JPH11234517A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a dynamic range from being decreased with reduction in a luminous amount of a lighting source. SOLUTION: A sensor 10 reads an original or a reference white board. A gain control amplifier 12 amplifiers an output of the sensor 10, an A/D converter 14 receiving the output converts it into a digital signal, which is fed to a shading correction circuit 16 and a CPU 18. The CPU 18 stores a result of reading of the reference white board as initial reference data. The CPU 18 reads again the reference with board in a proper timing and compares the read result with initial reference data. When the difference between is them more than a prescribed value, a gain correction arithmetic circuit 20 changes the gain of the gain control amplifier 12.

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 reading an image on a document.

[0002]

2. Description of the Related Art Image readers are used as image scanners and as part of copiers. An image signal read by a CCD image sensor or a contact type image sensor used in an image reading device generally includes an output distortion called shading. The causes of this output distortion are 1) non-uniformity of the light amount distribution of the light source, and 2).
Peripheral light reduction corresponding to the angle of view due to the nature of the lens,
3) Non-uniformity due to variation in the amount of transmitted light of the optical system; 4)
And 5) a decrease in output in the one scanning line end direction due to the transfer efficiency of the CCD image sensor.

As a means for removing these output distortions,
There is known a shading correction technique for reading a reference plane in advance and using the read value to correct distortion of an output image signal of an image sensor.

FIG. 9 is a schematic block diagram of a conventional shading correction circuit. Prior to reading a document, a sensor (image sensor or line sensor) 110 reads a uniform white reference white plate. The analog output of the sensor 110 is converted into a digital signal by the A / D converter 112. The reciprocal converter 114 calculates the ratio (shading correction value) of the output data of the A / D converter 112 to the predetermined signal level when the reference white plate is read, for each pixel, and stores the ratio in the RAM 116. Control circuit 118
Is the reading of the reference white plate and the RA of the shading correction value.
The storage in M116 is controlled.

Next, the original is read by the sensor 110. The output of the sensor 110 is converted into a digital signal by the A / D converter 112 and applied to the multiplier 120.
The multiplier 120 outputs the output of the A / D converter 12 to the RAM 1
16 and multiplied by the shading correction value and output to the image processing circuit or the output interface.

FIG. 10 shows image signals before and after shading correction. a is the sensor 11 before shading correction
The output of 0, b is the output of the sensor 110 with respect to the reference white plate (reference white level), and c is the image signal after shading correction (the result of dividing the signal a by the reference white level b).

[0007]

When a xenon lamp is used as a document illuminating means, light amount adjustment (dimming) generally performed when a fluorescent lamp or the like is used is not performed, but is simply turned on. However, as shown in FIG. 11, the light quantity of the xenon lamp decreases from the initial light quantity in accordance with the use time due to deterioration with time. In FIG. 11, the horizontal axis indicates the use time and the vertical axis indicates the relative illuminance. As a result, the read value obtained by reading the white reference plate at the beginning and the readout value decrease as the use proceeds and the amount of light decreases, and the dynamic range becomes narrower and the S / N deteriorates as it is.

Therefore, an object of the present invention is to provide an image reading apparatus which does not cause such inconvenience.

Another object of the present invention is to provide an image reading apparatus that effectively compensates for the adverse effect of a decrease in the light amount of a light source.

[0010]

According to the present invention, there is provided an image reading apparatus comprising: a photoelectric sensor for converting an optical image into an image signal; a gain control amplifier for amplifying an image signal output from the photoelectric sensor; Shading correction means for shading correction of an image signal output from the amplifier, storage means for holding image data obtained when the reference white plate is read as initial reference data, and shading correction means for reading the reference white plate at a predetermined timing. Computing means for comparing the image data with the initial reference data to obtain a difference, and gain correcting means for correcting the gain of the gain control amplifier when the difference obtained by the calculating means is equal to or greater than a predetermined value. It is characterized by the following. By increasing the gain of the gain control amplifier in response to the decrease in the light amount of the illumination light source, it is possible to prevent the S / N from deteriorating due to the decrease in the dynamic range.

[0011]

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

FIG. 1 is a schematic block diagram showing the configuration of an embodiment of the present invention. Reference numeral 10 denotes a sensor such as a CCD line sensor, 12 denotes an amplifier whose gain can be externally controlled, that is, a gain control amplifier, 14 denotes an A / D converter for converting an analog output of the gain control amplifier 12 into a digital signal, and 16 denotes an A / D converter. D
A shading correction circuit for correcting output data of the converter 14 in accordance with a shading correction value, a CPU 18 for controlling the whole, and a gain correction arithmetic circuit 20 for controlling the gain of the gain control amplifier 12 based on a command from the CPU 18. Reference numeral 22 denotes an image processing circuit that performs image processing, for example, smoothing processing on the image signal that has been subjected to shading correction by the shading correction circuit 16.

FIG. 2 is a schematic block diagram showing the configuration of a digital copying machine using this embodiment. The image reading device 24 having the configuration shown in FIG. 1 outputs the read image data to the printer 26 and / or the image input / output control circuit 28 according to a user's instruction. The printer 26 prints out image data from the image reading device 24 on recording paper. The image input / output control circuit 28 is connected to a computer, a workstation, a telephone line, or the like, controls the image reading device 24 according to a command from a computer or the like, and outputs image data from the image reading device 24 to these devices.

FIG. 3 is a flowchart showing the operation of this embodiment. First, the image signal output from the sensor 10 to the quasi-white plate is amplified at a predetermined gain by the gain control amplifier 12, converted into a digital signal by the A / D converter 14, and stored in the CPU 18. This is the initial value of the read data of the reference white plate.

Thereafter, the reference white plate is read at an appropriate timing (S1), the read image data is compared with the initial data in the CPU 18 (S2), and the difference affects a predetermined value, that is, the read result. When the difference is considered to be exerted (S3), the gain amount of the gain control amplifier 12 is adjusted by the gain correction operation circuit 20 so that the read data of the reference white plate becomes substantially the same as the initial read data. Calculation and correction (S4).

The shading correction circuit 16 obtains a shading correction coefficient from an average value obtained by reading the reference white plate a plurality of times. However, in the configuration in which the gain of the gain control amplifier 12 is increased according to the decrease in the light amount as in the present embodiment, the output of the sensor 10 is amplified with a large gain according to the decrease in the light amount. It will be amplified at the same time. Therefore, if the number of times of reading the reference white plate is small, the shading correction coefficient includes noise that cannot be ignored, and vertical streaks appear in the image after the shading correction. Thus, in the present embodiment, the number of times of reading the reference white plate for shading correction is increased according to the gain setting value corrected by the gain correction calculation circuit 20.

For example, assuming that the number of times of reading the reference white plate for shading correction is 16 at the beginning, when the gain G corrected by the gain correction operation circuit 20 is between the gain set value G1 and the gain G2, the reference white plate is read. When the number of plate readings is 24, and when the gain setting value is between G2 and G3, the number of reference white plate readings is 32. The shading correction coefficient is calculated from the average value of.

The output of the sensor 10 when reading a document is amplified by a gain control amplifier 12, converted into a digital signal by an A / D converter 14, and applied to a shading correction circuit 16. Shading correction circuit 1
6 performs shading correction on the output image data of the A / D converter 14 using the shading correction coefficient obtained by the above-described arithmetic processing. The output of the shading correction circuit 16 is
It is applied to the image processing circuit 22. The image processing circuit 22
For example, in order to absorb variations in image data for each pixel, the image data is smoothed between three adjacent pixels in the main scanning direction. In this embodiment, since the original image signal is amplified by the gain control amplifier 12, the noise of the circuit and the like is also amplified at the same time. As a result, the variation of the image data for each pixel increases, and the image is roughened by the normal smoothing.

Therefore, in the present embodiment, three adjacent pixels are smoothed by changing the smoothing parameter in accordance with the gain setting value corrected by the gain correction arithmetic circuit 20. The pixel values of three adjacent pixels are D (n-1), D
(N) and D (n + 1), the smoothing coefficients are initially set to 2/16, 12/16 and 2/16, respectively.
The pixel value D ′ (n) after smoothing is represented by D ′ (n) = (2/16) D (n−1) + (12/16) D (n) + (2/16) D ( n-1), and when the gain G corrected by the gain correction operation circuit 20 is between the gain set values G1 and G2, the smoothing coefficients are set to 3/16, 10/16 and 3/16, respectively.
The pixel value D ′ (n) after smoothing is represented by D ′ (n) = (3/16) D (n−1) + (10/16) D (n) + (3/16) D ( n-1), and when the gain G is between the gain set values G2 and G3, the smoothing coefficients are set to 4/16, 8/16 and 4/16, respectively, and the pixel value D '(n ) Is D ′ (n) = (4/16) D (n−1) + (8/16) D (n) + (4/16) D (n−1).

As described above, by changing the smoothing coefficient in accordance with the gain of the gain control amplifier 12, the reading can suppress the noise component of the image signal and can reduce the image roughness.
This type of image roughness is not noticeable when printing characters, so it is preferable to change the smoothing coefficient only when printing an image such as a halftone original or a photograph.

In this embodiment, the smoothing coefficient is changed by focusing on smoothing of three pixels in the main scanning direction.
May be changed according to the set gain.

Since the attenuation of the light quantity of the xenon lamp progresses very slowly, this correction may be performed immediately after the power is turned on, before or after the copy job, or at an appropriate timing when the job is not performed.

According to the present embodiment, it is possible to correct the shift of the reference image signal caused by the deterioration of the xenon lamp with time, and at the same time, to reduce the shading value noise and the image roughness caused by the amplification.

FIG. 4 is a schematic block diagram of a second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In the present embodiment, the CPU 30 is required to determine the necessity of replacing the xenon lamp, and the display panel 32 displays the lamp replacement.

FIG. 5 is a flowchart showing the operation of the embodiment shown in FIG. S11 to S14 are exactly the same as S1 to S4 in FIG. In this embodiment, after adjusting the gain of the gain control amplifier 12, it is determined whether or not the gain setting value of the gain control amplifier 12 exceeds a predetermined value A. If the gain setting value exceeds the predetermined value A (S17), xenon A message urging the replacement of the lamp is displayed on the display panel 32 (S18).

FIG. 6 shows the gain control amplifier 12 with respect to time.
5 is a schematic diagram showing a relationship between a change in the gain setting value and a threshold value A, wherein the vertical axis represents the gain setting value and the horizontal axis represents time.

With this configuration, the user or the administrator can be notified of the time for replacing the xenon lamp accurately.

Further, when the gain setting value further increases, the reading operation may be stopped and the replacement of the xenon lamp may be prompted. FIG. 7 shows an operation flowchart modified in such a manner. Steps having the same operations as those in FIG. 5 are denoted by the same reference numerals.

When the gain setting value of the gain control amplifier 12 becomes larger than the first threshold value A (S1).
7) A message urging the replacement of the xenon lamp is displayed on the display panel 32 (S18). Up to this point, it is the same as FIG.

When the xenon lamp deteriorates and the gain setting value reaches a value B indicating that the xenon lamp has deteriorated so that the image quality can no longer be guaranteed (S19), the reading operation is stopped, and the reading operation is stopped. An error message prompting the user or administrator to replace the xenon lamp is displayed on the display panel 32 (S20).

FIG. 8 shows the gain control amplifier 12 with respect to time.
5 is a schematic diagram showing a relationship between a change in gain setting value and threshold values A and B, wherein a vertical axis indicates a gain setting value and a horizontal axis indicates time.

With this configuration, it is possible to accurately notify the user or the administrator of the life of the xenon lamp, and to prevent a load on the power supply side (abnormal operation of the power supply) due to a failure in lighting of the xenon lamp. .

[0033]

As can be easily understood from the above description, according to the present invention, it is possible to prevent a decrease in dynamic range and a deterioration in S / N caused by a decrease in the amount of light of an illumination light source. In addition, the user can be properly notified of the replacement of the illumination light source.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a schematic configuration block diagram of a digital copying machine using the present embodiment.

FIG. 3 is an operation flowchart of the embodiment.

FIG. 4 is a schematic block diagram of a second embodiment of the present invention.

FIG. 5 is an operation flowchart of the embodiment shown in FIG. 4;

FIG. 6 is a schematic diagram showing a time change of a gain setting value of the gain control amplifier 12.

FIG. 7 is an operation flowchart of a modification of the embodiment shown in FIG. 4;

FIG. 8 is a schematic diagram showing threshold values A and B in FIG. 7;

FIG. 9 is a schematic block diagram of a conventional example.

FIG. 10 shows examples of image signals before and after shading correction.

FIG. 11 is a schematic diagram of a temporal change of a light amount of a xenon lamp.

[Explanation of symbols]

10: Sensor 12: Gain control amplifier 14: A / D converter 16: Shading correction circuit 18: CPU 20: Gain correction operation circuit 22: Image processing circuit 24: Image reading device 26: Printer 28: Image input / output control circuit 30 : CPU 32: Display panel 110: Sensor (image sensor or line sensor) 112: A / D converter 114: Reciprocal converter 116: RAM 118: Control circuit

Claims (6)

[Claims] 1. A photoelectric sensor for converting an optical image into an image signal, a gain control amplifier for amplifying an image signal output from the photoelectric sensor, and a shading correction for shading correction of the image signal output from the gain control amplifier. Means for storing image data obtained by reading the reference white plate as initial reference data; and comparing the image data obtained by reading the reference white plate at a predetermined timing with the initial reference data to determine a difference. An image reading apparatus comprising: a calculating means for calculating; and a gain correcting means for correcting a gain of the gain control amplifier when a difference obtained by the calculating means becomes a predetermined value or more. 2. The reading of the reference white plate is performed before or after a copy job, at an appropriate interval during which the job is not performed, at a warm-up time when the main body is turned on, or at an appropriate interval of the copy count. The image reading device according to claim 1. 3. The shading correction means according to a gain setting value set by the gain correction means,
The image reading device according to claim 1, wherein the number of times of reading the reference white plate for shading correction is increased, and a shading correction coefficient is calculated from an average value of the read values. 4. The image reading apparatus according to claim 1, further comprising image processing means for changing an image processing parameter according to a gain set value set by said gain correction means. 5. The image according to claim 1, further comprising an exchange message display unit for displaying a message prompting the exchange of the illumination light source when the gain setting value set by the gain correction unit becomes larger than the first threshold value. Reader. 6. An error for stopping reading operation and instructing replacement of said illumination light source when a gain setting value set by said gain correction means becomes larger than a second threshold value larger than said first threshold value. 6. The image reading apparatus according to claim 5, further comprising an error message display unit for displaying a message.