JPS63263971A - Image reader - Google Patents

Abstract

PURPOSE:To apply accurate shading correction without making a circuit complicated by obtaining shading correction data averaging image data in the subscanning direction in an image sensor at the scanning time of calibration plate. CONSTITUTION:An optical unit 9 scans in the sub-direction at the scanning time of calibration plate at a speed four times that at original scanning by switching a command speed signal 51 to an optical unit driver 5. The image sensor 1 receives reflected light from an area corresponding to 4 main scanning lines or the calibration plate 7 and stores the light as signal charge. By reading the signal charge, the image data averaged in the subscanning direction is obtained. An A/D converter circuit 2 converts the said image data into a digital signal and stores it in a memory 4 as shading correction data. The correction data stored in the memory 4 is used at the scanning time of original and the image data read by the sensor 1 is corrected by a shading correction circuit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device for reading multi-tone images, which is used in digital copying machines and the like.

2. Description of the Related Art In recent years, there has been a growing demand for image reading devices that can read multi-tone images.

In order to realize multi-gradation image reading, it is necessary to correct shading distortion caused by uneven sensitivity of the image sensor, uneven light amount of illumination, and the like.

Generally, when performing shading correction, a calibration plate serving as a white reference is scanned in advance to read shading correction data, and when scanning an original, the data is used to correct shading distortion included in image data.

In image reading devices that perform shading correction in this way, if the calibration plate is dirty or scratched, errors may occur in the shading correction data, and lines in the sub-scanning direction may appear in the corrected image. . Therefore, a countermeasure has been taken to find the average value of several pixels in the main scanning direction or sub-scanning direction from the image data obtained by scanning the calibration plate, and use it as data for shading correction (
For example, Japanese Patent Laid-Open No. 61-39777).

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a conventional image reading device in which an adding circuit calculates an average value of image data will be described below with reference to the drawings.

FIG. 2 shows a reading circuit of the conventional image reading device described above. In FIG. 2, 1 is an image sensor, 2 is an A/D (analog/digital) conversion circuit, 3 is a shading correction circuit, 4 is a memory, and 10 is an addition circuit.

The operation of the image reading apparatus configured as described above will be explained below.

First, when reading data for shading correction, the image sensor 1 scans the calibration plate, outputs image data, converts it into a digital signal by the A/D conversion circuit 2, and calculates the average value for every few pixels in the addition circuit 10. After the calculation, it is stored in the memory 4 as shading correction data. When scanning a document, the shading correction circuit 3 uses the shading correction data stored in the memory 4.
In the step, the image data read by the image sensor 1 is corrected.

Further, an example of a conventional image reading device that optically calculates the average value of image data will be described below with reference to the drawings.

FIG. 3 shows the reading section of the conventional image reading device described above. In FIG. 3, 1 is an image sensor;
6 is a light source for illumination, 7 is a calibration plate, 8 is a lens system, 11 is an original table, and 12 is a spatial distance.

The operation of the image reading apparatus configured as described above will be explained below.

The focus of the lens system 8 is adjusted so that it is focused when the original is placed directly on the original table 11. Therefore, due to the spatial distance 12, the image sensor 1 reads the calibration plate 7 with its focus shifted, and optically calculates the average value of the image data. The image data thus obtained is used as shading correction data to perform shading correction.

Problems to be Solved by the Invention However, when calculating the average value of image data using an adding circuit, it is necessary to newly provide an adding circuit and its peripheral circuits, which makes the circuit complicated.

In addition, when calculating the average value of image data optically, the calibration is performed in an out-of-focus state, so the shading distortion components caused by the illumination and lens system will differ from those when scanning the original, and sufficient correction will not be possible. There is a possibility that it cannot be done.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image reading device that can accurately perform shading correction even when a calibration plate has dirt, scratches, etc., without complicating the circuit.

Means for Solving the Problems In order to solve the above problems, the image reading device of the present invention includes:
An image sensor that operates in charge accumulation mode, a calibration plate with uniform density for reading data for shading correction, and a calibration plate that scans in the sub direction even when scanning, and that has a sub-scanning distance per charge accumulation time that is longer than when scanning the original. a shading correction circuit that corrects shading distortion of image data during document scanning by using the image data of the calibration plate averaged in the sub-scanning direction in the image sensor as shading correction data; It has a configuration.

Effect: With the above-described configuration, the present invention can obtain shading correction data obtained by averaging image data in the sub-scanning direction in the image sensor when scanning the calibration plate.
Image data with accurate shading correction can be obtained without complicating the circuit even if the calibration plate is dirty or scratched.

Embodiment Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the main parts of an image reading device in an embodiment of the present invention. In FIG. 1, 1 is an image sensor, 2 is an A/D conversion circuit, 3 is a shading correction circuit, 4 is a memory, 5 is an optical unit drive device, 6 is an illumination light source, 7 is a calibration plate, and 8 is a lens system. It is. The image sensor 1, the illumination light 'a6, and the lens system 8 are included in the optical unit 9.
The scanning in the sub-scanning direction is controlled by an optical unit driving device 5.

The operation of the reading circuit of the image reading apparatus configured as described above will be described below with reference to FIG.

By switching the command speed signal 51 to the optical unit drive device 5, the optical unit 9
scans in the secondary direction at four times the speed of original scanning. Therefore, the charge accumulation time when scanning the calibration plate, that is, the sub-scanning distance per main-scanning cycle, is four times as long as when scanning the original.

At this time, the image sensor 1 receives reflected light from an area corresponding to the four main scanning lines of the calibration plate 7, and accumulates it as a signal charge. Therefore, by reading out this signal charge, image data averaged in the sub-scanning direction can be obtained.

The A/D conversion circuit 2 converts the above averaged image data into a digital signal and stores it in the memory 4 as shading correction data. When scanning a document, the shading correction circuit 3 corrects the image data read by the image sensor 1 using the shading correction data stored in the memory 4.

As described above, according to the present embodiment, image data averaged in the sub-scanning direction can be obtained from the calibration plate by simply switching the speed when scanning the calibration plate and when scanning the original. Shading correction can be performed accurately even when there are scratches, etc.

In this example, the sub-scanning distance per charge accumulation time when scanning the calibration plate was varied by switching the sub-scanning speed, but the same effect can also be achieved by switching the charge accumulation time, that is, the main scanning period. It is clear that the effect can be obtained. However, in this case, the amount of exposure of the image sensor when scanning the calibration plate increases, so if the image sensor becomes saturated, it is necessary to reduce the amount of light from the illumination light source or increase the density of the calibration plate to reduce the amount of reflected light. .

Further, in this embodiment, the sub-scanning distance per charge accumulation time during scanning of the calibration plate is set to four times that of scanning the original, but it is clear that the magnification is not limited to this magnification.

Effects of the Invention As described above, the present invention provides an image sensor that operates in charge accumulation mode, a calibration plate with uniform density for reading shading correction data, and a sub-scanning distance per charge accumulation time when scanning the calibration plate. By providing a scanning control means that controls the scanning length to be longer than that during scanning, and a shading correction circuit that corrects shading distortion, shading correction data is obtained by averaging image data in the sub-scanning direction in the image sensor when scanning the calibration plate. Therefore, even if the calibration plate has dirt, scratches, etc., image data with accurate shading correction can be obtained without complicating the circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of an image reading device according to an embodiment of the present invention, and FIG. 2 shows the configuration of a reading circuit of a conventional image reading device in which an adding circuit calculates the average value of image data. FIG. 3 is a block diagram showing the configuration of a reading section of a conventional image reading device that optically calculates the average value of image data. 1... Image sensor, 2... A/D
Conversion circuit, 3... Shading correction circuit, 4
... Memory, 5 ... Optical unit drive device, 6 ... Light source for illumination, 7 ... Calibration plate, 8 ... Lens system , 9...optical unit. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 1/-Jmage tnsa 7-1 Comparison JE Osaka Figure 2 Figure 3

Claims (1)

[Claims] An image sensor that operates in a charge accumulation mode, a calibration plate with uniform density for reading shading correction data, and when reading shading correction data from the calibration plate, the calibration plate is scanned in the sub direction and What is claimed is: 1. An image reading device comprising: a scanning control means for controlling a sub-scanning distance to be longer than when scanning an original; and a shading correction circuit for correcting shading distortion of image data using read shading correction data.