JPH02116265A - Output correcting circuit for information read circuit - Google Patents

Abstract

PURPOSE:To especially improve the reproducibility of a dark part when gradation is expressed on a recording medium by altering dark time digital data according to the change of an amplification degree, and correcting the digital data from a photoelectric converting sensor by means of the altered dark time digital data. CONSTITUTION:The change of the illuminance of an illumination light is detected by an amplification degree regulating circuit 6 as the change of a reference white level outputted from a photoelectric converting sensor 1, the amplification degree regulating circuit 6 sends an amplification degree regulating signal to an AGC amplifier 2 so that the white level may be set at a prescribed constant value, and sets the amplification degree of the AGC amplifier 2 at a new value. Correspondingly, the multiplier of a multiplying device 7 is altered, and the value obtained by multiplying the multiplier by the changing ratio of the amplification degree of the AGC amplifier 2 is made into the new multiplier. The dark time digital data multiplied by the new multiplier are converted into an analog signal voltage by a D/A converter 8, applied to a reference voltage terminal Vref of an A/D converter 3 as the new reference voltage, and the digital data can be highly accurately corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an output correction circuit for an information reading circuit, and is particularly effective for use in information reading devices such as facsimiles and image readers.

(Prior Art) FIG. 3 is a block diagram showing an example of an output correction circuit in a conventional information reading circuit. A photoelectric conversion sensor l, which includes a large number of photoelectric conversion sensor elements arranged in a row and is used for reading originals in facsimile machines, image readers, etc., is connected to an A/D converter 3 via an AGC amplifier 2 whose amplification degree can be adjusted. The A/D converter 3 sequentially supplies digital data corresponding to the read document to the output terminal 4. On the other hand, the output of the A/D converter 3 is also connected to the input of a data memory 5 and an amplification adjustment circuit 6.

=4= Next, to explain the operation of this output correction circuit, in order to memorize the output of the photoelectric conversion sensor 1 in the dark before reading a document, the illumination light (not shown) is turned off or the photoelectric conversion sensor is turned off. Block 1 from light. The output of the photoelectric conversion sensor 1 at this time, that is, the dark output is amplified by the AGC amplifier 2, and then the A/D
The digital data is digitized by the converter 3, and digital data corresponding to the dark output of the photoelectric conversion sensor 1 is stored in the data memory 5 as correction data.

Thereafter, the original is read with the illumination light turned on or the light shielded, and the digital data output from the A/D converter 3 is corrected using the correction data stored in the data memory 5.

In addition, the A/D converter 3
In order to correct the digital data from the original, a photoelectric conversion sensor 1 reads a reference white plate at the end of the original table each time one original is read. The output at this time is amplified by AGC amplifier 2,
It is digitized by an A/D converter 3. This digital data represents the own level as a reference, and is used in the amplification adjustment circuit 6.
given to. The amplification degree adjustment circuit 6 sends an output to the AGC amplifier 2 in accordance with the digital data representing the white level, and adjusts the amplification degree of the AGC amplifier 2 so that the white level is constant.

(Problem to be Solved by the Invention) In such a conventional output correction circuit, the correction data representing the dark output of the photoelectric conversion sensor 1 is stored in the data memory 5.
When the amplification degree of the AGC amplifier 22 changes after the signal is accumulated, the following problem occurs.

FIG. 3 shows that when the amplification degree of the AGC amplifier 2 is doubled after the correction data is stored in the data memory 5, the level of the output from the AGC amplifier 2 of the dark output of the photoelectric conversion sensor l is amplified. This diagram schematically shows how the temperature changes before and after the degree adjustment. In the figure, the horizontal axis represents the position of each photoelectric conversion element of the photoelectric conversion sensor 1, and the vertical axis represents the AGC.
The level of the output from amplifier 2 is taken, and if the level of the dark output when the correction data is stored in the data memory 5 before adjusting the amplification degree of AGc Ang 2 is shown by the line (A), then the level of the output from AGC amplifier 2 is After doubling the amplification degree, the level of the dark output after being amplified by the AGC amplifier rises to the line (b).

Therefore, the correction data output from the data memory 5 to correct the data read from the original should be changed in accordance with the amplification degree adjustment of the AGC angle 2.
In the conventional output correction circuit, the correction data is sent to the AGC amplifier 2.
is constant regardless of changes in the degree of amplification, so even if the data read from the original is corrected using the correction data, there is a problem in that it does not mean that accurate correction has been made.

A way to solve the problem of inaccurate correction is to frequently take out the dark output of the photoelectric conversion sensor 1 and update the correction data stored in the data memory 5 each time. To do this, there is a method of interrupting the reading of the document at each required point, turning off the illumination light, extracting the digital data from the A/D converter 3, and storing it back in the data memory 5, or any other method. There is a method in which such a light shielding mechanism is provided, and the dark output is taken out from the photoelectric conversion sensor 1 between readings of one original and the data memory 5 is updated with digital data obtained by A/D converting it.

However, the former method requires the illumination light to blink frequently, which not only shortens the life of the illumination light but also increases power consumption.

In addition, the latter method requires the installation of an extra light shielding mechanism, which has the disadvantage of complicating the mechanism and increasing cost.

The present invention has been made in view of the problems of the conventional output correction circuits described above, and includes variations in the dark output of the photoelectric conversion sensor from pixel to pixel and illuminance caused by changes in document illumination light over time and temperature changes. It is an object of the present invention to provide an output correction circuit that can simultaneously and accurately remove drift in the output of a photoelectric conversion sensor caused by changes.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a photoelectric conversion sensor that reads information contained in an object, an amplifier that amplifies the output of the photoelectric conversion sensor, and an amplifier that amplifies the output of the photoelectric conversion sensor. A/D output of
In an information reading circuit comprising an A/D converter for conversion and an output terminal to which digital data output from the A/D converter is supplied, when the photoelectric conversion sensor reads a portion representing a reference white level. detecting the level of the output from the photoelectric conversion sensor, and applying an adjustment signal representing the difference between the detected level and a predetermined level corresponding to the reference white level to the amplifier, so that the difference becomes zero. amplification adjustment means for adjusting the amplification degree of the amplifier so that the output of the photoelectric conversion sensor is changed in accordance with a change in the adjustment signal; A data correction means for supplying the digital data corrected by the dark digital data to the output terminal is provided.

An embodiment of the output correction circuit according to the present invention detects the level of digital data output from the A/D converter when the photoelectric conversion sensor reads a portion representing a reference white level, and detects the level of digital data output from the A/D converter. amplification adjustment means for applying an adjustment signal representing a difference between the level and a predetermined level corresponding to the reference white level to the amplifier, and adjusting the amplification of the amplifier so that the difference becomes zero; storage means for storing dark time digital data corresponding to the output of the photoelectric conversion sensor during dark time; and changing the dark time digital data read from the storage means in accordance with a change in the adjustment signal; data changing means for supplying a reference signal corresponding to the changed dark time digital data to the reference signal terminal of the A/D converter, and the data changing means supplies a reference signal corresponding to the changed dark time digital data to the reference signal terminal of the A/D converter, and the data changing means is provided to control the variation in the dark time output from the photoelectric conversion sensor and the target object. The A/D converter outputs digital data from which the influence of changes in illuminance of the light source that illuminates the area has been removed.

Another embodiment of the information reading circuit according to the present invention detects the level of digital data output from the A/D converter when the photoelectric conversion sensor reads a portion representing a reference white level, and detects the level of digital data output from the A/D converter. an amplification adjustment means for applying an adjustment signal representing a difference between the reference white level and a predetermined level corresponding to the reference white level to the amplifier to adjust the amplification of the amplifier so that the difference becomes zero; , storage means for storing dark time digital data corresponding to the output of the photoelectric conversion sensor during dark time, and changing the dark time digital data read from the storage means according to a change in the adjustment signal, data changing means for adding the changed dark time digital data to the digital data output from the A/D converter; The data changing means outputs digital data from which the influence of illuminance changes has been removed.

(Function) In the first invention of the present application, the amplification degree adjustment means detects the level of the output from the photoelectric conversion sensor when the photoelectric conversion sensor reads a portion representing the reference white level, and An adjustment signal representing the difference between the reference white level and a predetermined level corresponding to the reference white level is applied to the amplifier, and the amplification degree of the amplifier is adjusted so that the difference becomes zero.

The data correction means changes the dark time digital data corresponding to the output of the photoelectric conversion sensor during the dark time according to the change in the adjustment signal, and also outputs the digital data corrected by the changed dark time digital data to the output terminal. Let it be supplied.

In the second invention of the present application, the amplification adjustment means detects the level of digital data output from the A/D converter when the photoelectric conversion sensor reads the portion representing the reference white level, and adjusts the level of the detected level. An adjustment signal representing the difference between the reference white level and a predetermined level corresponding to the reference white level is applied to the amplifier, and the amplification degree of the amplifier is adjusted so that the difference becomes zero.

The storage means stores dark digital data corresponding to the output of the photoelectric conversion sensor during dark.

The data changing means changes the dark time digital data read from the storage means according to the change in the adjustment signal, and converts the reference signal corresponding to the changed dark time digital data into a reference signal of the A/D converter. Supply to the terminal.

In the third invention of the present application, the amplification adjustment means detects the level of digital data output from the A/D converter when the photoelectric conversion sensor reads the portion representing the reference white level, and An adjustment signal representing the difference between the level and a predetermined level corresponding to the reference white level is applied to the amplifier, and the amplification degree of the amplifier is adjusted so that the difference becomes zero.

The storage means stores dark time digital data corresponding to the output of the photoelectric conversion sensor during dark time.

The data changing means changes the dark digital data read from the storage means according to the change in the adjustment signal, and adds the changed dark digital data to the digital data output from the A/D converter. do.

In this way, digital data is output from which the effects of variations in dark output from the photoelectric conversion sensor and changes in illuminance of the light source illuminating the object are removed.

(Embodiments) Below, some embodiments of the output correction circuit according to the present invention will be described as a first embodiment.
This will be explained in detail with reference to FIG.

FIG. 1 is a block diagram illustrating one embodiment of the invention, with like components in FIG. 4 being designated by the same reference numerals. In the figure, the output (dark digital data) of a data memory 5 that stores correction data, which is digital data corresponding to the dark output of the photoelectric conversion sensor 1, is connected to the input of a multiplier 7. Multiplier 7 multiplies the dark digital data output from data memory 5 by a predetermined multiplier. The output of the multiplier 7 is sent to A via the D/A converter 8.
It is connected to the reference voltage terminal Vref of the /D converter 3. On the other hand, the amplification adjustment circuit 6 is connected to the AGC amplifier 2 and also to the multiplier 7 as before.

First, before starting to scan the original, calculate the output of the photoelectric conversion sensor l when the original illumination light is turned off, that is, the dark output.
The GC amplifier 2 amplifies the signal, and the A/D converter 3 performs A/D conversion. Digital data from the A/D converter 3 at this time is stored in the data memory 5. On the other hand, as in the conventional case, the amplification adjustment circuit 6 uses the own level as a reference, for example, the digital data output from the A/D converter 3 when the photoelectric conversion sensor 1 reads the reference white plate at the end of the document table. Based on this, the self level is detected, and an amplification degree adjustment signal is applied to the AGC amplifier 2 to adjust the amplification degree of the AGC amplifier 2 so that the white level is always constant. This amplification adjustment signal is also applied to the multiplier 7, and the multiplier of the multiplier 7 is determined according to this amplification adjustment signal.

At the same time as scanning of the original is started, the digital data stored in the data memory 5 is read out. The read dark digital data is multiplied by a multiplier in a multiplier 7, converted into an analog signal voltage by a D/A converter 8, and inputted to a reference voltage terminal Vref of an A/D converter 3. Therefore, the A/D converter 3 is connected to the AGC amplifier 2.
The operation of digitally converting the analog signal outputted from the data memory 5 is performed based on this analog signal voltage, that is, the analog voltage corresponding to the dark digital data from the data memory 5 multiplied by a multiplier.

The multiplier by which the dark digital data is multiplied by the multiplier 7 is:
Changed by the amplification degree adjustment signal from the amplification degree adjustment circuit 6,
Since the digital data stored in the data memory 5 is not changed for a predetermined period of time once it has been stored, even if the amplification of the dark output of the photoelectric conversion sensor 1 changes during document reading, such changes will not occur. is appropriately corrected, and the digital data output from the output terminal 4 is not adversely affected.

Next, consider a case where after digital data corresponding to the dark output of the photoelectric conversion sensor is stored in the data memory 5, the illuminance of the illumination light changes due to some cause such as aging of the illumination light or temperature change.

A change in the illuminance of the illumination light is detected by the amplification adjustment circuit 6 as a change in the reference white level output from the photoelectric conversion sensor 1. Therefore, the amplification degree adjustment circuit 6 converts the amplification degree adjustment signal into an AGC so that the own level becomes a predetermined constant value.
The signal is sent to amplifier 2 and the amplification degree of AGC amplifier 2 is set to a new value.

Along with this, the multiplier of the multiplier 7 is changed, and the new multiplier is multiplied by the change ratio of the amplification degree of the AGC amplifier 2 (the ratio of the new amplification degree to the previous amplification degree). Since it becomes a multiplier, the dark digital data output from the data memory 5 is multiplied by a new multiplier in the multiplier 7. The dark digital data multiplied by the new multiplier is D
The /A converter 8 converts the voltage into an analog signal voltage, and applies it to the reference voltage terminal Vref of the A/D converter 3 as a new reference voltage. In this way, based on the new reference voltage, A/
The D converter 3 will perform a conversion operation.

In this way, even if the amplification degree adjustment circuit 6 changes the amplification degree of the AGC amplifier 2, the multiplier of the multiplier 7 is changed to the previous multiplier multiplied by the change ratio of the amplification degree of the AGC amplifier. , an analog signal voltage corresponding to the dark digital data multiplied by a new multiplier is applied to the reference voltage terminal V ref of the A/D converter 3. In other words, the signal for correcting the data read from the original is changed in response to the change in the amplification degree of the AGC amplifier 2. Based on the digital data, the digital data from the A/D converter 3 can be corrected with high accuracy.

FIG. 2 shows another embodiment of the invention.

Although FIG. 1 uses an analog method of converting dark digital data into analog voltage, FIG. 2 uses a digital method.

In the figure, an adder 9 is arranged between the output of the A/D converter 3 and the output terminal 4 instead of the D/A converter 8, and the output of the multiplier 7 is given to the adder 9. The first point is that
This is different from the embodiment shown in the figure.

In this embodiment as well, the operations of the data memory 5, the amplification adjustment circuit 6, and the multiplier 7 are the same as in the case of FIG. Changed according to amplification adjustment, data memory 5
The dark digital data outputted from the multiplier 7 is multiplied by a multiplier and supplied to the adder 9. In adder 9,
The digital data output from the A/D converter 3 is added to the dark digital data multiplied by a multiplier, and is corrected according to the amplification degree of the 〇〇 amplifier 2.

Above, two embodiments of the output correction circuit according to the present invention have been explained using a manuscript as an example. Inventions can be applied. Further, the multiplier 7 and the adder 9 in the embodiment can be realized by ROM or by calculation by a microprocessor, and instead of detecting the reference white level by the output of the A/D converter 3, the AGC Of course, the output of the amplifier 2 may be used for direct detection.

(Effects of the Invention) The present invention adjusts the amplification degree of the amplifier that amplifies the output of the photoelectric conversion sensor so that the level of the amplifier output corresponding to the reference white level is constant, and also adjusts the amplification degree according to the change in this amplification degree. Since the dark digital data is changed using the dark time digital data, and the digital data from the photoelectric conversion sensor is corrected using the changed dark time digital data, variations in the dark time output of the photoelectric conversion sensor are corrected, and the recording paper When performing gradation expression on recording media such as, the reproducibility of dark areas in particular is dramatically improved.

In addition, even if the illuminance of the light source drifts due to aging or temperature changes, there is no deterioration in reproducibility.
High precision readings are taken.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of an output correction circuit according to the present invention. FIG. 2 is a block diagram of another embodiment of the output correction circuit according to the present invention. FIG. 3 is a block diagram of an example of a conventional output correction circuit. FIG. 4 is a diagram for explaining the operation of the output correction circuit of FIG. 3. In these drawings, like numerals indicate like elements.

Claims (1)

[Claims] 1. A photoelectric conversion sensor that reads information contained in an object, an amplifier that amplifies the output of the photoelectric conversion sensor, and an A/D converter that converts the output of the amplifier from analog to digital. an output terminal to which digital data outputted from the A/D converter is supplied; A level is detected, and an adjustment signal representing a difference between the detected level and a predetermined level corresponding to the reference white level is applied to the amplifier, and the amplification degree of the amplifier is adjusted so that the difference becomes zero. an amplification adjustment means for adjusting, and changing dark digital data corresponding to the output of the photoelectric conversion sensor in the dark according to a change in the adjustment signal, and adjusting digital data corrected by the changed dark digital data. An output correction circuit comprising: data correction means for supplying data to the output terminal. 2. A photoelectric conversion sensor that reads information contained in an object, an amplifier that amplifies the output of the photoelectric conversion sensor, an A/D converter that converts the output of the amplifier into A/D, and the A/D converter and an output terminal to which digital data output from the A/D converter is supplied, the level of the digital data output from the A/D converter when the photoelectric conversion sensor reads a portion representing a reference white level. and applying an adjustment signal representing the difference between the detected level and a predetermined level corresponding to the reference white level to the amplifier, and adjusting the amplification degree of the amplifier so that the difference becomes zero. storage means for storing dark digital data corresponding to the output of the photoelectric conversion sensor during dark; and adjusting the dark digital data read from the storage means according to changes in the adjustment signal. and data changing means for supplying a reference signal corresponding to the changed dark time digital data to a reference signal terminal of the A/D converter; An output correction circuit that causes an A/D converter to output digital data from which the effects of variations in the brightness and illuminance changes of a light source illuminating an object have been removed. 3. The data changing means includes: a multiplier that receives the dark digital data and the adjustment signal and multiplies them; and a D/A that converts the output from the multiplier into an analog voltage.
The output correction circuit according to claim 2, comprising: a converter; 4. A photoelectric conversion sensor that reads information contained in an object, an amplifier that amplifies the output of the photoelectric conversion sensor, an A/D converter that converts the output of the amplifier into A/D, and the A/D converter and an output terminal to which digital data output from the A/D converter is supplied, the level of the digital data output from the A/D converter when the photoelectric conversion sensor reads a portion representing a reference white level. and applying an adjustment signal representing the difference between the detected level and a predetermined level corresponding to the reference white level to the amplifier, and adjusting the amplification degree of the amplifier so that the difference becomes zero. storage means for storing dark digital data corresponding to the output of the photoelectric conversion sensor during dark; and adjusting the dark digital data read from the storage means according to changes in the adjustment signal. data changing means for adding the changed dark time digital data to the digital data output from the A/D converter; An output correction circuit that causes the data changing means to output digital data from which effects due to changes in illuminance of a light source illuminating an object have been removed. 5. The data changing means includes: a multiplier that receives the dark digital data and the adjustment signal and multiplies them; and an adder that adds the output from the multiplier to the output from the A/D converter. The output correction circuit according to claim 4, comprising: and.