JPH05316299A - Picture reader - Google Patents

Abstract

PURPOSE:To provide the picture reader with high reliability capable of adjusting an optical system at the time of the fall of the functions of the optical system including a light source and maintaining the gradation of a dynamic range by correcting shading while detecting the fall of the functions CONSTITUTION:The reader is provided with a memory 13 for storing shading signals outputted from a solid-state image forming element and a comparator circuit 10 for comparing the shading signal in an initial usage stored in the storage means with the shading signal obtained after the lapse of time from the usage. The adjustment of optical systems 4 and 5 is enabled based on the compared result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly to an image reading device for performing optical reading using a line sensor of a solid-state image pickup device such as a CCD.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus using a solid-state image pickup device such as a CCD, the sensitivity of each pixel of the solid-state image pickup device varies based on the signal of the solid-state image pickup device obtained from a shading portion (standard white portion). And so-called shading correction have been performed for correcting unevenness in the amount of illumination light caused by the original document illumination system.

[0003]

However, in the shading correction by the conventional image reading apparatus as described above, a satisfactory image reading can be obtained in the initial stage, but when the usage time becomes long, a halogen lamp or the like is used. The following problems occur due to deterioration of the light source for illuminating the original, a decrease in the amount of light due to contamination of each element of the optical system, and the like.

That is, although the shading correction which has been conventionally performed can also correct the light amount reduction on the solid-state image pickup device such as the CCD, the dynamic range of the gradation related to the reading function cannot be reduced, and the image cannot be corrected. Since the signal deteriorates, there is a problem particularly when an image signal with high image quality (high gradation) is to be obtained. Further, even if the optical system is contaminated, there is a problem that the shading range is exceeded due to the decrease in the light amount because there is no means for detecting the decrease in the light amount.

The object of the present invention is to pay attention to the above-mentioned conventional problems, and in order to solve them, it is possible to monitor deterioration of the light source, contamination of the optical system, etc. An object of the present invention is to provide an image reading apparatus capable of performing a certain shading correction.

[0006]

In order to achieve the above object, the present invention provides a reference white part by the solid-state image pickup device for a read signal read from a document by a plurality of solid-state image pickup devices through an optical system. In an image reading apparatus in which shading correction is performed based on a signal output by reading, the means for storing the shading signal output from the solid-state imaging device for the shading correction, and the use stored in the storage means It is characterized in that it comprises means for comparing an initial shading signal with a shading signal obtained after a lapse of use, and the optical system can be adjusted based on the comparison result.

[0007]

According to the present invention, the shading signal obtained by the solid-state image pickup device from the reference white portion at the initial stage of use and stored in the storage means is read out, and after use, it is compared with the shading signal obtained in the same manner. The optical system can be adjusted based on the comparison result.By detecting the decrease in the light amount related to the optical system and adjusting this, the read image can be displayed in the same dynamic range gradation. Can be held.

[0008]

Embodiments of the present invention will now be described in detail and specifically with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. here,
Reference numeral 1 is a transparent original placing table made of glass or the like, 2 is an original placed on the original placing table 1, and 3 is a shading section (a portion arranged on the original placing table 1 at a position related to the original 2). The reference white part). The light source 4 provided on the lower surface side of the document table 1 for the shading section 3 and the document 2 as described above.
The reflected light from the shading portion 3 and the original 2 is received by the line sensor 7 formed of a solid-state image sensor array such as a CCD through the imaging lens 6 by scanning in the X direction of the mirror 5 and the mirror 5, and photoelectrically converted. Shading and reading of a two-dimensional image can be performed by the output signal.

In the figure, 8 is a driver circuit for the line sensor 7, 9 is a driver for controlling the light amount and ON / OFF of the light source 4, and 10 is a CPU function for controlling the whole, which will be described later. Is a circuit for comparing the output signal of the initial shading with the output signal of the shading after a lapse of time to judge the quality of the light source and other optical systems (hereinafter referred to as a comparison circuit). Also,
Reference numeral 11 denotes a shading correction circuit that performs correction as described later based on the comparison of the output signals obtained from the shading unit 3 by the comparison circuit 10, and 12 outputs an image signal with the gradation corrected by the shading correction circuit 11. Circuit.

Furthermore, 13 is a storage device RAM, which is output from the shading unit 3 in the initial stage and, as will be described later, from the shading unit 3 by a shading operation performed after a predetermined time elapses and before reading the original. Each output signal is stored. Then, the result of the comparison is fed back, and for example, the light amount of the light source 4 can be changed via the light source driver 9.

Here, the principle of shading correction that is normally performed will be described.

In this case, it is assumed that the reading system can obtain 256 levels of information relating to the density. To do so, first, a reference blank sheet is placed on the document surface mounting table 1 and the output ratio between the blank sheet and the shading portion (standard white portion) 3 is calculated to obtain the density correction coefficient W of the shading plate.

As a method of obtaining the coefficient W, the correction coefficient W can be obtained by the following equation by obtaining the output average value of several tens of pixels of the number of central portions in the line sensor 7, for example.

[0015]

[Equation 1]

When the image is read, the output signal Si (i represents the address of the pixel) from each pixel from the shading section 3 is first obtained, and then the original 2 is read. Then, the final output signal Xi can be obtained through the circuit 12 by performing shading correction on the output signal Ti obtained from the original 2.
This output signal Xi is obtained by the following equation.

Here, it is assumed that the output from the reference white board (shading section 3) is set to 256 levels.

[0018]

[Equation 2]

However, here, variations in the sensitivity of each pixel of the solid-state image pickup device, unevenness of the illumination system, and the like are caused by the above signals Ti and S.
Since each i is included at the same level, the final signal Xi can be obtained in a canceled form.

Therefore, for example, if the reference blank sheet is used as a blank original, an output signal of Xi = 256 is obtained for the entire surface if noise is ignored, and the original 2 is used.
2 as the dynamic range of the output Ti obtained from
You can keep 56 levels. Thus, by performing the shading correction as described above, the read image data (signal) that is satisfactory as the initial characteristic can be obtained.

However, as the use of the image reading apparatus progresses thereafter, the light source 4 for illuminating the original document deteriorates or the amount of light reaching the solid-state image pickup element of the line sensor 7 decreases due to stains on the optical system (mirror or the like). Will occur. In this case as well, as is apparent from the equation 2, both the outputs Ti and Si obtained from the original 2 and the reference blank sheet are similarly reduced, so that the value of Xi is the same as the initial value. Since the output value of the output Ti that should be obtained from the original document 2 has decreased, its dynamic range decreases. For example, assuming that the decrease in light amount is 30%, the gradation when the reference blank paper is read reaches 179 levels, and the signal levels between 180 and 256 levels disappear. Therefore, due to such a decrease in the dynamic range, it becomes impossible to read with high image quality (high gradation). Further, in the case of the conventional reading device, since only the corrected final output Xi is output, it is not possible to know how much the light amount has decreased and the dynamic range of the output Ti at that time during use.

However, in the present invention, the output signal Sia initially obtained from the shading portion (standard white board) 3 is used.
Is stored for at least some of the pixels, and a comparison value between the data and the output signal Si obtained by the shading operation performed at the beginning of reading by the image reading apparatus is obtained, whereby a decrease in light amount can be detected. it can. Further, by referring to the comparison value, for example, by increasing the light emission amount of the document illuminating light source 4 and adjusting so that S = Sia, the output signal from the document 2 is advanced when the document reading device is used. By solving the problem that the dynamic range of Ti is reduced, it is possible to always read with high image quality (high gradation).

Further, according to the above comparison result, when the decrease in the light amount is too large, for example, when the light amount becomes 50% or less, the display unit message of the reading device or the display unit message of the host device connected to the reading device is displayed. It is also possible to take out the lamp to prompt replacement of the lamp or cleaning of the optical system.

In the embodiment described above, the shading output signal obtained in the initial stage is compared with the shading output signal obtained when the number of times of use is increased, and the result is fed back to the light emission amount of the document illumination light source. Although the same dynamic range is always maintained in the reading system by adjustment, for example, cleaning means is provided in the mirror 5, and the mirror 5 is automatically cleaned based on the judgment from the above comparison result. It is also possible to do so.

Further, in order to reduce the memory amount for storing the shading output signal in the initial stage, only the average output value for all pixels is stored, and the pixels are divided into several areas, for example, 5 areas, and each area is divided. Only five average values may be stored and these may be compared.

[0026]

As described above, according to the present invention,
The shading signal output from the solid-state image sensor for shading correction; and means for comparing the shading signal in the initial stage of use stored in the storage means with the shading signal obtained after a lapse of use. However, since the optical system can be adjusted based on the comparison result, by comparing and processing the initial shading output signal and the shading output signal obtained when the use is advanced, deterioration of the light source and other It is possible to detect a decrease in the amount of light reaching the solid-state image pickup device, such as the CCD of the line sensor, due to the dirt of the optical system. Also, based on this detection result, it is possible to control the light emission amount of the illumination light source and maintain the same dynamic range as in the initial stage.Also, a message can be displayed to notify the user of replacement of the light source or dirt on the optical system to warn the user. it can.

In the above-described embodiment, the reading system is not particularly limited to black and white or color, but it goes without saying that the present invention can be applied to both monochrome and color reading systems.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration of the present invention.

[Explanation of symbols]

 1 Document Placement Table 2 Document 3 Shading Unit 4 Light Source 5 Mirror 7 Line Sensor (Solid-State Image Sensor Array) 10 Comparison Circuit 11 Shading Correction Circuit 13 Memory (RAM)

Claims (4)

[Claims] 1. An image in which shading correction is performed on the basis of signals output by reading the reference white portion by the solid-state image pickup devices, with respect to read signals read by a plurality of solid-state image pickup devices from an original through an optical system. In the reading device, a means for storing a shading signal output from the solid-state imaging device for the shading correction, and a shading signal at an initial use stored in the storage means and a shading signal obtained after a lapse of use are compared. And a means for adjusting the optical system based on the comparison result. 2. The image reading according to claim 1, wherein the shading signal output for the shading correction is output from a limited number of pixels selected from the plurality of solid-state image pickup devices. apparatus. 3. The shading signal output for the shading correction is that an average output output from the solid-state image sensor of each area is used for each divided area of the plurality of solid-state image sensors. The image reading apparatus according to claim 1, wherein the image reading apparatus is an image reading apparatus. 4. The image reading apparatus according to claim 1, wherein the shading signal output for the shading correction is an average output from all pixels of the solid-state image sensor.