JP2002281300A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader capable of determining whether the offset level of a black correction value obtained by counting the number of 0 in a black data for is a normal one in a black correction. SOLUTION: The image reader has an optical means for reading a picture on a manuscript, a solid-state image sensor 9 for photoelectrically converting optical data read by the optical means and outputting information data corresponding to the picture on the manuscript, an analog processor circuit 21 for analog-processing information signals outputted from the information sensor 9, an AD converter circuit 22 for AD-converting the information signals processed by the analog processor circuit 21, and an arithmetical circuit 23 for the shading correction and other processes. It comprises a memory 24 for storing black data read in an optically extinguished state to correct black offsets of the image signals and a means 25 for counting the number of zero data in the black data for correcting the black offsets.

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 such as a scanner and an electrophotographic copying machine, and more particularly to an image reading apparatus which converts an original image signal into a digital signal and processes the digital signal. The present invention relates to an improved technique for improving linearity characteristics.

[0002]

2. Description of the Related Art An original image is read by a photoelectric conversion element,
A conventional image reading apparatus that converts an image signal into a digital signal and processes the image signal includes a contact glass on which a document is placed, a first carriage including a halogen lamp for exposing the document and a first reflection mirror, and a second reflection mirror. And a second carriage comprising a third reflection mirror, a lens unit for forming an image on a CCD linear image sensor (CCD), and a white reference plate for correcting various distortions caused by a reading optical system and the like. The first and second carriages are moved in the sub-scanning direction by a stepping motor.

In a signal processing block for obtaining a digital image signal from a CCD output of a conventional image reading apparatus, an image signal is first output from the CCD in synchronization with a driving pulse, and the image signal is subjected to analog processing. In circuits, sample hold, black offset correction, signal amplification,
Multiplexing of odd and even pixel outputs is performed. Thereafter, this signal is converted into 8-bit digital data by an A / D conversion circuit, and predetermined correction processing is executed by a shading correction and dark output correction calculation circuit.

The correction data used in the calculation in the shading correction and dark output correction calculation circuit is usually obtained by reading a white reference plate prior to image reading and by reading black data when a light source, ie, a halogen lamp is turned off. The stored data is stored in a white data and black data storage memory as white data and black data, respectively.

In a conventional image reading apparatus, a black level correction of an image signal is performed in an analog processing circuit by using a value of black data when a lamp is turned off and stored in a black data storage memory before power-on and before scanning. Is called black offset correction). At the time of the correction, a level correction is performed in an analog manner by applying feedback so that the average value of the black data becomes equal to a certain adjustment target value of the offset correction. At this time, the black data is not adjusted to 0 (/ 255), but a value with a certain offset is set as the adjustment target value. or,
Normally, black data reading uses a light-shielded pixel of a CCD (a part that has a pixel but is shielded from light), and the average value of a plurality of read data read in the main scanning and sub-scanning directions becomes black data.

Here, the prior art is disclosed in Japanese Patent Application Laid-Open No. 10-42.
No. 111 publication. In this publication, there is a technical disclosure relating to an image reading apparatus capable of correcting fine linearity of image data with a simpler procedure.

[0007]

This black offset is C
Due to the temperature rise of the CD and other analog elements, some fluctuations will occur over time after adjustment, but before reading an image, always use the black data value stored in the black data storage memory when the lamp is turned off. Then, subtraction is performed in the dark time output correction arithmetic circuit (effective pixel data−black data). That is, since the output level at the time of darkness is set to 0 (/ 255), the fluctuation is canceled.

However, in recent years, the image density of the image reading apparatus has been increased and the reading speed has been increased.
In order to compensate for the lack of sensitivity, large gains are being applied to the amplifier circuit. Therefore, the S /
This is a situation where deterioration of the N ratio cannot be avoided. In such a situation, the image signal originally varies in the form of a normal distribution (FIG. 6).
The level of the image signal in darkness is low due to its low absolute value.
Since a large number of data of 0 is taken, the mode value and the average value of the normal distribution do not match (FIG. 7).
Since the black offset correction only uses the average value of the black reading, the linearity of the high-density region is lost depending on the adjustment of the black offset. On the other hand, if the black offset adjustment target value is set sufficiently high in advance,
Although such a state can be avoided, the dynamic range is narrowed accordingly. Also, the gain value of the amplifier circuit varies due to variations in CCD sensitivity, lamp light amount, etc.,
Naturally, the degree of data variation (S / N ratio) also varies. Therefore, it is difficult to determine an appropriate adjustment target value in advance.

Accordingly, the present invention provides an image reading apparatus capable of judging whether or not the offset level of a black correction value obtained by counting the number of 0s of black data at the time of black correction is a normal value. The purpose is to provide.

[0010]

In order to achieve the above object, according to the present invention, there is provided an optical unit for reading an image of an original, and optical conversion of optical data read by the optical unit, and A solid-state image sensor that outputs image data corresponding to an image, an analog processing circuit that performs analog processing on an image signal output from the solid-state image sensor, and performs A / D conversion of the image signal processed by the analog processing circuit In an image reading apparatus including an A / D conversion circuit and an arithmetic circuit for performing shading correction and other processes,
In order to perform black offset correction of an image signal, a memory for storing black data to be read at the time of optical turning off and a counting means for counting how many 0 data are included in the black data at the time of black offset correction are provided. And

According to a second aspect of the present invention, in the image reading apparatus of the first aspect, the number of 0 data in the black data is counted by the counting means, and the count value exceeds a certain value. In this case, the adjustment target value of the black offset correction is increased and the black offset correction is performed again.

According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the operation of performing the black offset correction again is performed at certain intervals.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the image reading apparatus. The image reading apparatus includes a contact glass 1 on which an original 14 is placed, a first carriage 6 including a halogen lamp 2 for exposing the original, and a first reflecting mirror 3, a second reflecting mirror 4 and a third reflecting mirror 5. Second carriage 7 made of
A lens unit 8 for forming an image on a CCD 9;
CD9, sensor board 10, sensor board 10
And a signal processing unit 12 connected by a cable 11 to the main body 13. Outside the image area of the contact glass 1, a white reference plate 15 for correcting various distortions due to a reading optical system or the like is provided. When reading an image, the first carriage 6 and the second carriage 7 are moved in the sub-scanning direction A by a stepping motor.
Go to

FIG. 2 is a block diagram of a signal processing unit of the image reading apparatus according to the embodiment of the present invention. First, image signals VE and VO are output from the CCD 9 in synchronization with the drive pulse.
In the analog processing circuit 21 for these VE and VO, sample hold, black offset correction, signal amplification,
Multiplexing of odd and even pixel outputs is performed, and an image signal V is obtained. This signal V is converted into 8-bit digital data by an A / D conversion circuit 22, and a predetermined correction process is executed by an arithmetic circuit 23 for shading correction and dark output correction.

The correction data used in the calculation in the calculation circuit 23 is normally obtained by reading white data (white data) by reading the white reference plate 15 prior to image reading, and by reading when the halogen lamp 2 is turned off. Black data (black data). Both data are stored in the color data storage memory 24 for white data and black data. Zero data counter 25 counts how many values of black data include zero.

Immediately after the power is turned on, first, the black offset correction and the determination of the image signal amplification factor are performed by the color data storage memory 2.
4 and the analog processing circuit 21, the determination of the amplification factor of the image signal is performed based on the white data read from the white reference plate 15, and the black offset correction is obtained by reading the black data when the light is turned off. This is performed based on the obtained black data.

The black offset correction is performed while applying feedback between the color data storage memory 24 and the analog processing circuit 21 so as to reach a preset adjustment target value. For example, the black data obtained when the correction target value of the black offset correction is set to 5 (/ 255) is shown in FIG.
In this case, the mode of the distribution and the average value do not match, so that the linearity on the black side is deteriorated.

Therefore, in this case, in such a case, the black offset correction is performed again by changing the correction target value from 5 to 10 (/ 255). As a result, the distribution becomes as shown in FIG. 4, and good linearity on the black side can be secured.

FIG. 5 is a flowchart showing the processing steps for black offset correction. By preventing the count value of data 0 from exceeding the desired value n in the zero data counter 25, an appropriate correction target value can be obtained. Further, in the image reading apparatus, since elements having temperature characteristics such as the CCD 9 and the amplifier are often used, the value of the black offset naturally changes with time. By performing the black offset correction shown in FIG. 5 at certain intervals (every scan, every certain time), it is possible to prevent linearity degradation due to the influence of level fluctuation over time.

Next, the contents will be described. The black offset target value is set to X (/ 255) (S1), and black data is set in the color data storage memory 24 (S2). Then, it is determined that the average value of the black data = X (S3). If so, 0 data of black data is counted (S
4). If not, the offset level of the analog processing circuit 21 is changed by one step (S5). Next, it is determined whether the number of 0 data <N (S6). If so, exit this flow. Otherwise, X = X + 1 (S7) and the process returns to step S2.

[0021]

In the image reading apparatus according to the first aspect, it is possible to know how much the black data contains a value of 0 at the time of the black offset correction, so that the black offset correction is correctly performed without deteriorating the linearity. You can judge.

In the image reading apparatus according to the present invention, the correction is performed while increasing the correction target value until the black data does not include a certain number of zeros at the time of black offset correction. However, the linearity can be ensured even in a bad state.

In the image reading apparatus according to the third aspect, the black offset correction according to the second aspect is performed at regular intervals (every scan, at every regular time), so that the linearity caused by the level fluctuation over time caused by the analog element is obtained. Deterioration can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image reading apparatus.

FIG. 2 is a block diagram of a signal processing unit of the image reading device according to the embodiment of the present invention.

FIG. 3 is a distribution diagram of black data.

FIG. 4 is a distribution diagram of black data obtained by correction according to the present invention.

FIG. 5 is a flowchart showing processing steps of black offset correction.

FIG. 6 is a distribution diagram of image signals in a normal state.

FIG. 7 is a distribution diagram of an image signal in a case where a mode value and an average value of a normal distribution do not match.

[Explanation of symbols]

 Reference Signs List 6 first carriage (optical means) 7 second carriage (optical means) 8 lens unit (optical means) 9 CCD (solid-state image sensor) 21 analog processing circuit 22 A / D conversion circuit 23 arithmetic circuit 24 color data storage memory (memory ) 25 Zero data counter (counting means)

Claims (3)

[Claims] 1. An optical unit for reading an image of an original, a solid-state image sensor for photoelectrically converting optical data read by the optical unit and outputting image data corresponding to the image of the original, and an output from the solid-state image sensor. An analog processing circuit for processing an image signal to be analogized, and an A / D for A / D converting the image signal processed by the analog processing circuit
In an image reading apparatus including a conversion circuit, an arithmetic circuit for performing shading correction, and other processing, a memory for storing black data to be read when the optical signal is turned off, and a black offset correction When
An image reading apparatus comprising a counting means for counting how many 0 data are included in black data. 2. The image reading apparatus according to claim 1, wherein
The number of 0 data in the black data is counted by the counting means, and when the count value exceeds a certain value, the black offset correction is adjusted again by increasing the adjustment target value of the black offset correction. Image reading device. 3. The image reading apparatus according to claim 2, wherein
An image reading apparatus wherein the operation of performing the black offset correction again is performed at certain fixed intervals.