of an image sensor. SOLUTION: An analog signal processing part 12 operates offset adjustment to an image signal from a CCD 11, and outputs it. The image signal outputted from the analog signal processing part 12 is digitized by an image processing part 13. A CPU 1 digitally calculates an offset value so that a digital picture signal when reading a black image can be a prescribed target value, and transmits the control signal of the offset value to the analog signal processing part 12. Thus, it is possible to uniformly control a black level due to the fluctuation of the CCD 11, and to improve the gradation of the black part. Moreover, it is possible to validly use a dynamic range in the digitization in the image processing part 13 by controlling the amplification factor of the image signal in the analog signal processing part 12. Thus, it is possible to further improve the gradation, and to obtain an image with high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing circuit for processing an image signal output from an image sensor.

[0002]

2. Description of the Related Art Generally, an image signal photoelectrically converted by an image sensor is analog / digital (A / A / D) after sampling and holding a signal of each pixel in the image sensor.
D) The image is processed as digital multi-value data by the converter. However, image sensors have slightly different characteristics due to individual manufacturing variations and the like, and even if the same image is read, a difference occurs in an output image signal.

For example, when a white image is read and saturated at the maximum voltage of the A / D converter, the gradation of a white portion is impaired, and an image defect such as white spots occurs. For this reason, the amplification factor of the amplifier is suppressed to some extent so that the voltage (white level) when a white image is read is not saturated. A certain voltage is also output when a black image is read, but the voltage (black level) when the black image is read also differs depending on each image sensor. If the voltage falls below the minimum voltage of the A / D converter, the gradation of the black portion is impaired,
For example, many black portions occur, and the image quality deteriorates. Therefore, a certain offset is provided for the black level.

FIG. 7 is an explanatory diagram showing an example of a relationship between an image signal output from an image sensor and a dynamic range of an A / D converter. As described above, the gain is suppressed for the white level to suppress the voltage, and the black level is offset to some extent. for that reason,
As shown in FIG. 7, the dynamic range of the image sensor (the signal range from the black level to the white level) is limited as compared with the dynamic range of the A / D converter. If the dynamic range of the image sensor is limited in this way, the dynamic range of the A / D converter cannot be used effectively, and as a result, the gradation of a read image is impaired. Was. Furthermore, since the white level and the black level vary, there is a problem that the dynamic range of an image differs for each device and the image quality varies.

As can be seen from FIG. 7, the white level and the black level correspond to the dynamic range of the image sensor of A / A.
It is desirable to set as close as possible to the dynamic range of the D converter. However, the amplification factor of the amplifier for determining the white level and the offset for determining the black level are realized by an analog signal processing circuit, and these are conventionally fixed by setting an allowable range. Alternatively, there has been a problem that it is necessary to adjust the analog signal processing circuit in order to make it variable, which takes time and effort.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to improve the gradation of an image and obtain a high-quality image irrespective of the variation of an image sensor. It is an object of the present invention to provide an image signal processing circuit.

[0007]

According to the present invention, in an image signal processing circuit, analog signal processing means for performing offset adjustment on an image signal from an image sensor, and digitizing the image signal from the analog signal processing means. And a control means for controlling an offset value in the analog signal processing means based on a black image signal digitized by the image processing means. Thereby, the black level different for each image sensor can be unified to a predetermined target value under the control of the control means. Therefore, it is not necessary to secure a margin in consideration of the variation in the black level, and it is possible to obtain a high-quality image by improving the gradation in the black portion. In addition, by performing such control digitally, without changing the analog circuit,
Further, the offset can be automatically adjusted without performing the adjustment in the analog circuit.

Further, the control means can control the amplification factor of the amplifying means of the analog signal processing means together with the offset value. For example, the amplification factor can be set according to the set offset value, or the amplification factor can be set according to the white image. As a result, the dynamic range of the image signal output from the analog signal processing means can be increased, and the dynamic range at the time of digitization can be effectively used to improve the gradation and obtain a high-quality image. it can.

In the above control, for example, when a plurality of pixel signals are output from the image sensor, the control means controls at least an offset value in the analog signal processing means for each system. can do. This makes it possible to at least control the offset value of the pixel signal for each system output from the image sensor in accordance with the characteristics of each system, and it is possible to obtain a higher-quality image. Of course, the amplification factor can also be controlled for each system.

[0010]

FIG. 1 is a block diagram showing an example of a facsimile apparatus including an embodiment of an image signal processing circuit according to the present invention. In the figure, 1 is a CPU, 2 is a ROM, 3
Is a RAM, 4 is an image memory, 5 is an operation unit, 6 is a communication unit,
Reference numeral 7 denotes a recording unit, 8 denotes a codec, 9 denotes a reading unit, 10 denotes a bus, 11 denotes a CCD, 12 denotes an analog signal processing unit, and 13 denotes an image processing unit.

The CPU 1 functions as control means for the entire facsimile machine. In particular, the CPU 1 functions as control means in the image signal processing circuit of the present invention. Reading unit 9
With respect to the control of (1), a digital image signal when a black image is read is obtained from the image processing unit 13 in the reading unit 9. Then, based on the obtained digital image signal, the analog signal processing unit 12 in the reading unit 9 controls an offset value and an amplification factor for the image signal output from the CCD 11. Further, if the digital image signal obtained when the white image is read is obtained, the amplification factor for the image signal in the analog signal processing unit 12 in the reading unit 9 can be controlled more accurately. With these controls, the dynamic range of the image signal output from the analog signal processing unit 12 matches or approaches the dynamic range when converting the image signal into a digital signal in the image processing unit 13, and high-quality images with improved gradation are provided. Images can be obtained. The control data for controlling the analog signal processing unit 12 of the reading unit 9 can be transmitted, for example, using a serial output port provided in the CPU 1 or from a separately provided serial interface. . Alternatively, via the image processing unit 13 in the reading unit 9,
Control data may be output to the analog signal processing unit 12.

The ROM 2 stores programs for controlling the operation of the entire apparatus, fixed data, and the like. R
The AM 3 stores data necessary for control by the CPU 1 and data that need to be temporarily stored during operation. The image memory 4 stores a digital image signal read by the reading unit 9, an image signal received by the communication unit 6 from the outside via a line, and the like. When the image signal is stored, the image signal may be stored as it is, or may be compressed by the codec 8 and stored.

The operation unit 5 has an input unit for receiving various settings and instructions, a display unit for displaying messages and the status of the apparatus, and the like, and realizes a user interface with users and maintenance personnel. I have. The communication unit 6 has an NCU, a modem, and the like, and can transmit and receive an image by communicating with a communication partner via a line such as a public telephone line. The recording unit 7 records a received image, a digital image signal read by the reading unit 9, and the like on a recording medium. The codec 8 encodes image data to be transmitted and decodes the received encoded data to obtain image data. Further, encoding of the digital image signal read by the reading unit 9,
Further, decoding of an image to be recorded by the recording unit 7 may be performed.

The reading section 9 reads an original image using an image sensor. Here, CC is used as an image sensor
The example which uses D11 is shown. An analog signal processing unit 12 that performs analog signal processing on an analog image signal photoelectrically converted by the CCD 11, an image processing unit 13 that digitizes and processes an analog image signal processed by the analog signal processing unit 12, and the like. have.

The analog signal processing unit 12 samples and holds the image signal output from the CCD 11, performs offset adjustment and amplification, and passes the image signal to the image processing unit 13. At this time, the offset amount and the amplification factor are controlled under the control of the CPU 1. Further, when the CCD 11 divides and outputs the pixel signal into a plurality of systems, the offset adjustment and amplification are performed for each system, and the pixels of each system are serially rearranged and output. Also in this case, the CPU 1
It operates according to the control by.

The image processing unit 13 includes the analog signal processing unit 1
2 is converted into a digital image signal, and further subjected to various image processing and output.
The image processing unit 13 has a memory for shading correction inside, and can correct the variation of the image signal due to the pixel position of the CCD 11. The memory for shading correction can be used for storing a black image and a white image when controlling the offset value and the amplification factor in the analog signal processing unit 12. Of course, a black image or a white image can be output as a read image as it is.

The bus 10 includes a CPU 1, a ROM 2, a RAM
3, an image memory 4, an operation unit 5, a communication unit 6, a recording unit 7, a codec 8, a reading unit 9 and the like are interconnected to enable data transfer between them. In addition to these, various devices such as an external storage device may be connected to the bus 10.

FIG. 2 is a block diagram showing an example of the reading unit. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals. 21 is a sample and hold circuit, 22 is an amplifier, 3
1 is an A / D converter, 32 is a RAM, 33 is a gamma correction unit, 34 is a binarization unit, and 35 is a register. In this example, the analog signal processing unit 12 includes the sample hold circuit 2
1 and an amplifier 22. The sample hold circuit 21 samples and holds an analog signal output from the CCD 11 for each pixel and outputs an image signal.

The amplifier 22 includes a sample hold circuit 21
, And amplifies and outputs the image signal output from. At this time, a signal indicating the offset value and the amplification factor is input from the CPU 1, and the offset (DC level) of the image signal is adjusted according to the given offset value, and the image signal is amplified and output with the given amplification factor.

The image processing unit 13 includes an A / D converter 3
1, a RAM 32, a γ correction unit 33, a binarization unit 34, and the like. The A / D converter 31 digitizes an analog image signal output from the analog signal processing unit 12. The CPU 1 outputs the offset value and the amplification factor to the amplifier 22 of the analog signal processing unit 12 so that the dynamic range of the A / D converter 31 can be used as widely as possible. Therefore, an analog image signal can be digitized by effectively utilizing the dynamic range of the A / D converter 31.

The RAM 32 is a memory for storing data for shading correction. For example, an image signal when a white image or a black image is read by the CCD 11 can be stored. The data for shading correction stored in the RAM 32 can be read by the CPU 1. Of course, CP
In addition to being configured to be directly accessible from U1, it may be configured to output to the bus 10 in the same manner as a normal read image in response to a request from the CPU 1.

The gamma correction section 33 performs gamma correction processing on the digitized image signal. The binarizing unit 34
The image signal after the γ correction processing is binarized according to a predetermined threshold. Of course, the correction characteristic at the time of γ correction, the threshold value at the time of binarization, and the like can be set by the CPU 1. When a multivalued image is required as an image to be read, the image may be output without going through the processing in the binarization unit 34.

In the above description, the offset and gain signals for controlling the amplifier 22 of the analog signal processing section 12 are directly transmitted from the CPU 1. However, the present invention is not limited to this.
A register 35 may be provided therein, and control data such as an offset and an amplification factor from the CPU 1 may be temporarily stored in the register 35 and output from the image processing unit 13 to the analog signal processing unit 12. In any of the configurations, the offset value and the amplification factor are set by digital processing by the CPU 1, so a configuration for changing the setting of the offset value and the amplification factor as an analog component is added to the analog signal processing unit 12. No need to do. Also, there is no need to handle analog signals during adjustment,
Since the adjustment is performed automatically, handling becomes easy. Of course, for example, a user or a maintenance person can be configured to be able to make adjustments from the operation unit 5, and even in such a case, since the CPU 1 only needs to perform digital processing, it is possible to easily cope with the situation.

FIG. 3 is an explanatory diagram of an example of the analog signal processing section in the case where the image signal from the CCD is divided and output in a plurality of systems. In the figure, 41 is a read cell, 42 is an odd-numbered shift register, 43 is an even-numbered shift register, 21-
1, 21-2 are sample hold circuits, 22-1, 22
-2 is an amplifier, and 23 is a multiplexer. CCD1
In some configurations, the output image signal is divided into plural forms and output. FIG. 3 illustrates an example of an analog signal processing unit corresponding to the CCD 11 that outputs an image signal divided into two systems.

The CCD 11 outputs the signals of the read cells 41 which perform photoelectric conversion for each pixel in accordance with the arrangement order, to odd-numbered shift registers 42 for odd numbers and to even-numbered shift registers 43 for even numbers. . Then, the signals of the respective pixels output to the odd-numbered shift register 42 and the even-numbered shift register 43 are sequentially output as signals of different systems.

The analog signal processing section 12 receives an image signal of an odd-numbered pixel and an image signal of an even-numbered pixel output from the CCD 11, respectively. The sample-and-hold circuit 21-1 samples and holds the image signal of the odd-numbered pixel, and then outputs the C signal to the amplifier 22-1.
Offset adjustment and amplification are performed according to the control of the offset value and the amplification factor from PU1. Similarly, for the image signal of the even-numbered pixel, the sample-and-hold circuit 21-2
After the sample and hold in the amplifier 22-2,
Offset adjustment and amplification are performed according to the control of the offset value and the amplification factor from the CPU 1. The sample hold circuits 21-1 and 21-2 are the same as the sample hold circuit 21 in FIG.
2-2 is a circuit similar to the amplifier 22 in FIG.

As described above, the image signal of the odd-numbered pixel and the image signal of the even-numbered pixel are separately subjected to offset adjustment and amplification. As shown in FIG. 3, in the case of a CCD which outputs image signals in a plurality of systems, the signal characteristics are often different for each system. Thus, by performing signal processing for each system, the signal characteristics between the systems can be improved. Can be absorbed.

The image signals subjected to the offset adjustment and the amplification in the amplifiers 22-1 and 22-2 are alternately selected by the multiplexer 23 and output after being rearranged in the order of pixels.

In this example, an example is shown in which an image signal is output from the CCD 11 in two separate ways. However, the present invention is not limited to this.
The same configuration can be applied to the case where the output is divided into three or more systems.

Next, an example of the operation of the image signal processing circuit according to the embodiment of the present invention will be described. FIG.
5 is a flowchart illustrating an example of an operation of setting an offset value in the image signal processing circuit according to the embodiment of the present invention. Here, as shown in FIG. 3, the CCD 11 outputs an image signal of an odd-numbered pixel and an image signal of an even-numbered pixel.
It is assumed that an image signal is output separately for each system.

In step S51, the learning coefficient of the offset for the odd-numbered pixels is set to αo, and the learning coefficient of the offset for the even-numbered pixels is set to αe. The learning coefficients αo and αe indicate the rate of change when the offset value is changed.

At S52, the offset value do for the odd-numbered pixels and the offset value de for the even-numbered images are obtained.
Set the initial value of. This initial value can be any value,
An optimal value may be given in consideration of convergence and the like.

In step S53, the CPU 1 instructs the analog signal processing unit 12 to set the offset value d for the odd pixel.
o and an offset value de for the even-numbered image are set, and S5
At 4, a black image is read from the CCD 11. C
The image data output from the CD 11 is subjected to offset processing according to the offset values do and de set in S53, digitized by the A / D converter 31 of the image processing unit 13, and stored in the RAM 32. The CPU 1 reads a digital image signal when a black image is read from the RAM 32 in the image processing unit 13. Then, in S55, the error Eo between the image signal of the odd-numbered pixel and the target value in the read digital image signal is calculated. Similarly,
In S56, of the read digital image signals,
The error Ee between the image signal of the even pixel and the target value is calculated.

In S57, the error E calculated in S55 is calculated.
It is determined whether o and the error Ee calculated in S56 are sufficiently small. If the error Eo or Ee is larger than the predetermined range, the offset values do and de are updated in S58 and S59. In this example, S58
, The learning coefficient αo and the error Eo are used as the offset value do, and a new offset value do is calculated by do = do + αo · Eo. Similarly,
In S59, the learning coefficient αe is set as the offset value de.
And the error Ee, a new offset value de is calculated by de = de + αe · Ee. Of course, there are various methods for updating the offset values do and de, and any known method may be used.

After updating the offset values do and de in this way, the process returns to step S53 and again executes the offset values do and d.
The setting of e, the reading of the black image, and the calculation of the errors Eo and Ee are repeated. If the errors Eo and Ee become sufficiently small while performing such a repetitive process, the operation of the offset values shown in FIG. 4 is terminated at that time, and the offset values do and de at that time are set at the time of actual reading. Will use it.

The setting operation of the offset values do and de can be performed before or at the time of shipment of the apparatus, or at a predetermined time such as at the time of maintenance, or even every time the power is turned on.

Further, when the offset value is set in this way, the amplification factor can be set according to the offset value. For example, according to the voltage difference between the initial value of the offset value and the actually set offset value, the amplification factor can be adjusted so that the dynamic range of the image signal is expanded by the voltage difference.

Alternatively, by further reading a white image, an amplification factor corresponding to the maximum value can be set. Normally, an image signal for white shading correction is obtained in order to correct dimming of a peripheral portion due to an influence of a light source, an optical system, or the like. The amplification factor may be set so that the maximum level at this time approaches the target value. This setting process can be performed, for example, in substantially the same manner as the process shown in FIG. 4 for a white image.

FIG. 5 shows the dynamic range of the image signal output from the analog signal processing unit 12 and the A of the image processing unit 13 in one embodiment of the image signal processing circuit of the present invention.
FIG. 4 is an explanatory diagram of an example of a relationship with a dynamic range of a / D converter 31; FIG. 5A shows a dynamic range of an image signal input to an A / D converter in a conventional image signal processing circuit, which is the same as that shown in FIG. As described above, in the related art, the target value of the black level is set to a somewhat higher voltage in consideration of the variation of the CCD 11 and the like, and the voltage at which the white level is suppressed to some extent is set as the target value. Therefore, the dynamic range of the A / D converter cannot be fully utilized.

In the present invention, as shown in FIG. 5B, for the black level, for example, a target value can be set to the lower limit value of the A / D converter 31 or near the lower limit value by automatic control of the offset value. Of course, since the offset value is set for each CCD 11 and a plurality of systems of the CCD 11, the black levels of the image signals input to the A / D converter 31 are uniform. For this reason, the occurrence of crushing and the like near black is reduced, and the gradation in the black portion is improved, so that a high-quality image can be obtained.

Further, by automatically controlling the amplification factor, the target value of the white level is also set to the A / D converter 31.
Can be set at or near the upper limit value of. Thus, the dynamic range of the image signal input to the A / D converter 31 can be made substantially the same as the dynamic range of the A / D converter 31 shown in FIG. Therefore, it is possible to effectively utilize the dynamic range of the A / D converter 31 and obtain a high-quality image with improved gradation.

In the above description, the black level is indicated as the lower voltage side and the white level is indicated as the higher voltage side. However, the present invention is not limited to this. Conversely, when the black level is higher and the white level is lower. Can be dealt with similarly. The same applies to an image sensor in which the amount of current changes.

In the example shown in FIG. 1, an example is shown in which the image signal processing circuit of the present invention is applied to a facsimile apparatus. However, the present invention is not limited to this. For example, the image signal processing circuit is shown as a multifunction machine having a copy function. 10 may be connected to an interface, and may be connected to an external computer or a LAN via the interface. Or, conversely, a copier without a communication function can be configured without the communication unit 6. FIG. 6 is a block diagram showing another example including an embodiment of the image signal processing circuit of the present invention. In the figure, reference numeral 14 denotes an interface. As in this example, the apparatus can be configured as an apparatus having only an image reading function. The read image is transferred to an external device such as a computer via the interface 14 directly or via a LAN or the like.

[0044]

As is apparent from the above description, according to the present invention, since the offset value is automatically adjusted digitally, the margin is taken into account by considering the influence of the black level variation due to the image sensor manufacturing variation. There is no need to set the black level, and the black level can be set at or near the target value. Therefore, it is possible to improve the gradation in a black portion and obtain a high-quality image. Further, by performing such control digitally, the offset can be automatically adjusted without changing the analog circuit and without performing adjustment in the analog circuit. Further, by setting the amplification factor according to the set offset value or according to the white image, the dynamic range of the image signal output from the analog signal processing means can be expanded. As a result, there is an effect that the dynamic range at the time of digitization is effectively utilized, the gradation is improved, and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a facsimile apparatus including an embodiment of an image signal processing circuit according to the present invention.

FIG. 2 is a block diagram illustrating an example of a reading unit.

FIG. 3 is an explanatory diagram of an example of an analog signal processing unit when an image signal from a CCD is output while being divided into a plurality of systems.

FIG. 4 is a flowchart illustrating an example of an operation of setting an offset value in an embodiment of the image signal processing circuit of the present invention.

FIG. 5 is an example of a relationship between a dynamic range of an image signal output from an analog signal processing unit 12 and a dynamic range of an A / D converter 31 of the image processing unit 13 in one embodiment of the image signal processing circuit of the present invention. FIG.

FIG. 6 is a block diagram showing another example including an embodiment of the image signal processing circuit of the present invention.

FIG. 7 shows an image signal output from an image sensor and A /
FIG. 4 is an explanatory diagram of an example of a relationship with a dynamic range of a D converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... ROM, 3 ... RAM, 4 ... Image memory, 5 ... Operation part, 6 ... Communication part, 7 ... Recording part, 8 ... Codec, 9 ... Reading part, 10 ... Bus, 11 ... CCD, 12 …
Analog signal processing unit, 13 image processing unit, 14 interface, 21, 21-1, 21-2 sample hold circuit, 22, 22-1, 22-2 amplifier, 23 multiplexer, 31 A / D Converter, 32 ... RA
M, 33: γ correction unit, 34: Binarization unit, 35: Register, 41: Read cell, 42: Odd number shift register, 4
3. Shift register for even numbers.

Continued on the front page F-term (reference)

Claims (3)

[Claims] 1. An analog signal processing means for performing offset adjustment on an image signal from an image sensor, an image processing means for digitizing and processing an image signal from the analog signal processing means, An image signal processing circuit, comprising: control means for controlling an offset value in the analog signal processing means based on a converted black image signal. 2. The apparatus according to claim 1, wherein said analog signal processing means further includes an amplification means for amplifying the image signal, and said control means controls an amplification factor in said amplification means together with an offset value. 2. The image signal processing circuit according to claim 1. 3. A plurality of pixel signals are output from the image sensor, and the analog signal processing means includes:
2. The apparatus according to claim 1, wherein at least offset adjustment is performed on a pixel signal for each system, and wherein the control unit controls at least an offset value in the analog signal processing unit for each system. 2
3. The image signal processing circuit according to claim 1.