JPH08223414A - Image reader - Google Patents

Abstract

PURPOSE: To prevent shading in the moving direction of an image read section and to realize reduction in a time till read start with a simple structure. CONSTITUTION: A read object 2 moved with an image read section 6 and mounted on a read window 8 is lighted by a lighting means 1 and the image is formed by a line sensor 5 to obtain an image signal being an electric signal corresponding to the image. In the image reader as above, a reference white plate 17 is arranged along the moving direction of the image read section 6. Thus, the image of the reference white plate 17 is read by the line sensor 5 and the image signal is controlled so that a white level based on the reference while plate 17 is made constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device,
In particular, it is useful when applied to those having an illumination means that takes a long time to reach a steady state.

[0002]

2. Description of the Related Art An image reading device is known as a device for reading image information of an object to be read, such as a photograph or a printed matter, and converting it into an electric signal.

FIG. 4 is a block diagram showing an image reading apparatus of this type. As shown in the figure, this image reading apparatus illuminates an object to be read 2 with an illuminating means 1 such as a fluorescent lamp, and an image of the object to be read 2 obtained by illuminating with this illuminating means 1 is a mirror 3, a lens 4, etc. An image is formed on the line sensor 5 via the optical system of. This line sensor 5
Is a one-dimensional assembly of an image pickup device composed of a CCD, and together with the line sensor 5, the illumination means 1 and the mirror 3
And an image reading unit 6 configured by integrating the lens 4
Is moved in a direction perpendicular to the longitudinal direction of the line sensor 5 (hereinafter referred to as a sub-scanning direction) by the drive of the drive unit 7 to scan and read the entire image of the reading target 2 having a planar spread. There is.

The reading object 2 is placed on the reading window 8 which is a flat surface formed of a transparent member such as glass so that the reading surface 2a faces the mirror 3 and an image can be formed on the line sensor 5. . Further, in order to secure a constant exposure level during image reading, a reference white plate 9 is provided so as to face the mirror 3 at the starting point position in the scanning direction so as to determine the reference white level prior to image reading. There is.

Thus, when the image is read by the image reading apparatus, the object 2 to be read is placed on the reading window 8 with its reading surface 2a facing down, and the image reading unit 6 is run in the sub-scanning direction. Thus, the images are sequentially captured by the line sensor 5.

The image signal converted into an electric signal by the line sensor 5 is converted into a digital signal by the A / D converter 11 after its gain is controlled by the gain controller 10.
It is output as a digitized image signal S ₀ . The image signal S ₀ is temporarily stored in the memory 12 and then output to the output unit 13.

The control unit 14 performs predetermined control on the dimming circuit 15 and the timing circuit 16 together with the gain controller 10 and the A / D converter 11, and the image signal S ₀ when the image of the reference white board 9 is read. Based on
The gain controller 10, the dimming circuit 15, and the timing circuit 1 are controlled so that this becomes a predetermined level.
Exposure is adjusted via 6 or the like. Further, the control unit 14 controls the moving speed of the image reading unit 6 via the driving unit 7 and controls writing and reading of the image signal S ₀ to and from the memory 12.

[0008]

In the above-mentioned image reading apparatus, due to the rising characteristic of the illuminating light quantity of the illumination means 1, if reading scanning is performed before the light quantity is stabilized, shading (unevenness) of the reproduced image in the sub-scanning direction is caused. ).

To prevent such shading, a method of waiting for the irradiation light quantity to stabilize before starting reading, a method of providing a rising characteristic table of the irradiation light quantity, and adjusting the gain of the gain controller 10 based on the data in this table have been conventionally used. Proposed.

However, in the former case, there is a problem that the waiting time becomes long and it takes time to start reading. In the latter case, not only the table holding means needs to be provided, but also the temperature detecting means for detecting the temperature of the lighting means 1 is required. This is because the rising characteristic of the lighting means depends on the ambient temperature. As a result, in the latter case, there is a problem that the device becomes complicated.

In view of the above-mentioned prior art, the present invention provides an image reading apparatus capable of preventing shading in the moving direction of the image reading section and shortening the time until the start of reading with a simple structure. To aim.

[0012]

In order to achieve the above object, the structure of the present invention illuminates an object to be read, such as a photograph or a printed matter, by an illuminating means, and an image of the object to be read is lined through an optical system such as a lens. An image is formed on the sensor, and the image reading unit having these optical system and line sensor is moved in one direction to read the entire image to be read, while the output signal of the line sensor is processed to electrically output the image. In an image reading apparatus configured to convert the image into a uniform image signal, a reference plate of uniform density arranged in parallel with the moving direction of the image reading unit and an image of the reference plate read as the image reading unit moves And a control means for controlling the signal level to be constant.

The structure of the control means is characterized by the following points. The exposure time of the line sensor is controlled based on the level of the image signal of the reference signal, the amplification gain of the image signal is controlled based on the level of the image signal of the reference plate, the image signal of the reference plate That the image signal is controlled by multiplying the image signal by an arbitrary coefficient based on the level of the reference level, a standard that defines the voltage level per bit when A / D converting the image signal based on the level of the image signal of the reference plate It controls the voltage, controls the aperture of the lens of the optical system based on the level of the image signal of the reference plate, and controls the light amount of the illumination means based on the level of the image signal of the reference plate. There is.

[0014]

According to the present invention having the above structure, the level of the image signal is adjusted with reference to the level of the image signal of the reference plate for each line corresponding to the line sensor so that the level becomes constant.

[0015]

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

FIG. 1 is an explanatory view conceptually showing the structure of a reading window of an image reading apparatus according to an embodiment of the present invention and its vicinity in a plan view, and FIG. 2 shows an embodiment of the present invention. It is a block diagram showing an image reading device.

As shown in FIG. 1, in the present embodiment, as in the conventional case, a reference white plate 9 extending in the main scanning direction for reading a reference white image prior to the scanning operation is provided, and a sub-scanning perpendicular to this is performed. It has a reference white plate 17 which is a reference plate of uniform density extending in the direction. The reference white plate 17 is arranged parallel to the edge of the reading window 8 in the field of view of the line sensor 5. As a result, the line sensor 5 is configured to read the image of the reading target 2 by the scanning of the image reading unit 6 and simultaneously read the white image serving as the reference of the reference white board 17 on the same line.

The control section 14 controls each section in the same manner as the conventional one, and extracts the white level of the part corresponding to the image of the reference white board 17 in the A / D converted image signal S ₀ , and the white level is extracted. The timing circuit 16 is controlled so that the level becomes a predetermined constant level, and the exposure time of the line sensor 5 is controlled.

According to the present embodiment, the exposure time of the line sensor 5 is adjusted so that the white level of the image signal becomes constant at each position which sequentially changes in the sub-scanning direction in synchronization with the reading of the image of the reading object 2. Is controlled. As a result, the white level of the image signal S ₀ read into the memory 12 becomes constant even if the light amount of the illumination means 1 continuously changes during the scanning of the image reading unit 6.

In the above embodiment, the exposure time of the line sensor 6 is adjusted by the timing circuit 16 so that the white level based on the reference white plate 17 is controlled to be constant, but this control means is not limited to this. Not something to do. The control unit 14 may be configured to control the gain of the image signal via the gain controller 10, and the control unit 14 controls the light amount of the illumination means 1, for example, the supply current value, via the dimming circuit 15. It may be configured as follows.

Besides, the reference white board 17 can be obtained by adjusting the diaphragm of the optical system, changing the reference voltage of the A / D converter 11, multiplying the output signal of the memory 12 by an arbitrary coefficient, and the like.
It is possible to control so that the white level based on is constant.

The adjustment of the aperture of the optical system can be realized by adjusting the aperture of the aperture with a control signal output from the controller 14. This can be easily achieved by using the existing auto iris mechanism.

Adjustment of the reference voltage of the A / D converter 11 is performed by
By adjusting the dynamic range when converting to digital
To be realized. That is, the voltage represented by a fixed number of bits
Value V _RTAccording to the signal level of the reference white board 17.

As shown in FIG. 3, the control by multiplying the coefficient is provided with a multiplier 19 for inputting a digitized image signal S ₀ which is an output signal of the memory 12, and a reference white board 17 is provided.
It can be realized by increasing or decreasing the coefficient multiplied by the multiplier 19 according to the signal level of the control signal from the control unit 14.

[0025]

As described above in detail with reference to the embodiments, according to the present invention, the level of the image signal of the reference plate is referred to for each line which moves in the moving direction of the image reading unit and is kept constant. Since it is possible to adjust the level of the image signal so that the level of the image signal is kept constant in accordance with the continuously changing light amount even in the transition period before the light amount of the illumination means reaches the steady state. Can be held. Therefore, even in such a transitional period, a high quality image signal can be obtained without causing shading in the moving direction (scanning direction) of the line sensor.

[Brief description of drawings]

FIG. 1 is an explanatory view conceptually showing the structure of a reading window and a portion in the vicinity thereof in a plan view according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the above embodiment.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illumination means 2 Reading object 3 Mirror 4 Lens 5 Line sensor 6 Image reading part 7 Driving part 8 Reading window 9 Reference white board 10 Gain controller 11 A / D converter 12 Memory 13 Output part 14 Control part 15 Dimming circuit 16 Timing circuit 17 Reference white board 19 Multiplier

Claims (7)

[Claims] 1. An illumination unit illuminates an object to be read such as a photograph or a printed matter, and an image of the object to be read is imaged on a line sensor through an optical system such as a lens, and the optical system and the line sensor are provided. In the image reading device configured to move the image reading unit in one direction to read the entire image to be read, while processing the output signal of the line sensor to convert the image into an electrical image signal, It has a reference plate of uniform density arranged parallel to the moving direction of the image reading unit, and a control means for controlling the level of the image signal of the read reference plate to be constant with the movement of the image reading unit. An image reading device characterized by the above. 2. The image reading device, wherein the control means controls the exposure time of the line sensor based on the level of the image signal of the reference signal. 3. The image reading apparatus according to claim 1, wherein the control means controls the amplification gain of the image signal based on the level of the image signal of the reference plate. 4. The image reading device, wherein the control means controls by multiplying the image signal by an arbitrary coefficient based on the level of the image signal of the reference plate. 5. The control means controls a reference voltage for defining a voltage level per bit when A / D converting the image signal based on the level of the image signal of the reference signal. Image reading device. 6. The image reading apparatus according to claim 1, wherein the control means controls the diaphragm of the lens of the optical system based on the level of the image signal of the reference signal. 7. The image reading device, wherein the control means controls the light amount of the illumination means based on the level of the image signal of the reference signal.