JPH0563906A - Picture reader - Google Patents

Abstract

PURPOSE:To attain reading with high quality and higher resolution and with less production of noise from three components of a color picture signal. CONSTITUTION:A light resulting from scanning a face of an original 2 and reflected therein is collected by an image forming lens 3 and made incident on a photoelectric conversion element 6. An electric signal in response to the reflectance of the original 2 is detected as a power supply and picture information is obtained thereby. The photoelectric conversion element 6 on which three kinds of read picture elements having different spectral distribution are arranged in a line sequentially is provided and optical low pass filters 4, 5 are provided to a front face of the photoelectric conversion element 6. A null frequency of low pass filters 4, 5 in the main scanning direction is set at least to 1/3 and 2/3 of the picture element pitch of the photoelectric conversion element 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image reading,
In particular, the present invention relates to an image reading device capable of capturing image information at high density.

[0002]

2. Description of the Related Art Conventionally, a large number of photoelectric conversion elements such as CCD sensors have been used to read original images in copying machines, facsimiles, image filing devices and the like. For example,
In a device such as disclosed in Japanese Patent Laid-Open No. 62-235872, the photoelectric conversion element has a one-line configuration of 1 mm.
It consists of minute cells that can be read with a resolution of several to several tens of lines, and the reading in the line direction is the electrical scanning (main scanning direction) of the sensor itself, and the vertical direction (sub scanning direction). The reading is performed by moving the entire photoelectric conversion element.

Also, as colorization has progressed in recent years, one method for color-separating and capturing image information is, for example, Japanese Patent Laid-Open No.
There are some which use a color sensor having a color filter on a chip, as disclosed in Japanese Patent No. 264058, Japanese Patent Laid-Open No. 1-233880, and the like.

[0004]

Generally, in order to obtain color information having gradation, the amount of information for each pixel needs to be three times (for example, R, G, B) as compared with monochrome. .. For this reason, a color sensor in which an area occupied by one pixel of the monochrome sensor is divided into three and R pixels, B pixels, and G pixels are arranged is used, and thereby colorization is achieved with the same resolution as monochrome. However, the size of each color pixel is 1/3. Therefore, under the limited fine processing technology of the sensor, colorization and high resolution (high density) are contradictory, and it is difficult to meet the demand. In addition, it is desirable that the pixel area is as large as possible in terms of ensuring the sensitivity, but it cannot be said that the conventional method sufficiently meets the demand.

[0005]

According to a first aspect of the present invention, the surface of the original is scanned, and the light reflected by the original is condensed by an imaging lens and made incident on a photoelectric conversion element. In an image reading apparatus that detects an electric signal corresponding to the reflectance as an image signal to obtain image information by this, a photoelectric conversion element in which three kinds of reading pixels having different spectral distributions are sequentially arranged in a line is provided, and the photoelectric conversion element is provided. An optical low-pass filter was provided on the front surface of, and the null frequency in the main scanning direction of this low-pass filter was set to at least 1/3 and 2/3 of the pixel pitch of the photoelectric conversion element.

According to the second aspect of the invention, the surface of the original is scanned, and the light reflected thereby is condensed by the imaging lens and is incident on the photoelectric conversion element. In an image reading device that detects a signal as an image signal and obtains image information by this, a photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is provided, and a higher density than the sequential output of this photoelectric conversion element is provided. An extracting means is provided for extracting the image information of.

According to the third aspect of the present invention, the surface of the original is scanned, and the light reflected by the original is condensed by the imaging lens and is incident on the photoelectric conversion element. In an image reading device that detects a signal as an image signal and obtains image information by this, a photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is provided, and a higher density than the sequential output of this photoelectric conversion element is provided. The extracting means is provided for extracting the high frequency component of the image information of, and the calculating means is provided for performing the operation so that the high density image information extracted by the extracting means is also provided as the high frequency components of the three kinds of color components. ..

[0008]

According to the first aspect of the present invention, at least the null frequency in the main scanning direction of the low-pass filter provided on the front surface of the photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is photoelectrically converted. Since the pixel pitches of the elements are set to 1/3 and 2/3, it is possible to effectively suppress the sampling aliasing distortion due to the read pixels and perform high-quality image reading.

According to the second aspect of the present invention, the high-density image information is extracted by using the extracting means from the sequential output of the photoelectric conversion element in which the three types of read pixels having different spectral distributions are sequentially arranged in a line. Therefore, it is possible to read an image with high resolution.

According to the third aspect of the invention, high-frequency components of high-density image information are extracted by using extraction means from the sequential output of the photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line. Since the extracted high-density image information is provided as the high frequency components of the three types of color components by the calculating means, the high-density image read signal is output as a set of three types of color signals. be able to.

[0011]

An embodiment of the present invention will be described with reference to the drawings. Here, the surface of the original is scanned, and the light reflected by the original is condensed by an imaging lens and is incident on a photoelectric conversion element, whereby an electric signal corresponding to the reflectance of the original is detected as an image signal. In an image reading apparatus for obtaining image information by means of a sensor (photoelectric conversion element) in which three types of read pixels having different spectral distributions are sequentially arranged in a line, an optical low-pass filter is provided in front of this sensor, and the low-pass filter is provided. The null frequency in the main scanning direction of the filter is set to at least 1/3 and 2/3 of the pixel pitch of the sensor. The reason why the sensor, the low-pass filter and the like are provided will be described below.

In such a structure, one pixel of the monochrome sensor is divided into three, and color reading pixels each having a pixel area of 1/3 have the same spectral characteristic, and the output is tripled in density. Treated as monochrome information. This information cannot be said to be a faithful read output for low-frequency components of the original, but for some high-frequency components, the visual characteristics of the naked eye are less sensitive to changes in hue, so it is approximately Can be considered That is, a minute change in color is not faithfully read as monochrome information, but a minute change in brightness is read (this matches the characteristics of the naked eye). A high-resolution color read signal can be obtained by using the high-frequency information of this monochrome information and adding it as the high-frequency information of each color component (that is, the read output for each color obtained by a normal method). .. Further, at this time, an optical low-pass filter is arranged in front of the sensor in order to suppress aliasing distortion due to sampling of the read pixels, which is caused by the openings of the pixels read for each color being scattered. This allows
Since the high frequency component is removed before sampling, the occurrence of aliasing distortion can be effectively suppressed.

The high frequency components included in the original are
The spatial frequency corresponding to at least the sampling pitch of each color of the low-pass filter and the spatial frequency twice as high are attenuated by the frequency characteristic. As a result, the influence of the folding component generated around the sampling frequency and twice the sampling frequency on the original band becomes very small. The sensor output (sequential signal of three color components) of the original image detected by the sensor in this way is regarded as a signal of a change in brightness with high resolution, and is set as a brightness signal Y. On the other hand, a signal for each color (reading density of 1/3 of the Y signal) is demultiplexed to form a sequential signal, and a luminance signal is synthesized as a linear combination from the three components. This luminance signal can have only a frequency component corresponding to the sampling density of the color component, so that the band is narrower than that of the luminance signal Y.
Now, it is displayed as Yl, and a high-frequency luminance component Yh is obtained by performing an operation (Y-Yl) with this and Y. This high-frequency luminance component Yh can be added to the signals of the respective color components to obtain a color image signal composed of three components. This color image signal has a component of each color as its low-frequency component and a component showing a change in luminance as its high-frequency component, and these represent read signals of a high-density color image that match visual characteristics. It is a thing.

Next, based on the above general theory,
A specific example of this embodiment will be described. First, as shown in FIG. 1, a document 2 is placed above the light source 1, and the light emitted from the light source 1 is applied to the document 2 and is reflected on the optical path of the light reflected thereby. A lens array 3 as an imaging lens is provided. Two optical low-pass filters 4 and 5 are provided on the optical path of the light passing through the lens array 3, and a sensor 6 as a photoelectric conversion element is provided below the low-pass filters 4 and 5. It is provided in a fixed form on the sensor substrate 7. The above-mentioned components are housed in the carriage 8a so that they can be moved in the sub-scanning direction (Y direction). Note that in FIG. 1A, the X direction in the longitudinal direction of the pixel row is the main scanning direction, and the direction perpendicular to the paper surface is the sub scanning direction.

In such a structure, the light illuminated on the surface of the original 2 by the light source 1 and reflected by the light is sequentially transmitted through the lens array 3 and the low-pass filters 4 and 5 to form an image on the sensor 6. At this time, the low-pass filters 4, 5
Due to this, the high frequency components of the light are attenuated. As shown in FIG. 2, the read pixels of the sensor 6 are arranged in the order of three color components R, G, and B. FIG. 3 shows the pixel R,
9 shows the spectral transmittance characteristics (spectral reading characteristics) of G and B. FIG. 4 shows the frequency characteristic of the low-pass filter 4, and FIG. 5 shows the frequency characteristic of the low-pass filter 5. In FIGS. 3 and 4, fsr represents the sampling spatial frequency of the R reading pixel, which is equal to the sampling spatial frequency fsg of the G reading pixel and the sampling spatial frequency fsb of the B reading pixel. fsy is a sampling spatial frequency when each read pixel is regarded as the same, that is, fsy = 3fsr (= 3fsg = 3fsb). The overall characteristics of the low pass filters 4 and 5 are as shown in FIG. As a result, the sampling frequency fsr (=
It is shown that the influence on the original band of the folding component generated around fsg = fsb) and its double or triple frequency is very small. The low-pass filters 4 and 5 can be made, for example, by utilizing the birefringence of quartz.

Next, an example of processing of the output signal of the sensor 6 will be described with reference to FIG. A sample hold circuit 9 (S / H circuit), an A / D conversion circuit 10, a shading correction circuit 11, and a demultiplexer 12 are sequentially connected in a subsequent stage of the CCD sensor 8 (which corresponds to the sensor 6 described above). ing. A clock generator 13 is connected to the CCD sensor 8, the sample hold circuit 9, and the A / D conversion circuit 10. The shading correction circuit 11 is provided with a correction memory 14. Further, three interpolation processing circuits 15, 16 and 17 are connected to the demultiplexer 12, and adder circuits 18, 19 and 20 as arithmetic means are correspondingly connected to the subsequent stages thereof. The interpolation processing circuits 15, 16 and 17 are connected to a Yl operation circuit 21, and the Yl operation circuit 21 is connected to a subtraction circuit 22. The Yl operation circuit 21 and the subtraction circuit 22 constitute extraction means. Further, a color carrier removing circuit 23 as an extracting means is connected between the subtracting circuit 22 and the shading correcting circuit 11. Then, the subsequent stages of the adder circuits 18, 19 and 20 have output terminals R ′,
It is connected to G'and B ', respectively.

In this case, the extraction means composed of the color carrier removal circuit 23 and the extraction means composed of the Yl calculation circuit 21 and the subtraction circuit 22 respectively correspond to the CCD.
It has a function of extracting high-density image information from the sequential output of the sensor 8. Further, the arithmetic means composed of the adder circuits 18, 19 and 20 has a function of performing arithmetic so that the high-density image information extracted by the extraction means is provided as the high frequency components of the three kinds of color components.

In such a structure, the CCD sensor 8
The sequential signals of the three color components detected by are transferred and output by the clock generator 13, and the output values thereof are guided to the sample hold circuit 9 so that the transfer clock components are removed. Next, the shading correction circuit 11 converts the digital signal by the A / D conversion circuit 10.
Sent to. The shading correction circuit 11 has a function of correcting variations in brightness due to the illumination system and the imaging system, variations in sensor sensitivity, and the like. This is because data stored in advance is called from the correction memory 14 and calculation is performed for each read pixel. The shading-corrected output is a sequential signal, as shown in FIG. The demultiplexer 12 internally produces a signal delayed by 1/2 pixel clock (see FIG. 8).
(E)), and further divided into R signal, G signal, and B signal.
This becomes like FIG.8 (f), (g), (h), respectively. The R signal, G signal and B signal are sent to the interpolation processing circuits 15, 16 and 17, respectively, and are interpolated. this is,
For example, for the R signal,

[0019]

[Equation 1]

The procedure is as follows. The G signal and the B signal can be processed in the same manner.

The outputs of the interpolation processing circuits 15, 16 and 17 are as shown in FIGS. 8 (i), (j) and (k). Since these signals are simply interpolated, the data rate is tripled, but only the frequency component up to 1/3 (that is, the original frequency component) can be held.
These R signal, G signal, and B signal are added to the adder circuit 1 respectively.
It is led to 8, 19 and 20, and is led to the Yl arithmetic circuit 21 to perform the arithmetic operation of Yl = rR + gG + bB. r + g + b
= 1 and, for example, when the spectral reading characteristics of the R, G, and B pixels are as shown in FIG. 3 described above, r = 0.
3, g = 0.6, b = 0.1 place. Therefore, as a result, the low-frequency part Yl of the luminance component can be obtained at the output of the Yl arithmetic circuit 21 (FIG. 8 (l)).

On the other hand, the output of the shading correction circuit 11 is guided to the color carrier removing circuit 23 to remove the color carrier. The color carrier is a frequency component with three pixels as a unit, which is generated when all the signals are sequentially regarded as outputs of the same pixel, which naturally results from repetition of three types of spectral distribution characteristics. .. To remove this component, for example, since it is a component in units of 3 pixels, it may be added by a signal delayed by 1.5 pixels, which is half the component. That is, a signal (FIG. 8 (b)) delayed by 1.5 pixels from the input of FIG. 8 (a) is created, and both are added. At this time, the data timing does not match, so
In accordance with the signal of FIG. 8B, the average value of two adjacent pixels is used in FIG. 8A. In the signal thus obtained, as shown in FIG. 8 (c), the positions indicated by the data have fractions such as 1.75, 2.75, 3.75, .... Therefore, these are approximated to 2, 3, 4, ... As they are, or interpolated data at that position are obtained, and output as shown in FIG. 8D. The demultiplexer 12 is delayed to match this timing.
The signal of FIG. 8D has a band up to immediately before the sampling frequency fsr (= fsg = fsb) of each color as a luminance signal.

Then, the output of the Yl operation circuit 21 described above is led to the negative side input of the subtraction circuit 22, and the output of the color carrier removal circuit 23 is led to the positive side input of the subtraction circuit 22, and Y
-Yl is calculated and the Yh signal (Fig.
(M)) as its output. The Yh signal is led to the adder circuits 18, 19 and 20, and the interpolation processing circuit 1
It is added to the outputs of 5, 16 and 17. This result is shown in Figure 8.
As shown in (o), (p), and (q), they are led to the output terminals R ′, G ′, and B ′, respectively. A high-resolution image can be obtained when these three color components have the respective color components in the low-frequency part and the luminance component in the high-frequency part and are combined as an image.

Next, the above-mentioned processing will be described based on the frequency band of each signal shown in FIG. FIG. 9A shows the band of the output of the color carrier removing circuit 23, which has a frequency band up to immediately before the sampling frequencies fsr, fsg, and fsb of each color. 9C, 9D, and 9E are output bands of the interpolation processing circuits 15, 16 and 17, respectively, and have effective color components up to 1/2 of the sampling frequency. FIG. 9E shows the output of the Yl operation circuit 21, which has the same band. FIG. 9F shows the subtraction circuit 2
2 and the high-frequency component of luminance is separated. 9 (g), 9 (h) and 9 (i) are addition circuits 18 and 1, respectively.
These are the outputs of 9 and 20. Therefore, from such a thing,
High-density information about twice the band of each color component can be obtained.

Here, the read pixel array of the sensor 6 shown in FIG. 1 may be the array shown in FIGS. 10, 11 and 12 in addition to the array shown in FIG. That is, the read pixel array in FIG.
The vertical ratio is 1.5, which is the main scanning direction X.
The length of the pixel in the sub-scanning direction Y is set according to the resolution characteristics of. In the arrangement of the read pixels shown in FIG. 11, the shape of each pixel is inclined, so that the sampling aperture for each component is prevented from being scattered and the aliasing distortion is further reduced. is there. Furthermore, in the read pixel array shown in FIG.
No. 0 and FIG. 11 are formed so as to have the characteristic portions of the arrangement together.

[0026]

According to the first aspect of the present invention, the surface of the original is scanned, and the light reflected by the original is condensed by the image forming lens and is incident on the photoelectric conversion element. In an image reading apparatus that detects an electric signal as an image signal and obtains image information by this, a photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is provided, and an optical signal is provided in front of the photoelectric conversion element. Since a typical low-pass filter is provided and the null frequency in the main scanning direction of this low-pass filter is set to at least 1/3 and 2/3 of the pixel pitch of the photoelectric conversion element, the aliasing distortion of sampling by the read pixel is effectively performed. It is possible to suppress and read a high-quality image.

According to a second aspect of the present invention, the surface of the original is scanned, and the light reflected by the original is condensed by an imaging lens and made incident on a photoelectric conversion element, so that the electric power corresponding to the reflectance of the original is obtained. In an image reading device that detects a signal as an image signal and obtains image information by this, a photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is provided, and a higher density than the sequential output of this photoelectric conversion element is provided. Since the extraction means for extracting the image information is provided, it is possible to read the image with high resolution.

According to the third aspect of the present invention, the surface of the original is scanned, and the light reflected by the original is condensed by the imaging lens and is incident on the photoelectric conversion element, so that the electric power corresponding to the reflectance of the original is changed. In an image reading device that detects a signal as an image signal and obtains image information by this, a photoelectric conversion element in which three types of read pixels having different spectral distributions are sequentially arranged in a line is provided, and a higher density than the sequential output of this photoelectric conversion element is provided. The extracting means is provided for extracting the high frequency component of the image information of, and the calculating means is provided for performing the operation so that the high density image information extracted by the extracting means is also provided as the high frequency components of the three kinds of color components. Therefore, a high-density image read signal can be output as a set of three kinds of color signals.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a front view of an image reading apparatus and (b) is a side view thereof.

FIG. 2 is a state diagram showing an arrangement of read pixels of a sensor.

FIG. 3 is a characteristic diagram showing a spectral reading characteristic of each reading pixel.

FIG. 4 is a characteristic diagram showing frequency characteristics of a low-pass filter.

FIG. 5 is a characteristic diagram showing frequency characteristics of another low-pass filter.

FIG. 6 is a characteristic diagram showing an overall characteristic of the two low-pass filters of FIGS. 4 and 5.

FIG. 7 is a circuit diagram showing a state of a signal processing circuit for an output signal of a sensor.

FIG. 8 is a state diagram showing an output state in each circuit of the signal processing circuit.

FIG. 9 is a characteristic diagram showing a state of a frequency band of each signal in each circuit of the signal processing circuit.

FIG. 10 is a state diagram showing a modified example of an array of read pixels of the sensor.

FIG. 11 is a state diagram showing another modification of the arrangement of the read pixels of the sensor.

12 is a state diagram showing a modified example of an array having the characteristics of the array of read pixels of the sensor of FIGS. 10 and 11. FIG.

[Explanation of reference numerals] 2 original 3 imaging lens 4,5 low-pass filter 6 photoelectric conversion elements 21, 22, 23 extraction means 18, 19, 20 calculation means

Claims (3)

[Claims] 1. An electric signal according to the reflectance of the original is detected as an image signal by scanning the surface of the original and condensing the light reflected by the original with an imaging lens to enter the photoelectric conversion element. In an image reading apparatus for obtaining image information by this, a photoelectric conversion element in which three types of reading pixels having different spectral distributions are sequentially arranged in a line is provided, and an optical low-pass filter is provided in front of the photoelectric conversion element. An image reading apparatus characterized in that a null frequency of a low-pass filter in a main scanning direction is set to at least 1/3 and 2/3 of a pixel pitch of the photoelectric conversion element. 2. An electric signal according to the reflectance of the original is detected as an image signal by scanning the surface of the original and condensing the light reflected by the original with an imaging lens to enter the photoelectric conversion element. Then, in the image reading apparatus for obtaining the image information by this, a photoelectric conversion element in which three kinds of read pixels having different spectral distributions are sequentially arranged in a line is provided, and high-density image information is extracted from the sequential output of the photoelectric conversion element. An image reading apparatus comprising extraction means. 3. An electric signal corresponding to the reflectance of the original is detected as an image signal by scanning the surface of the original and condensing the light reflected by the original with an imaging lens to enter the photoelectric conversion element. Therefore, in the image reading apparatus for obtaining the image information by this, a photoelectric conversion element in which three kinds of reading pixels having different spectral distributions are sequentially arranged in a line is provided, and the high range of the image information having a higher density than the sequential output of the photoelectric conversion element is provided. An image characterized by being provided with an extraction means for extracting a component, and provided with an operation means for performing operation so that the high-density image information extracted by this extraction means is also provided as high-frequency components of three types of color components. Reader.