JPH02230863A - Picture reader - Google Patents

Abstract

PURPOSE:To inexpensively carry out a shading correction by adjusting the storage time of each sensor chip of an image sensor correcting the inequality of luminous quantity distribution of a light source so as to select the period of a drive pulse. CONSTITUTION:Ten kinds of drive pulses Ta-Tj whose periods differ from each other are used as drive pulses driving a photodetector section 11 of sensor chips 9a-9j. When a light with uniform lightness is made incident on each photodetector section 11, the periods tsa-tsj of the drive pulses Ta-Tj are selected so that the levels of outputs Va-Vj are equal to each other by changing the storage time of the change. That is, the period at both ends of the image sensor is selected longer to extend the storage time, and the period tse corresponding to the sensor chip 9e at the middle part having a peak value is selected shortest to minimize the storage time. Thus, the shading is corrected inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reading device that uses an image sensor to read a document and also performs shading correction.

(Prior Art) FIG. 7 is a side view showing a conventional image reading device. In the figure, 1 is a document table made of a transparent plate such as glass, 2 is an original placed on the document table 1, and 3 is a side view of a conventional image reading device. A light source consisting of a fluorescent lamp, 4
5 is a rod lens array through which the light reflected from the original document 2 passes; 5 is an image sensor on which the light that has passed through the rod lanes array 4 is formed; and 6 is a reflection plate for shading correction arranged behind the light source 3. be. The light source 3, rod lens array 4, image sensor 5, reflection plate 6, etc. are integrally mounted in a case (not shown), and this case is mounted relative to the document table 1 in the direction of the arrow 7. It is made movable.

Figure 8 shows, for example, "How to choose and use an image sensor"
(Written by Mitsuo Oshima, January 1985, Published by Nikkan Kogyo Shimbun, p. 126, Figure 5.49)
In the figure, 6a indicated by diagonal lines is a non-reflective part made of a material that absorbs or transmits light, and 6b is a reflective part made of a material that reflects light, which is wide at both ends.
It is formed so that the width at the center becomes narrower. 8 indicates the direction of light from light source 3. Next, we will explain the operation.
The case is moved in the direction of arrow F with respect to the document table 1, and an image is formed on the image sensor 5. As a result, image signals obtained by reading the original 2 are output from the image sensor 5 line by line.

In this way, in the image reading device, from the light source 3 to the document 2,
The amount of light irradiated onto the document 2 is not uniform with respect to the main scanning direction of the image sensor 5 of the document 2. Therefore, if the original 2 is uniformly white, the 1
As shown in FIG. 9, the line image signal has a high level at the center and a low level at both ends. This phenomenon is particularly noticeable when a fluorescent lamp is used as the light source 3. In order to compensate for the above phenomenon, shading correction is performed using a reflector 6. That is, as shown in FIG.
By reducing the amount of light reflected at the center (in the axial direction of the fluorescent lamp as light source 3) and increasing the amount of light reflected at both ends,
This ensures that a uniform amount of reflected light is obtained as a whole. (Problems to be Solved by the Invention) Since the conventional image reading device is configured as described above, it uses a reflection plate 6 for performing the shedding correction, and this reflection plate 6 has a non-reflection portion 6a and a reflection plate 6. In order to form the portion 6b into the shape shown in FIG. 8, a special processing technique is required.
This has led to problems such as increased costs.This invention was made to solve the above problems, and allows shading without using a reflector that requires special processing technology. The purpose is to obtain an image reading device that can perform correction. [Means for Solving the Problems] An image reading device according to the present invention is such that when light of a predetermined brightness is incident on a plurality of sensor chips constituting an image sensor, the amount of charge accumulated in each sensor chip is approximately The periods of the drive pulses that drive the sensor chips are made to be equal to each other.

[Effect]

Each of the plurality of sensor chips in this invention accumulates a charge corresponding to the amount of light incident on each drive pulse cycle, so when uniform white light is incident, the output level from each sensor chip is approximately They become equal and the shading correction is performed. (Example) An example of the present invention will be described below. In FIG. 1, the same parts as in FIG. 7 are given the same reference numerals, and their explanation will be omitted. Reference numeral 9 denotes an image sensor driven by driving pulses having different periods, and an image of the reference standard 2 is formed through a rod de lens array 4. Note that the reflection plate 6 in FIG. 7 is omitted. FIG. 2 shows a plan view of the image sensor 9. In the figure, 10 is an insulating substrate, 9a to 9j are arranged on a straight line of length on the insulating substrate 10, and each is provided with a light receiving section that performs photoelectric conversion. The length of the ten sensor chips thus obtained is greater than the width of the document 2. X indicates the main scanning direction of the image sensor 9. As this image sensor 9, for example, a charge transfer device such as a CCD is used. Figure 's3 shows a circuit block diagram of the image sensor 9,
In the figure, 11 is a light receiving section corresponding to the sensor chips 98 to 9j, 12 is a transfer gate that takes out the charge accumulated in the light receiving section 11, 13 is a CCD channel to which the signal transferred to the transfer gate 12 is transferred, and 14 is a Drive pulse T, 2
This is a drive signal generator that generates phase drive clocks φ1, φ2, etc. FIG. 4 is a timing chart showing the operation of the circuit of FIG. 3, in which T is supplied to the transfer gate 12,
The transfer drive pulses φ1 and φ2 for reading out the charge of the light receiving section 11 and transferring it to the transfer gate 12 are two-phase drive clocks, v,+ ■b * vc++, which are supplied to the CCD channel 13 and have mutually opposite phases. - is the output of the image signal sequentially read out from each light receiving section 11.

FIG. 5 shows the respective periods tsa to ts for individually reading out each light receiving section 11 of the ten sensor chips 98 to 9j.
The drive pulses T of FIGS. 3 and 4 have drive pulses T. 〜T'' is shown as a representative.

Next, the operation will be explained. Image sensor 9 is the first
The zero sensor chips 9a to 9j are sequentially driven in the main scanning direction indicated by the arrow X in FIG. 2, so that the image signal output V. Vb, V. You can get 111. In FIGS. 3 and 4, assuming that each light receiving section 11 is driven by a common driving pulse T, the signal (charge) read out from each light receiving section 11 is once transferred to the transfer gate 12, and then A two-phase drive clock φ1. The signal is transferred to the CCD channel 13 by φ2, and one line of image signal outputs V, , V, , Vc- are sequentially obtained from the final stage amplifier.

In this case, a signal is read out from the light receiving section 11 when the driving pulse T is applied again after a period ts has elapsed since the driving pulse T was first applied.

The amount of charge read out at this time is the amount accumulated by the light incident on the period ts. Therefore, when light of uniform brightness is incident on each light receiving section 11 like a white original, the above-mentioned reflection plate 6 for shading correction
Since the accumulation time is the same in each light receiving section 11, the amount of incident light is different. Therefore, the waveform of one line of image signal obtained from this image sensor 9 is shown in FIG. 6(a). It will be shown.

The vertical dotted line in FIG. 6(a) indicates each light receiving section 11,
That is, it shows the boundaries of the outputs 1-V of the sensor chips 9a-9j. As shown in the figure, the level of the waveform of this image signal is a peak value VmaXs at the center of the main scan, a minimum value V at the right end, and a value slightly higher than ■1,1 at the left end. The non-uniformity R1 of the image signal in the case where shading correction is not performed as shown in FIG. 6(a) is generally given by the following equation.

In order to perform the shading correction according to the present invention, in this embodiment, as shown in FIG. Bars T,~T”
is used. Period tsa~ of each drive pulse T1~T''
tsj is selected to have a thickness such that when light of uniform brightness is incident on each light receiving section 11, the level of each output (1 to V) becomes equal by changing the charge accumulation time. There is. That is, at both ends of the image sensor, the cycle is lengthened to lengthen the accumulation time, and the cycle tsa corresponding to the sensor chip 9e in the center where the peak value is obtained is shortest to shorten the accumulation time. .

FIG. 6(b) shows the waveform of one line of image signals when the periods tsa to tsj are selected as described above. In this example, each output "1 to V" is approximately the peak value "II"
．． llx, and it can be seen that the shading correction has been performed. The non-uniformity R2 of the image signal in this case is
is given by In addition, by changing the accumulation time, V, > Figure 6 (a) (71V1n- - 11 (3)
Therefore, according to equations (1), (2), and (3) above,
It can be seen that R2 < Rl, and the non-uniformity of the image signal after shading correction has been improved.

In the above embodiment, the image sensor 9 is COD.
Although we have shown the case where an image sensor is used, any type of image sensor may be used as long as it has a method of accumulating electric charge. Further, in the above embodiment, the sensor chips 9a to 9j are equivalent, but even if they are different or have unequal lengths, each sensor chip can be used as described in the above embodiment. By changing the accumulation time of the chips, the same effect can be obtained by selecting the period of the drive pulse to adjust the accumulation time of each sensor chip of the image sensor so as to correct the non-uniformity of the distribution. There is no need for a specially processed reflector for shading correction,
This has the effect of being able to perform shading correction at low cost.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an image reading device according to an embodiment of the present invention, FIG. 2 is a plan view of an image sensor in the same device, FIG. 3 is a circuit block diagram of the image sensor, and FIG. 4 is a diagram of the image sensor. A timing chart showing the operation, FIG. 5 is a timing chart of drive pulses applied to the image sensor, FIG. 6 is a waveform diagram of image signals obtained before and after shading correction, and FIG. 7 shows a conventional image reading device. A side view, FIG. 8 is a perspective view showing a reflector and a light source in the same device, and FIG. 9 is an output waveform diagram of the image sensor of the same device when the reflector is not used. 2 is a document, 3 is a light source, 9 is an image sensor, 9a to 9j
is a sensor chip, T. ~Tj is the driving pulse, tsa
-tsJ is the period of the driving pulse. In addition, the same reference numerals in the figures indicate the same or equivalent parts. 〜nt゛9.

Claims (1)

[Claims] The document is irradiated with light from a light source, and the reflected light from the document is detected by an image sensor consisting of a plurality of sensor chips arranged linearly. In an image reading device configured to output an accumulated amount of charge according to the period of a driving pulse, when light of a predetermined brightness is incident on the plurality of sensor chips, each sensor chip An image reading device comprising a drive signal generation function that generates a plurality of drive pulses for driving each sensor chip, each of which is selected to have a different cycle so that the amount of charge output from the sensor chip is approximately equal. .