JPH07183998A - Image reader - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide an image reading apparatus capable of reading an image at high speed and improving the image quality during high-speed reading. [Configuration] Since the influence of the image signal of the immediately preceding pixel due to the afterimage phenomenon can be removed, the resolution of the image is improved. Further, since the amount of light received by the CCD line image sensor is set to be larger toward the main scanning end direction, it is possible to eliminate a decrease in the signal S / N ratio due to the afterimage phenomenon and obtain an image of good quality. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for focusing reflected light from an original image by a focusing lens to form an image on a CCD line image sensor and reading and inputting the original image line by line.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus for reading and inputting a manuscript image, the reflected light from the manuscript image is focused by a focusing lens and focused on a CCD (charge coupled device) line image sensor, and the manuscript image is line by line. Is read and input.

Here, the CCD line image sensor is
A large number of light receiving elements are arranged in one row, all the light receiving signals from the light receiving elements are simultaneously transferred to the CCD analog shift register, and the signals of the CCD analog shift register are transferred to the final stage charge / voltage converter (floating capacitor).
The image signals for one line are output for each pixel.

As described above, by using the CCD line image sensor, the read image is decomposed into pixels and photoelectrically converted, so that the image reading apparatus can be realized at a relatively low cost.

[0005]

By the way, in order to drive an image reading apparatus constructed by using a CCD line image sensor as described above at a high speed and obtain a high quality image, the following disadvantages are encountered. Was occurring.

First, in order to increase the operating speed of the image reading apparatus, it is basically necessary to drive the CCD line image sensor at high speed. When the CCD line image sensor is driven at high speed, the storage time (reading cycle) per line is shortened and the amount of light received by the light receiving portion of the CCD line image sensor is reduced, so that the light receiving signal output from one light receiving element is reduced. The level drops.

In order to prevent such a decrease in the level of the light receiving signal at the time of high speed driving, the sensitivity of the light receiving section may be improved, but the sensitivity of the light receiving section is limited. A drop in the signal level is unavoidable.

On the other hand, in order to obtain a high quality image, the resolution of the image needs to be good. For example, in FIG.
As shown in (a), when an image in which black and white patterns are alternately arranged in the main scanning direction (that is, the scanning direction of the CCD line image sensor) is read, if the CCD line image sensor is driven at a relatively low speed, As shown in (b) of the same figure, a read image with good resolution in which the boundaries of the black-and-white pattern clearly appear can be obtained, but when the CCD line image sensor is driven at high speed, it is shown in (c) of the same figure. As described above, a read image having a poor resolution in which the boundary of the black and white pattern becomes unclear can be obtained.

One of the causes of such a decrease in resolution is
There is an afterimage phenomenon of the CCD line image sensor.

That is, as described above, in the CCD line image sensor, all the light receiving signals from the light receiving elements of the light receiving portion are simultaneously transferred to the CCD analog shift register, and the signal of the CCD analog shift register is transferred to the charge / charge of the final stage. Sequentially transferring to the voltage conversion unit, pixel by pixel, 1
Image signals for lines are output.

Since the floating capacitor used in the final stage charge / voltage converter has a relatively high electrostatic capacitance, even if the floating capacitor is reset every time a pixel is output, the floating capacitor immediately before is reset. The charge corresponding to the image signal of the pixel remains in the floating capacitor, and as a result, an afterimage phenomenon occurs in which the influence of the immediately previous image state remains.

In particular, when the CCD line image sensor is driven at a high speed, the level of the received light signal is lowered as described above, so that the afterimage phenomenon is greatly affected.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an image reading apparatus capable of reading an image at high speed and improving the image quality at the time of high-speed reading.

[0014]

SUMMARY OF THE INVENTION The present invention is an image reading apparatus for focusing reflected light from a document by a focusing lens to form an image on a CCD line image sensor, and reading and inputting a document image line by line. The image signal output from the image sensor in pixel units is input, and the correction coefficient of the immediately preceding pixel is set to be significantly larger than the correction coefficient of the immediately following pixel based on the image signals of the immediately preceding pixel and the immediately following pixel of the target pixel to be processed. The image signal correction calculation means for executing the correction calculation and correcting the image signal of the pixel of interest is provided.

Further, in the image reading device for focusing the reflected light from the document by the focusing lens and forming an image on the CCD line image sensor, and reading and inputting the document image line by line, C
The image signal output from the CD line image sensor on a pixel-by-pixel basis is provided with image signal correction calculation means for correcting the image signal of the target pixel based on the image signal of the pixel immediately preceding the target pixel to be processed. .

Further, in the image reading device for focusing the reflected light from the original image by the focusing lens to form the image on the CCD line image sensor and reading and inputting the original image line by line, in the light receiving portion of the CCD line image sensor. The light receiving window formed in each light receiving cell is set to have a larger opening area as it is located in the main scanning end direction.

Further, in an image reading apparatus for focusing the reflected light from the original image by a focusing lens and forming an image on a CCD line image sensor to read and input the original image line by line, the above CCD is provided on the optical path of the optical system. A long opening is provided in the main scanning direction of the line image sensor to provide a shading plate for narrowing the light beam, and the opening provided in the shading plate is provided in the main scanning end direction of the CCD line image sensor. Is formed so that the opening area increases.

Further, in the image reading device for focusing the reflected light from the original image by the focusing lens to form the image on the CCD line image sensor and reading and inputting the original image line by line, the light receiving portion of the CCD line image sensor is used. Has a long ND filter in its extension direction.
The transmittance of the D filter is set to increase in the main scanning end direction of the CCD line image sensor.

[0019]

Therefore, since the influence of the image signal of the immediately preceding pixel due to the afterimage phenomenon can be removed, the resolution of the image is improved. Further, since the amount of light received by the CCD line image sensor is set to be larger toward the main scanning end direction, it is possible to eliminate a decrease in the signal S / N ratio due to the afterimage phenomenon and obtain an image of good quality. it can.

[0020]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIGS. 1A and 1B show an example of an image reading apparatus according to an embodiment of the present invention.

In FIG. 1, a document DD includes a pair of transport rollers 1 disposed upstream and downstream of a document transport direction.
By 1 ', the document is conveyed in the document conveyance direction (sub-scanning direction) while passing through the gap between the contact glass 2 and the pressure plate 2a.

An elongated light source 3 is arranged below the contact glass 2 in the main scanning direction. An image of the original DD on the reading line RL illuminated by the light source 3 is reflected by a mirror 4. Then, after passing through the opening 5a (see FIG. 2B) of the shading plate 5 for adjusting the light amount distribution, it is focused by the focusing lens 6 and focused on the light receiving portion of the CCD line image sensor 7.

In the present embodiment, the afterimage phenomenon can be reduced by performing the following correction calculation on the received light signal output from the CCD line image sensor 7.

That is, as shown in FIG. 2, the pixel of interest X (n) to be corrected and the pixel X (n) immediately before it.
−1) and the pixel X (n + 1) immediately after that, the following equation (I) is executed to form the correction signal Y (n) of the pixel of interest.

Y (n) = a · X (n) −b · X (n−1) −c · X (n + 1) (I)

Here, a, b and c are predetermined correction coefficients.

According to experiments conducted by the present inventor, the image signal output from the CCD line image sensor 7 by this correction operation is changed from a white image to a black image as shown in FIG. Also, as shown in FIG. 7B, the resolution of the image is improved at the edge portion where the black pixel changes to the white pixel.

Here, the graphs shown by the broken lines in FIGS. 3A and 3B are CCs when the correction of the formula (I) is not performed.
The change in the output from the D line image sensor 7 is shown, and the graph shown by the solid line shows the change in the output from the CCD line image sensor 7 when the correction of the formula (I) is executed. Further, in this case, the correction coefficients of the formula (I) are a = 1.3, b = 0.1, and c = 0.01, respectively.
Set to.

As described above, the fluctuation range of the solid line graph is larger than the fluctuation range of the broken line graph at both edge portions, and the image is improved so that the density difference appears clearly. I understand. That is, in this case, the resolution of the read image is improved.

FIG. 4 shows an example of a signal processing circuit according to this embodiment.

In the figure, the CCD driver 10 is a CC
It outputs various drive signals SS for driving the D-line image sensor 7. The analog image signal AV output from the CCD line image sensor 7 is converted into a digital image signal DV having a predetermined number of bits via an analog / digital converter 11, and the digital image signal DV is obtained.
Are added to the arithmetic unit 12 and the latch circuit 13.

The latch circuit 13 outputs the digital image signal D at the timing of the pixel clock EC (included in the drive signal SS) output from the CCD drive section 10 for pixel transfer.
V is latched, and its output is applied to the arithmetic unit 12 and the latch circuit 14 as a digital image signal DVa.

The latch circuit 14 latches the digital image signal DVa at the timing of the pixel clock EC, and the output thereof is output to the arithmetic section 12 as the digital image signal DVb.

Therefore, the digital image signals DV, DV
a and DVb are changed to new ones by one pixel in this order, whereby the digital image signal DV corresponds to the image signal of the pixel X (n + 1) immediately after the pixel of interest of the formula (I). DVa corresponds to the image signal of the target pixel X of the formula (I), and the digital image signal DVb corresponds to the pixel X (n-1) immediately before the formula (I).

The arithmetic unit 12 receives the input digital image signal D
V, digital image signal DVa, and digital image signal D
Vb is made to correspond to the image signals of the immediately following pixel X (n + 1), the pixel of interest X, and the immediately preceding pixel X (n−1), respectively, and the calculation of the above-mentioned formula (I) is executed to obtain the pixel of interest X. Correction signal Y (n) is calculated, and the calculation result is output to the next stage device as a digital image signal DD.

By the way, since the afterimage phenomenon is particularly affected by the immediately preceding pixel, the following equation (I) is used instead of the above equation (I).
The same effect can be obtained when I) is applied.

Y (n) = X (n) −α · X (n−1) (II)

Here, Y (n) represents the corrected image signal, X (n) represents the image signal of the pixel of interest, and X (n).
-1) represents the image signal of the immediately preceding pixel. Further, α is a correction coefficient, and a value that is sufficiently smaller than 1 is set.

FIG. 5 shows an example of the signal processing circuit in this case. In the figure, the same parts as those in FIG. 4 and corresponding parts are designated by the same reference numerals.

In the figure, the analog image signal AV output from the CCD line image sensor 7 is analog /
The digital image signal DV having a predetermined number of bits is converted via the digital converter 11, and the digital image signal DV is added to the arithmetic unit 20 and the latch circuit 13.

The latch circuit 13 latches the digital image signal DV at the timing of the pixel clock EC output from the CCD drive section 10 for pixel transfer.
The output is output as a digital image signal DVa to the multiplier 21.
Has been added to.

The multiplier 21 adds the digital image signal DVa to
The value of the predetermined correction coefficient α is multiplied, and the multiplication result is added to the calculation unit 20 as a digital image signal DVa ′.

Therefore, the digital image signals DV, DVa
(DVa ′) changes to a new one one pixel at a time in this order, whereby the digital image signal DV corresponds to the image signal of the pixel of interest X in the formula (II), and the digital image signal DVa ′.
Corresponds to the second term on the right side of the formula (II).

The arithmetic unit 20 receives the input digital image signal D
V and the digital image signal DVa ′ are added, and the addition result is a digital image signal DD ′.
It is output to the next stage device.

In this case, although the signal processing is executed by digital processing, equivalent processing can be realized by analog arithmetic processing. In that case, the latch circuit 1
A peak / hold circuit can be used as 3, and an analog multiplier can be used as the multiplier 21.
An analog subtractor can be used as the arithmetic unit 20.

6A and 6B show a CCD line image sensor 7 according to another embodiment of the present invention.

In the figure, a large number of light receiving elements are arranged in a line in the light receiving section 7a of the CCD line image sensor 7. In this light receiving section 7a, windows W1, W2, ... , Wn are formed such that the closer they are to the scanning end position of the CCD line image sensor 7, the larger the opening area thereof. Where CCD
In the line image sensor 7, the scanning operation is performed from the position indicated by "upper side" in the figure to the direction indicated by "lower side" in the figure.

As a result, for example, when the image of all white lines is read, the analog image signal AV output from the CCD line image sensor 7 is located on the upper side as shown in FIG. The pixel signal located lower than the pixel has a higher image signal level.

Therefore, for example, as shown in FIG. 7A, when an image of a black-and-white edge portion that changes from a white image to a black image is read, the CCD line image sensor 7 outputs the corresponding portion. The analog image signal AV to be reproduced is
It changes as shown in FIG.

Here, the light receiving amount of the pixel located on the upper side is smaller than the light receiving amount of the pixel located on the lower side, and the afterimage component Δi included in the analog image signal AV is the signal level ( That is, since the afterimage component Δi appears in proportion to the amount of received light, the afterimage component Δi changes for each pixel as indicated by the broken line in FIG. 7B. In this case, the afterimage component included in the signal level for each pixel. The ratio of Δi is
It is almost constant.

As described above, in this embodiment, the light receiving windows W1 to Wn of the light receiving portion 7a of the CCD line image sensor 7 are used.
The opening area of the pixel is set to be gradually increased from the upper side to the lower side, and the ratio of the afterimage component included in the analog image signal AV of each pixel is controlled to be substantially constant. The dynamic range of the signal level in the lower pixel where the influence of the afterimage component largely appears can be expanded, and the influence of the afterimage component appearing in the analog image signal AV can be significantly reduced.

As described above, the light receiving amount of the lower pixel is larger than the light receiving amount of the upper pixel, and the ratio of the afterimage component included in the signal level of each pixel becomes constant. By setting the light amount distribution, it is possible to remove the influence of the afterimage component appearing in the analog image signal AV output from the CCD line image sensor 7.

Therefore, for example, as shown in FIGS. 8A and 8B, if the light amount distribution of the light source 3 is set to be larger on the lower side than on the upper side in the above-described manner, As shown in (c), when a white image is read, CC
Since the analog image signal AV output from the D-line image sensor 7 is obtained, the influence of the afterimage component can be removed even in this case.

Here, as a method for setting the light quantity distribution of the light source 3 as shown in FIG. 8A, for example, the film thickness and the kind of the fluorescent paint applied to the inside of the tube of the fluorescent lamp used as the light source 3 are changed. It is possible to use a method of providing a filter on the surface.

Further, in FIG. 1, the mirror 4 and the focusing lens 6 are
As shown in FIG. 9, the shading plate 5 having the opening 5a 'is formed so that the opening width on the lower side is larger than the opening width on the upper side. The same effect can be obtained by using '.

That is, in this case, since the light quantity distribution of the image formed on the CCD line image sensor 7 is set so that the light quantity on the lower side is larger than the light quantity on the upper side in the above-described manner, the afterimage is generated. The influence of the components can be eliminated.

Further, as shown in FIG.
An ND (neutral density) filter 25 is provided in the light receiving portion 7a of the line image sensor 7, and the transmittance characteristic of the ND filter 25 is as shown in FIG.
The transmittance is set to be higher on the lower side than on the upper side.

As a result, the light amount distribution of the image formed on the light receiving portion 7a is set so as to be larger on the lower side than on the upper side in the above-described manner, so that the CCD line image sensor 7 outputs it. It is possible to remove the influence of the afterimage component on the analog image signal AV.

Thus, in each of the above-mentioned embodiments,
Since it is possible to remove the influence of the afterimage component included in the analog image signal output from the CCD line image sensor, CC
Even when the D-line image sensor is driven at high speed, a high-quality image can be obtained, and thus a high-speed and high-quality image reading device can be realized.

[0061]

As described above, according to the present invention,
Since the influence of the image signal of the immediately preceding pixel due to the afterimage phenomenon can be removed, the image resolution is improved. Further, since the amount of light received by the CCD line image sensor is set larger toward the main scanning end direction, the S of the signal due to the afterimage phenomenon is
The effect of being able to eliminate the decrease in the / N ratio and obtaining an image of good image quality is obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a correction calculation according to an embodiment of the present invention.

FIG. 3 is a graph for explaining that the resolution of the read image is improved by the correction calculation.

FIG. 4 is a block diagram showing an example of a signal processing circuit according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a signal processing circuit according to another embodiment of the present invention.

FIG. 6 is a schematic view illustrating the relationship between the structure of a light receiving portion of a CCD line image sensor and a signal level output from the CCD line image sensor according to still another embodiment of the present invention.

FIG. 7 is a schematic diagram for explaining the effect of the embodiment of FIG.

FIG. 8 is a schematic view for explaining a light source according to still another embodiment of the present invention.

FIG. 9 is a schematic view showing an example of a shading plate according to another embodiment of the present invention.

FIG. 10 is a schematic view showing an ND filter according to still another embodiment of the present invention.

FIG. 11 is a schematic diagram for explaining an inconvenience when an image is read using a CCD line image sensor.

[Explanation of symbols]

 3 light source 5, 5'shading plate 5a, 5a 'aperture 6 focusing lens 7 CCD line image sensor 7a light receiving unit 10 CCD drive unit 11 analog / digital converter 12, 20 arithmetic unit 13, 14 latch circuit 21 multiplier 25 ND Filter W1-Wn window

Claims (5)

[Claims] 1. An image reading apparatus for focusing reflected light from a document by a focusing lens to form an image on a CCD line image sensor, and reading and inputting a document image line by line, the CCD line image sensor outputs the image in pixel units. Image signal of the target pixel to be processed, and based on the image signals of the immediately preceding pixel and the immediately following pixel of the target pixel to be processed, a correction calculation is performed to set the correction coefficient of the immediately preceding pixel to be significantly larger than that of the immediately following pixel An image reading apparatus comprising image signal correction calculation means for correcting the image signal of 1. 2. An image reading device for focusing light reflected from a document by a focusing lens to form an image on a CCD line image sensor, and reading and inputting a document image line by line, the CCD line image sensor outputs the image on a pixel basis. An image reading apparatus comprising: an image signal correction calculation unit that corrects and calculates the image signal of the target pixel based on the image signal of the pixel immediately preceding the target pixel to be processed. 3. An image reading device for focusing reflected light from a document image by a focusing lens to form an image on a CCD line image sensor and reading and inputting a document image line by line. The document reading device is characterized in that a light receiving window formed in each light receiving cell is set to have a larger opening area as it is located in a main scanning end direction. 4. An image reading apparatus for focusing light reflected from a document image by a focusing lens to form an image on a CCD line image sensor, and reading and inputting a document image line by line, wherein the CCD is provided on an optical path of an optical system. A long opening is provided in the main scanning direction of the line image sensor to provide a shading plate for narrowing the light beam, and the opening provided in the shading plate is in the main scanning end direction of the CCD line image sensor. The image reading device is formed so that the opening area becomes larger as 5. An image reading apparatus for focusing reflected light from an original image by a focusing lens to form an image on a CCD line image sensor, and reading and inputting the original image line by line, wherein a light receiving portion of the CCD line image sensor is used. Is provided with a long ND filter in its extension direction, and the transmittance of the ND filter is set to increase in the main scanning end direction of the CCD line image sensor. Reader.