JP2004221729A - Close contact type image sensor and close contact type image reader using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact-type image sensor which is small in size, low in power consumption, and has a high S/N ratio; and to provide a contact-type image reader using the same. <P>SOLUTION: The contact-type image sensor is equipped with a light source 11 composed of LEDs (light emitting diodes) 11r, LEDs 11g, and LEDs 11b emitting light of specific color respectively; a light guiding member 12 guiding light emitted from the light source 11 in its lengthwise direction Y, and radiating it in a prescribed direction so as to irradiate a manuscript; an image forming optical system 14 forming the optical image of the manuscript; and a converting means 15 for converting the formed optical image of the manuscript into image signals. The LEDs 11r, LEDs 11g, and LEDs 11b are arranged at the end part in the lengthwise direction (Y) of the light guiding member 12. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a contact image sensor and a contact image reading device using the same.
[0002]
[Prior art]
2. Description of the Related Art As an image sensor for reading a document, a contact image sensor that reads a document while closely contacting the document is known. In such a contact type image sensor, LEDs of three colors of R (red), G (green), and B (blue) are arranged one by one at one end of the light guide in the longitudinal direction, and one LED is provided. There is known a device in which light is guided in a longitudinal direction by a light guide and irradiated in a predetermined direction to irradiate a document (for example, see Patent Document 1). The use of LEDs can reduce the physique and power consumption compared to the case of using fluorescent lights.
[0003]
[Patent Document 1]
JP-A-2000-196820 (paragraph 0007, FIG. 1)
[0004]
[Problems to be solved by the invention]
However, LEDs emit light at a lower brightness than fluorescent lamps, and conventional contact-type image sensors have one LED for each color, requiring high-brightness light, such as when reading a document at high resolution. In this case, there is a problem that light having a luminance required for reading cannot be obtained. If the luminance is low, the signal-to-noise (S / N) ratio decreases, and the image quality of digital image data deteriorates. Here, the S / N ratio is a level ratio between a signal and noise, and is a numerical value representing the quality of a signal. The lower the value, the lower the brightness of light and the more noise included in the image signal. Further, when the luminance is low, the shadow of the digital image data due to the lifting of the document becomes remarkable.
[0005]
The present invention has been made in view of the above problems, and provides a contact image sensor which is small in size and low in power consumption and has a good S / N ratio, and a contact image reading device using the same. With the goal.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a contact-type image sensor according to the present invention includes a light source unit having a plurality of LEDs that emit light of a specific color for one color, and a device that guides light emitted by the light source unit in a longitudinal direction of the light guide. A light guide that emits light in a predetermined direction to irradiate the original, an imaging optical system that forms an optical image of the original, and a conversion unit that converts an optical image of the formed original into an image signal. And the LED is disposed at a longitudinal end of the light guide. Since the size and power consumption of the LED are small, the contact type image sensor can be reduced in size and power consumption. Further, according to this contact type image sensor, since a plurality of LEDs are provided for one color, the document can be illuminated brighter than in a case where only one LED is provided for one color, and the S / N ratio can be improved.
[0007]
Furthermore, the contact type image sensor according to the present invention is characterized in that the LEDs are arranged at both ends in the longitudinal direction of the light guide. When the document is arranged at both ends, the document can be more uniformly irradiated as compared with the case where the document is arranged at only one of the ends.
Furthermore, a contact-type image reading device according to the present invention includes: a contact-type image sensor according to claim 1 or 2; and an image processing unit that converts an image signal converted by the contact-type image sensor into digital image data. It is characterized by having. The provision of the contact type image sensor according to claim 1 or 2 makes it possible to reduce the size and the power consumption of the contact type image reading device and improve the S / N ratio.
[0008]
Further, the contact type image reading apparatus according to the present invention determines the image quality of the document based on the digital image data converted by the image processing means, and changes the luminance of the light emitted from the light source unit according to the determined image quality. It is characterized by further comprising a light source control means for causing the light source to be controlled. Here, the luminance refers to a point on a light-emitting surface, a light-receiving surface, or a cross-section of a light propagation path, through a minute surface including the point, and passing a light beam in a certain direction to a surface perpendicular to the direction. The ratio per unit orthographic area per unit solid angle. According to this contact type image reading apparatus, it is possible to irradiate the original with light having a luminance corresponding to the image quality.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on a plurality of examples.
(First embodiment)
FIG. 1A is a perspective view of a contact image sensor (CIS) 1 as a contact image sensor according to an embodiment of the present invention, and FIG. 1B is a side view of the CIS 1. The CIS 1 includes a light source unit 11, a light guide 12, a light guide cover 13, a rod lens array 14, and a linear image sensor 15.
[0010]
The light source unit 11 includes an LED (light emitting diode) that emits light of a specific color as a light source. The light source unit 11 includes an LED 11r that emits red (R) light, an LED 11g that emits green (G) light, and an LED 11b that emits blue (B) light so that a color image can be read. It has a plurality of LEDs for one color. For example, the light source unit 11 of the present embodiment has two red LEDs 11r, two green LEDs 11g, and two blue LEDs 11b. As shown in the figure, each LED is positioned and attached to one end face 12a side of the light guide 12 in the longitudinal direction Y such that light emitted by the LED enters the light guide 12 from the end face 12a. That is, the LED is arranged at the longitudinal end of the light guide 12.
[0011]
The light guide 12 is formed of a light transmitting member such as glass. The light guide 12 has a diffusion surface 12b (see FIG. 2) and an emission surface 12c. The diffusion surface 12b is formed in a wavy shape. The emission surface 12c is formed at the opening of the light guide cover 13 in the light guide 12. The exit surface 12c is formed in a lens shape, and emits a part of the light scattered by the diffusion surface 12b in a direction of irradiating a portion of the document passing through the point P in FIG. 1 (B) and located on a scanning line perpendicular to the paper surface. discharge. As a result, light is emitted in a predetermined direction to irradiate the original. When the emission surface 12c is formed in a lens shape, a portion on the scanning line of the document can be illuminated more brightly than when the lens is not formed in the lens shape.
[0012]
In this embodiment, the LEDs are arranged only on one end face 12 side of the light guide 12 in the longitudinal direction, but some LEDs may be arranged on the other end face 12d side. That is, the LEDs may be arranged at both ends of the light guide 12 in the longitudinal direction Y. Specifically, for example, the LEDs 11r, 11g, and 11b may be arranged one by one on the end face 12a side, and the remaining one LED 11r, 11g, and 11b may be arranged on the end face 12d side. When the LEDs are arranged at both ends, the document can be irradiated more uniformly than when the LEDs are arranged only at one of the ends.
[0013]
Further, the light guide may be formed with a tapered surface so that the cross-sectional area of the light guide becomes smaller as the distance from the end face 12a on which the LED is arranged becomes longer in the longitudinal direction. When the tapered surface is formed, it is possible to irradiate the original with light having a more uniform brightness over the entire region in the longitudinal direction of the light guide.
The light guide cover 13 is formed of, for example, a white light-impermeable member having good light reflectivity, and is attached so as to cover the outside of the light guide 12 via an air layer. The light guide cover 13 returns light leaked from the light guide 12 in a direction different from the predetermined direction back into the light guide 12. When the light guide cover 13 is attached, the light use efficiency can be improved.
[0014]
The rod lens array 14 as an imaging optical system has a plurality of cylindrical lenses (rod lenses) 14 a arranged in a line along the longitudinal direction Y of the light guide 12. The rod lens 14a is provided in one-to-one correspondence with a light receiving element described later. The rod lens array 14 forms an optical image on the scanning line of the original on the linear image sensor 15 by the rod lens 14a at the same magnification as the original.
[0015]
The linear image sensor 15 as a conversion unit is composed of a plurality of light receiving elements, MOS transistor switches, and the like arranged linearly along the rod lens array 14. The linear image sensor 15 scans an optical image on a scanning line formed by the rod lens array 14 and outputs an electric signal correlated with the density of the optical image. Thus, the optical image is converted into an image signal. The linear image sensor 15 accumulates a charge obtained by photoelectrically converting light in a predetermined wavelength region, such as visible light, infrared light, or ultraviolet light, in a light receiving element such as a photodiode for a certain period of time. Is output using a MOS transistor switch.
[0016]
Next, the operation of the light guide 12 will be described.
FIG. 2 is a schematic diagram showing a state in which light emitted by the light source unit 11 is guided in the longitudinal direction Y of the light guide 12 and emitted in a predetermined direction to irradiate a document. The light emitted by the LED of the light source unit 11 enters the inside of the light guide 12 from the end surface 12a of the light guide 12, and is guided in the longitudinal direction Y of the light guide 12 while repeating internal reflection. When the guided light is incident on the diffusion surface 12b, the incident light is diffused and / or reflected, and a part of the light is emitted from the emission surface 12c. As shown in FIG. 1B, light emitted from the exit surface 12c irradiates a portion of the document located on the main scanning line, and an optical image of the portion located on the main scanning line of the document, that is, an optical image of one line. The image is formed on the linear image sensor 15 by the rod lens array 14.
[0017]
According to the CIS 1 according to the first embodiment of the present invention described above, since the light source unit 11 uses an LED as a light source, the size of the CIS 1 can be reduced, and the power consumption can be reduced. Since the light source unit 11 has two LEDs for each of the R, G, and B colors, the document can be illuminated brighter than when only one LED is provided for one color. If the document can be illuminated brightly, noise included in the image signal can be reduced. Therefore, according to CIS1, it is possible to reduce the size and power consumption and to improve the S / N ratio.
[0018]
(Second embodiment)
FIG. 3 is a schematic diagram showing a so-called flat-bed image scanner 2 as a contact-type image reading device according to an embodiment of the present invention, and FIG. 4 is a block diagram of the image scanner 2. It is to be noted that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0019]
The document table 21 is formed of a transparent plate such as a substantially rectangular glass plate, and a document M such as a photograph or a printed document is placed on the board surface 21a.
The carriage 31 houses the CIS 1. The carriage 31 is pulled by a belt (not shown) of the sub-scanning drive unit 26, is guided by a shaft 32, moves parallel to the board surface 21 a of the document table 21, and transports the CIS 1 parallel to the board surface 21 a of the document table 21.
[0020]
The D / A converter 22 includes a plurality of D / A converters. When a digital signal is output from the control unit 30, the D / A conversion unit 22 applies an output voltage of a magnitude represented by the digital signal to the light source unit 11. The D / A converter 22 will be described later in detail. The main scanning drive unit 25 is a circuit that controls the driving of the linear image sensor 15, controls ON / OFF of a MOS transistor switch, and controls reading of charges stored in the light receiving element.
[0021]
The sub-scanning drive unit 26 includes a belt locked on the carriage 31, a motor and a gear train for rotating the belt, a drive circuit, and the like. When the sub-scanning drive unit 26 pulls the carriage 31 by the belt, the scanning line moves in a direction perpendicular to the carriage 31 (sub-scanning direction), so that a two-dimensional image can be scanned.
An AFE (Analog Front End) unit 23 serving as an image processing unit includes an analog signal processing unit, an A / D converter, and the like. The analog signal processing unit performs signal processing such as amplification and noise reduction processing on the analog image signal output from the CIS 1 and outputs the processed signal. The A / D converter quantizes the image signal output from the analog signal processing unit into digital image data of a predetermined bit length in digital representation, and outputs the digital image data.
[0022]
The digital image processing unit 24 performs processes such as gamma correction, interpolation of defective pixels by pixel interpolation, shading correction, and sharpening of image signals on the digital image data output from the AFE unit 23. Note that the above-described various processes performed by the digital image processing unit 24 may be replaced with processes by a computer program executed by the control unit 30. The digital image data processed by the digital image processing unit 24 is transferred to a personal computer (PC) or the like via an interface (not shown).
[0023]
The control unit 30 includes a CPU 27, a ROM 28, and a RAM 29. The CPU 27 executes a computer program stored in the ROM 28 and controls each unit of the image scanner. The ROM 28 is a memory that stores computer programs executed by the CPU 27 and various data, and the RAM 29 is a memory that temporarily stores programs and various data.
[0024]
FIG. 5 is a block diagram illustrating the D / A conversion unit 22 and the light source unit 11. The D / A converter 22 has D / A converters 22r, 22g and 22b. One D / A converter is provided for each color. If one D / A converter is provided for each color, for example, a voltage is applied to only one of the two LEDs that emit light of the same color to reduce the luminance, or 1/2 of the maximum voltage that can be applied. The luminance of the light emitted by the light source unit 11 can be controlled for each color, for example, by applying a voltage of the magnitude to the two LEDs to suppress the luminance.
[0025]
FIG. 6 is a flowchart illustrating a flow of a process in which the image scanner 2 reads an image. The image scanner 2 performs temporary reading (pre-scan) to determine the image quality before executing the original reading (main scan), and changes the luminance of the light emitted from the LED according to the determined image quality. Execute the main scan.
In S105, the control unit 30 outputs a digital signal representing a predetermined magnitude set in advance to the D / A conversion unit 22 to turn on the LED, and controls the sub-scanning drive unit 26 to move the carriage 31 to the predetermined position. To the reading position. Thus, an optical image of one line of the document placed on the board surface 21 a of the document table 21 is formed on the light receiving element of the linear image sensor 15.
[0026]
In S110, the linear image sensor 15 converts the optical image into an image signal, and outputs the image signal to the AFE unit 23.
In S115, the AFE unit 23 converts the image signal into digital image data and stores it in the RAM 29.
In S120, it is determined whether or not reading of all the lines has been completed. If not, the control unit 30 controls the light source unit 11 to move the carriage 31 at a constant speed while sequentially switching the color of emitted light. , S105 to S115 are repeatedly executed. As a result, digital image data representing an optical image of the document is obtained. If it has been completed, proceed to the next step.
[0027]
In S125, the control unit 30 determines the image quality of the document based on the digital image data stored in the RAM 29. Specifically, for example, the contrast is determined as the image quality. Generally, in digital image data, the color of one pixel is represented by 256 gradations of R, G, and B, white is represented by (0, 0, 0), and black is represented by (255, 255, 255). Usually, a thing with a clear difference between black and white is expressed as having high contrast. Therefore, for example, the maximum value and the minimum value of the gradation value for the pixels constituting the digital image data are obtained for each of R, G, and B, and when the difference is less than a predetermined value in all of R, G, and B, the contrast is reduced. Judge as low. Thus, the pre-scan is completed.
[0028]
In S130, when it is determined that the contrast is low in the pre-scan, the control unit 30 sets a digital signal representing a larger value than in the pre-scan so as to increase the luminance of the light emitted from the LED. Thus, the luminance of the light emitted by the light source unit 11 in the main scan is changed. It should be noted that how large the digital signal is set at this time is a matter of design, and may be set according to the difference between the maximum value and the minimum value, or may be uniformly set to a predetermined value. May be set.
[0029]
In S135, the control unit 30 outputs a digital signal of the set magnitude to the D / A conversion unit 22 and turns on the light source unit 11 while performing the same processing as in S105 to S120 to perform the main scan.
In S140, the digital image processing unit 24 performs a predetermined process on the digital image data stored in the RAM 29, and outputs the processed digital image data to a personal computer (PC) connected via an interface (not shown). .
[0030]
According to the image scanner 2 according to the second embodiment of the present invention described above, since the CIS 1 is provided, the contact type image reading device can be reduced in size and power consumption, and the S / N ratio can be improved.
Further, according to the image scanner 2, it is possible to irradiate the original with light having a luminance corresponding to the image quality of the original. Therefore, for example, even if the document is entirely dark, the color change in the document can be more accurately reflected on the digital image data.
[0031]
In this embodiment, a flatbed type image scanner that reads a document placed on the document table 21 by moving the CIS 1 is described as an example of the image reading apparatus. However, the CIS 1 is fixed, and the document is moved. A so-called sheet feed type image scanner for reading may be used.
Further, the image reading device may be a facsimile.
[Brief description of the drawings]
FIG. 1A is a perspective view of a contact image sensor, and FIG. 1B is a side view of the contact image sensor.
FIG. 2 is a schematic diagram showing a state in which emitted light is guided in a longitudinal direction.
FIG. 3 is a schematic diagram illustrating a contact-type image reading device.
FIG. 4 is a block diagram illustrating a contact image reading apparatus.
FIG. 5 is a block diagram showing a light source control unit and a light source unit.
FIG. 6 is a flowchart illustrating a flow of a process of reading an image.
[Explanation of symbols]
Reference Signs List 1 CIS (contact image sensor), 2 image scanner (contact image reading device), 11 light source unit, 11r LED, 11g LED, 11b LED, 12 light guide, 14 rod lens array (imaging optical system), 15 Linear image sensor (conversion unit), 22 D / A conversion unit (light source control unit), 23 AFE unit (image processing unit), 30 control unit (light source control unit)

Claims (4)

A light source unit having a plurality of LEDs for one color that emit light of a specific color;
A light guide that irradiates a document by guiding the light emitted by the light source unit in the longitudinal direction of the light guide and radiating the light in a predetermined direction,
An imaging optical system for imaging the optical elephant of the original,
Conversion means for converting the formed optical image of the document into an image signal,
Wherein the LED is disposed at a longitudinal end of the light guide. The contact type image sensor according to claim 1, wherein the LEDs are disposed at both ends in a longitudinal direction of the light guide. A contact image sensor according to claim 1 or 2,
Image processing means for converting the image signal converted by the contact image sensor into digital image data,
A contact type image reading apparatus comprising: The image processing apparatus further includes a light source control unit that determines the image quality of the document based on the digital image data converted by the image processing unit, and changes the luminance of light emitted by the light source unit according to the determined image quality. The contact type image reading device according to claim 3.

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