JPH10117277A - Shading correction circuit and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shading correction circuit, which has a small nonlinear error in A/D conversion and also has no breakage of elements of a light source by storing the read result of a reference white plate that is obtained via the photoelectric transfer tube and controlling the bias voltage of the tube based on the stored read result. SOLUTION: Before an original is read, a reference white plate is read and an equalizer 5 takes an average of several lines to store it in a memory 6. The output of the memory 6 is converted into an analog signal by a D/A converter 7, and the high-frequency component of the analog signal is eliminated by an LPF 8. When the original is read, the voltage outputted from the LPF 8 is selected by a selector 9 and inputted to a power supply 11 which shows the input/output characteristic, where the control voltage Vc is proportional to the drive voltage Vb. The relation Vb=K.Vc exists between the voltage Vc and Vb. Therefore, if the voltage Vc varies for a period from the start and end of read of an original, the voltage Vb and thereafter the bias voltage of a photoelectric transfer tube vary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a shading correction circuit and a shading correction method, and more particularly to a shading correction circuit and a shading correction method used for an image scanner.

[0002]

2. Description of the Related Art In general, a scanner device is an image input device that optically reads newspaper advertisements, black and white photographs, etc., converts them into electric signals, and inputs them to a host computer. This scanner apparatus has various image processing functions for electrically correcting a dark original, a blurred photograph, and the like, in addition to a function of faithfully reading an original.

A conventional shading correction circuit used in this scanner will be described with reference to the drawings. FIG. 4 is a block diagram showing a configuration of a scanner device including a conventional shading correction circuit. The illustrated scanner device includes a photomultiplier tube power supply (Ppm) 11 controlled by a reference voltage Vp, and a photomultiplier tube (PM) 1 driven by an output voltage Vb (bias voltage) of the power supply 11. A current-voltage converter (I / V) 3 for converting the output current Ii of the PM 1 into a voltage, an analog / digital converter (A / D) 2 for converting an analog signal to a digital signal, A selector (SEL) 4 for switching a destination of an output signal to an output section of an output image signal or an averaging unit 5 by a control signal S2.

The scanner shown in FIG. 1 has an averager (AVE) 5 for averaging several lines of an image signal, and a memory for storing an output signal of the averager 5 (AVE). MEM) 6, a digital-to-analog converter (D / A) 7 for converting an input digital signal into an analog signal and outputting the same, a low-pass filter (LPF) 8 for removing high-frequency components, a reference voltage Vp and an LPF 8 A selector (SEL) 9 for switching the output signal between the two by the signal S1 and outputting the same, and a CPU 10 for controlling the output of the control signals S1 and S2.

The light source of the photomultiplier tube 1 is not shown. A semiconductor laser element or the like is used as the light source.
Then, the light emitted from this light source is collected by a lens,
By reflecting the light on a deflecting polygon mirror, a document or the like on an image forming surface is scanned. During this scanning, the reflected light of the original is converted into a current by the photomultiplier 1.

The following operation is performed in the scanner having the above configuration.

Before reading an original, the following preprocessing is performed. First, the CPU 10 sets the reference voltage V
p, the selector 4 outputs the control signals S1 and S2 so that the output selects the averager 5 side. In this state, the reference white plate is read. The output signal Ii of the photomultiplier tube 1 obtained by this reading is input to the current-voltage converter 3 and the voltage Vi
Becomes This voltage Vi is input to the Vi terminal of the converter 2 and is converted into a digital signal.

Further, the result of averaging the signals of the reference white plate for several lines by the averaging unit 5 is stored in the memory 6.
Thereafter, the CPU 10 switches and outputs the signals S1 and S2 so that the selector 9 selects the filter 8 side and the selector 4 selects the output image signal side.

Next, the original is read. The output signal Ii of the photomultiplier 1 is input to the current-to-voltage converter 3 to be a voltage Vi, and is input to the Vin terminal of the converter 2. At the same time, the signal read from the memory 6 is synchronously input to the reference voltage input terminal Vr of the converter 2 via the converter 7 and the filter 8. By doing so, a shading-corrected digital signal can be obtained from the output terminal Vout of the converter 2.

[0010]

In the conventional shading correction circuit described above, the analog-to-digital converter 2
Is varied. For this reason, the converted digital signal has a disadvantage that the non-linear error is likely to be large, which adversely affects the image quality of the read original.

The reason why the averaging unit 5 averages several lines of the image signal is that a correct signal cannot be obtained if foreign matter such as dust adheres to the reference white plate to be read. It is.

A technique for solving such a drawback is described in Japanese Patent Application Laid-Open No. 56-93384. However, since the output of the semiconductor laser device as a light source is controlled in the publication, the input to the semiconductor laser device becomes excessive depending on the amount of shading correction, and there is a disadvantage that the device is destroyed. Further, there is a disadvantage that it takes time to replace the broken element.

In Japanese Patent Application Laid-Open No. 3-106178, the reference voltage of the digital-to-analog converter is controlled. As in the case of the above-mentioned prior art, the non-linear error is likely to be large, and adversely affects the image quality of the read original. There is a disadvantage of giving.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has as its object to reduce the non-linearity error caused by analog-to-digital conversion and to destroy light source elements. It is an object of the present invention to provide a shading correction circuit and a shading correction method that do not have any problem.

[0015]

A shading correction circuit according to the present invention is a shading correction circuit for performing shading correction on an output of a photoelectric conversion tube for outputting a signal corresponding to an input light amount. A power supply voltage control means for controlling a bias voltage of the photoelectric conversion tube according to a result of reading the object to be read is included.

The shading correction method according to the present invention comprises:
A shading correction method for an output of a photoelectric conversion tube that outputs a signal corresponding to an input light amount, wherein a step of reading a reference reading target by the photoelectric conversion tube, and a bias voltage of the photoelectric conversion tube according to the read result. Controlling).

According to the present invention, instead of controlling the output of the light source or the reference voltage of the analog-to-digital converter, the bias voltage of the photomultiplier is controlled to be changed. As a result, the non-linearity error due to the correction is small, and the elements of the light source are not destroyed.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a shading correction circuit according to the present invention, and shows a configuration when the shading correction circuit is used in a scanner device. In this figure, the same parts as those in FIG. 4 are indicated by the same reference numerals.

In this figure, this circuit is different from the conventional circuit (FIG. 4) in that it does not control the reference voltage of the analog-to-digital converter but changes the bias voltage of the photomultiplier tube. is there. That is, the reference voltage input terminal V of the analog / digital converter 2
The reference voltage Vp input to r is kept constant. Then, the power supply 11 for the photomultiplier is controlled by the control voltage Vc, which is switched between the reference voltage Vp and the output of the low-pass filter 8 by the selector 9, to obtain the drive voltage (bias voltage) Vb of the photomultiplier 1. I do. As described above, since the bias voltage of the photomultiplier tube 1 is controlled in accordance with the result of reading the reference white plate in the preprocessing described above, the non-linearity error due to the correction is small, and the light source element is destroyed. There is no.

The operation of the shading correction circuit having such a configuration will be described with reference to FIGS.

As a pre-process for reading an original, a reference white plate is read, an average of several lines is averaged by an averaging unit 5 and stored in a memory 6. After the output of the memory 6 is converted into an analog signal by a digital / analog converter 7, a high-frequency component is removed by a low-pass filter 8. The operation so far is the same as the conventional operation.

When reading an original, the voltage output from the filter 8 is selected by the selector 9 and input to the power supply 11.
The power supply 11 exhibits input / output characteristics in which the control voltage Vc and the drive voltage Vb are proportional, as shown in FIG. Therefore,
The control voltage Vc and the drive voltage Vb have the following relationship: Vb = K · Vc (1) Accordingly, when the control voltage Vc changes from the start to the end of the reading of the document, the drive voltage Vb also changes. Note that K in Expression (1) is a constant.

Here, it is assumed that the drive voltage Vb, which is the bias voltage of the photomultiplier tube 1, changes as shown in FIG. Then, since the drive voltage Vb of the photomultiplier tube 1 and the output current Ii are in a proportional relationship as shown in FIG. 2A, the output current Ii is indicated by a solid line J in FIG. Change as you do.

The output current before the shading correction changes as shown by a broken line H in FIG. In contrast,
The output current after the shading correction is corrected as shown by the solid line J in FIG. 3B, and the output current with respect to a constant amount of incident light on the photomultiplier tube 1 can be made constant.

Therefore, the output current Ii of the photomultiplier tube 1
Is changed to the voltage Vi by the current-to-voltage converter 3 in the next stage, and the digital signal converted by the analog-to-digital converter 2 is subjected to shading correction.

Thus, according to the present circuit, the reference voltage Vp is input to the reference voltage input terminal Vr of the analog / digital converter 2 to fix the voltage value, and the nonlinear voltage of the converter 2 due to the fluctuation of the reference voltage. Sex errors are minimized. Further, by correcting a shading phenomenon caused by a change in the amount of light incident on the photomultiplier tube 1 and a shading phenomenon due to a variation in characteristics of the photomultiplier tube 1, an output image signal faithful to the read original can be obtained. It is. Since the light source elements are not controlled, the light source elements are not destroyed by any shading correction.

In short, the shading correction circuit is a shading correction circuit that performs shading correction on the output of the photoelectric conversion tube that outputs a signal corresponding to the amount of input light, and according to the result of reading the reference reading target by the photoelectric conversion tube. Thus, the bias voltage of the photoelectric conversion tube is controlled. In this circuit, first, a correction method is realized by a step of reading a reference reading target by a photoelectric conversion tube and a step of controlling a bias voltage of the photoelectric conversion tube according to the read result.

Although the present invention has been described with reference to the case where the present invention is applied to a scanner device, it is apparent that the present invention can be applied to other devices, such as a printer device, a plotter device, a copying device, and a facsimile device. is there.

The present invention can take the following aspects in connection with the description of the claims.

(1) A conversion means for converting an analog signal output from the photoelectric conversion tube into a digital signal, wherein a reference signal used for the conversion is fixed at a constant level. A shading correction circuit as described.

(2) a memory for storing the read result;
The conversion device further includes another conversion means for converting a digital signal, which is stored in the memory, into an analog signal, and a filter for removing a high-frequency component of the signal after the conversion. 3. The shading correction circuit according to claim 1, wherein said bias voltage is controlled.

[0033]

As described above, the present invention does not control the output of the light source or the reference voltage of the analog-to-digital converter, but controls the bias voltage of the photomultiplier to change the analog-to-digital value. There is an effect that the non-linearity error due to the conversion is small and the elements of the light source are not destroyed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a scanner device including a shading correction circuit according to an embodiment of the present invention.

FIG. 2 is an input / output characteristic diagram of a power supply for a photomultiplier tube in FIG.

3A is a characteristic diagram of a driving voltage versus an output current of a photomultiplier tube, and FIG. 3B is a diagram illustrating a relationship between an output current before shading correction of the photomultiplier tube and an output current for correcting the shading correction. FIG. 3C is a diagram showing an input voltage characteristic of a photomultiplier tube power supply for generating a correction drive voltage.

FIG. 4 is a block diagram illustrating a configuration of a scanner device including a conventional shading correction circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photomultiplier tube 2 Analog-digital converter 3 Current-voltage converter 4,9 Selector 5 Averager 6 Memory 7 Digital-analog converter 8 Low-pass filter 10 CPU

Claims (4)

[Claims] 1. A shading correction circuit for performing shading correction on an output of a photoelectric conversion tube for outputting a signal corresponding to an input light amount, wherein the photoelectric conversion tube performs a shading correction on the basis of a result of reading a reference reading target by the photoelectric conversion tube. A shading correction circuit comprising power supply voltage control means for controlling a bias voltage of a tube. 2. The shading correction circuit according to claim 1, wherein the reference reading target is a reference white plate. 3. A shading correction method for an output of a photoelectric conversion tube that outputs a signal corresponding to an input light amount, wherein a step of reading a reference reading target by the photoelectric conversion tube, and the photoelectric conversion according to the reading result. Controlling the bias voltage of the tube. 4. The shading correction method according to claim 3, wherein the reference reading target is a reference white plate.