JP2016225689A - Image reading device and image reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reading device which allows for highly accurate reproduction, by reading a monochromatic character original with high resolution and high contrast, by using a color area image sensor, without using a complicated interpolation processing.SOLUTION: An image reading device 100 for acquiring the image information of a manuscript M placed on a placement surface 101 includes an imaging unit 103 including multiple light-receiving elements corresponding to multiple colors arranged on the same plane, an illumination unit 104 capable of illuminating the placement surface 101 with monochromatic light, and an operation unit 106 for acquiring image information by performing addition processing of information based on the light-reception intensity of each of the multiple light-receiving elements, obtained by imaging the manuscript M illuminated with monochromatic light by the imaging unit 103.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image reading apparatus using a color area image sensor.

  In a color area image sensor used in an image reading unit in a conventional image reading apparatus, as shown in FIG. 14, so-called Bayer type, R (red): G (green): B (blue) = 1: 2. The light receiving elements of the respective colors are arranged in a planar shape at a pixel number ratio of 1.

In a color area image sensor arranged in a Bayer type, information is missing in 3/4 pixels for R and B colors and 1/2 pixels (missing pixels) for G color.
In a conventional image reading apparatus, when output as image information, information on missing pixels is interpolated by interpolation processing from adjacent pixels. Various methods have been proposed as an interpolation processing method. However, in many methods, contrast reduction and coloring of an image called false color occurs.
In particular, in black and white character originals such as printed matter, a lot of fine black characters are used on a white background.
Various proposals have been made for these countermeasures, and Patent Document 1 proposes an interpolation process using an iterative algorithm.

Japanese Patent Laid-Open No. 2003-179941

The Institute of Electronics, Information and Communication Engineers, “Knowledge Forest,” 8th Group, 4th Edition, 2nd Chapter (Ver. Oct. 25, 2011)

However, in the interpolation processing such as the iterative algorithm disclosed in Patent Document 1, the amount of calculation until convergence is increased, so that the calculation time is increased.
In addition, since information on missing pixels is estimated from adjacent pixels to the last, an original image cannot always be reproduced with high accuracy.
Therefore, the present invention provides an image reading apparatus that can read a black and white character document or the like with high resolution and high contrast without using complicated interpolation processing and reproduce it with high accuracy using a color area image sensor. With the goal.

  An image reading apparatus according to the present invention is an image reading apparatus that acquires image information of a document placed on a placement surface, and includes an image pickup device including a plurality of light receiving elements corresponding to a plurality of colors arranged on the same surface. Information based on the received light intensity of each of the plurality of light receiving elements obtained by imaging the document, the illumination unit capable of illuminating the mounting surface with monochromatic light, and the document illuminated with monochromatic light by the imaging unit And a calculation unit that acquires image information.

  According to the present invention, it is possible to provide an image reading apparatus that can read a black and white character document or the like with a high resolution and a high contrast without using a complicated interpolation process by using a color area image sensor, and can reproduce it with high accuracy. Can do.

1 is a schematic perspective view of an image reading apparatus according to a first embodiment. 1 is a schematic cross-sectional view of an image reading apparatus according to a first embodiment. 6 is a flowchart of the operation of the image reading apparatus according to the first embodiment. The figure which showed the spectrum of LD of G color. The figure which showed each spectrum acquired when each light receiving element of the color area image sensor 1032 light-receives the light ray reflected from the white base | substrate of the monochrome character original illuminated by G color LD. The figure which showed the spectrum of the general white LED. The figure which showed each spectrum acquired when each light receiving element of the color area image sensor 1032 light-receives the light reflected from the white base | substrate of the monochrome character original illuminated by white LED. FIG. 5 is a diagram illustrating an addition process performed in the image reading apparatus according to the first embodiment and an interpolation process performed in a conventional image reading apparatus. 10 is a flowchart of the operation of the image reading apparatus according to the second embodiment. The figure which showed the spectrum of G color LED. The figure which showed each spectrum acquired when each light receiving element of the color area image sensor 1032 light-receives the light ray reflected from the white base | substrate of the monochrome character original illuminated by G color LED. The figure which showed the addition process and binarization process performed in the image reading apparatus which concerns on 2nd embodiment. The figure which showed the spectral characteristic of each light receiving element of the color area image sensor 1032. The figure which showed arrangement | positioning of each light receiving element of the color area image sensor 1032.

  Hereinafter, an image reading apparatus according to the present invention will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present invention can be easily understood.

  FIG. 1 is a schematic perspective view of an image reading apparatus 100 according to the first embodiment.

  The image reading apparatus 100 includes a mounting table 101, a frame 102, a camera (imaging unit) 103, a projector (illumination unit) 104, and a control unit (calculation unit) 106.

For example, the document M is placed on the placement surface of the placement table 101.
The frame 102 is fixed to the mounting table 101 and supports and fixes the camera 103 and the projector 104.
The camera 103 reads an image within the projection reading range of the mounting table 101.
The projector 104 projects an image within the projection reading range of the mounting table 101. In other words, the projector 104 can illuminate the projection reading range of the mounting table 101 with monochromatic light or white light.
The control unit 106 controls operations of the camera 103 and the projector 104. Specifically, the control unit 106 transmits a projection image signal for projecting an image onto the projector 104. In addition, the control unit 106 transmits a reading instruction signal for instructing the camera 103 to read an image. Further, the control unit 106 receives and processes a read image signal based on the image read by the camera 103.

  FIG. 2 is a schematic cross-sectional view of the image reading apparatus 100 according to the first embodiment.

The camera 103 includes a reading lens 1031, a color area image sensor (imaging device) 1032, and a shutter 1033.
The reading lens 1031 forms an image of the projection reading range on the color area image sensor 1032 surface.
A mechanical shutter 1033 is provided in the middle of the optical path, and the shutter 1033 is controlled so as to have an appropriate exposure amount according to the opening / closing timing and the opening time.
As the color area image sensor 1032, a CCD (Charge Coupled Device) method, a CMOS (Complementary Metal-Oxide Semiconductor) method, or the like is employed. The color area image sensor 1032 can obtain two-dimensional image information by laying a plurality of fine light receiving elements in the plane.
In the color area image sensor 1032, as shown in FIG. 14, the light receiving elements of each color (plural colors) are arranged in a plane shape with a Bayer-type ratio of R: G: B = 1: 2: 1. (A Bayer array is formed).
The light receiving elements for each color are composed of color filters and photodiodes.
The color area image sensor 1032 has spectral characteristics (relative spectral sensitivity) as shown in FIG. 13 (see Non-Patent Document 1).
In other words, the color area image sensor 1032 includes a plurality of light receiving elements corresponding to a plurality of colors arranged on the same plane.

The projector 104 includes a projection lens 1041, an image display element 1042, and a light source device 1043.
The projection lens 1041 forms an image displayed by the image display element 1042 within the projection reading range.
The image display element 1042 partially changes the light beam emitted from the light source device 1043 by changing the in-plane reflectance or transmittance according to the image information.
The light source device 1043 includes R, G, and B color laser diode (LD) light sources, and emits light beams of respective colors. The light source device 1043 projects pseudo white light within the projection reading range by sequentially and repeatedly turning on the light sources of the respective colors. However, the present invention is not limited to this, and white light may be projected by simultaneously turning on the light sources of the respective colors.
That is, the projector 104 can project an image on the mounting table 101.

  FIG. 3 shows a flowchart of the operation of the image reading apparatus 100 according to the first embodiment.

First, when image reading is instructed in the image reading apparatus 100 (S10), white light is projected within the projection reading range of the mounting table 101 by the projector 104 (S11), and the camera 103 is an image within the projection reading range. Is read (S12).
Then, the control unit 106 determines whether the read image is a single color image (S13). If the read image is a monochrome image such as a black and white character document (Yes in S13), the projector 104 projects (illuminates) G light (monochromatic light) within the projection reading range (S14). ).
Then, the camera 103 reads an image within the projection reading range in a state where the G light is projected (S15). Then, the control unit (arithmetic unit) 106 performs an addition process on the read image (S16), the processed read image information is output (S18), and the image reading apparatus 100 finishes reading the image. (S19).
On the other hand, if the image read in S12 is not a monochrome image (No in S13), the control unit 106 performs color interpolation processing on the image read in S12 (S17). Then, the processed read image information is output (S18), and the image reading apparatus 100 finishes reading the image (S19).
Details of the addition processing in S16 will be described later. Further, the color interpolation processing in S17 is out of the scope of the present invention, and thus description thereof is omitted.

  FIG. 4 shows a spectrum of the G-color LD of the light source device 1043. It can be seen that the G-color LD has a narrow spectral characteristic centered at about 520 nm and a half width of 11 nm. .

When the light receiving elements of the R, G, and B colors of the color area image sensor 1032 receive light reflected from the white background of the black and white character document illuminated by the G color LD, FIG. A spectrum as shown in FIG.
As shown in FIG. 5, the spectra obtained by the light receiving elements of the R, G, and B colors of the color area image sensor 1032 are almost overlapped, that is, the light receiving elements of the respective colors both emit light in the same wavelength band. It can be seen that the received image can be read.
Note that each spectrum shown in FIG. 5 is normalized so that the peak intensity is 1.

FIG. 6 shows a spectrum of a general white LED (B color LED + phosphor). When the light receiving elements of the R, G, and B colors of the color area image sensor 1032 receive the light beam reflected from the white background of the black and white character document illuminated by the white LED, FIG. A spectrum as shown is obtained.
In this case, the spectra obtained by the R, G, and B light receiving elements of the color area image sensor 1032 do not overlap. That is, it is not preferable because the light receiving elements of the respective colors receive light in wavelength bands that are greatly different and are affected by chromatic aberration and the like existing in the reading lens 1031.
It should be noted that each spectrum shown in FIG. 7 is normalized so that the peak intensity is 1.

  Next, the addition process in S16 will be specifically described.

  FIG. 8 is a diagram illustrating an addition process performed in the image reading apparatus 100 according to the first embodiment and an interpolation process performed in the conventional image reading apparatus.

First, consider a case where a monochrome character document image (black and white document) as shown in (I) is read by a color area image sensor 1032 as shown in (II). Here, the numbers in (I) represent lightness, that is, 0 and 1 are black and white, respectively.
When the color area image sensor 1032 reads the original image in a state where the G color light is projected on the original, the light receiving intensities of the R, G, and B light receiving elements are acquired as shown in (III). .
Here, as shown in (III), it should be noted that each spectrum obtained by each light receiving element is normalized so that the peak intensity becomes 1 as in FIG.
Then, the normalized received light intensity (information based on the received light intensity) of the R, G, and B light receiving elements shown in (III) is added (addition process), and (IV) shows The read image information as described above can be obtained.
Therefore, the image reading apparatus 100 according to the present embodiment can obtain read image information that reproduces a black and white character original image with high accuracy by performing addition processing.

  On the other hand, in the conventional image reading apparatus, adjacent to the missing pixels around each light receiving element based on the light receiving intensity of each of the R, G, and B light receiving elements shown in (III). An interpolation process as shown in (IIIa) is performed by estimating from the received light intensity of the pixel to be performed. Then, when the intensities shown in (IIIa) are added and averaged (normalized), read image information as shown in (IVa) is obtained. Thus, it can be seen that the interpolation processing performed in the conventional image reading apparatus cannot obtain read image information in which a monochrome character original image is reproduced with high accuracy.

  Note that the addition processing according to the present embodiment can be applied to gray scale original images as long as the gain for normalizing the peak intensity of each spectrum obtained by each of the R, G, and B light receiving elements is determined. Is possible.

  Next, operations performed for the image reading apparatus according to the second embodiment will be described. Note that the image reading apparatus according to the second embodiment has the same configuration as that of the image reading apparatus 100 according to the first embodiment, except that the light source provided in the light source device 1043 is different from that of the first embodiment. Therefore, the same constituent elements are denoted by the same reference numerals, and description thereof is omitted.

  The light source device 1043 provided in the image reading apparatus according to the second embodiment is composed of R, G, B color light emitting diode (LED) light sources. LED light sources are more widely used than LD light sources and are suitable for mass production.

  FIG. 9 shows a flowchart of the operation of the image reading apparatus according to the second embodiment.

First, in the image reading apparatus according to the second embodiment, when an image reading is instructed (S20), white light is projected within the projection reading range of the mounting table 101 by the projector 104 (S21), and the camera 103 projects. An image within the reading range is read (S22).
Then, the control unit 106 determines whether the read image is a single color image (S23). If the read image is a monochromatic image such as a black and white character original (Yes in S23), the projector 104 projects (illuminates) G light (monochromatic light) within the projection reading range (S24). ).
Then, the camera 103 reads an image within the projection reading range in a state where the G light is projected (S25). The control unit (arithmetic unit) 106 performs addition processing (S26) and binarization processing (S27) on the read image, and the processed read image information is output (S29). The image reading apparatus according to the embodiment finishes reading the image (S30).
On the other hand, if the image read in S22 is not a single color image (No in S23), the control unit 106 performs color interpolation processing on the image read in S22 (S28). Then, the processed read image information is output (S29), and the image reading apparatus according to the second embodiment finishes reading the image (S30).
Details of the addition process in S26 and the binarization process in S27 will be described later. Further, the color interpolation processing in S28 is out of the scope of the present invention, so the description is omitted.

  FIG. 10 shows the spectrum of the G-color LED of the light source device 1043. It can be seen that the G-color LED has a spectral characteristic having a center at about 520 nm and a half-value width of 37 nm. Therefore, the spectrum width of the G-color LED is somewhat wider than the spectrum of the LD shown in FIG. 4, but is sufficiently narrower than the spectrum of the white LED shown in FIG.

When the light receiving elements of the R, G, and B colors of the color area image sensor 1032 receive the light beam reflected from the white background of the black and white character document illuminated by the G color LED, FIG. A spectrum as shown in FIG. 11 is obtained.
As shown in FIG. 11, the spectra obtained by the R, G, and B light receiving elements of the color area image sensor 1032 overlap each other with a slight deviation from the spectrum shown in FIG. 5. That is, it can be seen that image reading can be performed in which the light receiving elements of the respective colors receive light in sufficiently close wavelength bands.
It should be noted that each spectrum shown in FIG. 11 is normalized so that the peak intensity is 1.

  Next, the addition process in S26 and the binarization process in S27 will be specifically described.

  FIG. 12 is a diagram illustrating addition processing and binarization processing performed in the image reading apparatus according to the second embodiment.

First, consider a case where a monochrome character document image (black and white document) as shown in (I) is read by a color area image sensor 1032 as shown in (II). Here, the numbers in (I) represent lightness, that is, 0 and 1 are black and white, respectively.
When the color area image sensor 1032 reads the original image in a state where the G color light is projected on the original, the light receiving intensities of the R, G, and B light receiving elements are acquired as shown in (III). .
Here, as shown in (III), since an LED light source having a somewhat wide spectral characteristic is used, it is affected by the axial chromatic aberration of the reading lens 1031, thereby causing the R color. The light receiving intensities of the light receiving elements of G, B and B are 0.6, 1, and 0.9, respectively.
Then, when the received light intensity (information based on the received light intensity) of each of the R, G, and B light receiving elements shown in (III) is added (addition process), as shown in (IV) Read image information can be obtained.
In the read image information as shown in (IV), since the intensity value varies, unevenness as an image is generated. Therefore, by performing binarization processing with 0.5 as a threshold value, read image information such as (V) can be finally obtained.
Therefore, in the image reading apparatus according to the present embodiment, read image information that reproduces a monochrome character original image with high accuracy can be obtained by performing addition processing and binarization processing.

  Read image information obtained in the image reading apparatus 100 according to the first embodiment and the image reading apparatus according to the second embodiment is transferred to a memory unit such as an SD card (not shown). Alternatively, by transferring the obtained read image information to a printer or personal computer, the image reading apparatus can be used as a copying machine or an image scanner. In the image reading apparatus, a preview display can be performed by projecting the read image information with the projector 104.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

For example, the image display element 1042 may be a liquid crystal, and the light source of the light source device 1043 may be a combination of a white light source and a color filter. Further, the reading lens 1031 and the projection lens 1041 may include a reflection optical system.
Also, the binarization processing is not limited to white and black binary processing, and binarization processing may be performed for each channel so as to output to white and red, white and magenta, or the like.

  In the present invention, the projector 104 preferably includes an LD or LED light source having a half width of 100 nm or less.

100 Image reading apparatus 101 Mounting table (mounting surface)
103 Camera (imaging part)
104 Projector (lighting unit)
106 Control unit (calculation unit)
1032 Color area image sensor (multiple light receiving elements)
M manuscript

Claims (19)

An image reading apparatus for acquiring image information of a document placed on a placement surface,
An imaging unit including a plurality of light receiving elements corresponding to a plurality of colors arranged on the same plane;
An illumination unit capable of illuminating the mounting surface with monochromatic light;
When the original is a black and white original, by adding information based on the received light intensity of each of the plurality of light receiving elements obtained by imaging the original illuminated with the monochromatic light by the imaging unit, An arithmetic unit for obtaining the image information;
An image reading apparatus comprising:   The image reading apparatus according to claim 1, wherein the calculation unit performs binarization processing after adding information based on the received light intensity.   The image reading apparatus according to claim 1, wherein the information based on the received light intensity is information normalized by the peak intensity of each received light intensity of the light receiving elements of the plurality of colors.   The image reading apparatus according to claim 1, wherein the illumination unit can illuminate the placement surface with white light.   5. The image reading apparatus according to claim 4, wherein when the document is not a monochrome document, the illumination unit illuminates the placement surface with white light, and the calculation unit performs a color interpolation process.   6. The image reading apparatus according to claim 1, wherein when the original is a black and white original, the arithmetic unit does not perform color interpolation processing.   7. The image reading apparatus according to claim 1, wherein the plurality of light receiving elements correspond to colors of R, G, and B and are arranged in a Bayer array. 7.   The image reading apparatus according to claim 1, wherein the illumination unit includes an LD or LED light source having a half width of 100 nm or less.   The image reading apparatus according to claim 1, wherein the illumination unit is capable of projecting an image on the placement surface. An image reading method for acquiring image information of a document placed on a placement surface,
A first illumination step of illuminating the original with monochromatic light;
An imaging step of imaging the illuminated original with a plurality of light receiving elements corresponding to a plurality of colors arranged on the same surface;
A first calculation step of acquiring the image information by adding information based on the received light intensity of each of the plurality of light receiving elements obtained by the imaging step when the document is a black and white document;
An image reading method comprising:   The image reading method according to claim 10, wherein the first calculation step further includes a step of performing binarization processing after adding information based on the received light intensity.   12. The image reading method according to claim 10, wherein the information based on the received light intensity is information normalized by the peak intensity of each received light intensity of the light receiving elements of the plurality of colors.   The image reading method according to claim 10, further comprising a second illumination step of illuminating the original with white light.   When the original is not a black and white original, the original is illuminated by the second illumination step, and color interpolation processing is performed on information based on the received light intensity of each of the plurality of light receiving elements obtained by the imaging step. The image reading method according to claim 13, further comprising a second calculation step of acquiring the image information.   15. The image reading method according to claim 14, wherein when the original is a black and white original, the second calculation step is not performed.   16. The image reading method according to claim 10, wherein the plurality of light receiving elements correspond to each color of R, G, and B and are arranged in a Bayer array.   17. The image reading method according to claim 10, wherein the first illumination step is performed by an LD or LED light source having a half width of 100 nm or less.   The image reading method according to claim 10, wherein the first illumination step is performed by projecting an image onto the document.   16. The image reading method according to claim 13, wherein the second illumination step is performed by projecting an image on the document.

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