JP2013198084A - Image reader, image forming apparatus and original end detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect an original end even in an original having thickness or an original without a background of photograph image quality in image reading for reading an image of the original by moving the original.SOLUTION: An operation section 33: calculates a difference between light volume value data of each pixel when an original readable region of an image sensor 21 reads a white reference board in a state where the white reference board is moved to a prescribed position and an original is not transported between the image sensor 21 and the white reference board, and light volume value data of each pixel when the original readable region of the image sensor 21 reads a part where the original is superposed on the white reference board by transporting the original between the image sensor 21 and the white reference board for each pixel in a corresponding position in a main scanning direction; compares a difference between light volume values for the respective pixels with a first prescribed threshold and a second prescribed threshold; and detects the pixel corresponding to an original end of the original from the light volume value data of the respective pixels when the part where the original is superposed on the white reference board is read in response to comparison results.

Description

  The present invention relates to an image reading apparatus that irradiates a document with light and reads an image of the document with reflected light, an image forming apparatus that includes the image reading apparatus, and a document edge detection method that detects a document edge.

In an image reading device such as a scanner device, when reading an image of a document having a large document size, the volume of the image reading device becomes large if the document is read by scanning a reading sensor.
Therefore, there is a sheet-through type image reading apparatus that reads an image of a document by moving the document with respect to a reading sensor such as a contact image sensor.
In a sheet-through type image reading apparatus, in order to read an image of an original (for example, a plate-like original having a thickness of several millimeters to 1 cm) thicker than plain paper, an original conveyance path to the reading sensor is used. It is necessary to widen by the thickness of the document.

  Conventionally, when the conveyance path from the document insertion side to the discharge side is formed linearly, and the document is thicker than a predetermined thickness, the movable guide plate is manually or automatically opened for thick paper so that the gap between the document conveyance paths is reduced. There is known an image reading apparatus (see, for example, Patent Document 1) that reads an image surface of a document that is widened and conveyed along the conveyance path by a reading unit.

In addition, some image reading apparatuses can identify an edge portion of a document.
For example, the following image reading apparatus is known.
An original is placed on the platen glass, and the platen cover is opened so that it does not cover the platen glass. The original is irradiated with light from the platen glass side, and images in the original area and the outside area of the original are read. Then, the peak value portion where the luminance of the image is extremely low is set as the outside region of the document, the peak value portion where the luminance of the image is extremely high is set as the outer periphery of the document region, An image reading apparatus that sets a threshold for distinguishing between a document area and a document outside area (see, for example, Patent Document 2).

However, since the sheet-through image reading apparatus as described above cannot read the original image with the platen cover open, the peak value of the luminance of the original image is used as in the above-described image reading apparatus. Therefore, there is a problem that it is impossible to distinguish the document area from the document outside area.
In addition, there is a problem in that an original area and an area outside the original cannot be accurately detected with an original having no background such as a picture quality.
The present invention has been made in view of the above points, and accurately detects the edge of a document, whether it is a thick document or a document having no background such as photographic image quality, by moving the document and reading the image of the document. The purpose is to be able to.

In order to achieve the above object, the present invention provides a light source for irradiating light on a document, image reading means for reading an image of the document by reflected light from the document, and shading correction of an image read from the document. In order to obtain an interval according to the thickness of the original between the image reading means and the reference member, a reference member arranged opposite to the image reading means for acquiring an image, and the reference member A reference member moving means for moving to a predetermined position in a direction opposite to the image reading means; and after moving the reference member to the predetermined position by the reference member moving means, the document is moved to the image reading means and the reference member. The image reading means is irradiated with light reflected from the document by irradiating the document with light from the light source for each line in the main scanning direction of the document. An image reading apparatus for reading an image in the main scanning direction of each line of the paper,
After the reference member is moved to the predetermined position by the reference member moving means, at least the original in the main scanning direction of the image reading means without conveying the original between the image reading means and the reference member. A first light amount value data which is a light amount value of each pixel in the predetermined region read by the image reading unit by irradiating light from the light source to a region of the reference member read by a predetermined region which is larger than the readable region; In the state where the original is conveyed between the image reading means and the reference member, the image reading is performed by irradiating light from the light source to the reference member and an area corresponding to the predetermined area of the original. A light amount holding unit that holds second light amount value data that is a light amount value of each pixel in the predetermined area read by the unit, and the first light amount held in the light amount holding unit. The difference between the light quantity value data and the second light quantity value data is calculated for each pixel at the corresponding position in the main scanning direction, and the difference between the light quantity value data for each pixel is set for the difference in the light quantity value data. Each of the predetermined first threshold value and a predetermined second threshold value smaller than the first threshold value, and a pixel corresponding to the document edge from the second light quantity value data based on the comparison result. Document edge detection means for detecting the document is provided.

  According to the image reading apparatus, the image forming apparatus, and the document edge detection method according to the present invention, in the image reading in which the document is moved and the image of the document is read, the document edge is accurately detected even in a thick document or a document having no background such as photographic quality. Can be detected.

FIG. 3 is a block diagram illustrating a functional configuration of a main part of the image reading unit 2 illustrated in FIG. 2. 1 is an overall schematic configuration diagram of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram of a portion related to image reading of an image reading unit 2 and movement of an upper cover 10 shown in FIG. 2. It is the top view which looked at the lower platen 11 shown in FIG. 3 and its periphery from the upper side. It is a side view of the stopper 18 shown in FIG. FIG. 6 is a diagram illustrating another configuration example of a portion related to image reading of the image reading unit 2 and movement of the upper cover 10 illustrated in FIG. 2. It is the top view which looked at the lower platen 11 shown in FIG. 6 and its periphery from the upper side. FIG. 2 is a flowchart showing a process for moving an upper cover 10 when a document 6 is inserted performed by a central control unit 30 shown in FIG. 1. The amount of light value data of each pixel obtained when the original reading area of the image sensor 21 reads the white reference plate 15 shown in FIG. 3 and the portion where the original 6 is superimposed on the white reference plate 15 are read by the image sensor 21. It is a wave form diagram which shows an example of a change of the difference with the light quantity value data of each pixel obtained when a possible area | region is read. FIG. 3 is an explanatory diagram of processing for finding a pixel corresponding to a document edge in a document edge detection process by the calculation unit 33 shown in FIG. FIG. 10 is an explanatory diagram of another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process. FIG. 11 is an explanatory diagram of still another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process. FIG. 12 is an explanatory diagram of still another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process. FIG. 6 is a flowchart showing document edge detection processing of the image reading unit 2 shown in FIG. 1. FIG. 15 is a flowchart showing processing subsequent to FIG. 14. It is a flowchart figure which shows the detailed process in the case of setting threshold value Y1, Y2 by a fixed value by step 12 of FIG. It is a flowchart figure which shows the detailed process in the case of calculating | requiring and setting threshold value Y1, Y2 in step 12 of FIG. It is a flowchart figure which shows the other process example in the case of calculating | requiring and setting threshold value Y1, Y2 in step 12 of FIG. FIG. 4 is a plan view of the lower platen 11 and its periphery viewed from above when the document 6 shown in FIG. 3 is inserted obliquely.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 2 is a schematic configuration diagram of the entire image forming apparatus 1 according to an embodiment of the present invention.
The image forming apparatus 1 includes an image reading unit 2 and an image forming unit 3.
The image reading unit 2 is an image reading device that is disposed above the image forming unit 3 and optically reads an image on the document 6.
The image forming unit 3 includes an image forming unit 4 and a paper feeding unit 5.
The image forming unit 4 includes various parts such as a known optical writing unit, a developing unit, a transfer unit, and a fixing unit (not shown).

The image forming unit 4 feeds paper on the basis of image data read from the document 6 by the image reading unit 2 or image data received from an external information processing apparatus (not shown) via a network. A toner image is printed (formed) on the paper fed from the unit 5 by an electrophotographic method.
The paper feeding unit 5 stores paper and feeds the paper to the image forming unit 4.
The electrophotographic image forming process is well known, and a detailed description of the image forming process is omitted.
In this embodiment, the case where the image forming unit 3 includes the electrophotographic image forming unit 4 will be described. However, in addition to this, other image forming units such as a droplet discharge method such as an ink jet method may be used. A known image forming unit may be provided.

Next, the configuration of the image reading unit 2 will be described.
FIG. 3 is a schematic configuration diagram of a portion related to image reading of the image reading unit 2 and movement of the upper cover 10 shown in FIG.
FIG. 4 is a plan view of the lower platen 11 shown in FIG.
FIG. 5 is a side view of the stopper 18 shown in FIG.
The image reading unit 2 includes an upper cover 10 and a lower platen 11 as shown in FIG.
The upper cover 10 is a cover for transporting the document 6 while holding the document 6 against the lower platen 11.
The upper cover 10 includes an operation unit 12 in the upper part and a distance detection sensor 13, a front roller 14a, a white reference plate 15, and a rear roller 16a in order from the insertion side to the discharge side of the document 6 on the lower part. Yes.

On the other hand, the lower platen 11 is a document table.
The lower platen 11 includes an original insertion detection sensor 17, a front roller 14b, a stopper 18, a contact glass 19, and a rear roller 16b in order from the insertion side to the discharge side of the original 6 on the upper part. A light source 20 and an image sensor 21 are provided below the contact glass 19.
Further, at the left ends of the upper cover 10 and the lower platen 11, as shown in FIG. 4, a frame 22, as a mechanism for moving the upper cover 10 in the vertical direction (A direction shown in FIG. 3) with respect to the lower platen 11, A gear 23 and an upper cover drive motor 24 are provided.
The operation unit 12 of the upper cover 10 is an operation panel for a user to input various operation information to the image forming apparatus 1.

The distance detection sensor 13 detects the distance C <b> 1 between the original 6 and the upper cover 10 when the original 6 is inserted in the lower part of the upper cover 10.
The front roller 14 a is a pair of rollers with the front roller 14 b of the lower platen 11, and is rotated by a drive motor (not shown) to convey the document 6 in the sub-scanning direction of the document 6 when reading the image of the document 6. To do.
The white reference plate 15 is a reference member for acquiring an image (shading correction data) for shading correction of an image read from the document 6, and is disposed to face the image sensor 21.
The rear roller 16a is a pair of rollers with the rear roller 16b of the lower platen 11, and is rotated by a drive motor (not shown) to convey the original 6 to the discharge side in the sub-scanning direction when reading the image of the original 6. .

The document insertion detection sensor 17 of the lower platen 11 detects whether or not the document 6 has been inserted.
The front roller 14b is a pair of rollers with the front roller 14a of the upper cover 10, and is rotated by a drive motor (not shown) to convey the document 6 in the sub-scanning direction when reading the image of the document 6.
The stopper 18 is a mechanism that stops the leading edge of the document 6 and temporarily stops the entry of the document 6 when the document 6 is inserted. This mechanism prevents the conveyance of the original 6 during reading.
The stopper 18 is used to temporarily stop the document 6 so that the document 6 does not advance too much. The height when the stopper 18 is raised is smaller than the distance C (when the document 6 is at the minimum thickness).

As shown in FIG. 5, the stopper 18 can be moved in the direction B in the figure by driving a stopper drive motor 25. When the document 6 is inserted, the stopper drive motor 25 is driven so that the document 6 does not advance too much. 18 is set up (indicated by the solid line in the figure), and when reading the original 6, the stopper driving motor 25 is driven so that the original 6 can pass through to tilt the stopper 18 (indicated by the broken line in the figure).
The drive control of the stopper drive motor 25 is performed by the central control unit 30 shown in FIG.
Note that the structure of the stopper 18 shown in FIG. 5 is merely an example, and the stopper 18 may be moved up and down via the gear 23 shown in FIG.
Furthermore, although the upper and lower mechanisms of the upper cover 10 and the lower platen 11 are provided on the left side of the image reading unit 2 in FIG. 4, they may be provided on the right side or mounted on both sides. May be.

The stopper drive motor 25 is a motor for moving the stopper 18 by being driven before the reading of the document 6 is started and after the reading is completed.
As shown in FIG. 4, the contact glass 19 includes a light source 20 and an image sensor 21 on the lower side, protects the light source 20 and the image sensor 21, and transmits light emitted from the light source 20 and its reflected light. Possible transparent cover.
The rear roller 16b is a pair of rollers with the rear roller 16a of the upper cover 10, and is rotated by a drive motor (not shown) to convey the original 6 to the discharge side in the sub-scanning direction when reading the image of the original 6. .

The light source 20 is, for example, a light source such as a xenon lamp, a fluorescent lamp, and a light emitting diode (LED), and the main scanning direction of the original 6 with respect to the original 6 and the white reference plate 15 provided on the upper cover 10. Irradiate light uniformly.
The image sensor 21 includes various lenses (not shown) inside, receives reflected light from the document 6 and the white reference plate 15, and photoelectrically converts the reflected light to generate an image of the document 6 and the white reference plate 15. Read.

A part of the frame 22 is attached to the upper cover 10, and the upper cover 10 provided with the white reference plate 15 is moved in the direction indicated by the arrow A in FIG. It is a member moved in the A direction.
The gear 23 is a gear for moving the frame 22 in the direction of arrow A in FIG.
The upper cover drive motor 24 is a motor for moving the frame 22 in the direction of arrow A in FIG. 3 by rotating the gear 23.
By driving the upper cover drive motor 24 under the control of the central control unit 30 shown in FIG. 1, the upper cover 10 is raised to a predetermined position with respect to the lower platen 11 before the document 6 is read. Further, when the document insertion detection sensor 17 detects that the document 6 has been inserted up to the stopper 18, the upper cover 10 is lowered and the document 6 is sandwiched between the front rollers 14a and 14b.

In this way, the white reference plate 15 is moved to a predetermined position in the direction facing the image sensor 21 in order to leave a space corresponding to the thickness of the document 6 between the image sensor 21 and the white reference plate 15.
Then, after the white reference plate 15 is moved to a predetermined position, the document 6 is conveyed between the image sensor 21 and the white reference plate 15, and is fed from the light source 20 to the document 6 for each line in the main scanning direction of the document 6. By irradiating light, the image sensor 21 reads an image of each line of the document 6 in the main scanning direction by reflected light from the document 6.
That is, the frame 22, the gear 23 in FIG. 3, the upper cover drive motor 24 in FIG. 4, and the central control unit 30 shown in FIG. 1 serve as the reference member moving means.

The upper cover 10 of the image reading unit 2 of this embodiment may be configured to be manually movable.
FIG. 6 is a diagram showing another configuration example of the image reading unit 2 shown in FIG. 2 and the portion related to the upper cover 10.
FIG. 7 is a plan view of the lower platen 11 shown in FIG.
As shown in FIGS. 6 and 7, a gear 27 to which a lever 26 is attached and a gear 28 for transmitting a driving force of the gear 27 via a belt 29 around the gear 23 are provided.
When the user depresses the lever 26 downward in FIG. 6, the frame 22 can be moved upward in the direction of arrow A in FIG. 6, and the upper cover 10 can be raised to a predetermined position with respect to the lower platen 11. .

Thereafter, the user manually inserts the document 6 up to the stopper 18 and pushes the lever 26 upward in FIG. 6 to move the frame 22 downward in the direction indicated by the arrow A in FIG. The upper cover 10 can be lowered with respect to the lower platen 11 until the document 6 is sandwiched between them.
That is, in this case, the frame 22, the gears 23, 27, and 28, the lever 26, and the belt 29 shown in FIGS. 6 and 7 function as a reference member moving unit.
In the example shown in FIGS. 6 and 7, three gears are used, but any number may be used.
In this way, the distance between the image sensor 21 and the white reference plate 15 can be set according to the thickness of the original 6, and the thickness of the original 6 can be read even when an image of the thick original 6 is read. Accordingly, the document 6 can be conveyed in accordance with the above.

Next, the functional configuration of the main part of the image reading unit 2 will be described.
FIG. 1 is a block diagram showing a functional configuration of a main part of the image reading unit 2 shown in FIG.
The image reading unit 2 includes a central control unit 30, an analog / digital (A / D) conversion unit 31, and a signal processing unit 32 as functional units realized by a microcomputer including a CPU, a ROM, and a RAM.
The signal processing unit 32 includes a calculation unit 33, a memory 34, a black subtraction unit 35, a shading processing unit 36, and an image processing unit 37.
The central control unit 30 controls the entire image reading unit 2. Further, the light source 20 for irradiating the original with light is controlled to be turned on and off, and the reading operation of the image sensor 21 which is an image reading means for reading the image of the original with reflected light from the original is controlled. Further, a signal indicating the distance C1 detected by the distance detection sensor 13 and a signal indicating that the document insertion detection sensor 17 has detected the insertion of the document 6 in FIG. 3 are input.

Further, the central control unit 30 also controls driving of the upper cover drive motor 24 and the stopper drive motor 25.
The A / D conversion unit 31 converts the read data read and photoelectrically converted by the image sensor 21 from analog data to digital data, and outputs the converted data to the black subtraction unit 35 of the signal processing unit 32.
The read data includes read data W (n) when only the white reference plate 15 is read after the white reference plate 15 is moved to a predetermined position, and the document 6 is conveyed to the white reference plate 15. Is read data X (n).
That is, the read data W (n) is light amount value data (corresponding to first light amount value data) of each pixel obtained when the original readable area of the image sensor 21 reads the white reference plate 15.
Further, the read data X (n) is the light quantity value data (second light quantity value data) of each pixel obtained when the original readable area of the image sensor 21 reads the portion where the original 6 is superimposed on the white reference plate 15. Equivalent to

The black subtracting unit 35 of the signal processing unit 32 removes the black noise component of the read data W (n) and the read data X (n) input from the A / D conversion unit 31 to calculate the calculation unit 33 and the shading processing unit 36. To each output.
Based on the read data W (n) input from the black subtractor 35, the shading processor 36 performs shading correction on the read data X (n) and outputs it to the image processor 37.
In the shading correction, the white reference plate 15 is read prior to reading a document, white level reference data that is white data of each pixel is acquired, and shading correction data is generated based on the acquired white level reference data. This is a process for correcting the unevenness of the light amount of the light source 20 and the error of the image sensor 21 for the read data X (n) of the document read using the shading correction data.

The arithmetic unit 33 stores the read data W (n) and the read data X (n) input from the black subtractor 35 in the memory 34, and the read data X (n) input from the black subtractor 35 and the memory 34. Based on the stored read data W (n), threshold value Y1, and threshold value Y2, a document edge detection process for detecting pixels corresponding to the left and right document edges in the sub-scanning direction of the document 6 is executed. Information (for example, position information) of the detected pixel at the edge of the document is output to the image processing unit 37.
The memory 34 stores read data W (n) and read data X (n) input from the black subtracting unit 35, and threshold values Y1 and Y2 used for document edge detection processing.

The image processing unit 37 includes light amount value data of each pixel obtained by reading the document 6 and the white reference plate 15 by the document readable area of the image sensor 21 based on the pixel corresponding to the document edge detected by the calculation unit 33. Then, each pixel in the external area at the edge of the document is removed or whitened, and then various known processes are performed and output as image data to be printed. That is, the image processing unit 37 functions as a removing unit.
The image data output by the image processing unit 37 is input to the image forming unit 3 in FIG. 2 and an image is printed on a sheet.

The image reading unit 2 of the image forming apparatus 1 according to this embodiment reads the white reference plate 15 before reading the document 6 after moving the white reference plate 15 to a predetermined position by moving the upper cover 10 in advance. The data W (n) (n: main scanning position) is acquired, and then the read data X (n) read from the document 6 is acquired, and the read data X (n) -read data W (n) and the threshold value Y1 Pixels corresponding to the document edge of the document 6 are detected from the threshold Y2.
Then, the pixels other than the document area are removed (the image itself is cut) or white pixels are formed based on the pixels corresponding to the detected document edge of the document 6. In order to obtain a white pixel, for example, the signal level of the pixel is set to 255 digits.
Therefore, even when an irregular thick paper original is read by the sheet-through method, the original area can be accurately detected even if the original has no background.

Next, when the user inserts the document 6 between the upper cover 10 and the lower platen 11 on the document insertion side, the moving process of the upper cover 10 performed so that the image reading unit 2 can transport the document 6 will be described. To do.
When the configuration of the image reading unit 2 is the configuration shown in FIGS. 3 and 4, the image reading unit 2 is configured such that when the document 6 is inserted between the upper cover 10 and the lower platen 11 on the document insertion side, 6 is automatically performed so that the upper cover 10 is sandwiched between the upper cover 10 and the lower platen 11.

FIG. 8 is a flowchart showing the moving process of the upper cover 10 when the document 6 is inserted by the central control unit 30 shown in FIG.
The central control unit 30 in FIG. 1 is in a state where the upper cover 10 is raised so that the distance C between the upper cover 10 and the lower platen 11 is maximized as an initial state.
In step (indicated by “S” in FIG. 8) 1 in FIG. 8, it is determined whether or not the document insertion detection sensor 17 is on. If it is determined that the document insertion detection sensor 17 is not on (in the case of N), this determination processing is repeated. If it is determined (in the case of Y), the process proceeds to Step 2.
When the document 6 is inserted between the upper cover 10 and the lower platen 11 by the user operation, the document insertion detection sensor 17 is turned on and the insertion of the document 6 is detected.
At this time, since the leading edge of the document 6 is stopped by the stopper 18, the path is prevented so that the document 6 is not inserted too much before the document 6 can be conveyed by the front rollers 14a and 14b.

In step 2, the distance C1 between the upper cover 10 and the original 6 is detected by the distance detection sensor 13, and the process proceeds to step 3.
In step 3, the upper cover 10 is moved by driving the upper cover drive motor 24, and the distance C between the upper cover 10 and the lower platen 11 is changed until the document 6 is sandwiched between the front rollers 14a and 14b. Go to 4.
In the process of step 3, the upper cover drive motor 24 is driven in accordance with the distance C1, and the upper cover 10 is lowered downward with respect to the lower platen 11 until the document 6 is sandwiched between the front rollers 14a and 14b. Move.

In step 4, the stopper drive motor 25 is driven to release the stopper 18, and this process is terminated.
By the process of step 4, the path of the leading edge of the document 6 is opened, and the documents 6 are conveyed toward the contact glass 19 by rotating the front rollers 14a and 14b, so that the image of the document 6 can be read.

Next, a case where the user manually performs all the movement processing of the upper cover 10 by the image reading unit 2 will be described.
When the configuration of the image reading unit 2 is the configuration shown in FIGS. 6 and 7, the user manually moves the upper cover 10.
The user tilts the lever 26 downward in FIG. 6 to move the frame 22 upward in FIG. 6 via the gears 27, 28, the belt 29, and the gear 23. The space between the platen 11 and the platen 11 is increased beyond the thickness of the original 6.
Thereafter, the document 6 is inserted between the upper cover 10 and the lower platen 11 on the document insertion side.

At this time, as described above, since the leading edge of the document 6 is stopped by the stopper 18, the path is prevented so that the document 6 is not inserted too much before the document 6 can be conveyed by the front rollers 14a and 14b. .
Next, the user raises the lever 26 upward in FIG. 6 to move the frame 22 downward through the gears 27 and 28, the belt 29, and the gear 23 in FIG. The upper cover 10 is moved to a position where the document 6 is sandwiched between the 11 front rollers 14a and 14b.

When the user inputs an instruction to start image reading through the operation unit 12, the central control unit 30 in FIG. 1 drives the stopper driving motor 25 to release the stopper 18 and starts reading the image of the document 6.
As for the movement process of the upper cover 10, it is preferable to automatically raise the upper cover 10 so that the distance C between the upper cover 10 and the lower platen 11 is maximized again at the end of reading the document 6.
In this way, when the original to be read next is thicker than the original before reading, there is an advantage that the user does not need to move the upper cover 10 to insert the original.

Alternatively, the upper cover 10 may be held in the same position when the reading of the document 6 is completed.
In this way, when the next document to be read has the same thickness as the previous document that has been read, or when the thickness is small, the next reading starts earlier.
Further, when reading of the document 6 is completed, the operation unit 12 sets the user to automatically move the distance C between the upper cover 10 and the lower platen 11 so as to maximize the distance C and to leave the document 6 at the time of reading. It should be possible.
When the reading of the document 6 is completed, the stopper driving motor 25 is driven to raise the stopper 18 so that the next document can be inserted.

Next, an outline of the document edge detection process will be described.
Here, a case where the background density of the document 6 in FIG. 3 is brighter (white) than the white reference plate 15 is shown.
First, after the upper cover 10 moves to pass the document 6, the read data W (n) is acquired.
At this time, as the read data W (n), it is possible to detect the document edge more accurately by using the average value read a plurality of times.

Next, the document 6 is conveyed, and reading data X (n) in all main scanning directions when the document 6 passes over the image sensor 21 is acquired. This read data X (n) corresponds to the light quantity value data of each pixel (corresponding to the second light quantity value data) obtained when the original readable area of the image sensor 21 reads the portion where the original 6 is superimposed on the white reference plate 15. ).
FIG. 9 shows the light amount value data of each pixel obtained when the white readable plate 15 of FIG. 3 is read by the original readable area of the image sensor 21 and the portion where the original 6 is superimposed on the white reference plate 15. It is a wave form diagram which shows an example of a change of the difference with the light quantity value data of each pixel obtained when the original readable area of this is read.
A waveform 40 in FIG. 9 is a waveform showing a change in read data X (n) −read data W (n). Regarding the read data W (n), since the white reference plate 15 is after the upper cover 10 has moved, the white reference plate 15 is output darker than when the shading correction data is acquired according to the amount of movement.

Further, regarding the read data X (n), the white reference plate 15 is read in the area where the original 6 does not exist in the main scanning direction of the original 6, and therefore substantially coincides with the read data W (n) (the difference is 0).
In the area of the original 6, the output corresponding to the original density is output, so that the difference from the read data W (n) becomes large (portions E to F in the waveform 40).
Therefore, by detecting a pixel in which the difference between the read data W (n) and the read data X (n) counted from both sides in the entire main scanning direction is equal to or greater than the threshold value Y1 or less than the threshold value Y2, it corresponds to the document edge. Pixels can be detected.
In FIG. 9, since the pixel E and the pixel F are the first and last pixels whose read data X (n) -read data W (n) is equal to or greater than the threshold value Y1, the area of the document 6 is between the pixel E and the pixel F. Other than that, it can be determined to be out of the area.

However, depending on the thickness of the document 6, there may be a shadow at the document edge in the main scanning direction.
There is a possibility that the shadow portion is equal to or higher than the threshold Y1 or lower than the threshold Y2.
Therefore, if the read data X (n) −read data W (n) is not less than the threshold value Y1 or not more than the threshold value Y2 and the first and last pixels are regarded as the document edge, the shadow portion may be regarded as the document region. .
As described above, in the document edge detection process, the pixel corresponding to the document edge of the document 6 can be detected correctly if the process described with reference to FIGS. Can do.

Next, a process for finding a pixel corresponding to the document edge in the document edge detection process will be described.
FIG. 10 is an explanatory diagram of a process in which the arithmetic unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process.
A waveform 41 in FIG. 10 is a waveform showing a change in the light amount value of the read data X (n) −read data W (n) when the background density of the document 6 in FIG. 3 is brighter than that of the white reference plate 15.
In this case, since the read data X (n) -read data W (n) is 0 (almost 0, random noise components are not considered) in the outer area of the document 6, it does not fall below the threshold Y1 and below the threshold Y2. In the area of the document 6, the background of the document 6 is bright, so that the read data X (n) -read data W (n) is equal to or greater than the threshold Y1.

Therefore, the calculation unit 33 in FIG. 1 selects pixels whose light amount difference is initially equal to or greater than the threshold Y1 among the pixels that have not been decreased to the threshold value Y2 or less until the light amount value difference is initially equal to or greater than the threshold value Y1. It is detected as a pixel corresponding to the document edge of the document 6. That is, the leftmost pixel E and the rightmost pixel F of the document 6 in the sub-scanning direction are detected.
In this way, pixels at both ends of the document 6 having a background density brighter than the white reference plate 15 can be detected correctly.

FIG. 11 is an explanatory diagram of another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process.
A waveform 42 in FIG. 11 is a waveform showing a change in the light amount value of the read data X (n) −read data W (n) when the background density of the document 6 in FIG. 3 is darker than that of the white reference plate 15.
In this case, since the background density of the document 6 is dark, a predetermined number of pixels G1 or more from the pixel in which the light amount value of the read data X (n) −read data W (n) is equal to or less than the threshold Y2 in the region of the document 6 The threshold value Y2 is not exceeded.
The predetermined pixel number G1 is a value obtained in advance by an original reading experiment, and is preferably stored in the memory 34 of FIG.

Therefore, the calculation unit 33 in FIG. 1 first calculates the difference in light amount value among the pixels in which the predetermined number of pixels G1 or more does not become greater than or equal to the threshold value Y2 from the pixel in which the difference in light amount value initially becomes less than or equal to the threshold value Y2. Pixels that are equal to or less than the threshold Y2 are detected as pixels corresponding to the document edge of the document 6. That is, the leftmost pixel E1 and the rightmost pixel F1 of the document 6 in the sub-scanning direction are detected.
In this way, the pixels at both ends of the document 6 whose background density is darker than the white reference plate 15 can also be detected correctly.

FIG. 12 is an explanatory diagram of still another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process.
A waveform 43 in FIG. 12 indicates that when the background density of the document 6 in FIG. 3 is brighter than the white reference plate 15 and a shadow is formed at the edge of the document 6, the read data X (n) −read data W (n). It is a waveform which shows the change of a light quantity value.
In this case, since the read data X (n) -read data W (n) is 0 (almost 0, random noise components are not considered) in the outer area of the document 6, it does not fall below the threshold Y1 and below the threshold Y2. When a shadow is generated at the edge of the document 6, the read data X (n) -read data W (n) has a portion where the threshold value Y2 or less occurs, so that the pixel E1 and the pixel F1 are detected.

Further, when the pixel E1 and the pixel F1 are shadowed, the read data X (n) -read data W (n) is equal to or greater than the threshold value Y2 within the predetermined number of pixels G1, so that the pixel E2 and the pixel F2 are Detect.
Then, since the background of the document 6 is bright within the area of the document 6, the read data X (n) −read data W (n) is equal to or greater than the threshold value Y 1. F is detected as a pixel corresponding to the document edge.

That is, the calculation unit 33 in FIG. 1 has the threshold Y2 or more within the predetermined number of pixels G1 from the pixel where the difference in the light amount value first becomes the threshold Y2 or less, and further exceeds the threshold Y1 within the predetermined number of pixels G2. Among the pixels, the first pixel that is equal to or greater than the threshold Y1 within the predetermined number of pixels G2 is detected as a pixel corresponding to the document edge of the document 6. That is, the leftmost pixel E and the rightmost pixel F of the document 6 in the sub-scanning direction are detected.
The predetermined pixel number G2 is also a value obtained in advance by an original reading experiment, and is preferably stored in the memory 34 of FIG.
In this manner, pixels at both ends of the document 6 can be correctly detected even if shadow portions occur at both ends of the document 6.

FIG. 13 is an explanatory diagram of still another process in which the calculation unit 33 shown in FIG. 1 finds a pixel corresponding to the document edge in the document edge detection process.
A waveform 44 in FIG. 13 shows a change in the light amount value of the read data X (n) −read data W (n) when the background density of the document 6 in FIG. 3 becomes a density near the read data W (n). It is a waveform to show.
In this case, the pixels E1 and E2 and the pixels F1 and F2 are detected in the same manner as described above when a shadow is generated at the edge of the document 6, but the background density of the document 6 is determined based on the read data W. (N) Since the density is in the vicinity, the read data X (n) −read data W (n) does not exceed the threshold Y1 within the predetermined number of pixels G2.

In this case, the pixel E2 and the pixel F2 are detected as pixels corresponding to the document edge of the document 6.
That is, the calculation unit 33 in FIG. 1 does not exceed the threshold Y2 within the predetermined number of pixels G1 within the predetermined number of pixels G1, and does not exceed the threshold Y1 within the predetermined number of pixels G2 from the pixel where the difference in the light amount value first becomes the threshold Y2 or less. Among the pixels, the pixel that first becomes equal to or greater than the threshold Y2 after being equal to or less than the threshold Y2 is detected as a pixel corresponding to the document edge of the document 6. That is, the leftmost pixel E2 and the rightmost pixel F2 of the document 6 in the sub-scanning direction are detected.
In this way, even when the background density of the document 6 is a density near the read data W (n), the pixels at both ends of the document 6 can be correctly detected.

As described above, the pixels corresponding to the document edge of the document 6 can be detected in the document edge detection process by the processes shown in FIGS.
10 to 13 exemplify the case where the background density of the document 6 is constant, the edge of the document is detected by performing each of these processes even for the document 6 without the background. can do.

Next, document edge detection processing in the image reading unit 2 will be described.
14 and 15 are flowcharts showing the document edge detection process of the image reading unit 2 shown in FIG.
This document edge detection process is executed when the calculation unit 33 in FIG. 1 stores the read data W (n) and X (n) in the memory 34.
In step (indicated by “S” in FIG. 14) 11 in FIG. 14, the read data W (n) is acquired from the memory 34, and the process proceeds to step 12. The read data W (n) is light amount value data of each pixel in the document readable area of the image sensor 21 when the white reference plate 15 is read after the white reference plate 15 is moved to a predetermined position. Is a variable for indicating the pixels from the head to the tail in the main scanning direction, and is an integer of 1 or more.

For the read data W (n), after the white reference plate 15 in FIG. 3 is moved to a predetermined position under the control of the central control unit 30 in FIG. 1, the image sensor 21 moves the white reference plate 15 in the main scanning direction. The calculation unit 33 stores the light amount value data of each pixel in the document readable area of the image sensor 21 in the memory 34, and then the light amount value data for the multiple times in the main scanning direction. The average value of the light quantity value data of each corresponding pixel is obtained, and the calculation unit 33 in FIG. 1 uses the average value as the light quantity of each pixel obtained by the reflected light from the white reference plate 15 in the document readable area of the image sensor 21. Value data may be used.
If the reading data W (n) of the white reference plate 15 is read from the start of reading the document 6 in FIG. 3 to before the document 6 passes under the white reference plate 15, There is an advantage that the speed until the reading of the document 6 is completed becomes faster.

In step 12, threshold Y1 and threshold Y2 are set, and the process proceeds to step 13.
Detailed processing contents of step 12 will be described later with reference to FIGS.
In step 13, read data X (n) is acquired from the memory 34, and the process proceeds to step 14. The read data X (n) is light amount value data of each pixel obtained when the original readable area of the image sensor 21 reads the portion where the original 6 is superimposed on the white reference plate 15.
In step 14, n = 1 is set, and the process proceeds to step 15.
In step 14, n = 1 is set as an initial value indicating a pixel to be referred to in order to compare the difference in light amount value data from the leading end (reading start pixel) of the document 6 in the main scanning direction.

Then, the processing in the following steps 15 to 29 is performed from n = 1 (the first pixel of the light quantity value data obtained from the document readable area in the main scanning direction) to N (N is obtained from the document readable area in the main scanning direction). Repeat until the last pixel of the obtained light quantity value data).
In step 15, it is determined whether read data X (n) −read data W (n) ≧ threshold Y1, and if read data X (n) −read data W (n) ≧ threshold Y1 (in the case of Y). Advances to step 29, and if the read data X (n) −read data W (n) ≧ threshold Y1 is not satisfied (in the case of N), the process advances to step 16.
In step 29, the leftmost pixel E = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 31 in FIG.

In step 16, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y2. If read data X (n) −read data W (n) ≦ threshold Y2 (in the case of Y). Advances to step 18, and if read data X (n) −read data W (n) ≦ threshold Y <b> 2 (in the case of N), the process advances to step 17.
In step 17, n = n + 1 is set, and the process returns to step 15.
In this way, the processing of steps 15 to 17 is repeated, and among the pixels that did not become the threshold value Y2 or less until the light quantity value data difference first becomes the threshold value Y1 or more, the light quantity value data difference first becomes the threshold value Y1 or more. Find the pixel n. The pixel n found here is detected in step 29 as the leftmost pixel E = n in the sub-scanning direction of the document 6. The detection processing of the leftmost pixel E = n in the sub-scanning direction of the document 6 has been described with reference to FIG.

In step 18, the pixel E1 = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 19. In the process of step 18, the pixel E1 shown in FIGS. 11 to 13 is detected.
In step 19, n = n + 1 is set, and the process proceeds to step 20.
In step 20, it is determined whether or not n <pixel E1 + predetermined pixel number G1. If n <pixel E1 + predetermined pixel number G1 is not satisfied (in the case of N), the process proceeds to step 21, where n <pixel E1 + predetermined pixel number G1. If yes (Y), go to Step 22.
In step 21, the leftmost pixel E = E1 in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 31 in FIG.

As a result of the processing in steps 15, 16, and 20, the difference in the light quantity value data among the pixels in which the difference in the light quantity value data from the pixel that has initially become the threshold value Y2 or less and the predetermined number of pixels G1 or more does not become the threshold value Y2 or more. First, the pixel E1 that is equal to or less than the threshold Y2 is found. The pixel E1 found here is detected as a pixel E = E1 at the left end in the sub-scanning direction of the document 6 in step 21. The detection processing of the pixel E = E1 at the left end of the original 6 in the sub-scanning direction has been described with reference to FIG.
In step 22, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y2. If read data X (n) −read data W (n) ≦ threshold Y2 (in the case of Y). Returns to step 19 and proceeds to step 23 if read data X (n) −read data W (n) ≦ threshold Y2 (N).

In step 23, the pixel E2 = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 24. In the process of step 23, the pixel E2 shown in FIGS. 12 and 13 is detected.
In step 24, n = n + 1 is set, and the process proceeds to step 25.
In step 25, it is determined whether or not n <pixel E2 + predetermined pixel number G2. If n <pixel E2 + predetermined pixel number G2 is not satisfied (in the case of N), the process proceeds to step 26, where n <pixel E2 + predetermined pixel number G2. If yes (Y), go to step 27.
In step 26, the leftmost pixel E = E2 in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 31 in FIG.

As a result of the processing of steps 15, 16, 20, 22, and 25, the difference in the light quantity value data is equal to or greater than the threshold Y2 within the predetermined number of pixels G1 from the pixel that initially becomes equal to or less than the threshold Y2, and further within the predetermined number of pixels G2. Among the pixels that did not become Y1 or more, the pixel E2 that first became the threshold Y2 or less after the threshold Y2 or less was found. The pixel E2 found here is detected as a pixel E = E2 at the left end in the sub-scanning direction of the document 6 in step 26. The detection process of the pixel E = E2 at the left end of the document 6 in the sub-scanning direction has been described with reference to FIG.
In step 27, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y1, and if read data X (n) −read data W (n) ≦ threshold Y1 (in the case of Y). Returns to step 24, and proceeds to step 28 if the read data X (n) -read data W (n) ≦ threshold Y1 is not satisfied (in the case of N).

In step 28, the leftmost pixel E = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 31 in FIG.
As a result of the processing of steps 15, 16, 20, 22, 25, and 27, the difference in the light quantity value data becomes equal to or greater than the threshold Y2 within the predetermined number of pixels G1 from the pixel that initially becomes equal to or less than the threshold Y2, and further within the predetermined number of pixels G2. Among the pixels having the threshold Y1 or more, the first pixel E having the threshold Y1 or more within the predetermined number of pixels G2 is found. The pixel E found here is detected at step 28 as the leftmost pixel E = n in the sub-scanning direction of the document 6. The detection processing of the leftmost pixel E = n in the sub-scanning direction of the document 6 has been described with reference to FIG.
In this way, the pixel E at the left end of the document 6 is detected.

Next, the rightmost pixel F of the document 6 is detected by the processing of the flowchart shown in FIG.
First, in step 31, n = N is reset and the process proceeds to step 32. The reference order of each pixel of the light amount value data obtained from the document readable area in the main scanning direction in the process of step 31 is set opposite to the process shown in FIG.
Then, the processing of the following steps 32 to 46 is performed from n = N (N is the last pixel of the light amount value data obtained from the document readable area in the main scanning direction) to n = 1 (document reading in the main scanning direction is possible). Repeat until the first pixel of the light quantity value data obtained from the area).

In step 32, it is determined whether read data X (n) −read data W (n) ≧ threshold Y1, and if read data X (n) −read data W (n) ≧ threshold Y1 (in the case of Y). Advances to step 46, and if read data X (n) −read data W (n) ≧ threshold Y1 is not satisfied (in the case of N), the process advances to step 33.
In step 46, the rightmost pixel F = n in the sub-scanning direction of the document 6 is detected, and this process ends.
In step 33, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y2, and if read data X (n) −read data W (n) ≦ threshold Y2 (in the case of Y). Advances to step 35, and if the read data X (n) −read data W (n) ≦ threshold Y2 is not satisfied (in the case of N), the process advances to step 34.

In this way, the processing of steps 32 to 34 is repeated, and among the pixels that did not become the threshold value Y2 or less until the light quantity value data difference first becomes the threshold value Y1 or more, the light quantity value data difference first becomes the threshold value Y1 or more. Find the pixel n. The pixel n found here is detected at step 46 as the rightmost pixel F = n in the sub-scanning direction of the document 6. The detection processing of the rightmost pixel F = n in the sub-scanning direction of the document 6 has been described with reference to FIG.
In step 34, n = N-1 and the process returns to step 32.
In step 35, the pixel F1 = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 36. In the process of step 35, the pixel F1 shown in FIGS. 11 to 13 is detected.
In step 36, n = N-1 and the process proceeds to step 37.

In step 37, it is determined whether or not n <pixel F1 + predetermined pixel number G1. If n <pixel F1 + predetermined pixel number G1 is not satisfied (in the case of N), the process proceeds to step 38, where n <pixel F1 + predetermined pixel number G1. If yes (Y), go to step 39.
In step 38, the rightmost pixel F = F1 in the sub-scanning direction of the document 6 is detected, and this process ends.
As a result of the processing of steps 32, 33, and 37, the difference in the light quantity value data among the pixels in which the predetermined number of pixels G1 or more does not become the threshold value Y2 or more from the pixel in which the difference in the light quantity value data first becomes the threshold value Y2 or less. First, the pixel F1 that is equal to or less than the threshold Y2 is found. The pixel F1 found here is detected as the rightmost pixel F = F1 in the sub-scanning direction of the document 6 in step 38. The detection process for the rightmost pixel F = F1 in the sub-scanning direction of the document 6 has been described with reference to FIG.

In step 39, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y2. If read data X (n) −read data W (n) ≦ threshold Y2 (in the case of Y). Returns to step 36, and if not the read data X (n) −read data W (n) ≦ threshold Y2, the process proceeds to step 40.
In step 40, the pixel F2 = n in the sub-scanning direction of the document 6 is detected, and the process proceeds to step 41. In step 40, the pixel F2 shown in FIGS. 12 and 13 is detected.
In step 41, n = N−1 and the process proceeds to step.
In step 42, it is determined whether or not n <pixel F2 + predetermined pixel number G2. If n <pixel F2 + predetermined pixel number G2 is not satisfied (in the case of N), the process proceeds to step 43, where n <pixel F2 + predetermined pixel number G2. If yes (Y), go to step 44.

In step 43, the rightmost pixel F = F2 in the sub-scanning direction of the document 6 is detected, and this process ends.
As a result of the processing of steps 32, 33, 37, 39, and 42, the difference in the light quantity value data first becomes equal to or greater than the threshold Y2 within the predetermined number of pixels G1 from the pixel that is initially equal to or less than the threshold Y2, and further within the predetermined number of pixels G2. Among the pixels that did not become Y1 or more, the pixel F2 that first became the threshold Y2 or less after the threshold Y2 or less was found. The pixel F2 found here is detected as a rightmost pixel F = F2 in the sub-scanning direction of the document 6 in step 43. The detailed detection processing of the rightmost pixel F = F2 in the sub-scanning direction of the document 6 has been described with reference to FIG.

In step 44, it is determined whether or not read data X (n) −read data W (n) ≦ threshold Y1, and if read data X (n) −read data W (n) ≦ threshold Y1 (in the case of Y). Returns to step 41, and proceeds to step 45 if read data X (n) −read data W (n) ≦ threshold Y <b> 1 (in the case of N).
In step 45, the rightmost pixel F = n in the sub-scanning direction of the document 6 is detected, and this process ends.

As a result of the processing of steps 32, 33, 37, 39, 42, and 44, the difference in the light quantity value data becomes equal to or greater than the threshold Y2 within the predetermined number of pixels G1 from the pixel that first becomes the threshold Y2 or less, and further within the predetermined number of pixels G2. Among the pixels having the threshold Y1 or more, the first pixel F having the threshold Y1 or more within the predetermined number of pixels G2 is found. The pixel F found here is detected in step 45 as the rightmost pixel F in the sub-scanning direction of the document 6 = n. Detailed detection processing of the rightmost pixel F = n in the sub-scanning direction of the document 6 has been described with reference to FIG.
In this way, the rightmost pixel F of the document 6 is detected.

Next, the threshold Y1 and threshold Y2 setting processing in step 12 of FIG. 14 will be described in detail.
In step 12 of FIG. 14, the threshold value Y1 and the threshold value Y2 are set by any one of the following setting processes (1) to (3).
The selection of any one of the setting processes (1) to (3) may be switched by the user from the operation unit 12 in FIG. 3, or any setting process may be performed when the image reading unit 2 is manufactured. Alternatively, the function of the calculation unit 33 may be set.

(1) Setting Processing for Setting Fixed Values In this setting processing, predetermined fixed value threshold values Y1 and Y2 are stored in the memory 34 of FIG. 1, and are read and set during document edge detection processing. .
The threshold values Y1 and Y2 correspond to the distance between the white reference plate 15 and the image sensor 21 when the white reference plate 15 in FIG. 3 is moved to a predetermined position in the direction facing the image sensor 21 by the movement of the upper cover 10. The threshold values Y1 and Y2 are stored in the memory 34 at the time of factory shipment.

FIG. 16 is a flowchart showing detailed processing when the threshold value Y1 and the threshold value Y2 are set as fixed values in step 12 of FIG.
1 reads the threshold value Y1 and threshold value Y2 from the memory 34 at step 51 in FIG. 16, sets the threshold value Y1 and threshold value Y2 at step 52, and returns.
In the reading of the threshold value Y1 and the threshold value Y2 in step 51, the threshold value Y1 and the threshold value Y2 corresponding to the movement amount of the upper cover 10 in FIG. In step 52, a threshold Y1 and a threshold Y2 are set in preparation for document edge detection processing.
In this way, the fixed values stored in advance in the memory 34 are set in the threshold Y1 and the threshold Y2, and therefore the document edge detection process can be performed at high speed because the process is simple.

(2) Processing in the case where the optimum threshold value Y1 and threshold value Y2 are set every time The threshold value Y1 and threshold value Y2 may be determined and set every time the document 6 is read.
In this setting process, the threshold value Y1 and the threshold value Y2 are respectively set to the standard deviations of the light amount value data of the plurality of pixels output from the document readable area of the image sensor 21 when the white reference plate 15 of FIG. Each value is obtained by multiplying or adding different constant values.

FIG. 17 is a flowchart showing detailed processing when the threshold value Y1 and the threshold value Y2 are obtained and set in step 12 of FIG.
1 obtains m times of read data W (n) of the white reference plate 15 in FIG. 3 after being moved to a predetermined position in step 61 in FIG. 17 (n and m are positive integers). , Go to Step 62.
In the process of step 61, by acquiring the read data W (n) a plurality of times (m times of reading of the original readable area), data of a certain n pixel can be acquired m times.

In step 62, the standard deviation δ (n, m) of the read data W (n) of the white reference plate 15 is calculated, and the process proceeds to step 63.
In the process of step 62, the standard deviation δ (n, m) of the read data W (n) for m times is calculated.
In step 63, threshold value Y1 = δ (n, m) × α is calculated (α is a margin determined in advance), and the process proceeds to step 64.
In step 64, threshold Y2 = δ (n, m) × β is calculated (β is a margin obtained in advance), and the process proceeds to step 65.
In steps 63 and 64, the standard deviation δ multiplied by the margins α and β are calculated as the threshold Y1 and the threshold Y2.

In step 65, threshold values Y1 and Y2 are set, and the process returns.
In the document edge detection process, the difference between the read data X (n) and the read data W (n) is compared. When the white reference plate 15 is read to obtain the read data W (n), the light quantity is stabilized. Noise, photoelectric conversion noise, signal processing noise, and the like are generated.
Since the amount of noise varies with time depending on the amount of light, gain, and the like, the optimum threshold values Y1 and Y2 can be set by calculating the amount of noise every time by the setting process shown in FIG.
As described above, according to the threshold value Y1 and the threshold value Y2 set by the setting process shown in FIG. 17, it is possible to provide a margin and prevent erroneous detection.
Although the margins α and β are multiplied in the above-described processing, addition (subtraction) may be performed.
In this way, by using the standard deviation δ of the read data W (n) for m times, it is possible to set optimum values for the threshold value Y1 and the threshold value Y2 even when the noise component fluctuates.

(3) Other Processes for Setting Optimal Threshold Y1 and Threshold Y2 Each Time Other processes for obtaining and setting optimal thresholds Y1 and Y2 each time the document 6 is read will be shown.
In this setting process, the threshold value Y1 and the threshold value Y2 are set to the maximum value and the minimum value of the light amount value data of each of the plurality of pixels output from the document readable area of the image sensor 21 when the white reference plate 15 of FIG. Each difference is a value obtained by multiplying or adding a different constant value.

FIG. 18 is a flowchart showing another processing example when the threshold value Y1 and the threshold value Y2 are obtained and set in step 12 of FIG.
The calculation unit 33 in FIG. 1 acquires the read data W (n) of the white reference plate 15 in FIG. 3 after moving to a predetermined position in step 71 in FIG. 18 for m times (n and m are positive integers). The process proceeds to step 72.
In the processing of step 71, by acquiring the read data W (n) a plurality of times (m times of reading of the original readable area), data of a certain n pixel can be acquired m times.

In step 72, MAX (n, m) −MIN (n, m) of the read data W (n) of the white reference plate 15 is calculated, and the process proceeds to step 73. The MAX (n, m) corresponds to the maximum value of the light amount value data of each of the plurality of pixels output from the document readable area of the image sensor 21 when the white reference plate 15 of FIG. (N, m) corresponds to the minimum value of the light amount value data of each of the plurality of pixels output from the document readable area of the image sensor 21 when the white reference plate 15 of FIG. 3 is read a plurality of times.
In the process of step 72, the difference between MAX (n, m) which is the maximum value of the read data W (n) for m times and MIN (n, m) which is the minimum value is calculated.
In step 73, threshold Y1 = {MAX (n, m) −MIN (n, m)} × α is calculated (α is a margin determined in advance), and the process proceeds to step 74.
In step 74, threshold Y2 = {MAX (n, m) −MIN (n, m)} × β is calculated (β is a margin determined in advance), and the process proceeds to step 75.

In Steps 73 and 74, the difference between the maximum value and the minimum value multiplied by the margins α and β is calculated as the threshold Y1 and the threshold Y2.
In step 75, threshold values Y1 and Y2 are set, and the process returns.
Although the margins α and β are multiplied in the above-described processing, addition (subtraction) may be performed.
In this way, even when the difference between the maximum value and the minimum value of the read data W (n) is used, optimum values can be set for the threshold value Y1 and the threshold value Y2 when the noise component fluctuates.
In the setting processing of FIGS. 17 and 18, only the data of the n-th pixel may be used, or some data of all the main scans (in the region of the white reference plate 15) is used. The standard deviation, the maximum value-the minimum value may be the maximum.

The calculation unit 33 of FIG. 1 performs the processing of FIGS. 14 and 15 described above on a part of the document front end region (one document readable region) in the conveyance direction (sub-scanning direction) of the document 6 and is obtained thereby. If the leftmost pixel E and the rightmost pixel F of the original 6 are applied to other lines in the main scanning direction of the original 6, it is not necessary to repeat the process for every line in the main scanning direction of the original, and the original end detection process. Can be done in a short time.
However, in this case, although there is an advantage that the processing is simplified, when the document 6 is inserted obliquely, the document edge cannot be detected correctly over the entire surface of the document 6.
FIG. 19 is a plan view of the lower platen 11 and its periphery viewed from above when the document 6 shown in FIG. 3 is inserted obliquely.

As shown in FIG. 19, when the document 6 is inserted obliquely, skewed, or the document 6 itself has an irregular shape, the document front end region in the conveyance direction (sub-scanning direction) of the document 6 is If document edge detection processing is performed on a part (one document readable area) and pixels corresponding to the detected document edge are applied to the entire surface of the document 6, the document edge cannot be detected correctly.
Therefore, the calculation unit 33 in FIG. 1 performs the above-described processing in FIGS. 14 and 15 in all the reading areas for each original readable area in the conveyance direction (sub-scanning direction) of the original 6. The document edge can be correctly detected over the entire surface of the document 6, and the document edge detection process can be performed with high accuracy.

Information on the pixels E and F corresponding to the document edge of the document 6 detected by the calculation unit 33 in FIG. 1 is sent to the image processing unit 37 by the processing described above.
Then, the image processing unit 37 removes each pixel other than the document area of the document 6 from the read data X (n) based on the information of the pixels E and F corresponding to the document edge of the document 6 (cuts the image itself). Or make it a white pixel.
The read data X (n) in the document area of the document 6 obtained in this way is sent to the image forming unit 3 in FIG. 2 for printing, so that the image quality of copy printing of the document 6 can be improved.

  The image reading unit 2 of this embodiment moves the white reference plate 15 in a direction perpendicular to the document conveyance direction after obtaining the shading correction data to be read for shading correction of the image read from the document 6, and moves the white reference plate 15 to the image sensor 21. Thus, in reading a sheet-through type image in which the original 6 is moved and the image of the original 6 is read, the edge of the original can be accurately detected for both the thick original 6 and the original 6 having no background such as the picture quality.

In this embodiment, the reading data in the document readable area of the image sensor 21 has been described. However, if the white reference plate 15 exists in an area of one line or more of the document readable area, the document can be read in the main scanning direction. You may use the read data of the predetermined area | region of the main scanning direction beyond an area | region.
For example, if the effective pixel area of the image sensor 21 is larger than the document readable area, and the white reference plate 15 is in the range read by the effective pixel area of the image sensor 21, the read data of the effective pixel area of the image sensor You may process similarly to the above-mentioned using.

Although the description of the embodiment has been completed above, in the present invention, the specific configuration of each unit, the content of processing, the data format, and the like are not limited to those described in the embodiment.
Further, it goes without saying that the configurations of the embodiments described above can be implemented in any combination as long as they do not contradict each other.

1: Image forming apparatus 2: Image reading unit 3: Image forming unit 4: Image forming unit 5: Paper feeding unit 6: Document 10: Upper cover 11: Lower platen 12: Operation unit 13: Distance detection sensors 14a and 14b: Front Roller 15: White reference plate 16a, 16b: Rear roller 17: Document insertion detection sensor 18: Stopper 19: Contact glass 20: Light source 21: Image sensor 22: Frame 23, 27, 28: Gear 24: Upper cover drive motor 25: Stopper drive motor 26: Lever 29: Belt 30: Central control unit 31: A / D conversion unit 32: Signal processing unit 33: Calculation unit 34: Memory 35: Black subtraction unit 36: Shading processing unit 37: Image processing unit 40 ~ 44: Waveform

JP 2001-220044 A JP 2002-84409 A

Claims (14)

A light source for irradiating light on the document, and an image reading means for reading an image of the document by reflected light from the document;
A reference member disposed opposite to the image reading means to obtain an image for shading correction of an image read from the original;
Reference member moving means for moving the reference member to a predetermined position in a direction facing the image reading means in order to provide an interval according to the thickness of the document between the image reading means and the reference member;
After the reference member is moved to the predetermined position by the reference member moving means, the original is transported between the image reading means and the reference member, and is sent from the light source to the original in the main scanning direction of the original. An image reading device that irradiates light for each line and the image reading unit reads an image for each line in the main scanning direction of the original by reflected light from the original,
After the reference member is moved to the predetermined position by the reference member moving means, at least the original in the main scanning direction of the image reading means without conveying the original between the image reading means and the reference member A first light amount value data that is a light amount value of each pixel in the predetermined region read by the image reading unit by irradiating light from the light source to the region of the reference member that is read by a predetermined region that is larger than the readable region; The image reading is performed by irradiating light from the light source to an area corresponding to the reference member and the predetermined area of the document in a state where the document is conveyed between the image reading unit and the reference member. Light quantity value holding means for holding second light quantity value data which is a light quantity value of each pixel in the predetermined area read by the means;
The difference between the first light quantity value data and the second light quantity value data held in the light quantity value holding means is calculated for each pixel at a corresponding position in the main scanning direction, and the light quantity value data for each pixel. Is compared with each of a predetermined first threshold set for the difference in the light quantity value data and a predetermined second threshold smaller than the first threshold, and based on the comparison result, the first An image reading apparatus comprising: document edge detection means for detecting pixels corresponding to the document edge from the light quantity value data of 2. The image reading apparatus according to claim 1,
Based on the pixels corresponding to the document edge detected by the document edge detection means, each pixel in the external region of the document edge is removed from the pixels corresponding to the reference member and the predetermined region of the document or white. An image reading apparatus having a removing means for converting into pixels.   After the reference member is moved to the predetermined position, the first light quantity value data read by the image reading means is stored in a predetermined area at least as large as the original readable area in the main scanning direction of the image reading means. The image reading apparatus according to claim 1, wherein the average value of the light amount value data of each pixel corresponding to the main scanning direction in each region obtained by reading the reference member a plurality of times is used.   The document edge detection means calculates the difference between the first threshold value and the second threshold value for each pixel in order from the pixels on both ends of the reference member and the predetermined region of the document in the main scanning direction. Each of the pixels that did not fall below the second threshold until the light quantity value difference first became equal to or greater than the first threshold value. 4. The image reading apparatus according to claim 1, wherein the detected pixel is detected as a pixel corresponding to the document edge. 5.   The document edge detection means calculates the difference between the first threshold value and the second threshold value for each pixel in order from the pixels on both ends of the reference member and the predetermined region of the document in the main scanning direction. Each of the pixels whose light quantity value difference was initially less than or equal to the second threshold value, and from among the pixels whose predetermined pixel number or more did not exceed the second threshold value, 4. The image reading apparatus according to claim 1, wherein a pixel that is equal to or less than the second threshold is detected as a pixel corresponding to the document edge. 5.   The document edge detection means calculates the difference between the first threshold value and the second threshold value for each pixel in order from the pixels on both ends of the reference member and the predetermined region of the document in the main scanning direction. Are compared with each other, and the difference between the light quantity value data is equal to or greater than the second threshold within a predetermined number of pixels from the pixel that first becomes the second threshold or less, and is further equal to or greater than the first threshold within the predetermined number of pixels. 4. The first pixel that is equal to or more than the first threshold value within the predetermined number of pixels among the pixels that have become is detected as a pixel corresponding to the document edge. 5. The image reading apparatus according to one item.   The document edge detection means calculates the difference between the first threshold value and the second threshold value for each pixel in order from the pixels on both ends of the reference member and the predetermined region of the document in the main scanning direction. Are compared with each other, and the difference between the light quantity value data is equal to or greater than the second threshold within a predetermined number of pixels from the pixel that first becomes the second threshold or less, and is further equal to or greater than the first threshold within the predetermined number of pixels. 2. The pixel that is not equal to or less than the second threshold and is first detected to be equal to or greater than the second threshold among the pixels that have not become false is detected as a pixel corresponding to the document edge. 4. The image reading apparatus according to claim 1.   The first threshold value and the second threshold value are respectively determined according to a distance between the reference member and the image reading unit when the reference member is moved to a predetermined position in a direction facing the image reading unit. The image reading apparatus according to any one of claims 1 to 7, wherein the image reading apparatus has a predetermined value.   The first threshold value and the second threshold value are multiplied or added by different fixed values to the standard deviation of the light amount value data of each pixel corresponding to the main scanning direction of each region obtained by reading the reference member a plurality of times. The image reading apparatus according to claim 1, wherein the image reading apparatus has a calculated value.   The first threshold value and the second threshold value are obtained by multiplying or adding a different constant value to the difference between the maximum value and the minimum value of the light amount value data of each pixel in each region obtained by reading the reference member a plurality of times. The image reading apparatus according to claim 1, wherein the image reading apparatus is a value.   11. The document edge detection means has means for detecting a pixel corresponding to the document edge in a part of a document leading edge region in the document conveyance direction. The image reading apparatus described.   The document edge detection means detects the pixels corresponding to the document edge in all of a plurality of areas corresponding to the reference member and the predetermined area of the document read by the image reading means in the document conveyance direction. The image reading apparatus according to claim 1, further comprising a unit for performing the operation.   An image forming apparatus comprising the image reading apparatus according to claim 1. A light source for irradiating light on the original, an image reading means for reading an image of the original by reflected light from the original, and an image reading means for acquiring an image for shading correction of the image read from the original The reference member is placed up to a predetermined position in a direction facing the image reading means in order to provide a gap corresponding to the thickness of the original between the reference member arranged opposite to the image reading means and the reference member. A reference member moving means to be moved; and after the reference member is moved to the predetermined position by the reference member moving means, the original is conveyed between the image reading means and the reference member, and the light source is supplied to the original. The image reading unit reads an image for each line in the main scanning direction of the document by reflected light from the document. A document edge detection method in the apparatus,
After the reference member is moved to the predetermined position by the reference member moving means, at least the original in the main scanning direction of the image reading means without conveying the original between the image reading means and the reference member A first light amount value data that is a light amount value of each pixel in the predetermined region read by the image reading unit by irradiating light from the light source to the region of the reference member that is read by a predetermined region that is larger than the readable region; The image reading is performed by irradiating light from the light source to an area corresponding to the reference member and the predetermined area of the document in a state where the document is conveyed between the image reading unit and the reference member. A light quantity value holding procedure for holding second light quantity value data which is a light quantity value of each pixel in the predetermined area read by the means;
A difference between the first light amount value data and the second light amount value data held by the light amount value holding procedure is calculated for each pixel at a corresponding position in the main scanning direction, and the light amount value data of each pixel is calculated. The difference is compared with each of a predetermined first threshold set for the difference in the light quantity value data and a predetermined second threshold smaller than the first threshold, and the second is based on the comparison result. And a document edge detection procedure for detecting a pixel corresponding to the document edge from the light quantity value data of the document.

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