JP2005236530A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an excellent read image while avoiding influence of color unevenness due to a spectral characteristic of a white LED as much as possible. <P>SOLUTION: In an image reader which has at least one reflecting surface in an optical path from a document surface to an optical detecting means and uses the white LED, a reflectivity characteristic of the reflecting surface is properly set. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus, and in particular, when various color aberrations are corrected in a balanced manner and when a color image is read using a line sensor such as an image scanner, a digital copying machine, or a facsimile using a small imaging optical element having high resolution. It is suitable for.

  Conventionally, a flat bed type image scanner has been proposed as an image reading device (image scanner) for reading image information on a document surface.

  The flatbed image scanner reads the image information by fixing the imaging lens and the line sensor and moving only the reflection mirror to slit exposure scan the document surface.

  In recent years, in order to simplify the structure of the apparatus, a carriage-integrated scanning system in which a mirror, an imaging lens, a line sensor, and the like are integrated to scan a document surface has been increasingly employed.

  FIG. 7 is a schematic view of the main part of a conventional carriage-integrated scanning image reading apparatus. In the figure, the light beam emitted from the illumination light source 10 directly illuminates the document 3 placed on the document table 5, and the reflected light beam from the document 3 is sequentially converted into first, second, and third reflecting mirrors 9a, 9b, The optical path is bent inside the carriage 6 via 9c, and an image is formed on the surface of the line sensor 8 by the imaging lens (imaging optical system) 7. Then, the image information of the document 3 is read by moving the carriage 6 in the arrow A direction (sub-scanning direction) shown in FIG. The line sensor 8 in the figure has a configuration in which a plurality of light receiving elements are arranged in a one-dimensional direction (main scanning direction). Here, a xenon tube, a cold cathode tube, or the like is generally used as the illumination light source. This is because in order to illuminate the reading line, it is necessary to illuminate a bar, and also from the viewpoint of light quantity, the xenon tube and the cold cathode tube have excellent characteristics.

  However, these illumination light sources have a problem that they generate a large amount of heat as well as emitted light. In compact reading optical systems and the like, problems such as focus shift occur due to the temperature rise due to this heat generation, and it is necessary to take measures such as installing a fan, which causes a cost increase. It was.

  In addition, there is a problem that power consumption is large, and there is also a problem with recent energy saving.

  In addition, since the startability is poor, there is also a problem that it is necessary to wait for a while until the light is stabilized after lighting.

  On the other hand, various illuminations using LEDs that do not have the above-mentioned problems have been proposed. For example, as disclosed in Patent Document 1, various types of lighting devices in which three RGB LEDs are arranged at the end of a light guide have been proposed. In recent years, white LEDs have started to spread, and an image reading apparatus in which three LEDs of RGB are replaced with one white LED has been proposed. For example, Patent Document 2 discloses an illumination system using a white LED. Also, as disclosed in Japanese Patent Application Laid-Open No. 2003-228688, a large number of white LEDs are arranged in the main scanning direction.

However, since white LEDs have spectral characteristics different from those of xenon tubes and cold cathode tubes, there is a problem that color unevenness occurs. Disclosed.
JP-A-11-136439 JP-A-11-55465 Japanese Patent Laid-Open No. 2002-247296 JP 2000-261614 A

  However, Patent Document 4 discloses that the intensity of RGB should be within 10: 1 by dimming with a filter or the like, and also shows that an LED having a wide spectrum band, that is, a currently popular white LED itself can be used. However, if the white LED is provided with a filter to reduce light, the filter characteristics become complicated and the number of parts increases by one. If the ratio is within 10: 1, white LEDs do not need to take effective measures against color unevenness. To compensate for this, correction by image processing is required, and the image quality is low. It will get worse. Therefore, the present invention has at least one reflection surface in the optical path from the document surface to the light detection means, and in the image reading apparatus using a white LED, the above-mentioned problem is obtained by appropriately setting the reflectance characteristics of the reflection surface. Accordingly, an object of the present invention is to provide a high-quality image reading apparatus while avoiding the influence of uneven color due to the spectral characteristics of the white LED as much as possible.

The image reading apparatus according to claim 1 is mainly formed by an illuminating unit that illuminates a document, an imaging optical system that forms image information of the document illuminated by the illuminating unit, and an image formed by the imaging optical system. In an image reading apparatus having a light detecting means for detecting the reflected light,
The illumination unit is a white LED, and has at least one reflection surface in the optical path from the document surface to the light detection unit, and the reflectance at 400 nm of the reflection surface is Ref-B, and the reflectance at 600 nm is Ref. -R
Ref-B <Ref-R
It is characterized by satisfying the following conditions. This is because the blue output is the weakest in a combination of a normal xenon tube or a cold cathode tube and a line sensor, and a process for raising the blue output is performed in a normal image reading apparatus. However, in the case of a white LED, the intensity of blue emission is strong, so it is necessary to increase the red output by electrical processing. However, in this case, the image deteriorates. Therefore, by setting the spectral characteristic of the mirror in the image reading apparatus to have a large red reflectance, the rate of gain increase in the output from the line sensor by electrical processing is reduced, and the deterioration of the image is prevented.

  According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the reflectances Ref-B and Ref-R are reflectances at an incident angle equivalent to that at the time of image reading. This is a regulation regarding the reflectance of the reflecting surface, and the reflectance varies depending on the incident angle. Therefore, the incident angle equivalent to that at the time of image reading which is most required as the regulation is set. However, in general, a value at 45 degrees incidence is often used as a reflectance measurement, and a relatively large number of reflecting surfaces are used at 45 degrees incidence in image reading apparatuses. It is good.

  According to a third aspect of the present invention, in the image reading apparatus according to the first aspect, the white LED is a GaN-based LED and a YAG-based phosphor, or a ZnSe-based LED. . This prescribes the type of white LED, but is a white LED having spectral characteristics as shown in FIG. 9 and prescribes that the output of blue is large.

  According to a fourth aspect of the present invention, in the image reading apparatus according to the second or third aspect, the output ratio from each of the R, G, and B channels of the light detection means is a maximum of 4 or less. It is said. In order to eliminate variations in RGB output in an image reading apparatus, the output from a channel with a weak normal output is usually gained up, and electrical processing is usually performed so that RGB is within a predetermined value. However, increasing the gain also increases the noise component of the output signal, so it is desirable that the gain is as small as possible. By setting the output ratio to 4 or less, the influence of noise is eliminated.

  According to a fifth aspect of the present invention, in the image reading device according to the first aspect, the reflecting surface is at least one surface of the imaging optical system.

  As described above, according to the present invention, in the image reading apparatus using white LEDs, the reflectance characteristics of the reflecting surface are appropriately set, thereby avoiding the influence of color unevenness due to the spectral characteristics of the white LEDs as much as possible. However, a good read image can be obtained.

(First embodiment)
1 to 4 show a first embodiment of the present invention.

  FIG. 1 is a schematic cross-sectional view of the image reading apparatus of the present embodiment. On the carriage 6 provided in the image reading apparatus 1, a lens 7, a CCD line sensor 8, first, second, and third reflecting mirrors 9a, 9b, and 9c and an illumination light source (white LED) 10 are mounted. ing. The CCD line sensor 8 converts an image into an electrical image signal, and a plurality of image sensors are arranged in a straight line. The carriage 6 is fitted with the carriage guide shaft 11 and can move in the sub-scanning direction.

  FIG. 2 is an internal block diagram of the image reading apparatus of the present embodiment. Hereinafter, each functional block will be described with reference to FIG. The image reading apparatus 1 is connected to the host computer 21 by a signal cable. The image reading apparatus 1 operates in accordance with a command from the host computer 21 to read an image and transfers an image signal to the host computer 21. Reference numeral 7 denotes an image forming optical system for forming an image of light from the original irradiated from the light source 14 on the CCD 8 which is a solid-state image sensor, and 24 is a light source lighting circuit for lighting the light source 10. In addition, you may use CMOS other than CCD as an image pick-up element. Next, in the electric board 19, reference numeral 25 denotes a motor drive circuit for driving the pulse motor 20, and an excitation switching signal of the pulse motor 20 is generated by a signal from the system controller 26 which is system control of the image reading apparatus (image scanner) 1. Output. Reference numerals 27R, 27G, and 27B denote analog gain adjusters that variably amplify the analog signal output from the CCD line sensor 8. Reference numeral 28 denotes an A / D converter, which performs offset correction, shading correction, digital gain adjustment, and color balance adjustment on a signal image obtained by converting the analog image signals output from the analog gain adjusters 27R, 27G, and 27B into digital signals. Image processing such as masking and resolution conversion in the main and sub scanning directions is performed. A line buffer 30 is a part for temporarily storing image data, and 31 is an interface unit for communicating with the host 21. Here, it is realized by a SCSI controller, but other interfaces such as Centronics and USB can also be adopted. An offset RAM 32 is used as a working area when performing image processing. The offset RAM 32 is used for correcting the offset between the RGB lines because the line sensor 8 has the RGB line sensors arranged in parallel with a predetermined offset. The offset RAM 32 also temporarily stores various data such as shading correction. Here, it is realized by a general-purpose random access memory. Reference numeral 33 denotes a gamma RAM for storing a gamma curve and performing comma correction. A system controller 26 stores a sequence of the entire scanner as a program, and performs various controls in accordance with commands from the host 21. A system bus 34 connects the system controller 26, the image processing unit 29, the line buffer 30, the interface unit 31, the offset RAM 32, and the gamma RAM 33, and includes an address bus and a data bus.

  Next, a document reading operation will be described.

  First, the light source 10, that is, the white LED is turned on, and the carriage 6 is moved in the sub-scanning direction so that the image information on the reflection original is projected onto the CCD line sensor 8 via the reflection mirrors 9 a, 9 b, 9 c and the lens 7. Is done.

  At this time, the reflection original 3 is placed on the upper side of the original platen glass 5 and pressed from above by the pressure plate 2, so that it is almost in close contact with the original platen glass 5. In general, when reading a reflective original, the required resolution is low, and even if it is fine, the depth is deep because it is about 600 dpi. Therefore, even if the focus position is set on the upper surface of the original platen, the original can be slightly lifted or even a slight three-dimensional object can be read without any problem.

  The read image information is reflected by a total of three reflection mirrors 9a, 9b, and 9c, and the spectral characteristics of the light source, the reflection mirror, and the CCD when the mirror characteristics of the present invention are used on these three surfaces. 3 shows an integrated value, FIG. 4 shows an integrated value of spectral characteristics of a light source, a reflective mirror, and a CCD in a conventional mirror, and FIG. 8 shows a spectral reflectance characteristic of the mirror of the present invention. By applying the mirror characteristics of the present invention to the reflecting surface used as an optical path folding mirror in this way, the RGB color balance is changed to a better balance without the need for additional components such as a filter. The output of the B channel exceeding 4 times the R channel is improved to about 3 times the output. As a result, it is possible to reduce the rate of gain increase in the analog gain adjuster 27 and obtain a good image with less noise.

(Second Embodiment)
5 and 6 show a second embodiment of the present invention.

  FIG. 5 is a schematic sectional view of the image reading apparatus of the present embodiment. FIG. 5 is a graph showing an integrated value of spectral characteristics of a light source, a reflective mirror, and a CCD according to the present embodiment when a reflective original is read. On the carriage 6 provided in the image reading apparatus 1, a light source 10, a CCD line sensor 8, a lens 7, and reflection mirrors 9a and 9b are mounted. The carriage 6 is fitted with the carriage guide shaft 11 and can move in the sub-scanning direction.

  In the first embodiment, the lens is a refractive lens, but in the second embodiment, the lens is a lens made of a reflective free-form surface. In this case, the four colors of the reflection type free-form surface have the mirror characteristics of the present invention, thereby improving the RGB color balance.

  In the embodiment of the present invention, a scanner that obtains image information by moving the carriage is disclosed, but the effect of the present invention can be obtained by setting the reflection mirror in the same manner in a 2: 1 mirror scanning scanner. .

2 is a schematic cross-sectional view of the image reading apparatus according to the first embodiment of the present invention when reading a reflection original. FIG. 1 is a configuration block diagram of an image reading apparatus according to a first embodiment of the present invention. The graph which integrated the spectral characteristic of white LED of the image reading apparatus which concerns on the 1st Embodiment of this invention, a reflective mirror, and CCD Graph that integrates spectral characteristics of white LED, reflection mirror, and CCD of conventional image reader 4 is a schematic cross-sectional view of the image reading apparatus according to the second embodiment of the present invention when reading a reflection original. FIG. Graph in which spectral characteristics of white LED, free-form surface reflecting mirror and CCD of the image reading apparatus according to the second embodiment of the present invention are integrated. Schematic sectional view for explaining a conventional image reading apparatus Spectral reflectance characteristics diagram of the mirror of the present invention Spectral characteristics of white LED

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image reader 2 Pressure plate 3 Reflected original document 4 Pulse motor 5 Original plate glass 6 Carriage 7 Lens 8 CCD line sensor 9 Reflecting mirror 10 Illumination light source 11 Carriage guide shaft

Claims (5)

Illuminating means for illuminating a document, an imaging optical system for imaging image information of the document illuminated by the illuminating means, and a light detecting means for detecting light imaged by the imaging optical system In the image reading device,
The illumination unit is a white LED, and has at least one reflection surface in the optical path from the document surface to the light detection unit, and the reflectance at 400 nm of the reflection surface is Ref-B, and the reflectance at 600 nm is Ref. -R
Ref-B <Ref-R,
An image reading apparatus satisfying the following condition:   2. The image reading apparatus according to claim 1, wherein the reflectances Ref-B and Ref-R are reflectances at an incident angle equivalent to that at the time of image reading.   2. The image reading apparatus according to claim 1, wherein the white LED is a GaN-based LED and a YAG-based phosphor, or a ZnSe-based LED.   4. The image reading apparatus according to claim 2, wherein an output ratio from each of the R, G, and B channels of the light detection means is 4 or less at maximum.   2. The image reading apparatus according to claim 1, wherein the reflecting surface is at least one surface of the imaging optical system.

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