JPH08223411A - Image reader - Google Patents

Abstract

PURPOSE: To read a stable image without unevenness in the brightness by starting image read operation based on the result of detection of a means detecting that an output level of a sensor exceeds a prescribed value when a reference density plate is read. CONSTITUTION: A lighting means 1 lights a read object 2 or a reference density plate 8 and its image is formed on a sensor 5 through an optical system such as a mirror 3 and a lens 4 and the sensor 5 converts the image into an electric signal 10. Furthermore, a sensor output signal is given to an A/D converter 12 thorough a sample-and-hold circuit 11, in which the signal is converted into a digital image signal 13 and the signal is stored in an image memory 14. A detection means 21 compares digital image data 13A equivalent to one line with a prescribed value Vref every time the data are stored in a specific area of the image memory 14 and when in excess of the prescribed value Vref , a command 22 is given to a drive device 9 to conduct scanning. Since the image read operation is started, the lighting luminous quantity is made stable and the stable image without uneven brightness is obtained.

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 the fluctuation of the illumination light quantity immediately after the illumination means is turned on.
The present invention relates to a technique for obtaining a stable image without uneven brightness.

[0002]

2. Description of the Related Art An image reading device is widely known as a device for converting an appropriate image to be read into an electric signal including photographs, printed matter, various documents, and other three-dimensional objects.

<Outline of Apparatus> FIG. 5 is a diagram showing a main structure of a conventional image reading apparatus. As shown in the figure, in this device, a reading target 2 is read by an illumination means 1 such as a fluorescent lamp.
Is illuminated, the image is formed on the sensor 5 through the optical system such as the mirror 3 and the lens 4, and the sensor 5 converts the image into an electric signal 10.

An electrical signal output from the sensor 5 (hereinafter,
Since the sensor output signal 10 is an analog signal, it is given to the A / D converter 12 through the sample and hold circuit 11 so that signal processing using digital technology can be performed. It is converted to digital image data 13) and stored in the image memory 14.

The digital image data stored in the image memory 14 is supplied to a monitor television, a printer, and various other devices as it is or after being subjected to appropriate signal processing as necessary.

The sensor 5 is an assembly of image pickup devices such as CCD, and includes a one-dimensional array of line sensors and a two-dimensional array of area sensors. Since a line sensor is normally used, the illumination means 1, the mirror 3 and the lens 4 are provided together with the sensor 5.
Are integrated into an image reading unit 6, and the image reading unit 6 and the reading target 2 are driven by the drive mechanism 9 under the control of the control circuit 15 in the longitudinal direction of the sensor 5 (the arrangement direction of the image pickup elements). Relative to the direction perpendicular to. By this movement, the sensor 5 can scan and read the entire image of the reading target 2 having a planar spread. Note that this relative movement direction is called the sub-scanning direction.

The reading target 2 is opposed to the image reading unit 6.
A window 7 formed of a transparent member such as glass is installed to mount the.

The control circuit 15 is composed of a microcomputer, and in addition to signal processing such as correction and compression of digital image data in the image memory 14, the operation panel 1 is also provided.
On / off (power on / off) control of the illuminating means 1 and scan control of the drive mechanism 9 are performed based on the operation command from the driver 6 or the like.

Specifically, when the operator gives a driving command, the control circuit 15 turns on the illumination means 1, then controls the drive mechanism 9 to start the relative movement in the sub-scanning direction, and the image is displayed. Start a read operation. This allows the sensor 5
Scans the read object 2 and reads the entire image. After the reading is completed, the drive mechanism 9 is returned to the starting point position in the sub scanning direction. In addition, the power supply of the lighting unit 1 is cut off.

<Instability of Intensity of Illumination Light and Countermeasures> However, immediately after the illumination means 1 is turned on, the amount of illumination light is unstable, and this tendency is remarkable because a fluorescent lamp has a strong temperature dependency. is there. Therefore, when the image reading operation is started immediately after the power supply to the illumination unit 1 is turned on, the illumination light amount is not stable, so that the shading and the like are included along with the movement (scanning) of the sensor 5 in the sub-scanning direction. There is a problem in that an image having uneven brightness is read and it is necessary to perform the image reading operation again, which is troublesome.

As a measure against the uneven brightness in the above-mentioned image, Japanese Patent Laid-Open No. 3-285448 and Japanese Patent Publication No. 2-15.
There are techniques disclosed in Japanese Patent Publication No. 146 and Japanese Patent Publication No. 62-50869. Hereinafter, these outlines will be described.

In the technique disclosed in Japanese Patent Laid-Open No. 3-285448, after the fluorescent lamp is turned on, the inclination of the illumination light amount change is detected from the change in the output level of the image reading sensor when the reference density object is received. The image reading operation is not started and waits until the inclination of the change in the illumination light amount becomes almost zero. However, even if the inclination of the change of the illumination light amount becomes zero, the illumination light amount itself does not always reach the predetermined value. In such a case, the illumination is insufficient and a dark image may be read. However, it is not possible to read a stable image with no unevenness in brightness.

In the technique disclosed in Japanese Patent Publication No. 2-15146, a photoelectric conversion element dedicated to detecting the light amount is used in addition to the image reading sensor, and the output signal of the photoelectric conversion element is differentiated to change the illumination light amount. The rate is measured, and after the light source is turned on, the image reading operation is not started and waits until the rate of change of the illumination light amount decreases to a predetermined level. Therefore, also in the case of this technique, as in the case of Japanese Patent Laid-Open No. 3-285448, even if the rate of change of the illumination light amount drops to a predetermined level, the illumination light amount itself does not always reach the predetermined value. However, a dark image may be read due to insufficient illumination.

In the technique disclosed in Japanese Patent Publication No. 62-50869, it is checked whether or not the current supplied to the illumination lamp reaches a steady value, and the image reading operation is not started until the steady value is reached. stand by. However, in the case of a fluorescent lamp, the amount of light varies greatly depending on the temperature of the fluorescent lamp itself, so it is not preferable to judge that the amount of illumination light is stable even if the current reaches a steady value, and there is no unevenness in brightness. It cannot read a stable image.

Further, in any of the techniques disclosed in Japanese Patent Laid-Open No. 3-285448 and Japanese Patent Publication No. 2-15146, when the illumination light quantity vibrates over time, the inclination of the change in the illumination light quantity is once. It is not always effective because the amount of illumination light may fluctuate greatly even after it has become zero or after the rate of change of the amount of illumination light has once dropped to a predetermined level.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus which can solve the above-mentioned problems of the prior art and can read a stable image without uneven brightness.

[0017]

Means for Solving the Problems A first method for solving the above problems is described below.
According to the configuration of the invention described above, in an image reading apparatus including an illuminating unit that illuminates the reading target and the reference density plate, and a sensor that reads the reading target and the reference density plate, the output level of the sensor when the reference density plate is read is The image reading device is characterized in that it has a detecting means for detecting that the value exceeds a predetermined value, and starts the image reading operation based on the detection result.

Further, according to the second aspect of the invention, in the image reading apparatus including the illuminating means for illuminating the reading object and the reference density plate, and the sensor for reading the reading object and the reference density plate, the reference density plate is repeatedly read. When the output level of the sensor has converged within a predetermined range defined by a predetermined lower limit value and an upper limit value, a detection means is provided, and the image reading operation is started based on the detection result. Is an image reading device.

Further, in the structure of the third invention, the detecting means in the second invention detects peak values of peaks and troughs of the output of the sensor, and two consecutive peak values. It is characterized by comprising a convergence determination means for determining that the output level of the sensor has converged within a predetermined range when it is between the predetermined lower limit value and the upper limit value.

[0020]

The output level of the sensor when the reference density plate is read takes a value according to the amount of illumination light. Therefore, a predetermined value is obtained from the sensor output level when the lighting means is stable after the power is turned on in advance by an experiment or the like, so that the image reading operation is started after the sensor output level exceeds the predetermined value during actual device operation. By doing so, a stable image with uniform brightness can be obtained.

When the amount of illumination light vibrates,
Similarly, by experimentally determining the predetermined lower and upper limits from the fluctuations in the sensor output level until the lighting means stabilizes after the power is turned on by experiments, etc. If the image reading operation is started after the light has converged within the range, a stable image with no uneven brightness can be obtained.

Basically, any means may be used for detecting that the light has converged within a predetermined range, but as one method example, peaks and troughs (or valleys) of the output of the sensor when the reference density plate is repeatedly read (or, If two consecutive peak values (valley and mountain) are between the lower limit value and the upper limit value, it can be determined that they have converged.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings with reference to the drawings. In the drawings, FIG. 1 shows the configuration of the main part of the image reading apparatus according to the first embodiment of the present invention, and FIG. 2 shows the waveform for explaining the operation thereof. Further, FIG. 3 shows a configuration of a main part of an image reading apparatus according to the second embodiment of the present invention, and FIG. 4 shows a waveform for explaining the operation thereof.

<First Embodiment> An image reading apparatus of the embodiment shown in FIGS. 1 and 2 will be described. In FIG. 1, the image reading apparatus of the present embodiment includes an illuminating means 1 such as a fluorescent lamp and a mirror 3.
And an optical system such as a lens 4, a sensor 5, a window 7 made of a transparent member, a reference density plate 8 of uniform density, for example, all white, a drive mechanism 9, a sample and hold circuit 11, and A / D conversion. It is composed of a container 12, an image memory 14, an operation panel 16, and a control circuit 20. Further, the control circuit 20 is provided with a detection means 21 using a comparator. As can be seen by comparing FIGS. 1 and 5, the image reading apparatus of this embodiment is different from the apparatus of FIG. 5 with respect to the reference density plate 8 and the control circuit 20, and therefore, the same reference numerals are given to the same functional units. It is attached.

That is, in FIG. 1, the object to be read 2 or the reference density plate 8 is illuminated by the illumination means 1, and the image thereof is formed on the sensor 5 through the optical system such as the mirror 3 and the lens 4, and the same sensor 5 is used. The image is converted into an electrical signal 10.
Further, the sensor output signal 10 is input to the A / D converter 12 through the sample and hold circuit 11, converted into digital image data 13 and stored in the image memory 14.

In this embodiment, the sensor 5 is a line sensor, and the sensor 5 is integrated with the illumination means 1 and the optical systems 3 and 4 to form an image reading section 6, and the image reading section 6 is driven by a driving mechanism 9. It is assumed that the sensor 5 scans the entire image of the reading target 2 while moving in the sub-scanning direction.

The reference density plate 8 is also used for shading correction, has a size corresponding to the field of view of the sensor 5, and has the mirror 3 of the image reading unit 6 at the starting position in the sub-scanning direction.
Are arranged so as to face each other.

The control circuit 20 is constituted by using a microcomputer, and in addition to signal processing such as correction and compression of the digital image in the image memory 14, the control circuit 20 operates the illuminating means 1 based on an operation command from the operation panel 16 or the like. On / off control is performed, and scan control is performed on the drive mechanism 9 to start the image reading operation based on the detection result of the detection means 21.

That is, when the operator gives a driving command, the control circuit 20 powers on the illuminating means 1, but initially the driving mechanism 9 is not operated and is stopped at the starting point position in the sub-scanning direction. In this state, the sensor 5 reads the reference density plate 8 at a constant cycle, and each time, the sensor output signal 10 for one line is converted into digital image data 13A by the A / D converter 12, and the specific area of the image memory 14 is converted. To overwrite and store. The digital image data 13A is equivalent to the sensor output signal 10, and in general, the digital image data 13A monotonically increases as time passes after the lighting means 1 is turned on, as shown in FIG.

Therefore, the detecting means 21 uses the image memory as described above.
One line worth of data is stored in a specific area of memory 14 each time.
The digital image data 13A is set to a predetermined value V_refCompared with predetermined
Value V _refWhen it exceeds, give a command 22 to the drive mechanism 9
Perform scan operation. This makes the image reading operation
Start.

When the image reading operation is started, the sensor 5 reads the image of the reading object 2 while scanning, and the sensor output signal 10 of each line is converted into digital image data 13 by the A / D converter 12 one after another, and the image is read. It is stored in the memory 14.

The control circuit 20 uses the digital image data 13A just when it exceeds the predetermined value V _ref as shading correction data, and performs shading correction on the digital image data 13 of each line when the reading target 2 is read. .

[0033] Here, when comparing the predetermined value V _ref digital image data 13A, the value of each pixel of the digital image data 13A is compared with a predetermined value V _ref, if exceeds the predetermined value V _ref of which even one The image reading operation may be started, or the image reading operation may be started when the values of all pixels exceed the predetermined value V _ref . Furthermore,
Sum or average of the values of all the pixels, or a specific single pixel values, or the sum or average of the values of a particular plurality of pixels is compared with a predetermined value V _ref, the image reading operation when exceeding the predetermined value V _ref May be started.

On the other hand, as a method of setting the predetermined value V _ref ,
After the power supply to the lighting means 1 is turned on in advance by an experiment or the like, the digital image data 13A when the reference density plate 8 is read when the lighting means 1 is stable is set corresponding to the above-described various comparison methods. deep.

It should be noted that the reference density plate 8 may be used for shading correction without any problem.

<Second Embodiment> Next, the image reading apparatus of the embodiment shown in FIGS. 3 to 4 will be described. In FIG. 3, the image reading apparatus according to the present embodiment includes an illuminating unit 1 such as a fluorescent lamp, an optical system such as a mirror 3 and a lens 4, a sensor 5, a window 7 made of a transparent member, and a uniform density, for example, all. It is composed of a white reference density plate 8, a driving mechanism 9, a sample and hold circuit 11, an A / D converter 12, an image memory 14, an operation panel 16, and a control circuit 30. The control circuit 30 includes a peak-side peak detector 32, a valley-side peak detector 33,
The detection means 31 using the convergence determination unit 34 is provided. As can be seen by comparing FIG. 3 and FIG. 1, the image reading apparatus of the present embodiment has a control circuit 30 which is the first circuit of FIG.
Since the apparatus is different from that of the embodiment, the same reference numerals are given to the other same functional units.

That is, in FIG. 3, the object to be read 2 or the reference density plate 8 is illuminated by the illuminating means 1, and the image thereof is formed on the sensor 5 through the optical system such as the mirror 3 and the lens 4, and the same sensor 5 is used. The image is converted into an electrical signal 10.
Further, the sensor output signal 10 is input to the A / D converter 12 through the sample and hold circuit 11, converted into digital image data 13 and stored in the image memory 14.

Also in this embodiment, the sensor 5 is a line sensor, and the sensor 5 is integrated with the illuminating means 1 and the optical systems 3 and 4 to form an image reading section 6, and the image reading section 6 is driven by the driving mechanism 9. It is assumed that the entire image of the reading target 2 is scanned by moving in the sub-scanning direction.

The reference density plate 8 is also used for shading correction, has a size corresponding to the field of view of the sensor 5, and faces the mirror 3 of the image reading unit 6 at the starting position in the sub-scanning direction. Is located in.

The control circuit 30 is constructed by using a microcomputer, and in addition to signal processing such as correction and compression of the digital image in the image memory 14, the control circuit 30 operates the illuminating means 1 based on an operation command from the operation panel 16 or the like. On / off control is performed, and scan control is performed on the drive mechanism 9 to start the image reading operation based on the detection result of the detection means 31.

That is, when the operator gives a driving command, the control circuit 30 powers on the illuminating means 1, but initially the driving mechanism 9 is not operated and is stopped at the starting point position in the sub-scanning direction. In this state, the sensor 5 reads the reference density plate 8 at a constant cycle, and each time, the sensor output signal 10 for one line is converted into digital image data 13A by the A / D converter 12, and the specific area of the image memory 14 is converted. To overwrite and store.

By the way, when the amount of illumination light of the illumination means 1 converges while oscillating with the passage of time after the power is turned on,
Each time the reference density plate 8 is read, the digital image data 13A also converges while vibrating as time passes, as shown in FIG.

Therefore, in the detection means 31, each time one line of digital image data 13A is stored in the specific area of the image memory 14 as described above, the detection means 31 compares it with the past digital image data to determine the mountain side peak detection section 32. The valley-side peak detection unit 33 detects each peak value V _Ti and valley V _Bi of the peak P _Ti and the valley P _Bi , respectively. When the two consecutive peak values V _Ti and V _Bi are both between the upper limit value V _U and the lower limit value V _L , the convergence determination unit 34 determines the predetermined upper limit value V _U and the lower limit value V _L. It is determined that the digital image data 13A has converged within the range 35, and at this time point 36, the command 37 is given to the drive mechanism 9 to perform the scanning operation. As a result, the image reading operation is started.

When the image reading operation is started, the sensor 5 reads the image of the reading object 2 while scanning it, and the sensor output signal 10 of each line is converted into digital image data 13 one after another by the A / D converter 12 to obtain the image. It is stored in the memory 14.

The control circuit 30 uses the digital image data 13A at the time point 36 when it is determined that it has converged within the predetermined range 35 as shading correction data, and scans the reading target 2 to read the digital image data 13 of each line. Shading correction is applied to.

Here, the peak detectors 32 on the mountain side and the valley side,
As the digital image data 13A used when detecting a peak at 33, the value of one specific pixel, or the sum or average of the values of a plurality of specific pixels, or the sum or average of the values of all pixels for one line, Furthermore, either the maximum value or the minimum value in one line may be used.

Regarding the method of setting the upper limit value V _U and the lower limit value V _L , it corresponds to the above-mentioned various peak detecting methods until it becomes stable after the lighting means 1 is powered on by experiments in advance. The variation status of the digital image data 13A when the reference density plate 8 is repeatedly read is checked and set.

Also in the case of this embodiment, it does not matter even if the reference density plate 8 is not used for shading correction.

[0049]

As described above with reference to the embodiments, the image reading apparatus according to the present invention has the following effects.

According to the first aspect of the invention, the image reading operation is started by detecting that the level of the sensor output signal when the reference density plate is read exceeds a predetermined value, so that the illumination light amount is stable, A stable image with uniform brightness can be obtained with a simple configuration.

According to the second aspect of the invention, the image reading operation is started by detecting that the level of the sensor output signal when the reference density plate is repeatedly read is converged within a predetermined range, so that the illumination light amount is stabilized. Even when it vibrates with time, it is possible to obtain a stable image having a uniform brightness with a simple configuration.

The invention of claim 3 embodies the convergence detection of claim 2, wherein the peak value of continuous peaks and valleys of the sensor output signal when the reference density plate is repeatedly read is a predetermined upper limit value. If it is between the lower limit value and the lower limit value, it is determined that the illumination light amount has converged, so that the convergence detection can be performed easily and reliably.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining the operation in FIG.

FIG. 3 is a diagram showing a main configuration of an image reading apparatus according to a second embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining the operation in FIG.

FIG. 5 is a diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Illumination means 2 Object to be read 3 Mirror 4 Lens 5 Sensor 6 Image reading section 7 Window 8 Reference density plate 9 Driving mechanism 10 Sensor output signal 11 Sample and hold circuit 12 A / D converter 13, 13A Digital image data 14 Image memory 16 Operation panel 20,30 Control circuit 21,31 Detecting means 22,37 Command 32,33 Peak detecting means 34 Convergence determination time point 35 Predetermined range 36 Convergence determination time point V _ref Specified value V _U Upper limit value _VL Lower limit value

Claims (3)

[Claims] 1. An image reading apparatus comprising an illuminating means for illuminating an object to be read and a reference density plate, and a sensor for reading the object to be read and the reference density plate, wherein an output level of the sensor when the reference density plate is read is predetermined. An image reading apparatus having a detection means for detecting that the value has been exceeded, and the image reading operation is started based on the detection result. 2. An image reading apparatus comprising an illuminating means for illuminating an object to be read and a reference density plate and a sensor for reading the object to be read and the reference density plate, the output level of the sensor when the reference density plate is repeatedly read. An image reading apparatus having a detecting means for detecting convergence to a predetermined range defined by a predetermined lower limit value and an upper limit value, and starting an image reading operation based on the detection result. 3. The peak detecting means for detecting peak values of peaks and troughs of the output of the sensor, and two consecutive peak values between the predetermined lower limit value and the upper limit value. 3. The image reading apparatus according to claim 2, further comprising convergence determination means for determining that the output level of the sensor has converged within a predetermined range.