JP2872236B2 - Image reading device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus that reads reflected light from a document surface using a light receiving element, and more particularly to an image reading apparatus such as a copying machine or a facsimile. [Prior art] In a copier, facsimile, or the like, in order to electrically handle document image information, a document is exposed by a light source, and the intensity of the reflected light is detected by a light receiving element such as a CCD image sensor, whereby the image is 2. Description of the Related Art An image reading apparatus that converts a shade into an electric signal and outputs the electric signal is used. In such an apparatus, the light source and the amplification factor of the output signal can be controlled so that the output value obtained by reading the white reference member by the light receiving element is constant so that the read output is always at a predetermined level. Are known. However, for example, in a method in which a white member is provided outside the document reading area of the light receiving element, the peak holding voltage of the reading output is compared with a reference voltage, the gain of the amplifier is controlled, and the peak holding voltage is kept constant. There were the following disadvantages. That is, the relative value between the peak holding voltage obtained by reading the member and the peak holding voltage obtained by reading the same density original is not equal due to the non-uniformity of the light source light amount and the variation of the optical system. Therefore, the gain of the amplifier is not optimized at the peak value of the white end member, and the image quality is degraded. [Purpose] The present invention aims to eliminate the above-mentioned drawbacks of the conventional example, and it is possible to obtain a good result even when there is a variation in peak voltage due to a variation in a light source and a variation in assembly of mechanical parts on an optical system. An object of the present invention is to provide an image reading apparatus capable of obtaining an output and improving the image quality. EXAMPLES Hereinafter, the present invention will be described in detail using preferred examples. 1, 2 and 3 show an embodiment of an image reading apparatus to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a light source, 2 denotes a document, 3 denotes a light receiving element, and 4 denotes a gain variable by external control. 5 is the operation timing control of each part and A / D
A control unit that operates on the converted digital data and outputs the optimum gain data of 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 B, and 10 is a peak holding circuit. The peak voltage held in circuit A8 is
A / D converters A and 11 for A / D conversion are A / D converters B and 20 for A / D converting the peak voltage held in the peak holding circuit B9, and a white member. In FIG. 2, 21 is a white member at the end,
22 is a reading white member, and 23 is a lens. Next, the operation of the above configuration will be described. Before reading the original 2, the reading white member 22 and the end white member 21 of the white member 20 provided at the original reading position of the light receiving element 3 are read by the light receiving element. The white member 20 is
It has at least the main scanning width of the light receiving element 3 and is larger than the width of the original to be read. The white reading member 22 corresponds to the original reading area L2 of the light receiving element 3 and the white end member 21
Corresponds to the end area L1 outside the document reading area L2.
Further, both white members 21 and 22 have the same density. When the document 2 is not present in the document 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 of one line in time, and the vertical axis shows the voltage. In the range of the output l ₁ obtained by reading the end white member 21, the read white member
Output obtained by reading the 22 is in the range of l _2. When the control unit 5 closes the switch A6 by the control signal S1, a voltage value VP1 is obtained as an 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. As described above, 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 in spite of the same white color.
Therefore, if the level correction of the output from the light receiving element 3 with respect to the document reading area L2 is performed based on the peak value obtained by reading the end white member 21, it differs from the actual peak value in the document reading area L2. Correction operation is performed based on the values, and if there is a large difference between the two peak values, good correction operation is not performed. Therefore, the gain of the amplifier 4 is determined in consideration of the difference between the two peak values _VP1 and _VP2 . That is, each peak value V _P1, V _P2 the original 2 are obtained as described above with no document reading position s, the control unit 5 via the A / D converter A10, B11 upon uptake document read therefrom value , The peak value V ′ to be obtained corresponding to the end white member 21
Calculate and find _P1 . That is, _assuming that the optimum peak output voltage of the amplifier 4 is V _PREF , the peak holding output voltage by the peak holding circuit A of the reading output of the end white member 21 at the time of reading the document is The gain of the amplifier 4 is adjusted so that As a result, optimal analog video data can be obtained. During reading of the document, the peak value _{VP1 of the} output obtained by reading the end white member 21 at the beginning of the reading period of each line of the document is held in the peak holding circuit A8, and the output voltage _VP1 is The control unit 5 takes in the data via the A / D converter A10. Then, the control unit 5 controls the gain of the amplifier 4 so that the captured value V _P1 becomes V ′ _P1 obtained by the equation (1). As described above, the peak value V _P1 corresponding to the end white member 21 is obtained.
, 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. However, the amplifier 4 was set to have a fixed gain, the light amount of the light source 1 was changed, and the peak obtained from the end white member 21 was changed. it is clear that the ease similar results obtained by a value is controlled to be V _'P1. Further, a reference level of a converter for converting an analog output into a digital signal may be controlled. In the above embodiment, VP2> VP1, but VP2 = VP1
, The same result is obtained. Further, in the above embodiment, the reading white member 22
When reading documents with higher reflectance than the peak holding voltage held in the peak value holding circuit B9 at the optimum gain
A / D conversion of V _P2MAX by A / D converter B11, The gain of the amplifier 4 may be controlled by the control unit 5 so as to obtain the peak holding voltage of the end white member 21 as follows. [Effect] As described above, in the image reading apparatus of the present invention, the first white member provided outside the document reading area, the second white member provided inside the document reading area, First, the first and second white members are read by a light receiving element to form first and second reference level signals, respectively.
Forming means for forming a third reference level signal based on the ratio of the reference level signals; and obtaining an image signal of the original by reading the original while reading the original.
The fourth reference level signal is obtained by reading the white member of the above with the light receiving element, and the reference level of the obtained fourth reference level signal is the same as the reference level of the third reference level signal. And signal level correcting means for correcting the signal level of the original image signal. With such a configuration, aging of the light source or the like or variation in the tolerance of mechanical assembly occurs, and a first reference level signal formed by reading the first white member with the light receiving element; Even when the ratio of the second reference level signal formed by reading the second white member by the light receiving element changes, the second reference level signal based on the ratio between the first reference level signal and the second reference level signal changes. 3 and the reference level of the fourth reference level signal obtained by reading the first white member during reading of the document becomes the same as the reference level of the third reference level signal. As described above, since the signal level of the document image signal is corrected, the output image can be stabilized and the image quality can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an image reading apparatus to which the present invention is applied, FIG. 2 is a view showing a relationship between a white member 20 and a light receiving element, and FIG. FIG. 7 is a diagram showing an example of an analog video signal waveform at the time. 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 and 7 are switches, 8, 9 are peak voltage holding circuits, 10, 11 are A / D converters, 20 is a white member.

Claims (1)

(57) [Claims] A first white member provided outside the document reading area, a second white member provided inside the document reading area, and reading the first and second white members with a light receiving element before reading the document. Forming means for forming first and second reference level signals and forming a third reference level signal based on a ratio of the first and second reference level signals; A document image signal is obtained by reading the document, and a fourth reference level signal is obtained by reading the first white member with the light receiving element. The reference level of the obtained fourth reference level signal is Signal level correction means for correcting the signal level of the original image signal so as to be the same as the reference level of the third reference level signal. Image reading device.