JPS61147666A - Optical image reader - Google Patents

Abstract

PURPOSE:To perform precise PRNU correction with a relatively low cost by constituting a light source with plural light emitting elements whose intensity of light can be controlled. CONSTITUTION:A white plate is used as an image 103 to adjust a variable voltage power source 102 on a basis of an obtained sensitivity characteristic. The intensity of emitted light of each light emitting diode is controlled independently by adjusting the variable voltage power source which supplies the voltage to individual light emitting diodes. The adjusting is so performed that the intensity of emitted light of the light emitting diode which supplies light to a high- sensitivity photo diode is reduced and that of the light emitting diode which supplies light to a low-sensitivity photo diode is increased. When the adjustment is performed completely, the sensitivity characteristic obtained by using the white plate as the image 103 is uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical image reading device, and particularly to an optical image reading device used for reading originals in devices such as copying machines and facsimile machines.

[Technical background of the invention]

2. Description of the Related Art Optical image reading devices used in copying machines, facsimile machines, etc., generally irradiate a document with light from a single light source and detect the reflected light using an image sensor. This image sensor is composed of a plurality of photoelectric conversion elements (usually a plurality of photodiodes). However, there are variations in the photoelectric conversion characteristics of each photodiode, and the photoelectric conversion characteristics within the image sensor become non-uniform. This heterogeneity is generally explained by PRNLI (PhO
-todiode Re5ponsibility N
on Uniformity).

This PRNU is defined by the following equation.

SAv Here, SAv is the average value of the sensitivity of all photodiodes constituting the image sensor, and S□8 is the sensitivity of the photodiode showing the maximum sensitivity. An example of this sensitivity characteristic is shown in FIGS. 3(a) and 3(b). The photodiodes are arranged in a section T, and each line indicates the sensitivity of each photodiode.

Note that in this figure, the sensitivity axis points toward the bottom of the figure.

FIG. 5(a) shows an example in which only one photodiode has a higher sensitivity than the others, and FIG. 2(b) shows an example in which the sensitivity decreases from right to left. Currently, the PRNU of commercially available image sensors is about 10%.

If PRNU exists in this way, faithful image reading will not be possible. Therefore, conventional devices employ various correction methods. FIG. 4 shows an example of a conventional device using an optical correction method. The light emitted from the fluorescent lamp 1 serving as the light source is
The light is reflected by the image 2, condensed by the condensing lens 3, and incident on the image sensor 4, but a shading correction plate 5 is inserted in the path of this reflected light to perform correction. The shading correction plate 5 has a light transmittance that differs depending on the location, and is designed to correct differences in sensitivity of the image sensor 4 depending on the location.

FIG. 5 is a block diagram of a conventional device using an electrical correction method. The light emitted from the light source 6 is reflected by the image 7 and passes through the reading section 8.
Detected in To perform the correction, first, a white plate is placed as a reference as the image 7, the light reflected from this white plate is detected by the reading section 8, and the result is stored in the memory 9. Next, the correction control unit 10 determines the sensitivity of each photodiode from the data stored in the memory 9, calculates a correction value for each photodiode based on this, and stores this correction value in the memory 9 again. . The above steps complete the correction preparation. When reading an actual image, the signal detected by the reading section 8 is sent to the correction section 11.

The correction control unit 10 retrieves the necessary correction value from the memory 9,
This is given to the correction section 11. The correction unit 11 performs correction based on the given correction value, and stores the result in the storage unit 12.
The image is recorded.

[Problems with background technology]

The device using the optical correction method described above only needs to be provided with the shading correction plate 5, and is relatively inexpensive.
The drawback was that precise correction was not possible. That is, it is extremely difficult to manufacture a shading correction plate for precise correction, and it is impossible to correct each pixel of an image sensor. Another disadvantage is that a space is required to insert the shading correction plate between the image and the image sensor.

On the other hand, the device using the electrical correction method described above enables precise correction of each pixel of the image sensor, but as shown in the block diagram in Figure 5, various devices are required and the cost is high. There were drawbacks.

[Purpose of the invention]

Therefore, an object of the present invention is to provide an optical image reading device that can perform precise PRNtJ correction and can be manufactured at relatively low cost.

(Summary of the Invention) The present invention is characterized in that an optical tooth reading device includes a light source made up of a plurality of light emitting elements that irradiates light onto an image to be read, and a plurality of photoelectric conversion elements that receive reflected light from the image. and a light emission intensity control means for controlling the light emission intensity of each of the plurality of light emitting elements, so that precise PRNU correction can be performed and it can be manufactured at relatively low cost be.

[Embodiments of the invention]

The present invention will be described below based on illustrated embodiments. 1st
1 is an overall configuration diagram of an optical image reading device according to the present invention, and FIG. 2 is an explanatory diagram showing an actual reading state using the device shown in FIG. 1. As shown in FIG. 1(a), the light +19i101 of this device is transmitted through a plurality of light emitting diodes 101-1.
101. -2. ..., and each light emitting diode is connected to a variable voltage power supply 102-1.1.
012. Voltage is supplied from... Light from a light source 101 is irradiated onto an image 103 as shown in FIG. 2, and this reflected light is received by an image sensor 104. The image sensor 104 is composed of an array of a plurality of photodiodes 104-1, 104-2, etc., as shown in FIG. After that, the light is received by several corresponding photodiodes.As mentioned above, the sensitivity of each photodiode varies, and as shown in Figure 1 (
b) shows this sensitivity characteristic, with each line showing the sensitivity of each photodiode. Note that the sensitivity axis is directed toward the bottom of the drawing in this figure as well.

PRNU caused by such variations in sensitivity characteristics
To correct this, you can perform the following operations. That is, after using a white plate as the image 41103 and obtaining sensitivity characteristics as shown in FIG. 1(b), the variable voltage power source 102 may be adjusted based on the sensitivity characteristics. The light emission intensity of each light emitting diode can be independently controlled by adjusting the variable voltage power supply supplying voltage to each light emitting diode.

Therefore, the light emitting intensity of the light emitting diode that supplies light to the photodiode with high sensitivity may be weakened, and the light emission intensity of the light emitting diode that supplies light to the photodiode with low sensitivity may be increased. When complete adjustment is made, the sensitivity characteristics shown in FIG. 1(b) when a white plate is used as the image 103 become uniform.

Incidentally, the light source 101 and the image sensor 104 can be integrated into an integral structure, and the image 103 can be brought into close contact with the image sensor 103 for reading. Further, as the variable voltage power supply, a voltage dividing circuit having resistive elements connected in series may be used. In this embodiment, the light emitting intensity of all of the light emitting diodes constituting the light source can be changed independently, but it may also be possible to change the light emitting intensity independently of only those parts that require PRNU correction. . For example, if the sensitivity of only the central portion of the photodiode array that makes up the image sensor tends to be high, it is sufficient to make the light emission intensity variable only for the light emitting diodes in the central portion of the light source. .

In this way, with the above-mentioned device, if the correction is made only once when the product is completed, that is, the variable voltage power supply is adjusted, there is no need to perform correction using a white plate every time the device is started up, as in the past. It disappears.

〔Effect of the invention〕

As described above, according to the present invention, in an optical image reading system, the light source is composed of a plurality of light emitting elements whose intensity can be adjusted, so that precise PRNU correction can be performed at a relatively low cost. I can do it.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an optical image reading device according to the present invention, FIG. 2 is an explanatory diagram showing a reading state using the device, FIG. 3 is a general sensitivity characteristic diagram of an image sensor, and FIG. The figure is an explanatory diagram of a conventional apparatus using an optical correction method, and FIG. 5 is a 10-step diagram of a conventional apparatus using an electrical correction method. DESCRIPTION OF SYMBOLS 1... Fluorescent lamp, 2... Image, 3... Condensing lens, 4... Image sensor, 5... Shading correction plate, 6... Light source, 7... Image, 8 ...Reading unit, 9...Memory, 10...Correction control unit, 11...
Correction section, 12... Recording section, 101... Light source, 102
...Variable voltage power supply, 103...Image, 104...
image sensor. Applicant's agent Kiyoshi Inomata 3rd drawing 5th drawing

Claims (1)

[Scope of Claims] 1. A light source consisting of a plurality of light emitting elements that irradiates light onto an image to be read, an image sensor consisting of a plurality of photoelectric conversion elements that receive reflected light from the image, and the plurality of light emitting elements. An optical image reading device comprising: a light emission intensity control means for controlling the light emission intensity of each of the above. 2. The optical image reading device according to claim 1, wherein the light emitting element is a light emitting diode. 3. The optical image reading device according to claim 1 or 2, wherein the photoelectric conversion element is a photodiode. 4. The optical image reading device according to any one of claims 1 to 3, wherein the light emission intensity control means is a variable voltage power supply.