JP2001268322A - Image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading device capable of improving the gradation of an image, an obtaining an image whose quality is high regardless of the fluctuation of an image sensor or a light source. SOLUTION: An object is illuminated by a light source 15, and an image is read by a CCD 11. An image signal from the CCD 11 is amplified by an analog signal processing part 12, and digitized by an image processing part 13. A CPU 1 digitally controls the light quantity of the light source 15 so that a digital signal at the time of reading a white image can reach a prescribed target value, and transmits control data to a light source driving part 14. Thus, it is possible to control a white level to be the target value, and to validly use a dynamic range when digitized in the image processing part 13, and to improve the gradation of the image, and to obtain the image whose quality is high regardless of the fluctuation of the CCD 11 or the light source 15.

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 for irradiating an object with light, photoelectrically converting light from the object by an image sensor, and reading an image.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus, an object is illuminated with light emitted from a light source, and light from the object is photoelectrically converted by an image sensor. The image signal photoelectrically converted by the image sensor is analog / digital (A / D) after sampling and holding the 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. Such a difference between the image signals also occurs due to, for example, a variation in a light source that illuminates an object. For example, when the light source is replaced, the brightness of the image differs before and after that.

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.

FIG. 7 shows a conventional image signal after amplification and A / D
FIG. 4 is an explanatory diagram of an example of a relationship with a dynamic range of a converter. As described above, the voltage is suppressed by suppressing the amplification factor for the white level. Therefore, as shown in FIG. 7, compared with the dynamic range of the A / D converter,
The dynamic range (the signal range from the black level to the white level) of the image signal input to the A / D converter is limited. If the dynamic range of the image signal is limited in this way, the dynamic range of the A / D converter cannot be used effectively, and as a result, the gradation of the read image is impaired. Was. Further, as described above, since the white level varies depending on the individual image sensor and also varies depending on the light source, there is a problem that the dynamic range of the image differs from device to device and the image quality varies. Was.

As can be seen from FIG. 7, it is desirable to set the white level such that the dynamic range of the image sensor approaches the dynamic range of the A / D converter as much as possible. However, the amplification factor of the amplifier that determines the white level is 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. It is considered to adjust the light amount of the light source, but it is also realized by an analog circuit,
There is a problem that the adjustment takes time and the number of circuits for the adjustment increases.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims to improve the gradation of an image and obtain a high-quality image irrespective of variations in image sensors and light sources. It is an object of the present invention to provide an image reading apparatus capable of performing the following.

[0007]

According to the present invention, in an image reading apparatus, a light source for irradiating an object, an image sensor for photoelectrically converting light from the object, and at least an image signal from the image sensor are digitally converted. And a control unit for controlling the amount of light of the light source based on a white image signal digitized by the image processing unit. Thus, the white level different for each image sensor and each light source can be unified to a predetermined target value by controlling the light amount of the light source by the control unit. For this reason, it is not necessary to secure a margin in consideration of variations in the white level as in the past, and the dynamic range for digitalization is expanded and gradation is improved regardless of the variations in image sensors and light sources. High-quality images can be obtained. Further, by performing such control digitally, adjustment can be automatically performed without changing the analog circuit and without performing adjustment in the analog circuit.

When the light amount is controlled by the control unit, a predetermined portion is extracted from the white image signal digitized by the image processing unit, and the light amount of the light source is controlled based on the extracted predetermined portion of the image signal. Can be. When a white image is read, shading occurs due to the influence of a light source, an optical system, and the like, which lowers the signal level of the image signal in the peripheral portion. More accurate control can be performed by controlling the light amount of the light source using the image signal of the portion having less influence.

An LED can be used as a light source. In this case, the control circuit can control the amount of light by controlling the current supplied to the LED.

[0010]

FIG. 1 is a block diagram showing an example of a facsimile apparatus including an embodiment of an image reading apparatus according to the present invention. In the figure, 1 is a CPU, 2 is a ROM, 3 is R
AM, 4 an image memory, 5 an operation unit, 6 a communication unit, 7 a recording unit, 8 a codec, 9 a reading unit, 10 a bus, 1
1 is a CCD, 12 is an analog signal processing unit, 13 is an image processing unit, 14 is a light source driving unit, and 15 is a light source.

The CPU 1 functions as control means for the entire facsimile machine. In particular, the CPU 1 functions as a control unit in the image reading device of the present invention. Regarding the control of the reading unit 9, a digital image signal at the time of reading a white image is acquired, and the light source 1 is transmitted via the light source driving unit 14 in the reading unit 9.
5 is controlled. Thereby, the dynamic range of the image signal output from the analog signal processing unit 12 matches or approaches the dynamic range when the image signal is converted into a digital signal in the image processing unit 13,
A high-quality image with improved gradation is obtained. The control data for controlling the amount of light emitted from the light source 15 of the reading unit 9 is transmitted, for example, by using a serial output port provided in the CPU 1 or by outputting from a serial interface provided separately. Can be. Alternatively, when a reading control unit is separately provided in the reading unit 9, control data may be output to the reading control unit.

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 the analog image signal processed by the analog signal processing unit 12, It has a light source driving unit 14 for driving the light source 15, a light source 15 for illuminating an object to be read such as a document, and the like.

The analog signal processing unit 12 samples and holds the image signal output from the CCD 11, performs analog signal processing such as offset adjustment and amplification, and transfers the image signal to the image processing unit 13. At this time, the offset amount, the amplification factor, and the like can be set, for example, under the control of the CPU 1. Further, when the CCD 11 divides and outputs the pixel signals into a plurality of systems, the offset adjustment and amplification may be performed for each system, and the pixels of each system may be serially rearranged and output.

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 a change in an image signal due to a pixel position of the CCD 11. The image signal of the white image stored in the shading correction memory is transmitted to the light source 1.
5 can be used when the CPU 1 controls the amount of light emitted from the CPU 5. Of course, when controlling the light amount,
An image signal of a white image may be output to the CPU 1.

The light source driving section 14 is a light source 1 from the CPU 1.
The light source 15 is driven in accordance with instructions such as ON / OFF control and light quantity control of the light source 5. The light source 15 is driven by the light source driving unit 14 and emits light to the reading target. Light source 1
5 may be any type as long as the light amount can be controlled. For example, the light amount is controlled by current control using an LED, or the light source driving unit 1 is controlled using a cold cathode tube.
In step 4, the light amount may be controlled by inverter control.

The bus 10 includes a CPU 1, a ROM 2, and 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, for example, an interface for light source control may be connected, and in addition, 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 section. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals. 21-1 and 21-2 are sample and hold circuits, 22
-1, 22-2 are amplifiers, 23 is a multiplexer, 31
Is an A / D converter, 32 is a RAM, 33 is a γ correction unit,
34 is a binarization unit. This example shows a case where the CCD 11 alternately outputs image signals into two systems of odd-numbered pixels and even-numbered pixels according to the arrangement order of read pixels. Of course, the CCD 11 may output three or more systems separately, or all pixels may be serially output in one system. According to the number of systems output from the CCD 11,
What is necessary is just to provide a sample hold circuit and an amplifier in the analog signal processing unit 12. If only one system is used, the multiplexer 23 is unnecessary.

In this example, the analog signal processing section 12 includes sample and hold circuits 21-1 and 21-1 and amplifiers 22-1 and 22-1.
2. It has a multiplexer 23. The analog signal processing unit 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 image signal of the odd-numbered pixel is sampled and held by the sample and hold circuit 21-1, and then amplified by the amplifier 22-1 with a predetermined gain go. Similarly, the image signal of the even-numbered pixel is sampled and held by the sample and hold circuit 21-2, and then amplified by the amplifier 22-2 with a predetermined gain ge. The gains go and geo may be configured to be controllable by the CPU 1, for example. In the amplifiers 22-1 and 22-2, the black level may be adjusted by performing offset adjustment. By setting the gain for each system from which an image signal is output from the CCD 11 as described above, it is possible to suppress variations among the systems.

The image signals of the odd-numbered pixels and the image signals of the even-numbered pixels amplified by the amplifiers 22-1 and 22-2 are alternately selected by the multiplexer 23 and output after being rearranged in the order of the pixels. .

The image processing unit 13 includes the 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 can control the amount of light emitted from the light source 15 so that the dynamic range of the A / D converter 31 can be used as widely as possible. Thereby, the gradation of the read image can be improved.

The RAM 32 is a memory for storing data for shading correction. For example, if the white image is C
An image signal when read by the CD 11 can be stored. Shading is caused by, for example, a light source or an optical system used for reading, and is generally a phenomenon in which a central portion is bright and a peripheral portion is dark. In order to prevent such a density change, the image signal can be corrected (shading correction) using the data for shading correction stored in the RAM 32. Further, the data for shading correction stored in the RAM 32 can be read by the CPU 1 and can be used for controlling the amount of light emitted from the light source 15 in the CPU 1. Of course, in addition to being configured to be directly accessible from the CPU 1, 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.

Further, as described above, the light source control unit 14
A control signal for controlling the amount of light emitted from the light source 15 is received from the CPU 1 and the light source 15 is driven. Light source 1
Reference numeral 5 emits light in response to this, and illuminates the object to be read. As described above, since the light amount of the light source 15 is performed by digital processing by the CPU 1, there is no need to add an analog component for controlling the light amount. Also, when adjusting the amount of light emitted from the light source 15, it is not necessary to handle an analog signal, and the adjustment is performed automatically, so that the handling becomes easy.
Further, for example, the user or the maintenance
Can be configured to be adjustable, and even in such a case, since the CPU 1 only needs to perform digital processing, it is possible to easily cope with this.

FIG. 3 is a flowchart showing an example of the light amount adjusting operation in the embodiment of the image reading apparatus of the present invention. In S41, the learning coefficient of the amount of light emitted from the light source 15 is set to α. The learning coefficient α indicates a rate of change when the light amount is changed. Further S4
In 2, an initial value is set to a light amount control value L for controlling the amount of light emitted from the light source 15. This initial value may be any value, but it is preferable to give an optimal value in consideration of the convergence during repetition.

In step S43, the CPU 1 sets a light amount control value L for the light source driving unit 14, and in step S44,
A white image is read from the CCD 11. At this time, the light source driving unit 14 drives the light source 15 so that the light amount corresponding to the set light amount control value L is emitted from the light source 15. For example, if the light source 15 is an LED, the light amount control value L
The LED is caused to emit light by a current amount corresponding to. Also, when lighting the cold cathode tube by inverter control,
The light emission amount can be controlled by controlling the drive pulse interval and the pulse width according to the light amount control value L. The same applies to other light sources.

The image data output from the CCD 11 is
After being sampled and held and amplified by the analog signal processing unit 12, it is 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 white image is read from the RAM 32 in the image processing unit 13. Then, in S45, an error E between the read digital image signal and the target value is calculated.

When calculating the error E in this step S45, for example, in the white image of one line,
It can be configured to use a specific portion of the image signal. FIG. 4 is an explanatory diagram of an example of a white image signal read by the CCD 11. When the white image is read in S44,
For example, an image signal having a waveform as shown in FIG. 4 is obtained. For example, when a cold-cathode tube is used as the light source 15, the light amount decreases at the end. Further, for example, when an optical system such as a lens exists on the optical path from the light source 15 to the CCD 11, the amount of light in the peripheral portion also decreases due to the influence. Therefore, as shown in FIG. 4, the signal level decreases in the peripheral portion.

When the comparison with the target value is performed using the entire image signal having the waveform as shown in FIG. 4, the error increases in the peripheral portion, and conversely, when the peripheral portion approaches the target value, the image signal in the central portion increases. Is saturated and white spots occur. For this reason, it is possible to determine the error using only the image signal of the central portion where the signal level can be regarded as substantially flat. Although FIG. 4 shows a large area as the central portion,
Further, the determination of the error may be performed only in the vicinity of the center. In FIG. 4, the white level is set to the higher signal level,
Although the black level is shown as the lower signal level, the same goes for the opposite case.

The error E calculated in S45 is
For example, the average value of the error with respect to the target value can be set for the pixel at the center in FIG. Of course, it is possible to calculate a value according to various scales that can determine an error from a target value, such as using an integrated value of an error, calculating a mean square error, or calculating a variance or a deviation value.

In S46, the error E calculated in S45 is calculated.
Is determined to be sufficiently small. If the error E is larger than the predetermined allowable range, the light amount control value L is updated in S47. In this example, a light amount learning coefficient α and an error E are used as the light amount control value L, and a new light amount control value L is calculated by L = L + α · E. For example, when the white level is higher than the target value, the light amount control value L is updated so that the light amount emitted from the light source 15 is reduced. When the white level is lower than the target value, the light amount control value L is updated so that the light amount emitted from the light source 15 is increased.

After updating the light amount control value L in this manner, the flow returns to S43 and again the light source drive unit 14 of the light amount control value L
, The reading of the white image, and the calculation of the error E are repeated. If it is determined in step S46 that the error E is sufficiently small during such repetitive processing, the operation of the light amount control shown in FIG. Is used at the time of actual reading. Further, when the light amount control value L to be used at the time of reading is determined, the image signal obtained by reading the white image at that time can be stored in the RAM 32 and used for shading correction.

The setting operation of the light quantity control value L can be performed before or at the time of shipment of the apparatus, at a predetermined time, such as during maintenance, or even every time the power is turned on. In particular, the light source 15 often changes over time, and such a change in the light source 15 can be dealt with. Of course, there are various methods for updating the light amount control value L, and the method is not limited to the above method, and any known method may be used.

FIG. 5 is an explanatory diagram showing an example of the relationship between the dynamic range of an analog image signal and the dynamic range of the A / D converter 31 of the image processing section 13 in one embodiment of the image reading apparatus of the present invention. . FIG. 5A shows a dynamic range of an image signal input to an A / D converter in a conventional image reading apparatus.
This is the same as that shown in FIG. Thus, conventionally, C
The white level has been suppressed to some extent in consideration of variations in the CD 11 and the light source 15. Therefore, the dynamic range of the A / D converter cannot be fully utilized.

In the present invention, as shown in FIG. 5B, by controlling the amount of light emitted from the light source 15, the target value of the white level is set at or near the upper limit value of the A / D converter 31. be able to. And the light source 15
By controlling the amount of light emitted from the light source, even if the manufacturing variation of the image sensor, the manufacturing variation of the light source 15 and the secular change occur, the control is performed so that the variation of the image signal is eliminated. 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, regardless of variations in the CCD 11 and the light source 15, the dynamic range of the A / D converter 31 can be effectively used, and a high-quality image with improved gradation can be obtained.

In the example shown in FIG. 1, the image reading apparatus of the present invention is applied to a facsimile apparatus. However, the present invention is not limited to this. For example, the image reading apparatus is shown as a multifunction machine having a copy function. May be connected to an external computer, a LAN, or the like 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 reading apparatus of the present invention. In the figure, reference numeral 16 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.

[0038]

As is apparent from the above description, according to the present invention, since the light amount of the light source is automatically adjusted digitally, the influence of the white level variation due to the variation of the image sensor and the light source as in the prior art. It is not necessary to set the margin in consideration of
The white level can be set at or near the target value. Therefore, the gradation of the read image can be improved, and a high-quality image can be obtained. Further, by performing such control digitally, there is an effect that the light amount of the light source can be automatically adjusted without changing the analog circuit and without performing adjustment in the analog circuit.

[Brief description of the drawings]

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

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

FIG. 3 is a flowchart illustrating an example of a light amount adjustment operation in the image reading apparatus according to the embodiment of the invention.

FIG. 4 is an explanatory diagram of an example of a white image signal read by a CCD 11;

FIG. 5 is an explanatory diagram illustrating an example of a relationship between a dynamic range of an analog image signal and a dynamic range of an A / D converter 31 of the image processing unit 13 according to the embodiment of the image reading apparatus of the present invention.

FIG. 6 is a block diagram showing another example including one embodiment of the image reading apparatus of the present invention.

FIG. 7 is a diagram illustrating an example of a relationship between a conventional image signal after amplification and a dynamic range of an 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 light source drive unit, 15 light source, 16 interface, 21-1,
21-2 ... Sample hold circuit, 22-1, 22-2
... Amplifier, 23 ... Mux, 31 ... A / D converter, 32 ... RAM, 33 ... Gamma correction unit, 34 ... Binarization unit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H109 AA13 AA26 5B047 AA01 AB02 DA03 DB01 DC01 DC07 5C072 AA01 BA08 BA15 CA05 CA14 EA05 FB12 UA03 UA06 UA11 UA13

Claims (3)

[Claims] A light source for irradiating the object; an image sensor for photoelectrically converting light from the object; image processing means for digitizing at least an image signal from the image sensor; An image reading apparatus, comprising: control means for controlling a light amount of the light source based on a converted white image signal. 2. The method according to claim 1, wherein the control unit extracts a predetermined portion from the white image signal digitized by the image processing unit, and controls a light amount of the light source based on the extracted predetermined portion image signal. The image reading device according to claim 1. 3. The image reading apparatus according to claim 1, wherein the light source is an LED, and the control circuit controls an amount of light by controlling a current supplied to the LED.