JPH07245680A - Image reader and copying machine incorporating it - Google Patents

Abstract

PURPOSE:To reduce a detection processing time while keeping detection accuracy required for an original placing position of the image reader. CONSTITUTION:An image of an original 55 placed on a platen glass 19 is subject to preliminary scanning prior to main scanning of the image of the original and the original placing position is detected in the preliminary scanning based on image information from a line sensor 17. The image information in the preliminary scanning is stored in a page memory in which addresses corresponding to the main scanning direction and the subscanning direction are set in the original placing position detection means of the image reader and the original placing position is obtained based on addresses of the image information stored in the page memory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device and a copying machine incorporating the same.

[0002]

2. Description of the Related Art Conventionally, there has been known an image reading apparatus which converts an image on a document table into an electric signal by a photoelectric conversion element such as a CCD to generate image data of the document image. Usually, the image reading apparatus is implemented in a form incorporated in a part of a digital copying machine or a form connected to a printer or a filing device.

Generally, an image reading apparatus performs image processing such as binarization before outputting image data. By the way, the original placed on the original table rarely has a size that covers the entire surface of the original table, and the original is often smaller than the original table. Therefore, if the position where the document is actually placed on the platen can be detected and the image processing can be performed only on the image data corresponding to the detected position, the time required for the image processing can be shortened. Is possible and desirable.

Therefore, various methods for detecting the position of the original document on the original table have been conventionally proposed. For example, Japanese Patent Application Laid-Open No. 56-105579 discloses an image reading device which reads the entire surface of a document table, stores image data in a page memory, and detects the position of a document from the image data in the page memory. There is.

Further, in Japanese Patent Laid-Open No. 61-244169, image reading is performed in which a document image area is discriminated by prescanning the document before reading the document image, and only image data in the document image area is output to a printer. A device is disclosed. In this image reading device, the main scanning direction 1
The image data for the line is stored in the line memory, and the edge of the image in the line is detected based on the image data stored in the line memory. By performing this step for every line in the sub-scanning direction, the position of the document is detected.

[0006]

Problems to be Solved by the Invention JP-A-56-1055
According to Japanese Patent Publication No. 79, since all the information on the platen including the original is read and stored in the page memory, image processing is performed on the entire area of the page memory. It has a problem that it takes time. For example, in a general image reading apparatus, in many cases, even a document table having an A3 size can be placed. However, in the image reading apparatus disclosed in Japanese Patent Laid-Open No. 56-105579, even when an A5 size original is placed, all image data on the original table is stored in an image memory corresponding to the A3 size, and an A3 size image is stored. A process for detecting the position of the document is performed on the entire area of the memory. If an image is read at 400 DPI, the amount of image data will be less than 4 megabytes.

In the apparatus disclosed in Japanese Patent Laid-Open No. 61-244169, the document position in the main scanning direction is detected by the image data stored in the line memory, and the document position in the sub scanning direction is the mechanical position of the scanning means. Is detected by. Therefore, there is a problem in the accuracy of detecting the document position in the sub-scanning direction.
Further, in order to accurately determine whether the image detected on a certain line is a document or dust adhering to the document table, information several lines before is also necessary. However,
In this conventional apparatus, since only one line of image data can be stored, it is impossible to detect whether or not the detected image is dust.

The present invention has been made in view of the above problems, and an object thereof is to provide an image reading apparatus capable of easily detecting the position of a document on a document table.

[0009]

In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an original table on which an original is placed, an original placed on the original table is read for each pixel, and each pixel is read. Reading means for outputting image data corresponding to the above, thinning means for thinning out the image data output from the reading means, and image data output from the thinning means for the entire area of the original table. A page memory for storing an amount corresponding to a predetermined amount, and a detection unit for detecting the position of the document on the document table based on the image data stored in the page memory.

According to a second aspect of the present invention, in the apparatus according to the first aspect, the reading means includes the line sensor in which a plurality of photoelectric conversion elements are arranged in the main scanning direction, the line sensor, and the original document. Of the page memory, and scanning means for scanning the image in the sub-scanning direction perpendicular to the main scanning direction, and control means for controlling the scanning means so that the line sensor performs preliminary scanning and main scanning of the document. Stores the image data output from the line sensor during the preliminary scanning, and the control means controls the scanning speed of the line sensor during the preliminary scanning to be faster than the scanning speed during the main scanning. It is characterized in that the scanning means is controlled.

According to a third aspect of the present invention, in the apparatus according to the first aspect, the detection means specifies an address designating means for designating an address in the page memory and an address designated by the address designating means. The leading edge determining unit that determines whether the image data is the leading edge of the document, and the leading edge determining unit detects the leading edge of the document,
A first address increment means for incrementing the address by 1 while incrementing the address by a first predetermined unit larger than 1 after the leading edge of the document is detected by the leading edge determination means. Is characterized by.

According to a fourth aspect of the present invention, in the apparatus according to the third aspect, the detecting means determines whether or not the image data of the address designated by the address designating means is the trailing edge of the original. When the trailing edge of the original is detected by the trailing edge discriminating means and the trailing edge discriminating means, the address is decremented by a second predetermined unit smaller than the first predetermined unit, and the trailing edge discriminating means is again generated. In order to detect the trailing edge of the document, a second address increment means for incrementing the address by 1 is provided.

According to a fifth aspect of the present invention, in the apparatus according to the third aspect, the leading edge discriminating means includes a third predetermined line including one line in the main scanning direction corresponding to the address designated by the address designating means. It is characterized in that the front end of the document is detected by referring to the image data for a unit.

According to a sixth aspect of the present invention, in the apparatus according to the fifth aspect, the image data at the address of the third predetermined unit corresponds to several millimeters on the original.

According to a seventh aspect of the present invention, in the apparatus according to the second aspect, first binarizing means for binarizing the image data output from the line sensor at the time of preliminary scanning, and at the time of main scanning. A second binarizing means for binarizing the image data output from the line sensor;
The threshold value of the binarizing means is higher than the threshold value of the second binarizing means.

The invention according to claim 8 relates to a copying machine in which the image reading device is incorporated, and a document table on which a document is placed and a line sensor in which a plurality of photoelectric conversion elements are arranged in the main scanning direction. And scanning means for causing the line sensor to scan an image of the original document in a sub-scanning direction perpendicular to the main scanning direction, and control for controlling the scanning means so that the line sensor performs preliminary scanning and main scanning of the original document. Means, thinning means for thinning out image data output from the line sensor during the preliminary scanning, and image data output from the thinning means in an amount corresponding to the entire area of the document table. With reference to a page memory and image data stored in the page memory, detecting means for detecting the position of the original on the original table, and the main scanning in relation to the detection result of the detecting means. An image processing unit that processes image data output from the line sensor at some times; and an image forming unit that forms an image corresponding to the image data processed by the image processing unit on a sheet. To do.

[0017]

In the image reading apparatus of the present invention, the image of the original placed on the original table is read by the reading means pixel by pixel. The image data output from the reading means is thinned out and then stored in the page memory. To thin out image data, there is a method of thinning out the image data by electrical processing. However, in an apparatus for reading an image by sub-scanning of a line sensor as described in claim 2, the scanning speed at the time of pre-scanning at the time of main scanning By making the scanning speed higher than the scanning speed of, the amount of image data thinned out in the sub-scanning direction can be obtained.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a digital copying machine to which the present invention is applied. The digital copying machine includes a reading unit 10 which is an image reading apparatus of the present invention, and a printing unit P which forms an image corresponding to image data transmitted from the reading unit 10 on a sheet.

The reading unit IR reads an image of a document placed on the platen glass 19 and generates image data corresponding to each pixel of the image of the document. A first scanner 11 having an exposure lamp 12 and a first mirror 13a
Driven by the second scanner 14 having the second and third mirrors 13b and 13c and the scan motor M2, arrows b and b '.
Direction (sub-scanning direction). The light from the exposure lamp 12 is reflected by the document on the platen glass 19 and is applied to the line sensor 17 via the mirrors 13a, 13b, 13c and the lens 15. The line sensor 17 has a large number of photoelectric conversion elements (CCD) arranged in a direction (main scanning direction) orthogonal to the paper surface of FIG. 1, reads an image at 400 DPI, and outputs image data corresponding to each pixel.
In addition, as described above, the first scanner 11 and the second scanner 1
By moving 4 in the directions of arrows b and b ′, the line sensor 17 can subscan the original image. The sensor SE3 is for detecting that the first scanner 11 is at the home position. The scan motor M
When moving the scanners 12 and 14 in the direction of arrow b, the scanner 2 moves at a higher speed than when moving in the direction of arrow b ′. That is, the scanning of the image by the line sensor 17 when the scanners 12 and 14 move in the direction of arrow b is the preliminary scanning, and the position of the document on the document table is determined based on the image data output from the line sensor 17 at this time. Is detected.
On the other hand, the scanning of the image by the line sensor 17 when the scanners 12 and 14 move in the direction of the arrow b ′ is the main scanning, and the printing of the image is performed based on the image data output from the line sensor 17 at this time. Be seen.

Further, the platen glass 1 of the original cover 50
The surface on the 9 side is colored in orange. As a result, the light reflected by the original cover 50 of the light from the exposure lamp 12 becomes a color having a low spectral sensitivity for the line sensor 17. That is, for the line sensor 17, it is the same as the document cover being black. Therefore, since the background of the document is normally white, the line sensor 17 can distinguish the document from the lower surface of the document cover 50 even when the document cover is closed. Even when the document cover 50 is not closed, the illumination light of the document cover 50 by the exposure lamp 19 does not reach the line sensor 17, and the illumination light of the document reaches the line sensor 17, so that the document area can be identified. is there.

The image data output from the line sensor 17 is processed by the image processing unit 20 and then transmitted to the memory unit 30. The memory unit 30 temporarily stores the image data received from the image processing unit,
Alternatively, it is directly transmitted to the print section P.

Next, the print section P will be described. The print processing unit 40 controls the laser optical system 60 based on the image data received from the memory unit 30. The laser optical system 60 emits a laser beam modulated (ON / OFF) controlled by the print processing unit 40, and a laser beam emitted from the semiconductor laser 61 for scanning the photosensitive drum 71. The polygon mirror 62, the fθ lens, the mirror 64a,
64b and 64c.

Around the photosensitive drum 71 which is rotationally driven in the direction of arrow c, along the rotational direction (direction of arrow c), a charging charger 72, a developing device 73, a transfer charger 74, a separation charger 75, and a cleaner 76 are provided. , An eraser lamp 77 is arranged, a toner image is formed by a well-known electrophotographic process, and is transferred onto a sheet. Paper is fed from the paper feed cassettes 81a and 81b to the paper feed roller 82.
It is supplied by a and 82b, and is sent to the position of the transfer charger 74 by the sheet conveying path 83 and the timing roller 84. The sheet on which the toner image is transferred at the position of the transfer charger 74 is ejected onto the sheet ejection tray 88 via the conveyor belt 85, the fixing device 86, and the ejection roller 87.
These various rollers and the photosensitive drum 71 are driven by the main motor M1. In addition, the paper feed cassette 81a,
In the vicinity of 81b, a paper size detection sensor SE1 for detecting the size of the paper stored in each cassette is provided.
SE2 is provided.

Next, the control circuit of this digital copying machine will be described with reference to FIG.

The image processing unit 20 includes a CPU 21 for controlling the timing of the entire apparatus, an A / D converter 22,
The shading correction unit 23, the gradation correction unit 24, the scaling processing unit 25, the line buffer 26, the binarization processing unit 27, the address decoder 28, and the document area detection unit 29 are included. An image reading synchronization signal is supplied from the CPU 21 to each of the line sensor 17, the image processing unit 20, the memory unit 30, and the print processing unit 40.

The signal output from the line sensor 17 for each line is analog data, and this analog data is converted by the A / D converter 22 into digital image data of 8 bits per pixel, and the shading correction unit 2
After the shading correction in 3, the gradation correction unit 24 performs gradation correction such as MTF correction and gamma correction, and the scaling processing unit 25 performs scaling processing. The line buffer 26 stores the image data after the scaling processing for one line, and sends the stored image data for one line to the document area detection unit 29 when the scanners 11 and 14 move (forward) in the b direction. It also has a switching function for sending the stored image data for one line to the binarization processing unit 27 when moving (returning) in the b'direction.

The original area detection unit 29 is a platen glass 19
Detect the position of the upper document. Further, the binarization processing unit 27 has 8
After the bit image data is converted into binary data by the error diffusion process, it is transferred to the address in the memory unit 30 designated by the address decoder 28. The memory unit 30 has a capacity enough to store 50 pages of A3 size original. The image memory 31 for one page is 2
It has a dimensional address, and an x address is set in the sub-scanning direction and a y address is set in the main scanning direction. Since this copying machine reads an A3 original at 400 DPI, x is set to 0 to 6799 and y is set to 0 to 4799. Another similar image memory for 49 pages is provided.

The image data written in the memory unit 30 is transferred to the print processing unit 40 based on the instruction of the CPU 21. In the print processing unit 40, the received image data is D / A converted by the D / A conversion unit 41, and the LD drive unit 42 drives and controls the semiconductor laser 61 based on the D / A converted image data. Also, CPU
Reference numeral 21 controls the input and display of signals from various operation keys of the operation panel 90.

Next, the operation panel 90 of the present digital copying machine will be described with reference to FIG.

Reference numeral 900 is a portion for inputting a numerical value such as the number of copies, and a numeric keypad is usually arranged. The message display unit 901 displays various guidances in addition to the set number. Reference numeral 902 denotes a key for selecting one from a plurality of copy magnifications displayed on the magnification display portion 903,
The selected magnification is switched every time the key 902 is pressed. 904 is a paper size display unit 905.
Paper size displayed on (paper cassettes 81a, 8a
This is a key for selecting one of the paper sizes set in 1b and the other paper sizes (not shown), and the selected paper size is switched every time the key 904 is pressed. It is like this. 906
Is automatic paper selection (APS) mode, automatic magnification selection (AM
S) is a key for selecting a mode and a manual mode in which paper selection and magnification selection are manually performed.
Each time the user presses 06, the selected mode is switched. Reference numeral 910 is a key for setting a non-document erasing mode, and 912 is a key for setting a free registration mode. Each key is pressed to set each mode, and the key is pressed again to cancel the setting. When each mode is set, the indicator lamp 9 provided on each setting key
11, 913 lights up.

Here, the outside-original erasing mode and the free registration mode will be described. The outside-original erasure mode is a mode in which an area on which an original is placed is determined, and image data other than the area is erased and output.

The free registration mode is a mode in which the center of the document is always copied to the center of the sheet even when the document is placed on the platen glass 19 at an arbitrary position. Hereinafter, a specific example will be described.

FIG. 4a shows a state in which an A4 size original 55 (see FIG. 4b) is set on the platen glass 19. On the right side and the front side of the platen glass 19, document scales 51 and 52 that serve as guides when setting a document are provided. Original scale 51, 52
Indices 53, 54 corresponding to the sheet size with the front right corner O as the reference position are engraved on the sheet. When the sheet size is designated as A4 and copying is executed without selecting the free registration mode, the image in the area OPQR on the platen glass 19 is copied. Similarly, when A3 size paper is selected, the image in the area OWUX is copied. In the state shown in FIG. 4A, the A4 original 55 has an area O.
It is placed in the area STUV which is deviated from the PQR. Therefore, the original document 55 is set without setting the free registration mode.
If the image is copied to A4 paper, the area OPQR
Only the image of the area SYQZ overlapping with is copied. The copy image thus obtained is shown in FIG. 5a. In addition,
In the figure, the shaded portion is the portion where the image of the document cover 50 appears as a solid black image on the sheet as it is because the outside-document erasing mode is not selected. On the other hand, when the free registration mode is set and copying is performed, as shown in FIG.
As shown in b, the center of the document is automatically detected, and copying is performed so that the image at the center of the document is copied to the center of the paper. Further, when the outside-original erasing mode is selected and copying is performed, it is automatically detected that the original exists only in the area SYQZ of the area OPQR on the platen glass 19, as shown in FIG. 5C, and the area SYQZ is detected. A copy image in which the image outside (the lower surface of the document cover 50) is erased is created. Note that FIG. 5d shows a copy image obtained when both the free registration mode and the out-of-document erasing mode are selected. Similarly, in FIGS. 6a to 6d, when the document is placed in the state of FIG. 4a and the paper size is A3 portrait and the magnification is 1: 1, the document image is copied on the paper according to each mode. It shows the situation.

When the APS mode is selected,
A copyable sheet is automatically selected at a magnification in which a rectangular area OWUX determined by a document setting reference position O and a corner U of the document most distant from the reference position is set. When the AMS mode is selected, the area SYQZ in which the in-frame OPQR corresponding to the selected sheet and the original area STUV overlap each other
However, it is copied at the maximum magnification that fits on the selected paper. It is also possible to consider the binding margin in the APS mode or the AMS mode. It is also possible to combine the out-of-document erasing mode and the free registration mode with the APS mode and the AMS mode.

Next, the CPU in this digital copying machine
An outline of the copying operation under the control of 21 will be described with reference to FIG.

When the copy start button 916 is pressed at time t0, the motor M2 of the reading section 10 drives the scanners 11 and 14, and scanning of the document in the b direction (forward movement) is started. At the same time, the exposure lamp 12 is turned on. When the scanner 11 separates from the home position sensor SE3 at time t1, the line sensor 17 outputs an image signal. At time t2, scanning of the document in the b direction (forward movement) is completed, the scan motor M2 reversely rotates, and the brake is applied. At time t4, the scan motor M2 reverses and scans the original in the b'direction (reverse movement). Start. It should be noted that the scanning speed is set to 16 times higher than that in the backward movement in which the image is read, since only the document placing area needs to be known in the forward movement.

After the time t2, the document area detecting section 29
The document placement position on the platen glass 19 is detected, and the detection result becomes clear at time t3. The document scanning speed is predetermined, and the time (t3-t1) required to detect the document position is also stored in the CPU 21.
Therefore, the time t5 when the line sensor 17 reads the trailing edge of the document and the time t6 when the leading edge of the document is read during the backward movement are the time t5.
It turns out in 3. Then, at time t5, the output of the line sensor 17 is output to the image memory 3 after the above-described image processing.
Written to 1.

Further, the document is not read from time t2 to time t5, but the exposure lamp 12 is on. This is because when the operator manually places the original on the platen glass 19 and makes a copy, it is mistaken that the image reading of the original is completed when the forward movement of the original is completed. This is to prevent the operator from moving or exchanging a document that has not been scanned. In particular, when the outside-original erasing mode or the free registration mode is selected and the enlargement copying is performed, if the original moves, a part of the original image is lost, which is a serious problem. Further, in the case where a high-speed copying machine is performing copying work while manually exchanging many documents, it is particularly important to be prepared for the above situation.

Thereafter, at time t6, the line sensor 17
Is the timing to read the trailing edge of the document, so here
Writing of the original image data to the image memory 31 is completed.

At time t7, the home position sensor SE3 is turned on again. Here, the scan motor M2 is braked to stop, the output of the line sensor 17 is stopped, and the exposure lamp 17 is turned off. Then, the reading of the original image and the writing of the image data in the image memory 31 are completed, the printer unit 100 is activated at time t8, and the reading and image formation of the image data from the image memory 31 is performed at time t9. Will start. At such a timing, the original image is copied on the paper according to the selected copy mode.

In this digital copying machine, as shown in FIG. 7, the platen glass 19 is used during the preliminary scanning (forward movement).
The scanning is performed over the entire area for the purpose of improving the accuracy of detection of the document placing area.

Next, the detection of the document placing area will be described. FIG. 8 shows the structure of the document area detection unit 29.

During forward scanning of the document, the line sensor 17
The output from is temporarily stored in the line buffer 26 after the image processing, and the image data from the line buffer 26 is
It is binarized by a binarizing circuit 291 in the document area detecting section 29. Since the purpose of the binarization circuit 291 is to detect the original area, a simple binarization process is performed unlike the case of the binarization circuit 27. The threshold value is higher than that of the binarization circuit 27, so that erroneous detection will not occur even if there is a large area black image in the document image or the binding portion of the book document is raised. Specifically, the binarization circuit 291 judges that the density level of 256/256 to 200/256 is black, whereas the binarization circuit 27 averages 256/256 to 128 /. The case where the density level is 256 is judged to be black. Further, at this time, the scaling processing unit 2 regardless of the scaling ratio specified by the copy scaling selection key 902.
In 5, the same magnification processing is performed by the magnification signal from the CPU 21.

The image data binarized by the binarizing circuit 291 is stored in the area memory 292 of the original area detecting unit 29 under the instruction of the address decoder 293 by the CPU 21. At this time, the CPU 21 processes the image data string in the main scanning direction in units of 2 bytes (16 pixels), but writes only the image data for one pixel of the most significant bit to the area memory 292. That is, the image data output from the line sensor at a resolution of 400 DPI is stored in the area memory 292 after being thinned by the CPU 21 so that the resolution in the main scanning direction becomes 1/16 (25 DPI).
Further, since the moving speed of the first scanner 11 in the forward movement is increased to 16 times the moving speed in the backward movement, the line sensor 1
When the speed at which 7 scans the original image in the sub-scanning direction is 1
6 times more. On the other hand, since the line sensor 17 is read out under the reference clock of a constant cycle, the resolution of the image read by the line sensor 17 in the sub-scanning direction is 25 DPI which is 1/16 of that in the backward movement in the forward movement. Become. In this way, the area memory 292 stores image data at low resolution (25 DPI) in both the main scanning direction and the sub scanning direction. This is because it is not necessary for the document area detection unit 29 to recognize only the document position, and therefore it is not necessary to recognize the image at the resolution, and the smaller the image data, the shorter the time required for the image processing for detecting the document position. Is. In addition,
The pixel spacing in an image with a resolution of 25 DPI is about 1
Since the size is mm, the position of the document can be detected in units of about 1 mm in this embodiment.

The area memory 292 is set with two-dimensional addresses of x and y, and the image data stored therein reproduces the state on the platen glass 19. In addition,
In many cases, the document is actually placed with a slight inclination, as shown in FIG.
8A shows a state in which the document is tilted counterclockwise and placed, and FIG. 8B shows a state in which the document is tilted clockwise and placed. In each of FIGS. 8A and 8B, the four end points of the document are labeled S, T, V, U in order from the right in the figure.
Is attached.

9 and 10 are flow charts showing the processing for the CPU 21 to detect the document position. Step S90
At 0, the value of the x address of the area memory 292 is set to 0, and the variable F is set to 0. Then, the check is started from the line of x = 0. In step S901, the number l of white pixels in each of five consecutive lines (third predetermined unit)
(X) to l (x + 4) (in the area memory 292 of FIG.
(X is shown) is counted, and in step S902, l
It is determined whether (x) to l (x + 4) are all larger than the predetermined value ε1. Note that ε1 and ε2 to ε4 described below
A value of 2 mm is suitable for each value. l (x) ~ l
If at least one of (x + 4) is smaller than ε1 (step S902: NO), x is incremented (step S903) while l (x) to l (x + 4) are all larger than ε1 (step S903). ~ The process of S902 is repeated. When l (x) to l (x + 4) are all larger than ε1, it is determined that the end point S of the document is detected,
The x coordinate Sx of the end point S is Sx = x, and the y coordinate Sy is Sy = y.
(X) +1 (x) / 2 (step S904).
It should be noted that y (x) is the minimum value of the y addresses of consecutive white pixels in the xth line. In this way, it is possible to prevent an erroneous determination due to dust on the platen glass by increasing the value of x one by one and making a determination in units of 5 lines.

Step S905 is for determining the inclination of the original on the platen glass. First, in step S9050, y (x) is compared with y (x + 1). If the document is skewed clockwise (Figure 8b), y
(X) is larger than y (x + 1) (step S905
0: Y), and the variable F is set to 1 (step S905).
1). On the other hand, if the original is tilted counterclockwise (see FIG.
a) and y (x) are smaller than y (x + 1) (step S
9050: N), and the variable F is set to 0. That is, if the variable F is 1, it means that the document is tilted clockwise,
If the variable F is 0, it indicates that the document is tilted clockwise.

Next, in steps S906 to S908, the end point T is detected. First, the difference in the number of consecutive white pixels on adjacent lines is compared with a predetermined value ε2 (step S
906). When the difference in the number of white pixels is larger than ε2 (step S906: N), x is incremented (step S907) and the determination in step S906 is repeated until the difference in the number of white pixels becomes smaller than ε2. When the difference in the number of continuous white pixels of the adjacent lines becomes smaller than ε2 (step S906: Y), it is determined that the end point T of the document is detected, and the x coordinate Tx of the end point T is Tx = x, y coordinate Ty.
Be Ty = Fy + (1-F) × (y + 1 (x)).

Next, in steps S909 to S914, the end point V is detected. First, while increasing the value of x by the first predetermined unit 3 until the difference between the number of consecutive white pixels of the adjacent lines becomes smaller than −ε3 (step S91).
0), the determination in step S909 is repeated. by the way,
Since there are a large number of lines between the end points S and Tk on the leading end side of the document and the end point V on the trailing end side, it may be time to judge whether each line is the end point V of the document. Takes too much. Further, at this time, since there is almost no influence of dust on the platen glass, it is desirable to increase the overall detection speed even if the accuracy is sacrificed. Therefore, in step S910, the value of x is increased by 3 and 3
The detection is made for each line as to whether or not it is the trailing edge of the document.

When the difference in the number of consecutive white pixels of the adjacent lines becomes smaller than -ε3 (step S909: Y), x
Value of the second predetermined unit 2 which is one less than the first predetermined unit
Only (step S911). This is because the determination in step S909 is every 3 lines, so step S9
The value of x when the judgment of 09 becomes Y is the x of the true end point.
This is because there is a risk of jumping over the coordinates. Then, the same determination as in step S909 is repeated while increasing x by 1 until the difference between the numbers of white pixels in adjacent lines becomes smaller than −ε3 (steps S912 to S913). When the difference in the number of consecutive white pixels of adjacent lines becomes smaller than −ε3 (step S9012: Y), it is determined that the end point V of the document is detected, and the x coordinate Vx of the end point V is set to Vx = x and the y coordinate Vy is set. Let Vy = (1-F) y + F (y + 1 (x)).

Then, the end point U is detected by the same procedure as the detection of the end point S. That is, the determination of step S916 is repeated while incrementing x until the number of consecutive white pixels l (x) to l (x + 4) in adjacent five lines are all smaller than ε4. When l (x) to l (x + 4) are all smaller than ε4, it is determined that the end point U of the document has been detected, and the x coordinate Ux of the end point U is Ux = x, y coordinate Uy.
Is set to Uy = y (x) +1 (x) / 2 (step S9
04). As described above, the coordinates of the document end points S, T, U, and V are all obtained, and the position where the document is placed and the size of the document can be determined from the coordinates of these end points. The determined position and size of the document can be used in the above-described free registration mode, outside-document erasing mode, APS, AMS mode.

[0053]

According to the first aspect of the invention, the position of the original on the original table is detected based on the image data stored in the page memory. The image data output from the reading means is stored in the page memory. , Thinned out and stored. Since the page memory stores the image data for the entire area of the document table, not only the image data of one line but also the image data of the lines before and after it can be taken into consideration when detecting the document position. . Therefore, even if dust or the like adheres to the document table, the document can be detected with high accuracy. Moreover, since the page memory stores a part of the thinned image data, the amount of data in the page memory is small. Therefore, since the amount of image data to be processed to detect the document position is small, the document position can be detected in a short time.

According to the second aspect of the invention, the position of the document is detected during the preliminary scanning, and the position of the document is detected by making the scanning speed during the preliminary scanning higher than the scanning speed during the main scanning. The amount of image data can be easily reduced.

According to the third aspect of the invention, the document edge is detected with high accuracy at the leading edge of the document, but the image data is processed with low accuracy behind the leading edge. Can be detected with high accuracy in a short time.

According to the fourth aspect of the invention, the trailing edge of the document can be detected with high accuracy.

Further, according to the invention of claim 5, since the document edge is detected based on the image data of a plurality of lines, the influence of dust on the document table can be reduced and the document edge can be detected with high accuracy. be able to. On the other hand, if there are too many third predetermined units, it takes a long time to detect the document edge.
According to the invention, since the third predetermined unit corresponds to several millimeters on the document, dust of about several millimeters does not affect the document edge detection, and the document edge can be detected in a short time.

Further, according to the invention of claim 7, it is possible to detect the document placing position with high accuracy regardless of the type of the image of the document.

When the present invention is applied to a copying machine as described in claim 8, the position of the original can be detected with high accuracy in a short time, so that a high quality copy can be made in a short time. Can be created with.

[Brief description of drawings]

FIG. 1 is a sectional view showing a digital copying machine to which the present invention is applied.

FIG. 2 is a block diagram showing a control circuit of a digital copying machine.

FIG. 3 is a front view showing an operation panel of the digital copying machine.

FIG. 4 is an explanatory diagram showing a state in which a document 55 is placed on the platen glass 19.

FIG. 5 is an explanatory diagram for explaining an out-of-document erasing mode and a free registration mode.

FIG. 6 is an explanatory diagram for explaining an out-of-document erasing mode and a free registration mode.

FIG. 7 is a time chart showing the operation timing of the digital copying machine.

FIG. 8 is a block diagram showing a document area detection unit 29.

FIG. 9 is a part of a flowchart showing a document area detection process.

FIG. 10 is a part of a flowchart showing a document area detection process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Reading part 17 ... Line sensor 19 ... Platen glass (document table) 20 ... Image processing unit 21 ... CPU 29 ... Document area detection part (detection means) 291 ... Binarization circuit 292 ... Area memory (page memory) 293 ... Address decoder M2 ... Scan motor (scanning means)

Claims (8)

[Claims] 1. A document table on which a document is placed, a reading unit which reads the document placed on the document table for each pixel, and outputs image data corresponding to each pixel, and output from the reading unit. Thinning means for performing thinning processing on the image data, a page memory for storing the image data output from the thinning means in an amount corresponding to the entire area of the document table, and image data stored in the page memory. An image reading apparatus comprising: a detection unit that detects the position of the document on the document table based on the above. 2. The image reading apparatus according to claim 1, wherein the reading means includes a line sensor in which a plurality of photoelectric conversion elements are arranged in a main scanning direction, the line sensor, and the image of the original document in the main scanning direction. The scanning means for scanning in the sub-scanning direction perpendicular to the scanning direction, and the control means for controlling the scanning means so that the line sensor performs preliminary scanning and main scanning of the document, and the page memory is provided during the preliminary scanning. The image data output from the line sensor is stored, and the control unit controls the scanning unit so that the scanning speed of the line sensor during the preliminary scanning is higher than the scanning speed of the main scanning. An image reading device characterized by the above. 3. The image reading apparatus according to claim 1, wherein the detecting means specifies an address in the page memory, and the image data at the address specified by the address specifying means is the original document. The leading edge determining means for determining whether the leading edge portion or not, and the address is incremented by 1 until the leading edge portion of the document is detected by the leading edge determining means.
An image reading apparatus comprising: a first address increment unit that increments the address by a first predetermined unit larger than 1 after the leading edge of the document is detected by the leading edge determination unit. 4. The image reading apparatus according to claim 3, wherein the detecting unit determines a trailing edge determining unit that determines whether the image data at the address designated by the address designating unit is the trailing edge of the document. When the trailing edge of the document is detected by the trailing edge determining means, the address is set to a second value smaller than the first predetermined unit.
And a second address incrementing means for incrementing the address by 1 in order to detect the trailing edge of the original by the trailing edge determining means again. 5. The image reading device according to claim 3,
The leading edge determining means detects the leading edge of the document by referring to image data of a third predetermined unit of line including one line in the main scanning direction corresponding to the address designated by the address designating means. Characteristic image reading device. 6. The image reading device according to claim 5,
An image reading apparatus characterized in that the line for the third predetermined unit corresponds to several millimeters on the document. 7. The image reading apparatus according to claim 2, wherein first binarizing means for binarizing image data output from the line sensor during preliminary scanning, and output from the line sensor during main scanning. Second binarizing means for binarizing the image data, the threshold value of the first binarizing means being higher than the threshold value of the second binarizing means. Characteristic image reading device. 8. A document table on which a document is placed, a line sensor in which a plurality of photoelectric conversion elements are arranged in the main scanning direction, the line sensor, and an image of the document is sub-scanned in a direction perpendicular to the main scanning direction. Scanning means for scanning in the direction, control means for controlling the scanning means so that the line sensor performs preliminary scanning and main scanning of an original, and thinning processing for image data output from the line sensor during the preliminary scanning. Based on the image data stored in the page memory, and a page memory for storing the image data output from the thinning means in an amount corresponding to the entire area of the document table. Detecting means for detecting the position of the document; image processing means for processing the image data output from the line sensor during the main scanning in association with the detection result of the detecting means; Copying apparatus comprising: the image forming means, the forming an image corresponding to the image data processed by the image processing means on the sheet.