JPH0514717A - Picture reader - Google Patents

Abstract

PURPOSE:To read a picture having high quality without generating reading the together the picture recorded on the back by arranging selectably a reference white member and a black member at a position opposed to a picture read sensor. CONSTITUTION:In the case that an original D is a thick original in which information is recorded on its both sides or a one-side original in which the information is recorded on only its one side, the reference white part 26a of a roller 26 is made opposite to a lower glass guide 22. In this state, the picture information of the original is read by a glass read sensor 25 while carrying the original D between both the glass guides 21, 22. Thus the picture having the high quality in which no black frame appears usually at the circumference of the original can be read. On the other hand, in the case of reading the ordinary original in which the information is recorded on both the black part 26b of the roller 26 is mad opposite the guide 22. Thus, the picture recorded on the back is noth read together with the picture recorded on a front side.

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, and more particularly to an image reading apparatus in which an image reading sensor reads reflected light from an original while the original is being conveyed along an original conveying path.

[0002]

2. Description of the Related Art In a moving original type image reading apparatus,
The image recorded on the original is read by the image reading sensor while the original is being conveyed along the conveying path. In an apparatus using such an image reading sensor, a CCD of a photoelectric conversion element that constitutes the image reading sensor
The unevenness of the output voltage of the photoelectric conversion element (shading unevenness) occurs due to variations in the sensitivity of each pixel, an illumination system including a light source, a reflecting mirror, and the like, and an imaging system including a lens, a mirror, and the like.

Therefore, in order to correct this shading unevenness, in the image reading apparatus disclosed in Japanese Patent Laid-Open No. 1-170166, a reference white member for shading correction is provided at a position facing the image reading sensor.
Further, in the image reading device disclosed in Japanese Utility Model Laid-Open No. 3-2774, a reference white surface for shading correction is formed on a roller provided at a position facing the image reading sensor.

[0004]

The shading correction is performed by reading the reference white reflected light with an image reading sensor and taking in the data of the shading unevenness. However, the white member and the roller for shading correction are described above. Since it is located at the position facing the sensor, when reading an image of a double-sided document with information such as characters recorded on both sides, the show-through that the image on the back side is read causes a high-quality image. There is a problem that it cannot be read, and this show-through becomes remarkable in the case of a thin original. An object of the present invention is to enable a high quality image to be read without causing show-through in an original moving image reading apparatus in which a member for shading correction is arranged facing an image reading sensor. To do.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides an image reading apparatus in which an image of a document conveyed along a document conveying path is read by the image reading sensor. Is an image reading apparatus in which a reference white member and a black member are arranged so as to be selectable at a position facing each other.

[0006]

To perform shading correction using the image reading device, the reference white member is positioned so as to face the image reading sensor. Then, when reading an image of a thin double-sided original, the black member is positioned so as to face the image reading sensor. This makes it possible to surely perform shading correction and read a high-quality image.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The image reading apparatus shown in the drawings will be described below. FIG. 1 is a diagram showing a schematic structure of the image reading apparatus, and a document conveyance path from the document guide 11 to the sheet discharge tray 12 is formed in the frame of the apparatus (not shown). At the position of the document guide 11, a document detection sensor 13 for detecting that the document D is placed thereon is provided. In the document transport path, a feed roller pair 14, a document transport roller pair 15, and a document discharge roller pair 16 are sequentially arranged from the document guide 11 toward the paper discharge tray 12.

An upper glass guide 21 and a lower glass guide 22 are installed between the roller pairs 15 and 16, and the original D is placed with the side on which information such as characters is recorded facing the upper glass guide 21. It is conveyed between both glass guides 21 and 22. Light source 23 arranged in the information of upper glass guide 21
An image reading sensor, that is, a line sensor 25 for receiving the reflected light from the light source through the imaging lens 24 and reading the information of the document D is arranged opposite to the glass guides 21 and 22. The image reading sensor 25 has a document D
A large number of CCD elements, that is, photoelectric conversion elements, are linearly arranged along the lateral direction with respect to the conveyance direction of.

A roller 26 for shading correction is rotatably mounted on the lower side of the lower glass guide 22, and the roller 26 has a length corresponding to the width of the document D.
This roller 26 has a reference white portion 26a whose outer peripheral surface is white.
And a black portion 26b whose outer peripheral surface is black. By rotating the roller 26, the reference white portion 26 a and the black portion 26 are moved with respect to the image reading sensor 25.
Either b can be selected.

The light source 23 in such an image reading apparatus
The output voltage from the image reading sensor 25 may be uneven due to the illumination system such as the above, the image forming system such as the image forming lens 24, and the photoelectric conversion system such as the variation of the sensitivity of the CCD image sensor degree. Therefore, first, shading correction is performed in order to remove this unevenness. To perform this shading correction, with the light source 23 turned on, the shading correction roller 26 provided below the lower glass guide 22 is moved to the reference white portion 26a by a driving member (not shown). As shown in FIG. 1 and FIG. 2, the reflected light from the light source 23 is directed to the image reading sensor 25 so as to face the lower glass guide 22. In this state, the reflected light of the reference white portion 26a is read by the image reading sensor 25 to obtain shading unevenness data. Based on this data, the output voltage of the photoelectric conversion element when the image of the document D is read is corrected.

To read the information recorded on the document D using the image reading device, the following procedure is performed. If the original D is a thick original with information recorded on both sides or a single-sided original with information recorded on only one side,
By driving the roller 26, the reference white portion 26 a of the roller 26 faces the lower glass guide 22. In this state, the image reading sensor 25 reads the image information of the document while the document D is being conveyed between the glass guides 21 and 22. As a result, it is possible to read a high-quality image in which a black frame does not normally appear around the document.

On the other hand, when reading a normal thickness or thin original having information recorded on both sides, the black portion 26b of the roller 26 is opposed to the lower glass guide 22. As a result, a high-quality image can be read without causing the show-through that would occur when the image recorded on the back surface is read together with the image recorded on the front surface.

FIG. 3 is a diagram showing a shading correction member according to another embodiment of the present invention.
Portions similar to FIG. 2 are shown. In this case, a part or the whole of the lower glass guide 22 is made of liquid crystal to serve as a liquid crystal shutter 27. Below the liquid crystal shutter 27, a white member 2 having a white surface is provided.
8 are arranged. When the shading correction data is obtained by using such a shading correction member, the liquid crystal shutter 27 is set to the transmissive state. As a result, the light from the light source 23 is reflected by the white member 28 and then read by the image reading sensor 25 to obtain shading unevenness data.

To read an image of a thick double-sided original or a single-sided original, the lower glass guide 22 is set in a transparent state. As a result, it is possible to read a high-quality image in which a black frame does not normally appear around the document. On the other hand, when reading a thin two-sided original, the lower glass guide 22 is set to the shielded state. This makes it possible to read a high-quality image in which show-through does not occur.

FIG. 4 is a block diagram showing a control circuit of the above-mentioned image reading apparatus. Signals from an operation panel 32 provided with the original detection sensor 13, the image reading sensor 25, a reading start switch, etc. in the CPU 31. Is entered. Further, the CPU 31 has a RAM 33 and a ROM 34.
Is connected, and the shading correction data is stored in the RAM.
32 is stored. In addition, the CPU 31
From here, control signals are sent to the main motor drive circuit 35 for driving the feed roller and the like, the drive circuit 36 for driving the drive member for driving the roller 26, and other devices such as the clutch. There is. On the other hand, the image signal from the image reading sensor 25 is amplified by the amplifier 41, converted into a digital signal through the A / D converter 42, then subjected to shading correction by the shading correction circuit 43, and further binarized by the binarization circuit 44. It is output after being digitized. An image is reproduced by a printer (not shown) based on this output signal, or the output signal is stored in a recording medium.

In the binarization circuit 44, the image reading sensor 2
From the density distribution of the shading-corrected CCD output data output from No. 5, whether the output data is a portion of information such as characters or the portion of the background of the document D is determined based on a threshold value. There is. When reading an image of a thin double-sided original, the back side of the original has a black portion 2 as described above.
Since it is blackened by 6b or the like, the contrast between the image on the back side such as characters and the background of the document is reduced, and the show-through is prevented. At this time, the contrast between the characters and the like on the front side of the document and the background is slightly smaller than that when the lower side of the document is white due to the white member. for that reason,
The threshold value in the binarization circuit 44 is changed.

FIG. 5 shows C when an image is read.
It is a histogram showing the relationship between the density value output data from the CD and the frequency of the number of pixels. When a normal line image is read, the output data distribution shown by the solid line in FIG. 5 is obtained. The black and white of the image are determined by the threshold value A divided into. This threshold value A is automatically set (AE) from the distribution state of output data. For thin documents, a black member will be placed on the back, so
The distribution of the output data is as shown by the broken line, and the threshold by AE changes to the value of B. As a result, the area of the density of the characters such as the show-through character is located on the right side of the threshold value B in FIG.

FIG. 6 is a flowchart showing the operation of the image reading apparatus shown in FIG. 1, and the image reading procedure will be described based on this flowchart. When the power of the device is turned on, the CPU 31 and the like are initialized in step S1. When the document D is set on the document guide 11, the document detection sensor 13 detects the document in step S2,
In step S3, it is determined whether or not shading correction is necessary. When the shading correction is necessary, the feeding roller 14 is not driven, and the shading correction roller 26 is set to the reference white portion 26a in step S4.
Are driven so as to face the lower glass guide 22. In step S5, the light source 23 is turned on, the light from the light source 23 is reflected, and then goes to the image reading sensor 25. In this state, the reflected light of the reference white portion 26a is reflected by the image reading sensor 2
Read in 5, data of shading unevenness is taken,
Based on this data, the correction value of the output voltage from the sensor when the image of the document D is read is obtained (step S
6), this data is stored in RAM. When the shading correction is not performed, step S8 is executed after step S7.

In step S8, it is determined whether the original is a single-sided original or a double-sided original according to the setting made by the key input provided on the operation panel. If the original is a one-sided original, the feed roller 13 is driven in step S9 to convey the original D between the glass guides 21 and 22, and in step S10, the image reading sensor 2
The image reading by 5 is executed. At this time,
In step S4, the reference white portion 26a of the roller 26 is opposed to the sensor 25, and the document D is synchronized between the document conveying roller pair 15 and the document discharging roller pair 16 between the glass guides 21 and 22. It is taken and transported. The document D that has been read is discharged to the paper discharge tray 12.

On the other hand, if it is determined in step S8 that the original is a double-sided original, it is determined in step S12 whether the original is thin. When it is determined that the original is thin, the roller 26 is driven by the driving member in step S13, and the black portion 26b is moved to the glass guide 21.
It faces the image reading sensor 25 via 22. The determination of the thickness of the original document in step S12 is performed by detecting the amount of light transmitted through the original document by a transmissive sensor or directly determining the thickness of the original document by a contact sensor. In addition to the reading procedure described above, the black portion 26b may always be opposed to the image reading sensor 25 except when the shading correction is performed.

[0021]

By the shading correction member arranged facing the image reading sensor, when reading the shading correction data and when reading the image of a single-sided original, the black frame around the original is not read, and the thin double-sided When reading an image on a document, show-through is prevented, and high-quality image reading can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall structure of an image reading apparatus according to an embodiment of the present invention,

FIG. 2 is a schematic diagram showing a main part of FIG.

FIG. 3 is a schematic diagram showing a portion similar to FIG. 2 in an image reading apparatus according to another embodiment of the present invention.

FIG. 4 is a block diagram showing a control circuit of the image reading apparatus,

FIG. 5 is a histogram showing the relationship between density value output data from a CCD element and pixel frequency.

FIG. 6 is a flowchart showing an operation procedure of the image reading apparatus.

[Explanation of symbols]

13: document detection sensor, 14: feed roller pair, 1
5: Document transport roller pair, 16: Document discharge roller pair, 2
1, 22 ... Glass guide, 23 ... Light source, 25 ... Image reading sensor, D ... Original document.

Claims (1)

Claim: What is claimed is: 1. An image reading apparatus configured to read an image of a document conveyed along a document conveyance path by an image reading sensor, wherein a reference white member is provided at a position facing the image reading sensor. And an image reading device in which a black member is selectively arranged.