JPS63258160A - Picture reader - Google Patents

Abstract

PURPOSE:To improve picture quality by correcting the output of a photodetector based on a peak voltage of a reflected luminous quantity of an original read region and a white member at its end so as to make the output picture stable. CONSTITUTION:A read white member 22 and an edge white member 21 of a white member 20 provided to an original read position of a photodetector 3 are read by the photodetector 3 prior to read of an original 2. A peak value obtained by reading the edge white member 21 and a peak value obtained by reading the white member 22 are fetched in a control section 5 respectively via A/D converters A10, B11, and the peak value to be obtained corresponding to the edge white member 21 is obtained by calculation in reading the original based on the values. An output voltage of the edge white member 21 obtained at the start of read period of each line of the original is fetched during the reading of the original and the gain of an amplifier 4 is controlled by the control section 5. Thus, the peak value corresponding to the edge white member 21 is used and excellent correction is executed to the picture signal obtained from the original read region L2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image reading device that uses a light receiving element to read reflected light from the surface of a document, and more particularly to image reading devices such as copying machines and facsimile machines.

[Prior art]

In copying machines, facsimile machines, etc., in order to handle document image information electrically, the document is exposed to light from a light source, and the intensity of the reflected light is detected by a light receiving element such as a COD image sensor, thereby converting the density of the image into an electrical signal. An image reading device is used that converts and outputs the image.

In such a device, in order to always keep the reading output at a predetermined level, it is necessary to control the light source and the amplification factor of the output signal so that the output value read by the light receiving element on the white reference member remains constant. Are known.

However, for example, a method that includes a white member outside the original reading area of the light receiving element, compares the peak holding voltage of the read output with a reference voltage, and controls the gain of the amplifier to keep the peak holding voltage constant is not possible. It had the following drawbacks.

That is, the relative values of the peak holding voltage obtained by reading the member and the peak holding voltage obtained by reading the original with the same density are not equal due to non-uniformity of the amount of light from the light source and variations in the optical system. Therefore, the gain of the amplifier is not optimal at the peak value of the end white member, which deteriorates the image quality.

〔the purpose〕

The present invention aims to eliminate the drawbacks of the above-mentioned conventional example, and it is possible to obtain good output even if there are variations due to variations in the light source, mechanical parts on the optical system, and assembly, and improve image quality. An object of the present invention is to provide an image reading device that enables improved performance.

〔Example〕

Hereinafter, the present invention will be explained in detail using preferred embodiments.

1, 2, and 3 show embodiments of an image reading device to which the present invention is applied. In FIG. 1, 1 is a light source, 2 is a document,
3 is a light receiving element; 4 is an amplifier whose gain is variable by external control; 5 is a control unit that controls the operation timing of each part and calculates A/D converted digital data to output optimal gain data for the amplifier 4; 6 is a switch A, 7 is a switch B, 8 is a peak holding circuit A, 9 is a peak holding circuit B110 is an A/D converter A111 which A/D converts the peak voltage held in the peak holding circuit A8 is a peak holding circuit A/D converts the peak voltage held in B9 to A/D
Transducer B120 is a white member. Further, in FIG. 2, 21 is a white end member, 22 is a reading white member, and 23 is a white end member.
is a lens.

Next, the operation of the above configuration will be explained.

Before reading the original 2, the white member 20 provided at the original reading position of the light receiving element 3 reads the white member 22 and the end white member 21 by the light receiving element. In addition, white member 2
0 has at least the main scanning width of the light receiving element 3, which is larger than the width of the original to be read, and the width of the white member to be read 2
0 corresponds to the document reading area L2 of the light receiving element 3, and the end white member 21 corresponds to the edge area L1 outside the document reading area L2. Moreover, both day-colored members 21 and 22 have the same density.

When the original 2 does not exist in the original reading area, a waveform as shown in FIG. 3 is obtained from the light receiving element 3 as analog video data. In FIG. 3, the horizontal axis shows the waveform for -line in time, and the vertical axis shows voltage. Output obtained by reading the end white member 21! , and the output obtained by reading the white member 22 is ! , in the range of .

When the control section 5 closes the switch A6 using the control signal S1, the voltage value VPI is obtained as the output of the peak holding circuit A8. Similarly, if the switch B7 is always kept closed here, the voltage value VP2 is obtained as the output of the peak holding circuit B9.

In this way, the peak value obtained by reading the end white member 21 and the peak value obtained by reading the read white member 22 are different even though they are for the same white color. Therefore, if the level correction of the output from the light receiving element 3 regarding the document reading area L2 is performed based on the peak value obtained by reading the end white member 21,
If the correction operation is performed based on a value different from the actual peak value in No. 2, and there is a large difference between the two peak values, a good correction operation will not be performed.

Therefore, the gain of the amplifier 4 is determined in consideration of the difference between the two peak values V pHV p2.

That is, the peak values V P r I V p 2 obtained as described above with the document 2 not at the document reading position are respectively expressed as A
/D converters AIO, Bll to the control unit 5, and from these values, the peak value V'2. that should be obtained corresponding to the end white member 21 when reading the original is determined. Calculate and find.

That is, the optimum peak output voltage of the amplifier 4 is vP□.

Then, the gain of the amplifier 4 is adjusted so that the peak holding output voltage of the reading output of the end white member 21 by the peak holding circuit A becomes as follows when reading a document. This provides optimal analog video data.

During reading of the original, the control unit 5 controls the output voltage of the peak holding circuit A8 of the end white member 21 obtained at the beginning of the reading period of each line of the original to the A/D converter A.
It is taken in via IO, and the taken-in value is V'2. The gain of the amplifier 4 is controlled by the control unit 5 so that .

As described above, using the peak value corresponding to the end white member 21, good correction is performed on the image signal obtained from the document reading area L2.

In the above embodiment, the output level was corrected by adjusting the gain of the amplifier 4, but the peak value obtained from the end white member 21 is adjusted by setting the amplifier 4 to a fixed gain and changing the light amount of the light source iff. fist so that it becomes V'PI
It is clear that similar results can be easily obtained by controlling the Furthermore, the reference level of a converter that converts analog output into digital may be controlled.

Further, in the above embodiment, VF6>VPI, but VP
Similar results can be obtained even if 2=VP1.

Furthermore, in the embodiment, the reading white member 22
When reading a document with a higher reflectance than , the peak holding voltage V P2MAI held in the peak value holding circuit B9 is A/D converted by the A/D converter Bll at the optimum gain, The gain of the amplifier 4 may be controlled by the control unit 5 so that the peak holding voltage of the end white member 21 can be obtained.

〔effect〕

As explained above, according to the present invention, by correcting the output of the light receiving element based on the peak voltage of the amount of light reflected from the document reading area and the white member at the end thereof, it is possible to prevent aging of the light source, etc. Variations in tolerance can also be easily absorbed, which has the effect of stabilizing the output image and improving the image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image reading device to which the present invention is applied, FIG. 2 is a diagram showing the relationship between the white member 20 and the light receiving element, and FIG. 3 is a diagram of the analog video signal waveform when the white member 20 is read. It is a figure showing an example. In the figure, 1 is a light source, 2 is a document, 3 is a light receiving element, 4 is an amplifier, 5 is a control unit, 6.7 is a switch, 8.9 is a peak voltage holding circuit, 10.11 is an A/D converter, 20 is a white member.

Claims (3)

[Claims] (1) In an image reading device that reads reflected light from a document using a light receiving element, a first white member is provided at the main scanning end of the light receiving element outside the document reading area, and a second white member is provided at the main scanning end within the document reading area. and a white member, and the document reading output is corrected based on each white peak voltage obtained by reading the first white member and the second white member with the light receiving element. Image reading device. (2) An image reading device according to claim 1, characterized in that the amount of amplification of the light receiving element output is adjusted. (3) An image reading device according to claim 1, characterized in that the amount of light of a light source for reading a document is adjusted.