JPH06292002A - Image reader - Google Patents

Abstract

PURPOSE:To detect dust and dirt of an image sensor section precisely. CONSTITUTION:White level data from an image sensor 1 are given to a differential data detection section 5, from which the data are outputted as differential data. A control section 7 subtracts differential data stored in an initial differential data RAM 6 from the former differential data and when the difference is not within a predetermined range, it is discriminated that there is dust or dirt or the like in the image sensor section and the control section 7 raises an alarm. Thus, only the dust and dirt of the image sensor section are precisely detected.

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 capable of detecting dust and dirt on an image sensor unit in advance.

[0002]

2. Description of the Related Art Conventionally, in an apparatus for reading an image with an image sensor, the white data when the image sensor is not dirty is compared with the current white data, and the dirt of the image sensor that adversely affects the reading of the original is read. By detecting in advance, it is possible to prevent black lines and white blemishes from entering the original image. This type of technique is disclosed in, for example, Japanese Patent Laid-Open No.
There is 288766 publication.

[0003]

However, since the conventional device simply compares two white data, not only the stain of the image sensor portion but also the deterioration of the light source, that is, the peripheral light amount of the fluorescent lamp is reduced. However, there is a problem that a stain alarm is issued even when the shading waveform changes gently. To deal with deterioration of the light source,
Normally, the white data is re-acquired each time before reading the original, and if there is a stain alarm when there is deterioration,
This measure against deterioration of the light source is completely meaningless.

Therefore, it is an object of the present invention to provide an image reading apparatus which does not issue a dirt alarm with respect to deterioration of a light source and accurately detects only dust and dirt on an image sensor section. .

[0005]

According to the present invention, the shading waveform changes gently when the light source deteriorates, and the waveform changes rapidly when the light source is dust or dirt, that is, white data between adjacent pixels. The difference data of is small in the former case,
In the latter case, paying attention to the fact that it becomes large, simply comparing the initial white data with the current white data and storing the difference data of the initial white data as the initial data rather than detecting the abnormality By providing a means for comparing the difference data of No. 1 and the difference data of the current white data, dust and dirt on the image sensor unit are accurately detected.

[0006]

According to the present invention, when a change in white data due to dust or dirt on the image sensor is detected by observing a change in the difference data of the white data, an alarm is issued and the white data due to the deterioration of the light source is detected. It becomes possible to turn off the alarm when a change in
Dust and dirt on the image sensor can be detected accurately.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image reading apparatus showing an embodiment of the present invention. The image sensor 1 converts light reflected from the document surface into an electric signal. Amplifier (AM
P) 2 amplifies the electric signal output from the image sensor 1. The analog / digital (A / D) converter 3 is AMP
The electric signal amplified in 2 is converted into digital data.
The initial value detection unit 4 detects the initial value of the white data before the deterioration which is the output of the A / D converter 3. The difference data detection unit 5 detects the difference data between the white data output from the A / D converter 3 and an adjacent pixel. Initial difference data RAM
6 stores the difference data of the initial white data. The control unit 7 compares the current difference data from the difference data detection unit 5 with the initial difference data stored in the initial difference data RAM 6 and issues an alarm if there is an abnormality. The initial value difference data RAM 8 stores the current output data of the initial value detecting unit 4 and the difference data detecting unit 5. This initial value difference data RA
The data of M8 will be used later when performing shading correction.

FIG. 2 is a diagram showing white data and difference data when the light source is deteriorated. A and B are white data output from the A / D converter 3 in FIG. White data, B is white data when light source deterioration, dust, and dirt are not present,
That is, the white data in the initial state. The initial difference data of the white data in the initial state is stored in the initial difference data RAM 6, and the difference data with respect to the current white data is detected by the difference data detection unit 5. The difference data of white data A is AD (dashed-dotted line), and the difference data of white data B is BD (dashed-dotted line). The difference data BD is the initial difference data RA
It is stored in M6, and the initial difference data RA is stored in the control unit 7.
The difference (AD-BD) (solid line) between the difference data BD of M6 and the difference data AD from the difference data detection unit 5 is obtained. It is determined whether or not this is within the determination value (-α <AD-BD <α). In this case, there is no problem because it is within the range.

FIG. 3 is a diagram showing white data and difference data when dust and dirt are present on the image sensor portion, and C is shown in FIG.
It is the white data output from the A / D conversion unit 3 in the above, and is the white data when dust or dirt is present. B is the initial white data described above. Same as above, 2 for 2 white data
Difference data CD of white data C
And the difference data BD of the white data B. Difference data BD
Is stored in the initial difference data RAM 6 and the control unit 7
Then, the difference (CD-BD) between both difference data is obtained, and it is determined whether the difference is within the determination value (-α <CD-BD <α). In this case, since the range is exceeded, the control unit 7 will generate an alarm.

As described above, according to the present invention, the difference between the difference value of the white data and the difference value of the initial white data is obtained and it is judged whether the difference is within the judgment value. It is possible to accurately detect dust and dirt on the image sensor unit.

The difference data is usually detected for each pixel, but it is also possible to reduce the data amount by reducing the number of times of detection.

[0013]

As described above, according to the present invention, by observing the change in the difference data of the white data, the alarm is not issued for the deterioration of the light source, and the image sensor unit is free from dust and dirt. Only accurately detect.

[Brief description of drawings]

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

FIG. 2 is a diagram showing white data and difference data at the time of light source deterioration and at the initial stage.

FIG. 3 is a diagram showing a case where dust and dirt are present in an image sensor unit and initial white data and difference data.

[Explanation of symbols]

1 ... Image sensor, 2 ... Amplifier (AMP), 3 ... Analog / digital (A / D) converter, 4 ... Initial value detector,
5 ... Difference data detection unit, 6 ... Initial difference data RAM, 7
... control unit, 8 ... initial value difference data RAM.

Claims (1)

[Claims] 1. A means for detecting difference data of white data in an image reading device for converting reflected light from a document into an electric signal by an image sensor, amplifying the output, and A / D converting the read image. An image reading apparatus comprising: a means for storing difference data of initial white data; and a means for comparing the difference data between the initial difference data and current white data.