JPH077607A - Picture reader - Google Patents

Abstract

PURPOSE:To save a subsequent and wasteful photographing operation by detecting abnormality and stopping a read operation at abnormal time when a reference board becomes dirty and an obstacle is placed on the reference board. CONSTITUTION:A CCD line sensor 12 sub-scans the reference board 5 of uniform density, which is installed at the end part of an original and the inside of a photographing range in a sub-scanning direction and reads it. An abnormality detection means detects the abnormality of dirt on the reference board 5 and the existence of the obstacle based on data obtained by reading the part of the reference board 5 by the CCD line sensor 12. A correction means corrects original read data in a line based on data obtained by reading the part of the reference board 5. Thus, the luminance unevenness of a read picture in the sub-scanning direction is corrected. When abnormality is detected in the abnormality detection means, a control means stops the subsequent read operation.

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 reading an original by optical scanning, and more particularly to a technique for correcting an image signal in reading in a sub-scanning direction.

[0002]

2. Description of the Related Art Conventionally, there has been an image reading apparatus which scans a document placed on a document table by scanning a line sensor. In this type of apparatus, since the light source that illuminates the document is generally lit at the commercial frequency, its illuminance changes with time, which may cause uneven brightness in the sub-scanning direction. Therefore, it is known to provide a reference plate for illuminance correction in the sub-scanning direction, measure the illuminance of the reference plate with a sensor, and correct the original reading data according to the detection result (called sub-scanning shading correction). Has been. Then, for example, in Japanese Patent Application Laid-Open No. 3-48565, in this type of image reading apparatus, a line sensor, a lens, a light source, and a white reference plate are integrated in order to prevent image distortion when the reference plate is soiled. It is shown that the same unit of the white reference plate is read and the correction is performed with the output thereof as a reference, each time the original is read by scanning the unit. In addition, Japanese Patent Laid-Open No. 2-7
In Japanese Patent Laid-Open No. 0170, measures are taken to obtain reference data for main scanning shading correction by reading a rotating white reference plate, that is, by changing the reading position so as not to be affected by dirt on the white reference plate. Is shown.

[0003]

However, in the device as disclosed in the above-mentioned Japanese Patent Laid-Open No. 3-48565, the sensor always looks at the same portion of the white reference plate, so that the reference plate is not contaminated. It is not possible to detect if there is one. Further, even in the apparatus disclosed in Japanese Patent Application Laid-Open No. 2-70170, although it is a countermeasure against the stain on the white reference plate, it does not control the useless reading operation when the stain is detected. The present invention is
It was made to solve the above-mentioned problems,
An object of the present invention is to provide an image reading apparatus capable of eliminating waste by detecting dirt of a reference plate for shading correction and placement of an obstacle on the reference plate and stopping the reading operation when an abnormality occurs. To do.

[0004]

In order to achieve this object, the present invention provides an image reading device for reading an original by optical scanning, and an image pickup means having a line sensor for reading the original by sub-scanning, and a photographing range. A reference plate of uniform density installed in the sub-scanning direction at the inner end, and a stain on the reference plate based on the data obtained by reading the reference plate portion by the image pickup means,
An abnormality detecting means for detecting an abnormality such as the presence of an obstacle, and a correction means for correcting the original reading data in the line based on the data obtained by reading the reference plate portion by the image pickup means for each sub-scanning line. A control means for stopping the reading operation when an abnormality is detected by the abnormality detecting means.

[0005]

In the above structure, the line sensor sub-scans the original and the reference plate of uniform density installed in the sub-scanning direction at the end portion within the photographing range. The abnormality detecting means detects an abnormality such as a stain on the reference plate or the presence of an obstacle based on the data obtained by reading the reference plate portion with the line sensor. The correction means is
For each sub-scanning line, the original reading data in the line is corrected based on the data obtained by reading the reference plate portion. As a result, the uneven brightness of the read image in the sub-scanning direction is corrected. Further, the control means suspends the subsequent reading operation when the abnormality detecting means detects an abnormality.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the image reading apparatus. The apparatus includes a document table 1 on which a document to be read is placed upward, an imaging unit 2 (imaging unit) arranged above the document table 1 for reading the document, and a DC light source 3 for illuminating the document.
An operation panel 4, a reference plate 5 arranged in the sub-scanning direction at the end of the document table 1 in the sub-scanning direction in the sub-scanning direction, and a white plate having a uniform density for performing sub-scanning shading correction, and a control unit described later. Composed of and. A predetermined space is maintained between the document table 1 and the imaging unit 2, and the space between them is used as a work space.

FIG. 2 shows a schematic configuration of the apparatus as viewed from the side. The image pickup section 2 includes a photographing lens 11 and a CCD line sensor 12 for scanning in the sub-scanning direction (a direction perpendicular to the paper surface in the figure). It consists of a document and reads the document as an image. CC
A part of the D line sensor 12 reads the image of the sub-scanning shading correction reference plate 5.

FIG. 3 shows the change in the sub-scanning direction of the output data of the CCD line sensor 12 obtained by reading the sub-scanning shading correction reference plate 5 during the actual photographing operation. The fact that the output increases near the center and decreases at the left and right ends is due to unevenness in illumination and unevenness due to the cosine fourth law of the lens 11. Further, the output fluctuates slightly because of the influence of the external lighting turned on by an alternating current (not shown), and the illuminance of the external lighting fluctuates at the commercial frequency.
Since these fluctuations appear as they are in the sub-scanning direction in the image data as they are, they need to be corrected.

The correction method is carried out so that the graph of FIG. 3 becomes horizontal, as in the normal main scanning shading correction.
Specifically, by taking in the data of the CCD line sensor 12 that has read the reference plate 5 for each sub-scanning line at the time of shooting, and multiplying each data of that line by a coefficient such that the value becomes a constant value, Apply correction. This can be expressed by the following formula.

[0010]

## EQU1 ## Dout = (k / Ds) × Din Ds: CCD data of a reference plate of a line Din: data before shading correction of that line Dout: data after shading correction of that line k: constant

By the way, in the image reading apparatus according to the present invention, an object is likely to be placed on the reference plate, and dirt may be attached to the reference plate. In such a case, the data on the reference plate cannot be read correctly, so normal correction cannot be performed. FIG. 4 shows a data change when the reference plate is read in such an abnormal condition. Due to the presence of dirt and obstacles, the CCD output is small in the X portion. By checking the CCD output of such a reference plate, an abnormality of the reference plate can be detected.

FIG. 5 shows a block configuration of a portion in the control unit which performs sub-scanning shading correction and reference plate abnormality detection. As shown in the figure, the input image data is input to each of the abnormality detection unit and the shading correction unit, the output of the abnormality detection unit is input to the CPU 31, and the output of the shading correction unit is output as image data. Each part is CPU3
1 and the control pulse generator 33.

The operation when the image data string of a certain line is input in the above configuration will be described. The image data sequence is arranged in the order of the reference plate data sequence and the document photographing data sequence. Input data is divided into three paths. Comparison unit 20
The entered data is compared with the set threshold value A of the CPU 31, and if it is smaller than the set threshold value A, the data is regarded as abnormal data and one pulse is generated and input to the counter 21. The counter 21 counts clocks synchronized with the image data corresponding to this pulse period. The enable signal of the counter is input from the control pulse generator 33 so as to count only the data string of the reference plate 5. How many lines are accumulated in the sub-scanning direction,
For example, it is continued over 16 lines, the count value is latched in the latch 34 every 16 lines, and the counter 2
A control pulse is output from each of the control pulse generators 33 so as to clear 1. Then, the CPU 31 fetches the output of the latch 34 every 16 lines. The CPU 31 compares the value with a certain threshold value, and if it is larger than the threshold value, the CPU 31 determines that the reference plate 5 has an abnormality.

The second path of input data enters selector 22. In this selector 22, the input data, the CPU 31
One is selected from the data B set in step 2 and the data in the latch 23 (select data for the input data immediately before). The control signal of the selector 22 is generated by the control pulse generator 33 from the output P of the comparator 20 and the signal indicating the head of the data string of the reference plate 5. The conditions for selecting each data are as follows.

[0015]

[Table 1]

In this manner, the selector 22 portion has a function of replacing the abnormal data with the setting data of the CPU 31 or the previous select data (correction of abnormal data). The output of the selector 22 enters the adding section 24 and is accumulated. The output of the adder 24 is the data clearer 2
Enter 5. Here, the data other than the reference plate data string is controlled so as to be cleared. Therefore, the addition unit 24
In, only the data of the reference plate data string is added and accumulated. When the number of pieces of addition data reaches, for example, 128 pieces, the output of the addition unit 24 is latched by the latch 26. The latch output enters the ROM 27 and is converted into a coefficient. This coefficient is the sub-scanning shading correction coefficient for that line. In the multiplication unit 28, the coefficient from the ROM 27 is multiplied by the input data, and the result is added again with the input data in the addition unit 29, and the correction calculation is completed. The delay unit 35 is the multiplication unit 28.
And the adder 29 function to delay the input data so that the same input data is calculated.

The correction calculation is shown by the equation (1), but in this embodiment,

## EQU00002 ## In the equation of Equation 1, k / Ds = 1 + k '(k
′: Constant), and the calculation of Dout = (1 + k ′) × Din = k ′ × Din + Din is performed.

Normally, the abnormality of the reference plate 5 is detected during the pre-scan before the main scan. Therefore, when the CPU 31 detects the abnormality, a warning is displayed on the operation panel 4 or a warning sound is generated and used. Tell the person about the abnormality. Alternatively, the output signal D from the CPU 31 may be used to select the selector 30.
It is also possible to output the input data as it is without performing shading correction by controlling. This allows
You can take a picture for the time being, and you can avoid unsightly images with poor correction. Further, when an abnormality is detected in the reference plate as a result of the pre-scan, the main scan can be stopped so as to avoid unnecessary photographing.

Next, the threshold value A set by the CPU 31 in the comparison section 20 for detecting an abnormal pixel and the selector 22 by C are set.
A method of determining the set value B set by the PU 31 will be described. Photographing is performed in advance without any external light, and the data of the reference plate 5 is read and stored for each sub-scanning line. These data are used as the set value B of the selector 22, and p times (0 <p ≦ 1) of these data are set to the threshold value A of each line.
And The set value and the threshold value may not be determined for each line, but may be one for every several lines, for example, 256 lines. In this case, the value may be the average of the 256 lines of data, or the data may be fetched every 256 lines.

The present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made. For example, although the apparatus for photographing a document from above has been described above, the same applies to a normal flat bed type apparatus. Can be applied.

[0021]

As is apparent from the above description, according to the present invention, the reference plate for shading correction in the sub-scanning direction in image reading is dirty or an obstacle is placed on the reference plate. In such an abnormal condition, this is detected and the reading operation is stopped, so that the unnecessary photographing operation thereafter can be omitted.

[Brief description of drawings]

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

FIG. 2 is a schematic view of the image reading device as viewed from the side.

FIG. 3 is a characteristic diagram of a CCD output obtained by reading a reference plate.

FIG. 4 is a characteristic diagram of a CCD output obtained by reading a reference plate when there is an abnormality.

FIG. 5 is a block diagram of a control unit of the image reading apparatus.

[Explanation of symbols]

 2 Imaging unit 5 Reference plate 12 Original document 20 Comparison unit 21 Counter 22 Selector 31 CPU 33 Control pulse generation unit

Claims (1)

[Claims] 1. An image reading apparatus for reading an original by optical scanning, comprising: an image pickup unit having a line sensor for reading the original by sub-scanning; and a uniform-density image sensor installed at an end portion within a shooting range in the sub-scanning direction. A reference plate, an abnormality detection unit for detecting an abnormality such as a stain on the reference plate or the presence of an obstacle based on the data obtained by reading the reference plate portion by the image pickup unit, and the image pickup for each sub-scanning line. A correction means for correcting the original reading data in the line based on the data obtained by reading the reference plate portion by means; and a control means for stopping the reading operation when an abnormality is detected by the abnormality detecting means. An image reading device characterized by.