JP2002158838A - Image reading device - Google Patents

Abstract

(57) [Problem] To provide an image reading device capable of improving the accuracy of level difference correction of even-numbered pixels and odd-numbered pixels. When a gain value is determined on the basis of read data of a white reference plate (S301), even-numbered pixels are determined as usual.
The level difference correction (S302) and the offset correction (S303) of the odd-numbered pixels are performed. The set gain value and offset adjustment value (voltage) are temporarily held in the registers a and b, respectively (S304). Gain value of 0
(S305), and offset correction is performed again (S306). The offset amount is corrected to a predetermined target value, and the level difference between the even and odd pixels is corrected (S3).
07), the gain value and the offset amount held are taken out from the registers a and b, the settings are refined (S308), and the process is terminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanner device which adjusts a level difference which is an output difference between an odd pixel and an even pixel of a plurality of registers when an original image signal is converted into a digital signal and image processing is performed. The present invention relates to an image reading device such as a copying machine.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus, an original image is read by a photoelectric conversion element, the read image data is converted into a digital signal, and black level correction and white level correction of the digital signal of the image data are performed. I have. In such an image reading apparatus, generally, when a black level correction circuit corrects an offset amount and a level difference between an even-numbered pixel and an odd-numbered pixel of a CCD (photoelectric conversion element) output, a predetermined value set in an amplifier circuit is used. Is corrected based on the gain value of. When the correction is performed based on the gain (amplification degree) value set in advance in this way, the offset amount and the difference between the even-numbered pixel and the odd-numbered pixel can be corrected in a state close to the actual output condition.

Japanese Patent Laid-Open Publication No. Hei 7-79342 discloses a second method which corresponds to a change in the output level difference between odd and even images.
Is prepared according to the output level at the time of reading the original and added to the correction value of the black correction, so that even if the read output level changes, odd and even numbers can appropriately correct the elementary output level difference. An image processing device is described. Japanese Patent Application Laid-Open No. 10-42111 discloses that at least two types of reference documents are integrally mounted and rotated, and the same body is rotated to obtain a plurality of types of shading data for correction. An image reading apparatus that corrects the linearity of an image signal using shading data is described.

[0004]

However, in the above-described method of performing correction based on a preset gain value, the size of one pixel has been reduced with the recent increase in the number of CCD pixels. In some cases, the reading speed cannot be increased, or the S / N (signal / noise) ratio of the CCD deteriorates. Further, even if a gain value is provided by an external circuit and correction is performed based on the gain value, the S / N ratio may be deteriorated. In particular, the accuracy of level difference correction between even-numbered pixels and odd-numbered pixels in black correction may be reduced. If the level difference between the even-numbered pixel and the odd-numbered pixel becomes large, depending on the value, this level difference may appear as a vertical streak in the read image, and the linearity of the output will be impaired. .

Accordingly, a first object of the present invention is to improve the accuracy of level difference correction between even-numbered pixels and odd-numbered pixels by performing level difference correction between even-numbered pixels and odd-numbered pixels while the gain value is 0. It is an object of the present invention to provide an image reading apparatus capable of performing the following. A second object of the present invention is to be able to hold the correction adjustment amounts of the level difference correction and the offset correction of the even-numbered pixels and the odd-numbered pixels at a predetermined gain value. It is an object of the present invention to provide an image reading apparatus capable of performing level difference correction and offset correction of even-numbered pixels and odd-numbered pixels with a correction adjustment amount held after performing level difference correction. A third object of the present invention is to correct and adjust only the offset value in a state where the gain value is 0 to correct the level difference between the even-numbered pixel and the odd-numbered pixel.
An object of the present invention is to provide an image reading apparatus capable of correcting a level difference between even-numbered pixels and odd-numbered pixels with high accuracy in a state where there is no gain, that is, in a state where an S / N ratio is good.

[0006]

According to a first aspect of the present invention, in an image reading apparatus for determining a predetermined density level by reading reflected light from a white reference plate, an original on a platen is exposed, Light-receiving means for receiving reflected light from the device, and photoelectric conversion means having a plurality of registers, converting the reflected light received by the light-receiving means into an electric signal and outputting from the register as a black reference pixel of an image signal. Amplifying a black reference pixel of an image signal output from a register of the photoelectric conversion unit based on a gain value set according to a predetermined density level determined by reading reflected light from the white reference plate. Amplifying means, and an adjusting value setting for setting an adjusting voltage value for reducing a difference between an odd pixel output and an even pixel output of a black reference pixel of the image signal amplified by the amplifying means. Means, and an odd pixel / even pixel adjusting means for adjusting the difference between the odd pixel output and the even pixel output of the black reference pixel of the image signal output from the register of the photoelectric conversion means based on the adjustment voltage value, When the odd pixel / even pixel adjustment unit adjusts the difference between the odd pixel output and the even pixel output based on the adjustment voltage value, the gain value of the amplification unit is set to 0, thereby achieving the first object. To achieve.

According to a second aspect of the present invention, in the first aspect of the present invention, there is further provided an adjustment value holding means for holding the adjustment voltage value set by the adjustment value setting means, wherein the gain value of the amplifying means is When the value is 0, when the odd pixel / even pixel adjusting means adjusts the difference between the odd pixel output and the even pixel output based on the adjustment voltage value, the adjustment value setting means sets the odd pixel / even pixel. After the adjustment of the difference between the odd-numbered pixel output and the even-numbered pixel output by the adjusting unit, the adjustment voltage value held in the adjustment value holding unit is set and refined to achieve the second object. According to a third aspect of the present invention, in the first aspect of the present invention, when the gain value of the amplifying unit is 0, the adjustment voltage value for reducing the difference between the odd pixel output and the even pixel output is the adjustment value setting. When set by the means, the odd pixel / even pixel adjustment means adjusts the difference between the odd pixel output and the even pixel output of the black reference pixel of the image signal output from the register of the photoelectric conversion means based on the adjustment voltage value. By doing so, the third object is achieved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a diagram illustrating a scanner main body of the image reading apparatus.
The scanner body 13 includes a contact glass 1, a halogen lamp 2, a first carriage 6, a second carriage 7, a lens unit 8, a CCD linear image sensor 9, a sensor board 10, a signal cable 11, a signal processing unit 12, and a white reference plate 15. It has. The first carriage 6 has a halogen lamp 2 for exposing an original 14 on the contact glass 1 and a first reflection mirror 3, and the second carriage 7 has a second reflection mirror 4 and a third reflection mirror 5. I have. The lens unit 8 forms original image data from a reading optical system on a CCD linear image sensor 9 (hereinafter, referred to as a CCD). The white reference plate 15 corrects various types of distortion due to a reading optical system or the like. During scanning, the first
The carriage 6 and the second carriage 7 are moved in the sub-scanning direction (the direction of arrow A in the figure) by a stepping motor (not shown). The document image data formed on the CCD 9 is transmitted to the signal processing unit 12 via the sensor board 10 and the signal cable 11.

FIG. 2 is a block diagram showing the configuration of the signal processing unit. The signal processing section 12 includes a sample hold circuit 16, a black level correction circuit 17, amplification circuits 18 and 20, a multiplex circuit 19, an A / D (analog / digital) conversion circuit 21, a shading correction circuit section 22, and a timing signal generation circuit. 23. Next, the operation of each unit until a digital image signal is obtained from the CCD output will be described with reference to FIG. First, the CCD 9 outputs image signals Ve and V0 synchronized with the driving pulse. In the sample and hold circuit 16, this image signal V
e and V0 are each sampled and held by a sample pulse, and the image signal is converted into a continuous analog signal. Next, the black level correction circuit 17 corrects the variation in the dark output level of the CCD 9, and then the amplification circuit 18 adjusts the output of the odd-numbered pixels and the even-numbered pixels of each color signal to a constant level. Then, in the multiplex circuit 19, the outputs of the odd-numbered pixels and the even-numbered pixels are multiplexed to obtain an image signal V.

The image signal V is amplified by the amplifier circuit 20 to the level of the reference voltage of the A / D conversion circuit 21, and is converted into an 8-bit digital image signal. The sensitivity variation of the CCD 9 of the digital image signal V and the uneven light distribution of the irradiation system obtained in this manner are obtained by reading the reflected light of the white reference plate 15 illuminated by the halogen lamp 2 with the CCD 9 and using the shading correction circuit unit. The correction is performed based on the predetermined density level obtained in step S22. A signal required for driving the CCD 9 is generated by the timing signal generation circuit 23 of the signal processing unit 12 and is input to the sensor board 10. A predetermined gain value set in the amplifier circuits 18 and 20 based on the read data of the white reference plate 15 and a black level correction circuit 17 based on the output data of the black reference pixel of the CCD 9.
The offset adjustment voltage obtained by the offset level adjustment and the odd-pixel / even-pixel output difference adjustment voltage obtained from the result of performing the level difference correction between the even-numbered pixels and the odd-numbered pixels are predetermined when reading the original image. And Further, the process of setting the gain in accordance with the read data of the white reference plate 15 is performed by a known method, and therefore, the description thereof is omitted in the present embodiment.

FIG. 3 is a flowchart showing a processing procedure for determining an offset adjustment voltage and an odd pixel / even pixel output difference adjustment voltage. First, when a gain value is determined based on the read data of the white reference plate 15 (step 30).
1) Perform level difference correction (step 302) and offset correction (step 303) of even and odd pixels as usual. It is assumed that the offset amount at this time is set to a predetermined target value. The set gain value and offset adjustment value (voltage) are temporarily held in the registers a and b, respectively (step 304).
Then, the gain value is set to 0 (step 30).
5), offset correction is performed again (step 306).
The offset amount is corrected to a predetermined target value, the level difference between the even-numbered pixels and the odd-numbered pixels is corrected (step 307), and the retained gain value and offset amount are extracted from the registers a and b, and the settings are reconfigured. (Step 308) to end the process. As described above, in the image reading apparatus of the present embodiment, the gain value and the offset value can be held, and the state where the gain value is 0, that is, S / S
Based on stable black reference image data having a low N ratio, level difference correction between even-numbered pixels and odd-numbered pixels can be performed with high accuracy.

FIG. 4 is a flowchart showing a processing procedure when the average value of the black reference pixel output is used for correction.
First, when the gain value is determined based on the read data of the white reference plate 15 (step 401), the level difference between the even and odd pixels is corrected (step 402) and the offset correction (step 403) as usual. It is assumed that the offset amount at this time is set to a predetermined target value.
Next, instead of the offset correction in which the second predetermined target value is set, the average value of the black reference pixel output of the CCD 9 is calculated (step 404), and the gain set based on the calculated average value is calculated. The value and the offset adjustment value (voltage) are once held in the registers a and b, respectively (step 405). Here, the result of calculating the average value of the black reference pixel output is used as the correction target value. Then, the gain value is set to 0 (step 4).
06), and perform offset correction again (step 40).
7). The offset amount is corrected to a predetermined target value, and the level difference between even-numbered pixels and odd-numbered pixels is corrected (step 40).
8) The gain value and the offset amount held are taken out from the registers a and b, and the settings are refined (step 309), and the process is terminated.

As described above, in the image reading apparatus according to the present embodiment, the average value of the black reference pixel output is used as the correction target value.
Level) reproducibility can be improved. Further, in the image reading apparatus of the present embodiment, at the time of image reading, first, the level difference correction and the offset correction of the even-numbered pixels and the odd-numbered pixels are performed with a predetermined gain value, and the adjustment amount of the offset correction at this time is temporarily adjusted. After the level difference between even and odd pixels is corrected while the gain value is 0, the offset correction amount is returned to the held offset correction amount. Even when the level difference correction and the offset correction are performed, it is possible to maintain the accuracy of the level difference correction of the even-numbered pixels and the odd-numbered pixels equivalent to the case where the predetermined gain value is given, and to obtain the predetermined offset amount (DC level). ). Furthermore, in the image reading apparatus according to the present embodiment, when performing offset correction, when setting a correction target value, the level difference between the even-numbered pixel and the odd-numbered pixel is corrected after performing the offset correction with the gain value being 0. Therefore, the level difference between the even-numbered pixels and the odd-numbered pixels can be accurately corrected with no gain value set, that is, with a good S / N ratio.

[0014]

According to the first aspect of the present invention, when the odd pixel / even pixel adjusting means adjusts the difference between the odd pixel output and the even pixel output based on the adjustment voltage value, the amplification value of the amplifying means is set to 0. Therefore, the correction can be performed more accurately than when a predetermined gain value is given. According to the second aspect of the present invention, the image processing apparatus further includes an adjustment value holding unit that holds an adjustment voltage value set by the adjustment value setting unit, and the odd pixel / even pixel adjustment unit sets the odd pixel / even pixel when the gain value is 0. After the level difference is corrected, the adjustment value can be returned to the held adjustment value.
In the state described above, the initial offset amount (DC level) can be easily reproduced. In the invention according to claim 3,
When the adjustment value setting unit sets an adjustment voltage value that reduces the difference between the odd-numbered pixel output and the even-numbered pixel output when the amplification value of the amplification unit is 0, the odd-numbered-pixel / even-numbered pixel adjustment unit uses the photoelectric conversion unit. Since the difference between the odd pixel output and the even pixel output of the black reference pixel of the image signal output from the register is adjusted based on the adjustment voltage value, there is no gain value (S / N
(Good) state, the level difference between the odd-numbered pixels and the even-numbered pixels is corrected again, and the correction accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a scanner main body of an image reading apparatus.

FIG. 2 is a block diagram illustrating a configuration of a signal processing unit.

FIG. 3 is a flowchart illustrating a processing procedure for determining an offset adjustment voltage and an odd pixel / even pixel output difference adjustment voltage.

FIG. 4 is a flowchart showing a processing procedure when an average value of black reference pixel outputs is used for correction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Contact glass 2 Halogen lamp 3 1st reflection mirror 4 2nd reflection mirror 5 3rd reflection mirror 6 1st carriage 7 2nd carriage 8 Lens unit 9 CCD linear image sensor 10 Sensor board 11 Signal cable 12 Signal processing part 13 Scanner main body 14 Document 15 White reference plate 16 Sample hold circuit 17 Black level correction circuit 18, 20 Amplification circuit 19 Multiplex circuit 21 A / D (analog / digital) conversion circuit 22 Shading correction circuit section 23 Timing signal generation circuit

Claims (3)

[Claims] 1. An image reading apparatus for determining a predetermined density level by reading reflected light from a white reference plate, a light receiving means for exposing a document on a platen and receiving reflected light from the document; A photoelectric conversion unit that converts reflected light received by the light receiving unit into an electric signal and outputs the signal as a black reference pixel of an image signal from the register, and reads reflected light from the white reference plate. Amplifying means for amplifying a black reference pixel of an image signal output from the register of the photoelectric conversion means, based on a gain value set in accordance with the determined predetermined density level; and an image amplified by the amplifying means. Adjusting value setting means for setting an adjusting voltage value for reducing a difference between an odd pixel output and an even pixel output of a black reference pixel of a signal; and a register of the photoelectric conversion means Odd-pixel / even-pixel adjusting means for adjusting the difference between the odd-pixel output and the even-pixel output of the black reference pixel of the image signal output from the image signal based on the adjustment voltage value. The image reading apparatus according to claim 1, wherein a gain value of the amplifying unit is set to 0 when adjusting a difference between the odd pixel output and the even pixel output based on the adjustment voltage value. 2. The image processing apparatus according to claim 1, further comprising an adjustment value holding unit configured to hold the adjustment voltage value set by the adjustment value setting unit, wherein when the gain value of the amplification unit is 0, the odd pixel / even pixel adjustment unit When the difference between the odd-numbered pixel output and the even-numbered pixel output is adjusted based on the adjustment voltage value, the adjustment value setting unit sets the difference between the odd-numbered pixel output and the even-numbered pixel output by the odd-numbered / even-numbered pixel adjusting unit. 2. The image reading apparatus according to claim 1, wherein after the adjustment, the adjustment voltage value held in the adjustment value holding means is set and refined. 3. The method according to claim 1, wherein the adjusting value setting means sets an adjustment voltage value for reducing a difference between the odd pixel output and the even pixel output when the gain value of the amplifying means is 0. 2. The even pixel adjusting unit according to claim 1, wherein the difference between the odd pixel output and the even pixel output of the black reference pixel of the image signal output from the register of the photoelectric conversion unit is adjusted based on the adjustment voltage value. Image reading device.