JP3152678B2 - Image reading device - Google Patents

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 facsimile apparatus, and more particularly to an image reading apparatus for correcting a shading distortion of a read image.

[0002]

2. Description of the Related Art Conventionally, image reading apparatuses such as facsimile machines, copiers and scanners have been widely used. This image reading apparatus illuminates a read original with a light source such as a fluorescent lamp, but since the light emission characteristics of the light source are not always uniform in the main scanning direction, illuminance unevenness, so-called shading distortion, occurs. For this reason, shading is performed by reading white information from a uniform white plate serving as a reference before image reading, detecting shading distortion from fluctuations in white information, which should be constant, and canceling the distortion from the read image. The distortion has been corrected.

In order to correct shading distortion, white information is read from the reference white plate as described above. However, the white surface of the reference white plate may become dirty due to aging, adhesion of dust, and the like. . In this case, the obtained white information includes an abnormal component due to dirt in addition to the shading distortion. Therefore, the shading correction using the dirty reference white plate is corrected based on the shading distortion including the abnormal component, and as a result,
This causes image failure due to dirt.

Therefore, various devices have been proposed in order to eliminate a correction error caused by a stain on the reference white plate. As a conventional image reading apparatus of this type, for example, Japanese Utility Model Laid-Open No. 2-2
The image reading apparatus described in Japanese Patent Application Laid-Open No. 3168/1995 changes the position on the reference white plate for reading the shading distortion when the shading distortion information is not good, and obtains good information. Until this is repeated.

[0005]

However, such a conventional image reading apparatus needs to be provided with a mechanism for changing the reading position on the reference white plate, and has a fixed reading position, for example, a CCD (Charge Coupled). Device) etc. and the reference white plate are fixed, and in the scanner section of the facsimile apparatus which reads an image while transporting the original in the sub-scanning direction, the reading position of the reference white plate is only one, If the area is dirty or the original enters the reading position on the white plate due to skew or the like, an image defect due to abnormal shading distortion information cannot be solved.

That is, if the reference white plate is dirty, a portion having an abnormally low white level is formed in the shading distortion information, and it is determined that this portion has occurred due to shading distortion of the light source. The level of image information is unduly raised beyond the distortion correction actually required. Further, the image reading level is defined by providing a predetermined period in the main scanning direction, detecting the peak value of the white level (referred to as white peak following), and adjusting the detected white peak level to a constant level. Since a portion that has been corrected more than necessary by the shading correction is detected as a white peak, an image reading level is defined based on the abnormal white peak, and the reading level is reduced as a whole. Become).

As a result, an image defect has occurred due to an abnormal reading density. In view of the above, the present invention provides an image reading apparatus that detects an abnormality in shading distortion information and does not follow a white peak during an abnormal period, thereby preventing an abnormal increase in a white peak and preventing an abnormal reading density. It is an object. According to the second aspect of the present invention, the longest period of the white peak following period divided by the abnormality detecting period is selected as the following period, so that the accuracy of the white peak detection can be maintained while shortening the following period. It is an object to provide an image reading device.

According to the third aspect of the present invention, the shading distortion correction is not performed during the abnormal period, thereby preventing the abnormal reading density due to the abnormal rise of the white peak and reducing the distortion of the level of the image information during the abnormal period. It is an object of the present invention to provide an image reading device that suppresses only shading distortion.

[0009]

According to the first aspect of the present invention,
To achieve the above object, a shading correction circuit for correcting shading distortion of white information read from a reference white plate, and a white level corrected by the shading correction circuit are tracked within a predetermined tracking period. An image comprising: a white peak tracking circuit for detecting a white peak level; and a white peak defining circuit for defining an image reading level so that the white peak level detected by the tracking operation matches a maximum level of a reading dynamic range. in reading apparatus, and a white level error reduction period detection circuit white levels for white information read from the reference white plate to detect the period in which abnormally low, the white level abnormality reduction period in the white peak tracking period Detection circuit
Bei example and a jog additionally従期between variable setting circuit from white peak tracking period the abnormal reduction period when an abnormality reduction period white bell is detected by the white peak tracking circuit, the abnormality
During the white peak tracking period excluding the falling period, the white peak tracking
Sub circuit is characterized that you detect the white peak level.

According to a second aspect of the present invention, in order to achieve the above object , the abnormal lowering period is set to follow the white peak.
If removed from the period, the longest follow-up period in the remaining white peak tracking period comprising the following period selection circuit shall be the inter-white peak tracking phase. According to a third aspect of the present invention, in order to achieve the above object, a prohibition circuit for prohibiting the shading correction of the read image by the shading correction circuit during the abnormal reduction period is provided.

[0011]

According to the first aspect of the present invention, the white information read from the reference white plate detects a period in which the white level is abnormally lowered by the white level abnormally low period detecting circuit, and the white peak is detected. If an abnormally low white level period is detected within the following period, the abnormally lower period is excluded from the white peak following period by the following variable period setting circuit, and the white peak following period divided into a plurality is newly added. Set.

In the invention according to claim 2 having the above configuration, when a plurality of divided white peak following periods are newly set, the longest following period among the divided white peak following periods is set to one. Select only one white peak tracking period. In the third aspect of the present invention having the above-described configuration, the shading correction circuit prohibits the shading correction of the read image by the shading correction circuit during the abnormal lowering period.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
FIG. 1 is a diagram showing an image reading apparatus according to one embodiment of the present invention. First, the configuration will be described. The image sensor 11 reads an original image in the main scanning direction by an image reading unit configured by a CCD or the like. The amplifier 12 amplifies the image data read by the image sensor 11 to a predetermined level. The A / D converter 13 converts the amplified image data into digital data. Prior to image reading, the shading correction circuit 14 detects and corrects shading distortion of white information read from a reference white plate (not shown). Also,
The shading correction circuit 14 corrects image information based on the shading distortion when reading an image. In addition,
The shading distortion and the correction data are stored in the shading data memory 15.

The white peak tracking circuit 16 follows the white level corrected by the shading correction circuit 14 within a predetermined tracking period, and detects the white peak level. The white peak voltage generating circuit 17 is a white peak specifying circuit for specifying an image reading level. The white peak level detected by the following operation matches the maximum level of the reading dynamic range, that is, the maximum conversion level of the A / D converter 13. A / D converter 13
Is defined.

The image processing circuit 18 performs, for example, binarization processing, dither binarization processing, and the like on the corrected image data output from the shading correction circuit 14 when reading an image, and outputs the result. CPU (Central Processing Unit) 19
Controls the entire apparatus in accordance with a program stored in a ROM (Read Only Memory) 20 and, as a white level abnormal decrease period detection circuit of the present embodiment, detects an abnormal white level of white information read from the reference white plate. Detect the period during which it has fallen. Further, the CPU 19 has a ROM
The white peak following period stored in the white peak following period is read out and transferred to the white peak following circuit 16, and the white level following period of the present embodiment is used as a variable following period setting circuit. If it is detected, the abnormal lowering period is excluded from the white peak following period, and a white peak following period divided into a plurality is newly set. Furthermore, CP
U19, as the tracking period selection circuit of the present embodiment, when a plurality of divided white peak tracking periods are newly set, only one of the longest tracking periods in the divided white peak tracking periods is used. Select for a period.

The prohibition circuit 21 prohibits the shading correction of the read image by the shading correction circuit 14 during the abnormal lowering period. Next, the basic operation of the present embodiment will be described with reference to the waveform diagram shown in FIG. Note that FIG.
5A and 5B are diagrams showing a white information waveform read from a reference white plate and a waveform after shading correction by following a white peak, FIG. 7A shows a normal tracking operation, and FIG. FIG. 7C shows a follow-up operation in the embodiment according to the above-described invention, and FIG.

When the reading is started, the reference white plate is first read as shown in FIG. The image data obtained by the image sensor 11, that is, white information, is boosted by the amplifier 12, converted into digital data by the A / D converter 13, and firstly by the shading correction circuit 14 by the shading data memory 15.
Is stored.

Thereafter, when the reading of the document is started, the shading correction circuit 14 reads out the white information, that is, the shading distortion data from the shading data memory 15, and as shown by the hatched portion in FIG. After performing shading distortion correction, the image data is transferred to the image processing circuit 18 and the white peak tracking circuit 16.

The image processing circuit 18 performs appropriate processing (binarization, dither binarization, etc.) on the input digital image data and outputs the result. The CPU 19 reads out the white peak following period WP ₀ stored in the ROM 20 and transfers it to the white peak following circuit 16. The white peak tracking circuit 16
The level of the white information that has been subjected to the shading correction is referred to as the tracking period W
Following within P ₀ , the white peak level is detected. Then
The white peak tracking circuit 16 determines that the detected white peak level is A
The white peak voltage generation circuit 17 is controlled so that the full scale of the / D converter 13 is obtained, and the reference voltage Vref
Increase or decrease.

The operation of the embodiment according to the first or second aspect of the present invention will be described below with reference to the flowchart of FIG. First, shading distortion information (white information) is read from the reference white plate (step S1), and the CPU 19 checks for an abnormal decrease in white level (step S1).
2). As shown in FIG. 2B, when the CPU 19 detects an abnormal lowering period, an error signal ER is generated during that period (step S3).

[0021] Next, CPU 19, in FIG. 2, WP1 compares the nascent between ER follow-up period WP0 and error signal for the positive constant (abnormal decrease period) to remove the overlap period, W
P2,... (Step S4) , that is, white
If an abnormal decline period of the bell is detected,
Excluded from the white peak tracking period. Then, the CPU 19 sets the divided follow-up periods WP1, WP2,... Instead of the normal follow-up period WP0 (step S5), and proceeds to reading of the document (step S6). Therefore, the follow-up period WP
1, WP2,..., A / D
The reference voltage Vref of the converter 13 can be defined, and the image reading level is not unduly reduced due to the abnormal white peak level in the follow-up period WP0.

As described above, in this embodiment, the white peak tracking, that is, the white peak detection is not performed during the generation period of the error signal ER. It can be excluded, preventing abnormalities in image reading level due to abnormal white information,
An abnormal output image can be prevented. In this embodiment, an image sensor 11 such as a CCD and a reference white plate are fixed, and in an image reading apparatus that conveys a document, white peaks due to shading distortion information abnormality caused by white plate contamination, document skew, etc. It is particularly effective for preventing abnormal rise.

On the other hand, step S7 is a process replacing step S5, and is effective in a system in which only one white peak follow-up period can be set. That is, in step S7, the CPU 19 compares the lengths of the divided follow-up periods WP ₁ , WP ₂ ,..., Selects the longest one, and selects this as the white peak follow-up period.

As described above, in this embodiment, even for a model in which only one white peak following period can be set, the longest period of the white peak following period divided by the abnormality detection period is followed. By selecting the period, the accuracy of white peak detection can be maintained while shortening the tracking period, and the best white peak tracking can be performed within a limited range. It should be noted that the selection from step S5 or step S7 for the processing after step S4 can be easily switched on the control program, and is appropriately set according to the model in which the present invention is implemented. I do.

Next, the operation of the embodiment according to the third aspect of the present invention will be described with reference to the flowchart of FIG. First, shading distortion information (white information) from the reference white plate
Is read (step P1), and the CPU 19 checks for abnormally low white level (step P2). FIG.
As shown in (c), when the CPU 19 detects an abnormal lowering period, it generates an error signal ER during that period (step P3).

Next, the CPU 19 starts reading the original (step P4), and monitors which period of the occurrence of the error signal ER corresponds to which period of the reading operation (step P4).
5). Then, in periods other than the occurrence period, the shading distortion is corrected (Step P6). On the other hand, when the occurrence period starts, an error signal ER is output to the prohibition circuit 21 and the correction operation by the shading correction circuit 14 is prohibited.
Thus, ON / OFF of shading distortion correction
Is repeated until the reading is completed while being switched depending on whether or not the error signal ER is being generated (step P
7).

As described above, in this embodiment, the shading distortion is not corrected during the period in which the error signal ER is generated, thereby preventing the reading density from being abnormally increased due to the abnormal increase in the white peak, and the image information during the abnormal period. Since the level distortion can be suppressed to only the shading distortion component, the disturbance of the output image data can be suppressed to the level of the shading distortion.

[0028]

As described above, according to the image reading apparatus of the first aspect, the white level of the white information read from the reference white plate is abnormally lowered by the white level abnormally low period detecting circuit. The abnormal period of the white level is detected within the white peak following period. Since the divided white peak follow-up period is newly set, the white peak follow-up, that is, the white peak detection is not performed during the period when the white level is abnormally reduced. Peaks can be excluded, and abnormalities in the image reading level due to abnormal white information can be prevented, and abnormalities in the output image can be prevented.

According to the image reading apparatus of the present invention, when a plurality of divided white peak following periods are newly set, the longest following period among the divided white peak following periods is set. Is selected as the white peak following period, so even if the model can set only one white peak following period, it follows the longest white peak following period divided by the abnormality detection period. By selecting the period, the accuracy of white peak detection can be maintained while shortening the tracking period, and the best white peak tracking can be performed within a limited range.

According to the image reading apparatus of the third aspect of the present invention, the shading correction circuit prohibits the shading distortion correction of the read image by the prohibition circuit during the abnormal reduction period, so that the white level is abnormally reduced. By not performing shading distortion correction during the period,
It is possible to prevent the reading density from being abnormally increased due to the abnormal increase of the white peak, and to suppress the distortion of the image information level during the abnormal period to only the shading distortion component. .

[Brief description of the drawings]

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

FIGS. 2A and 2B are diagrams showing a white information waveform read from a reference white plate and a waveform after shading correction based on white peak tracking. FIG. 2A shows a normal tracking operation, and FIG.
FIG. 4 shows a tracking operation in the embodiment according to the first or second aspect of the invention, and FIG. 7C shows a tracking operation in the embodiment according to the third aspect of the invention.

FIG. 3 is a flowchart showing the operation of the embodiment according to the first or second aspect of the present invention.

FIG. 4 is a flowchart showing the operation of the embodiment according to the third aspect of the present invention.

[Explanation of symbols]

14 Shading correction circuit 16 White peak follow-up circuit 17 White peak voltage generation circuit (White peak regulation circuit) 19 CPU (White level abnormal fall period detection circuit, Follow-up period variable setting circuit)

Claims (3)

(57) [Claims] 1. White information is read from a reference white plate,
Detects and detects shading distortion from fluctuations in white information.
Read the shading distortion and cancel it from the image
A shading correction circuit for correcting the shading distortion of the white information by, white information corrected by the shading correction circuit
A white peak tracking circuit for detecting a peak value of the level of the tracking and white information within track period set level in advance, the peak of the white level information detected by the follow-up operation
In the image reading apparatus and a white peak defining circuit for defining the image reading level so that the value matches the maximum level of the read dynamic range, white information about the white information read from the reference white plate
Level abnormally reduced to a white level abnormality reduction period detecting circuit for detecting the periods, the white level abnormality reduction period detection circuit thus detects abnormality reduction period level of the white information in the white peak tracking period is a follow-up period variably setting circuits except the white peak tracking period the abnormal decrease period if, wherein the white peak tracking circuit, the peak of the white level information in the white peak tracking period except the abnormal decrease period An image reading device for detecting a value . 2. A circuit according to claim 1, further comprising a tracking period selecting circuit for setting a longest tracking period in the remaining white peak tracking period as a white peak tracking period when said abnormally low period is excluded from said white peak tracking period. The image reading device according to claim 1. 3. A circuit according to claim 1, further comprising a prohibition circuit for prohibiting the shading correction of the read image by the shading correction circuit during the abnormal decrease period.
The image reading device according to claim 1.