JPH0779324A - Picture reader - Google Patents

Abstract

PURPOSE:To provide a picture reader reading a spatially bent original such as a book which measures a distance an original face with simple configuration by using a read sensor with high accuracy and in which all faces of the original are focused and a beautiful picture without fog is obtained. CONSTITUTION:A sensor 7 being an image pickup element reads an original 10 surface put on an original platen 1 and an original end face while scanning simultaneously the face of the original and an original end face reflected in a mirror 5 arranged to a rear part of a depth of the original platen 1 with a tilt. Number of picture elements of image pickup elements corresponding to an edge of a read original end face is detected and a distance up to a face of the original 10 is obtained through conversion based on the number of picture elements. The image of the original is formed onto the sensor 7 based on the measured distance.

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 for photographing a book document or the like from above, and relates to a technique for measuring the distance to the document surface and performing focusing processing at the time of image pickup.

[0002]

2. Description of the Related Art Conventionally, as an image reading device for reading a spatially bent original such as a book, a camera type device in which an area sensor is arranged in a film portion of a silver halide camera is known. In this device, within one area of the subject, the lens was focused only on the major part of the area. In addition, for example, in Japanese Utility Model Laid-Open No. 50-7811.
As disclosed in Japanese Patent Laid-Open No. 4 (1994), a film sensor of a silver halide camera provided with a line sensor in place of the film so as to be capable of scanning is also known. On the other hand, JP-A-3-11796
As disclosed in Japanese Patent No. 5 publication, it is known that an image is corrected by expanding the photographed image according to the degree of bending of the document surface. Although it is an apparatus for photographing a downward document, as shown in Japanese Patent Application Laid-Open No. 4-238457, the document height is obtained by scanning the document edge with a sensor and detecting the edge shape. Is known to be corrected.

[0003]

However, in the image reading apparatus using the area sensor, when the image of a bound document is read from above, the paper surface is usually bent at the seam of the book. Since the height of the original is high and low, if you focus on the main part in the area of the original, the other parts will not be in focus, and the focus will be blurred, and you will not be able to obtain a beautiful image. was there. Further, the above-mentioned Japanese Utility Model Laid-Open No. 50-78114 and Japanese Patent Laid-Open No. 3-117965 do not disclose focusing at the time of photographing. In addition, JP-A-4-23
The apparatus disclosed in Japanese Patent No. 8457 requires a sensor separate from the imaging sensor in order to detect the end shape of the document, and the document is not read by placing it upward.

The present invention is intended to solve the above-mentioned problems, and is an image reading apparatus for reading a spatially curved original such as a book, in which a reading sensor is used and the original surface up to the original is read. It is an object of the present invention to provide an image reading apparatus capable of measuring a distance with high accuracy and focusing on all surfaces of a document, and capable of obtaining a beautiful image without fear.

[0005]

In order to achieve the above object, the present invention is an image reading apparatus for reading a document placed on a document table by optical scanning, inclining to the rear rear side of the document table. Corresponds to the arranged mirror, the image sensor that reads while scanning the surface of the document placed on the document table and the document end face reflected on the mirror at the same time, and the edge part of the document end face read by the image sensor A distance measuring means for detecting the number of pixels of the image sensor and converting the number of pixels into a distance from the image sensor to the document surface, and an image of the document on the document table based on the distance measured by the distance measuring means. And an optical system for forming an image on the image pickup device.

[0006]

According to the above construction, the image pickup device simultaneously scans the document surface placed on the document table and the document end surface reflected on the mirror inclined at the rear of the document table. While reading. The distance measuring unit detects the number of pixels of the image pickup element corresponding to the edge portion of the read document end surface, and calculates the distance to the document surface from this number of pixels. The optical system forms a document image on the image sensor based on the measured distance value. In this way, the original can be imaged while focusing on all sides of the original.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of the image reading apparatus. In the figure, a document such as a book or a file is placed upward on a document table 1 of the image reading apparatus, and an imaging camera unit 2 for reading the document by reading scanning is provided at a position where the document can be read from above. A predetermined space is provided between the document table 1 and the imaging camera unit 2, and a work space is formed by this space. Further, in this apparatus, an illumination unit 3 arranged above the document table 1 for illuminating a document, an operation unit 4 for setting image reading conditions, and the like are provided at the end of the document table 1 at the end of the photographing range. A range-finding mirror 5 that is arranged in the sub-scanning direction and that captures the edge shape of the document is provided, and a control unit (not shown) is provided. The edge shape of the document imaged on the range-finding mirror 5 is read by the image capturing camera unit 2 and converted into the height distance of the document surface from the number of pixels of the image sensor of the image capturing camera unit 2.

FIGS. 2 and 3 respectively show schematic configurations of the apparatus as viewed from the front and the sides. The image pickup camera unit 2 is an optical system for forming a document image on an image pickup element, and a taking lens 6 driven by an autofocus (AF) motor,
CCD line sensor 7 that scans in the sub-scanning direction (direction indicated by an arrow in FIG. 2) on the focal plane on which the document image is formed.
Consists of. A part of the CCD line sensor 7 reads the image of the end shape of the original document reflected on the distance measuring mirror 5. The document 10 placed on the document table 1 is, for example, a book or file in which each page has a columnar shape in which each page is spatially curved when closed at one end and opened left and right. The distance measuring mirror 5 also functions as a stopper for document positioning that extends in the left-right direction on the back side of the document table 1, and is installed at an angle of 45 degrees with respect to the surface of the document table 1. The original 10 is aligned by applying the upper end of the original 10 to the lower end of the distance measuring mirror 5. The document table 1 is colored darker than the background density of the document.

FIG. 4 is a diagram showing the principle of distance measurement.
Is placed at a predetermined position, a mirror image 11 of the original 10 is formed by the distance measuring mirror 5, and a mirror image of the end surface of the original is continuously formed on the extension line of the image of the original table 1 to the original image. It should be noted that the reading range of the image pickup device is shown by a chain line 12. The pixels of the CCD line sensor 7 are indicated by 1 to n.

FIG. 5 shows the image data read in the state of FIG. In the figure, a is a document image, b is a document table image, and c.
Is a portion reflected on the range-finding mirror, d is an image of the end face of the document, and e is a reference for aligning the document. The image d on the end surface of the document is read as if the height of the image was slightly distorted upward due to its height change. Since the document and its end face are illuminated by the illumination unit 3, the entire document is read in white. On the other hand, since the document table 1 is colored, the amount of incident light is small and the image is read in black where the document end face of the distance measuring mirror is not visible.

Here, the factors that determine the angle of the distance measuring mirror 5 will be described. The distance-measuring mirror 5 has not only the function of simply obtaining a mirror image of the document end face, but also the function of applying illumination light to the document end face. As a result, it is possible to perform distance measurement even on a document whose paper has turned yellow over the years. In addition, by shooting the edge of the document slightly from the bottom (that is, from the front side), even if the document has a small thickness for a few pages and the edge shape is difficult to recognize due to the difference in density, measurement can be performed using the difference in density from the platen. It is possible to do. Further, if the image is taken from the bottom too much, an object other than the document may be reflected in the visual field. These external objects usually have little influence on the distance measuring function due to low illuminance, out of focus, and the like. However, if light from an external light source enters the sensor directly via the mirror, an error may occur. From the above viewpoint, it is necessary to set the mirror angle together with the focal length and the angle of view of the taking lens 6.

FIG. 6 shows an output example of one line in the main scanning direction by the CCD line sensor 7. The horizontal axis shows the number of pixels of the line sensor (left ... back side, right ... front side), and the vertical axis shows the sensor surface illuminance. Is the part of the document on which the edge of the document is not visible, is the part of the document that is projected on the ranging mirror,
Is a document portion, and is a document table portion. L1 is the illuminance threshold value, and n1 and n3 are the minimum pixels that pass the threshold value L1.
The maximum value, n2, is the pixel (fixed) corresponding to the document reference position. (N2-n1) is the number of pixels corresponding to the height of the document. Further, (n3-n2-α) is the number of pixels corresponding to the dimension of the document in the front-rear direction. α is a curved portion at the lower end of the document due to a change in the document height, and the document height at this portion (n2-n
It is a value determined by 1). When the CCD line sensor 7 moves in the left-right direction (sub-scanning direction), the value of n1 changes, so that the distribution of distance measurement values in the left-right direction of the document can be obtained. In addition, it is possible to detect the lateral dimension in which the illuminance on the sensor surface is entirely reduced.

FIG. 7 shows a block configuration of a distance measuring circuit in the control unit. The output of the sensor 7 is A / D converted by the A / D converter 21 and then input to the comparator 22. A threshold value is preset in the comparator 22 by the CPU 23. When the output that exceeds the threshold value is input to the comparator 22, the counter 24 is set. The CPU 23 stores the minimum / maximum value of the count value of the counter 24.
From this, the distance corresponding to the document height is calculated and
At the same time, the horizontal dimension of the document can also be obtained.
The CPU 13 uses the sensor moving unit 25 based on the document height distance.
To output a command to the sensor 7 for focusing operation,
In addition, a command is output to control the lighting of the lighting unit 3.

Next, the reading operation with the above configuration will be described with reference to the flowchart of FIG. When a reading operation start command is input, the lamp of the illumination unit 3 is turned on to illuminate the document 10 (# 1). Next, the prescan for the distance measuring operation is started (# 2). In this distance measuring operation, the CCD line sensor 7 is moved to the left from one end to capture an image, thereby counting a predetermined number of pixels as described above, storing this value (# 3), and ending the prescan. At that time (# 4), the document height and document size are calculated by calculation (# 5). Then, the CCD line sensor 7 is moved rightward this time while performing a main scan for picking up an image of a document (# 6). At this time, the focusing operation and magnification change of the taking lens 6 are performed based on the value obtained by the prescan. After that, the lamp is turned off (# 7), and the process ends. As described above, by performing the focusing operation of the taking lens 6 according to the height of the document imaged by the CCD line sensor 7, it is possible to obtain a beautiful image with no fear.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, the distance measurement operation is performed by the prescan before the image pickup operation is performed, but the distance measurement and the focus adjustment may be simultaneously performed during the image pickup operation. Further, in the above embodiment, the focusing is performed only by moving the lens using the single focus lens, but the zoom lens is used to correct the magnification in the main scanning direction at the same time as the focusing, and It is also conceivable to move the sensor integrally to correct the magnification in the main scanning direction simultaneously with focusing. Further, in the above-described embodiment, the distance measuring / focusing operation is performed every time the line sensor moves by one line, but it may be performed not every line but every several lines.

[0016]

As described above, according to the present invention, when a document such as a book is scanned by the image sensor and photographed,
Since the optical system is adjusted so that all the sides of the original are in focus, beautiful images can be obtained at all times. Further, since the distance measurement of the document surface and the reading of the document are performed by the same image sensor, the distance measurement can be performed with the same accuracy as the document reading resolution and at the same reading speed, and the configuration is simplified. In addition, operability is excellent because there is no need for strict document alignment. In addition, if you perform distance measurement with pre-scan and read with main scan,
Since the reading time does not increase, the reading accuracy does not decrease.

[Brief description of drawings]

FIG. 1 is a perspective view of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the image reading apparatus as viewed from the front.

FIG. 3 is a schematic configuration diagram of the image reading apparatus viewed from the side.

FIG. 4 is a diagram showing a principle of distance measurement in the image reading apparatus.

FIG. 5 is a diagram showing read image data.

FIG. 6 is a diagram showing an example of output for one line by an image sensor.

FIG. 7 is a block diagram of a distance measuring circuit of the image reading apparatus.

FIG. 8 is a flowchart showing a reading operation.

[Explanation of symbols]

 1 Document Plate 5 Distance Mirror 6 Lens 7 CCD Line Sensor 10 Document 23 CPU 24 Counter

Claims (1)

[Claims] 1. An image reading apparatus for reading a document placed on a document table by optical scanning, wherein a mirror disposed obliquely rearward and rearward of the document table, and a document placed on the document table. Surface of the document and the end face of the document reflected on the mirror are read while scanning, and the number of pixels of the image sensor corresponding to the edge portion of the end face of the document read by the image sensor is detected. Distance measuring means for converting the distance from the image pickup device to the document surface, and an optical system for forming an image of the document on the platen on the image pickup device based on the distance measured by the distance measuring device An image reading device characterized by.