JP3404955B2 - Document size detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document size detecting device for a copying machine, a facsimile or the like.

[0002]

2. Description of the Related Art Generally, a document set on a copying machine or the like has a standardized predetermined size such as A plate or B plate. From this fact, if the size of the original is specified, the size of the copy paper can be automatically set. Therefore, many copying machines are now equipped with the original size detecting device. As this type of document size detecting device, an image of a document set on a platen glass is optically read by an image reading unit equipped with a photoelectric conversion element such as a CCD image sensor, and the read predetermined line is read. 2 minutes by setting a threshold for minute image data
It is generally known that not only the value is binarized but also the change point of the density level after binarization is detected as the position of the document edge, and the document size is detected based on the detection result.

[0003]

However, in the above-mentioned prior art, when an original document having a remarkably higher transmissivity than a normal original document, such as a treshing paper, is set on the platen glass, the original document region and its background region,
That is, the density difference from the area outside the document becomes extremely small, and the density level above the threshold value cannot be obtained. For this reason, it has been virtually impossible to detect the size of a document having a high transmittance such as tressing paper. In addition, in connection with this, there is a problem that a document (tressing paper or the like) is set on the platen glass, but it is erroneously recognized as “no document”.

The present invention has been made in order to solve the above problems, and an object of the present invention is to accurately detect the document size even for a document having a high transmissivity such as treasuring paper. An object is to provide a document size detection device.

[0005]

According to the present invention, the size of a document set in an image reading unit for optically reading image information of the document is detected by detecting the position of the document edge. In the document size detection device, a predetermined one read by the image reading unit
Density levels above the first threshold from image data for lines
When the density difference is not obtained, a density difference calculating means for calculating the density difference of the image data for one line , and a density difference comparing means for comparing the density difference calculated by the density difference calculating means with a prescribed density difference. And the comparison result of this density difference comparison means
In addition, the calculated density difference is more than the specified density difference.
If it is too large, the set original is larger than the plain paper original.
Even if the original is considered to have a high transmissivity,
A threshold setting means for setting a value to a second threshold lower than the first threshold value, before that is set by the threshold value setting means
Using the threshold for detecting the document edge, the image data for one line is
The black-and-white change point of the data is detected, and the black-and-white change point is detected in the original document.
A document edge detecting means for detecting the edge position is provided.

According to a second aspect of the present invention, in the document size detecting apparatus according to the first aspect, a predetermined image is extracted from a pixel of interest.
Set a plurality of comparison pixels with a prime distance,
Document based on data change between pixel and said comparison pixel
When performing the edge detection processing, comparison by the density difference comparison means
In the results, the calculated density difference is the specified density.
If it is larger than the difference, the pixel interval at the time of detecting the document edge is normally set.
It is configured to include a pixel interval setting unit that sets the width wider than that in the case of a paper document .

According to a third aspect of the invention, in the document size detecting apparatus according to the first or second aspect, the density difference calculating means detects the main density value of the peak data value of the image data for a predetermined one line. a detection unit, and the sub-density value detecting unit for at least one detected density value next to the peak concentration value, and the peak concentration value detected by the primary density value detector
At least one concentration detected by the sub-concentration value detector
The level of the density value between two ranks using the frequency value and
2 having a level difference calculation section that calculates sequentially a difference from the peak density value side, the level difference when the level difference calculated is equal to or less than a prescribed level by the level difference calculation section
Using the peak concentration value selection unit that selects the concentration value on the side closer to the peak concentration value as the true peak concentration value, and the true peak concentration value selected by this peak concentration value selection unit. And a density difference calculation unit that calculates a density difference.

[0008]

In the invention of claim 1, the density difference calculated by the density difference calculating means and the specified density difference are compared by the density difference comparing means, and in the comparison result, for example, the density difference is less than the specified density difference. Is larger, it is considered that the document set in the image reading unit is a document (transparency paper or the like) having a higher transmissivity than a plain paper document (white or black document), and a threshold value suitable for it is a threshold value setting means. Set by. Therefore, even if the original has a high transmittance, the position of the original edge is detected by the original edge detecting means based on the threshold value set by the threshold value setting means.

According to the second aspect of the present invention, when the document is considered to be, for example, treasuring paper in the comparison result of the density difference comparing means, the pixel interval at the time of detecting the document edge is correspondingly larger than that of the plain paper document. Is also set wider so that a larger density difference can be obtained at the position of the document edge.

According to the third aspect of the present invention, for example, when the peak density value in the actually read image data is the density level due to the isolated point, the peak density value is detected by the main density value detecting section. The second and subsequent density values are detected by the sub-density value detection unit. In such a case, the level difference calculation unit first calculates the level difference between the peak density value and the second density value next to it, and thereafter,
The level difference between the second density value and the next third density value is calculated. At that time, since the peak density value detected by the main density value detection unit is due to an isolated point, the level difference between the peak density value and the second density value exceeds the prescribed level, and The level difference between the third density value and the third density value is less than the specified level. Then,
The peak density value selection unit selects the side closer to the peak density value, that is, the second density value as the "true peak density value", and the density difference calculation unit uses this to calculate the density difference.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention when applied to a digital copying machine will be described below in detail with reference to the drawings. The document size detecting device according to the present invention is
The invention is not limited to application to a copying machine, but can be applied to all electronic devices including an image reading unit that optically reads image information of a document.

FIG. 1 is a schematic configuration diagram of an image reading unit in an embodiment, which constitutes a part of a digital copying machine to which the present invention is applied. As shown in the figure, a platen glass (document table) 3 for setting a document 2 to be copied is provided on the upper surface of the unit main body 1.
The original 2 placed there is pressed from above by the platen cover 4. Platen cover 4
Has a white document pressing surface on the lower surface side, and is openably and closably attached to one end side (the left end side in the drawing) of the cover as a pivot point.

On the other hand, below the platen glass 3, an exposure lamp 5 for irradiating the original 2 with light and reflecting mirrors 6, 7, 8 for reflecting the reflected light from the original 2 in a predetermined direction.
And a CCD image sensor 10 that takes in the reflected light from the mirror through the imaging lens 9 is provided. Among the components of such an optical system, the exposure lamp 5 and the reflection mirrors 6, 7, and 8 are mounted on a carriage (not shown), and while moving in the left-right direction in the figure, that is, the sub-scanning direction Y, the original document is moved. The surface can be optically scanned. In addition, CCD image sensor 1
As 0, a line sensor in which a large number of pixels are linearly arranged is adopted, and a line sensor orthogonal to the sub-scanning direction Y, that is, the main scanning direction X is electrically scanned in a fixed state. It is configured to get. Furthermore, CCD
An image processing unit (not shown) is provided in the subsequent stage of the image sensor 10, and the exposure lamp 5 and the reflection mirrors 6, 7,
The presence or absence of the original 2 and the size of the original 2 are detected based on the image signal obtained by the optical scanning at 8.

In addition to this, sensors 11 and 12 which are turned on / off depending on the opened / closed state of the platen cover 4 are attached to the upper surface of the unit main body 1. One sensor 11 (hereinafter referred to as the first sensor) is arranged near the rotation fulcrum of the platen cover 4, and the other sensor 12
(Hereinafter, referred to as a second sensor) is arranged at a predetermined distance from the rotation fulcrum, for example, at an intermediate point of the platen glass 3 in the sub scanning direction Y. And the first
The sensor 11 is switched on / off when the platen cover 4 is not completely closed, that is, when the platen cover 4 is completely closed, and the second sensor 12 is switched on / off when the platen cover 4 is completely closed. The platen cover 4 is attached so as to be replaced, and the open / closed state of the platen cover 4 can be detected based on the outputs of these sensors (on / off signals).

FIG. 2 is a schematic configuration diagram of a digital copying machine to which the present invention is applied. In FIG. 2, an analog image signal output from the CCD image sensor 10 is converted into digital data by the image data generation circuit 20 and then supplied to the correction / filter circuit 21 as image data. The correction / filter circuit 21 performs shading correction on the input image data, and further performs filtering processing on the image data after the shading correction. The edit processing circuit 22 performs edit processing such as reduction and enlargement on the image data after filtering, and in this processing, for example, a RAM 23 having two memory areas A and B is used. The image data that has been subjected to predetermined editing processing is sent to the output interface circuit 23, and from there is supplied to the image forming unit 24 such as a printer. Although the RAM 23 having the two memory areas A and B is used for performing the editing process here, two separate RAMs may be used although not shown in the figure.

The CPU 25 has a data / address bus (C
The above-mentioned circuits are controlled via the PU bus) 25a, and a control program therefor is stored in the ROM 26. Further, in various processing operations of the CPU 25 (for example, shading correction processing), the RAM 27 is used for temporarily storing data. Furthermore, CPU
Sensors 11 and 12 for detecting the open / closed state of the platen cover 4 described above are connected to 25, respectively, and the open / closed state of the platen cover 4 is fully opened based on the respective sensor outputs (on / off signals). , Closed,
It is possible to recognize whether it is in the fully closed state. The CPU 25 supplies a motor drive signal via a motor driver circuit 29 to a drive motor 28 of a carriage that drives an optical system, and sets it on the platen glass 3 during prescan performed immediately after turning on the power of the apparatus. A process for detecting the size of the document 2 thus formed is performed. This document size detection processing will be described later in detail.

In the digital copying machine having the above structure, when the power source of the apparatus is turned on (ON), the exposure lamp 5 and the reflection mirrors 6, 7 mounted on the carriage (not shown),
The optical system including 8 and the like moves to the main scanning document reading position. Then, this optical system optically scans the original 2 set on the platen glass 3 so that the original image is CC-scanned.
The image is taken into the D image sensor 10 and photoelectrically converted there to be converted into an analog image signal. The analog image signal is converted into digital data by the image data generation circuit 20, and the converted image data is processed by the correction / filter circuit 21 and the editing / processing circuit 22 such as shading processing, filtering processing, and reduction / enlargement. After that, it is given to the image forming unit 24 via the output interface circuit 23, and is printed and formed on the copy paper there.

Next, an explanation will be given of the document size detecting process performed prior to the reading of the document image. This document size detection processing is performed by the CPU 25. First, when the original 2 is set on the platen glass 3 and the platen cover 4 is closed, the platen cover 4 is not completely closed, that is, a so-called closed state, for example, when the platen cover 4 is closed to the platen glass 3 by 20 times. ° ~
The first sensor 11 switches from the off state to the on state in the state of being inclined by 30 °. Then, at the same time as the on / off switching timing of the first sensor 11, a predetermined one line of image data is stored in one memory area A of the RAM 23. In the image data stored in the memory area A, since the platen cover 4 is slightly open and there is no reflected light, the background color of the area outside the document is "black". Further, when the platen cover 4 is closed and finally the platen cover 4 is completely closed, that is, when the platen cover 4 is fully closed, the second sensor 12 as well as the first sensor 11 is changed from the off state to the on state. Switch to. Then, at the same time as the on / off switching timing of the second sensor 12 (at the same time when both the first sensor 11 and the second sensor 12 are turned on), the image data for one predetermined line is transferred to the other side of the RAM 23. Stored in the memory area B of
In the image data stored in this memory area B,
Since the sheet color of the platen cover 4 is white, the background color of the area outside the document is "white" data.

In this way, the image data stored in the RAM 23 at each timing of the nearly closed state and the fully closed state are sequentially scanned from the outside area of the original to the original area on the reading line from the bidirectional direction. Then, a threshold value for detecting the document edge is set for each piece of scan information, and the change point of the scan information, that is, the pixel position at the boundary between the document area and the area outside the document is detected as the position of the document edge.

Here, taking as an example the case where a white original 2 is set on the platen glass 3, in this case, as shown in FIG. 3A, the platen cover 4 is in a state of being closed. Thus, in the image data stored in the memory area A, that is, in the image data in which the background color of the area outside the document is "black", the density level equal to or higher than the threshold value is obtained. On the other hand, when the original 2 is black,
As shown in (b), in the image data stored in the memory area B when the platen cover 4 is fully closed, that is, in the image data in which the area outside the document is "white", the density level equal to or higher than the threshold value is obtained. Will be done.

Therefore, as shown in FIGS. 3A and 3B, when the original 2 is white, when the image data stored in the memory area A is scanned from the area outside the original toward the original area. In addition, points X1 and X2 at which the pixel data changes from "black" to "white" are detected as the positions of the document edge. Further, when the original 2 is black, when the image data stored in the memory area B is scanned from the area outside the original toward the original area in the same manner as described above, the pixel data thereof changes from “white” to “black”. The changing points X3 and X4 are detected as the positions of the document edges. In this embodiment, since the length of the document 2 in the sub-scanning direction Y is detected by a fixed sensor (for example, a photo sensor) not shown, the position of the document edge in the main scanning direction X (X1 ~ X4) is detected, the document size can be detected.

When the original 2 has a low transmissivity such as white or black, as shown in FIG. 4A, one of the image data stored in the memory areas A and B is scanned. By doing so, a density level equal to or higher than the desired threshold value (1) can be obtained. However, when an original 2 having a high transmissivity such as treasuring paper is used, the outside original area and the original area are both closed and fully closed. There is no sudden change in density at the boundary of the
The above density level cannot be obtained.

Therefore, a CP for the document size detection process when the document 2 such as a tressing paper is used.
A functional block diagram of U25 is shown in FIG. In FIG. 5, the density value detecting means 30 sequentially scans one of the image data stored in each of the memory areas A and B of the RAM 23, for example, one line of image data stored in the memory area A. Then, the density value at each pixel position is detected. The density difference calculating means 31 is the density value detecting means 3
For example, the maximum value and the minimum value are extracted from the density data given from 0, and the density difference between the maximum value and the minimum value is calculated. The density difference comparing means 32 compares the density difference given from the density difference calculating means 31 with a prescribed density difference. In this case, the "specified density difference" that is the comparison standard is C
It is set to be larger than the upper limit level of the density difference generated by the shot noise component of the CD image sensor 10. By the way, in the experimental data of the applicant, since the upper limit level of the density difference generated by the shot noise component is about “20” at 256 gradations, “35” is adopted as the density difference specified above. .

The threshold setting means 33 is a density difference comparing means 32.
The threshold value for detecting the document edge is set on the basis of the comparison result in. Specifically, when the density difference comparing unit 32 determines that the density difference obtained by the density difference calculating unit 31 is larger than the upper limit level of the density difference generated by the shot noise component of the CCD image sensor 10, The manuscript 2 is regarded as treasuring paper and an appropriate threshold value (described later) is set. The document edge detecting unit 34 detects the position of the document edge based on the threshold value set by the threshold value setting unit 33, and the document size is detected from the position of the document edge detected here.

Next, the document size detection process executed by the CPU 25 when the document 2 has a high transmissivity such as treasuring paper will be described. First, in both the reading operation in the nearly closed state and the fully closed state, when the density level of the desired threshold value (1) or more is not obtained from the image data stored in the memory areas A and B of the RAM 23, , Memory area A or memory area B
The image data for one line stored in 1 is sequentially scanned by the density value detecting means 30, and the density information at each pixel position detected by this is supplied to the density difference calculating means 31. Next, the density difference calculating means 31 extracts, for example, the maximum density value and the minimum density value from the supplied density information, and the density difference obtained by subtracting the minimum density value from the maximum density value. Is calculated as the density difference in the image data for one line.

Next, in the density difference comparing means 32,
The density difference calculated as described above is compared with the specified density difference. At this time, if the treasuring paper is set on the platen glass 3, the previously calculated density difference is the specified density difference (in the present embodiment, the CCD image sensor 1).
The upper limit level of the density difference generated by the shot noise component of 0). On the other hand, when the original is not set on the platen glass 3, the density difference equal to or less than the shot noise component of the CCD image sensor 10 cannot be obtained, so the density difference calculated by the density difference calculating means 31 is defined. It is smaller than the density difference. Therefore, based on the comparison result of the density difference comparing means 32, it is possible to determine whether the tressing paper is set on the platen glass 3 or the original 2 is not set originally. If the density difference calculated by the density difference calculation unit 31 is less than or equal to the specified density difference, it is considered that the original 2 is not set on the platen glass 3, and the display unit (not shown) indicates that. A message is displayed, for example, "the original has not been set" or "the original size cannot be detected", and the original size detection process ends.

On the other hand, when the density difference comparing means 32 determines that the previously calculated density difference is larger than the specified density difference, the threshold value setting means 33 regards the set original 2 as a treasuring paper, A threshold value setting process for detecting the document edge is performed. The threshold value is set at a density level lower than the threshold value (1) set when the original 2 is white or black as shown in FIG. 4A. Incidentally, in this embodiment, as shown in FIG. 4, the density data actually obtained includes the density change due to the shot nozzle component of the CCD image sensor 10, and the experimental data of the applicant shows that The density difference MAX (1) obtained with a paper original (white original) is 180 to 190 at 256 gradations, while the density difference MAX (2) obtained with tressing paper is 55 to 6
Since it was 0, the threshold value (2) applied to the treasuring paper was set to 1/3 of the density difference MAX (1) obtained on the plain paper original.

Further, in the document edge detecting means 34,
Using the threshold value (2) set by the threshold value setting means 33,
For example, the image data stored in the memory area A is scanned from the area outside the document toward the document area, and the points X1 and X2 at which the pixel data changes from “black” to “white” (FIG. 4).
(B)) is detected as the position of the document edge, and the document width in the main scanning direction X is determined from the detected document edge positions X1, X2. After that, the document size is detected from the thus obtained document width in the main scanning direction X and the outputs of the photosensors arranged in the sub-scanning direction Y, and the series of processes is ended. Thus, even if the original 2 has a high transmissivity such as treasuring paper, by appropriately setting the threshold value for detecting the original edge, the position of the original edge can be accurately detected and the original size can be determined. Can be detected.

In the above embodiment, the RAM 23
The density difference is calculated only when the density level equal to or higher than the normal threshold value (1) is not obtained from the image data stored in the memory areas A and B, and based on the result of comparison with the specified density difference. Although the threshold value for detecting the document edge is changed from the threshold value (1) to the threshold value (2), the present invention is not limited to this, and the first sensor 11 that detects the open / closed state of the platen cover 4 is used. If there is enough time from when the second sensor 12 is turned on to when the second sensor 12 is turned on, the density difference is calculated from each image data from the time of reading in the nearly closed state or the fully closed state. It is also possible to properly set the threshold value for detecting the document edge depending on whether or not the density difference is larger than a specified density difference, for example, the lower limit level of the density difference obtained by the plain paper document. Specifically, the normal threshold value (1) is set when the calculated density difference is larger than the specified density difference, and the threshold value (2) is set when the calculated density difference is smaller, and the position of the document edge is detected. Further, no density level higher than that can be obtained with any of the threshold values (1) and (2),
If the position of the document edge cannot be detected, it is considered that there is no document, and a message similar to the above is displayed.

By the way, when the position of the document edge is actually detected, in order to prevent erroneous detection due to dust or scratches on the platen glass 3, for example, as shown in FIG. The comparison pixels 1 are set at a distance of, and the comparison pixels 2 to 6 are arranged at intervals of 8 pixels from the comparison pixel 1.
Is set. Then, for example, when the data changes from “white” to “black” between the pixel of interest and the comparison pixel 1, when the changed “black” state is continuously detected by the comparison pixels 2 to 6. The position of the comparison pixel 1 is detected as the position of the document edge. However, in the case of an original 2 having a high transmissivity, such as a treshing paper, even if the interval between the target pixel and the comparison pixel 1 is set to the same level as that of the plain paper original, the density change at the actual edge of the original is small, No significant difference appears between the pixel values of the pixel of interest and the comparison pixel 1.

Therefore, in this embodiment, the CPU 25 is provided with a pixel interval setting means 35 as a constituent element for the document size detection processing as shown in FIG. The pixel interval setting unit 35 sets the pixel interval at the time of detecting the document edge according to the comparison result of the density difference comparing unit 33.
It performs the following functions. That is, in the comparison result of the density difference comparing unit 33, when it is determined that the density difference calculated by the density difference calculating unit 31 is larger than the specified density difference (density difference due to the shot noise component), that is, the original document. When 2 is regarded as the treasuring paper, the pixel interval at the time of detecting the document edge is set to be wider than that in the case of the plain paper document.

Specifically, for example, as shown in FIG. 6B, in setting the interval between the pixel of interest and the comparison pixel 1,
It is set by adding the distance of β pixels to the interval of 16 pixels set for a plain paper original. Here, the β pixel corresponding to the extended distance depends on the output characteristics of the CCD image sensor 10 and the cover angle in the closed state (the timing when the first sensor 11 is turned on), and therefore, it is preferable to use a treasuring paper or the like. It is advisable to experimentally find the density difference obtained at the edge of the original when using, and to set it appropriately based on the experimental data obtained. Incidentally, in this embodiment, the resolution is set to about 320 (2 cm) at 400 dpl. As a result, a larger density difference can be obtained between the pixel of interest and the comparison pixel 1 at the actual position of the document edge, which facilitates the position detection of the document edge. In the present embodiment, when the pixel interval is extended as described above, when the position of the comparison pixel 1 is detected as the document edge like the plain paper document, the pixel interval is set wider than the actual document width. Since there is a risk of narrow recognition, the midpoint between the pixel of interest and the comparison pixel 1 is detected as the position of the document edge, as shown in FIG. 6B.

Further, in detecting the position of the document edge, the following problems may occur. That is, as shown in FIG. 7, when the original 2 set on the platen glass 3 is read along a predetermined reading line L, the density data obtained by this reading is stored in the CCD.
In some cases, an isolated point generated due to deterioration of the image sensor 10 is included. In such a case, the density difference calculating means 31
If the density level of the isolated point is taken as the peak density value as it is, the density difference Z1 calculated there becomes significantly larger than the target density difference Z2, and an appropriate threshold value should be set. Can not be.

Therefore, in the present embodiment, in order to eliminate the above-mentioned inconvenience, the structure shown in the block diagram of FIG. 8 is adopted as the density difference calculating means 31. In FIG. 8, a main density value detection unit 311 detects a peak density value of image data of a predetermined one line read by the image reading unit, and when an isolated point exists, the main density value detection unit 311 detects the density level of the peak. Detect as peak concentration value. In this case, when detecting the position of the document edge, the maximum density value is set to the peak density value depending on whether the change point from “black” to “white” or the change point from “white” to “black” is detected. It should be decided whether or not to set the peak concentration value on the minimum side. The sub-density value detection unit 312 detects at least one density value next to the peak density value (density value after the second density value), and one depending on how many density values after the peak density value are detected. Or, a plurality of them are provided. The level difference calculating unit 313 calculates the level difference between the density values detected by the individual density value detecting units 311, 312, ... In order from the peak density value side. Specifically, when a plurality of sub-density value detection units 312 are provided, after calculating the level difference between the peak density value and the second density value subsequent thereto, the second density value and the third density value subsequent thereto are calculated. The level difference with the density value is calculated, and thereafter, the level differences with the third and subsequent density values are sequentially calculated in the same manner.

The peak density value selection unit 314 monitors whether or not the level difference calculated by the level difference calculation unit 313 has become less than or equal to the specified level, and the calculated level difference has become less than or equal to the specified level. Sometimes, the density value closer to the peak density value is selected as the true peak density value. In this case, the "specified level" serves as a criterion for determining whether or not the isolated point is mistaken for the true peak density value, and normally, the density change does not occur near the peak of the density data that does not include the isolated point. Since it is extremely small, it can be set with an extremely small level difference. The density difference calculating unit 315 calculates the density difference using the true peak density value selected by the peak density value selecting unit 314. The density difference calculated here is given to the density difference comparing unit 32. Will be done.

Next, the processing procedure of the density difference calculating means 31 in the document size detection processing will be described. First,
When the scanning information of the image data for one line is given from the above-mentioned density value detecting means 30, the main density value detecting section 311 searches each pixel data, and detects the peak density value from them. For example, with the density data shown in FIG. 7, the density level at an isolated point is detected as the peak density value. On the other hand, the sub-density value detection unit 312 searches each pixel data in the same manner as described above, and sequentially detects density values next to the above-described peak density value from among them. For example, in the case of the density data shown in FIG. 7, the second density value next to the density level of the isolated point, the third density value next to it (not shown), and the second density value ...
For example, the density values are detected up to a preset rank.

Next, in the level difference calculation unit 313,
As described above, the level difference between the peak density value and the second density value next thereto is calculated, and then the level difference between the second density value and the third density value subsequent thereto is calculated. The level difference of the density values of is calculated in order, and each calculation result is supplied to the peak density value selection unit 314. Next, in the peak density value selection unit 314, the level difference calculation unit 3
The level difference given from No. 13 is sequentially compared with the specified level, and when the level difference calculated by the level difference calculation unit 313 becomes equal to or less than the specified level, the density value on the side close to the previous peak density value. Is selected as the true peak concentration value. After that, the true peak density value selected by the peak density value selection unit 314 is given to the density difference calculation unit 315, and the true peak density value is used to calculate the density difference.

This will be specifically described with reference to FIG.
The peak density value detected by the main density value detection unit 311 is the density level at the isolated point, and the second density value detected by the sub density value detection unit 312 is the peak level of the density change when the isolated point is not included. Becomes Therefore, the level difference between the peak density value and the second density value next thereto becomes a very large value, and as a matter of course, the level difference exceeds the specified level. On the other hand, the level difference between the second density value detected by the sub-density value detection unit 312 and the third density value (not shown) following the second density value is the peak of the true density change for all density values. Since it exists in the vicinity, it is calculated as an extremely small value, which is below the specified level. Therefore, in that case, the sub-density value detector 3
The second density value detected in 12 is selected as the “true peak density value” in the peak density value selection unit 314. As a result, the density difference calculating unit 315 erroneously recognizes the density level of the isolated point as the true peak density value as described above, even when the read image data for one line includes the isolated point. Since the density difference Z2 is calculated without using the second density value to be obtained as the true peak density value, the density difference calculated by the density value calculation unit 315 is used in the subsequent document size detection process. It is possible to appropriately set the threshold value for detecting the document edge based on Z2.

In the above embodiment, the sub-density value detecting section 312 for detecting the density value next to the peak density value.
Although the case where a plurality of isolated points are provided has been described, if the image data after the shading correction is used in the document size detection process, even if there are a plurality of isolated points, each peak level shows a constant value. Therefore, the peak level can be collectively detected by the main concentration value detection unit 311. Therefore, the second density value detected by the sub-density value detection unit 312 inevitably becomes the target true peak density value, and in that case, only one density value next to the peak density value is detected. That is, it is only necessary to provide one sub-density value detection unit 312. As a result, it is possible to simplify the configuration of the density difference calculating means 31 and the processing procedure.

[0040]

According to the first aspect of the present invention, the density difference calculating means calculates the density difference of the image data for one line read by the image reading unit, and the density difference obtained by this is defined. The density difference calculation means compares the difference in density with the density difference and the threshold setting means sets the threshold value for detecting the document edge suitable for the document based on the comparison result. Even for a document having a high rate, the document edge detecting unit can accurately detect the position of the document edge based on the threshold value set in advance. As a result, when a document (tressing paper, etc.) is set in the image reading unit, the position of the document edge can be reliably detected to detect the document size, and when the document is not set from the beginning. Enables the operator to correctly recognize the message to that effect, which causes the problem that the original (treshing paper, etc.) is mistakenly recognized as "no original" even though the original is set as before. Will be resolved.

According to the second aspect of the present invention, when the original is considered to be, for example, treasuring paper from the comparison result of the density difference comparing means, the pixel interval at the time of detecting the edge of the original is set to the plain paper original by the pixel interval setting means. It is possible to make the setting wider than in the case of. Therefore, since a larger density difference can be obtained at the actual position of the document edge, it is possible to easily obtain a density level equal to or higher than the threshold value even for a document having a high transmittance.

According to the third aspect of the present invention, the density value next to the peak density value detected by the main density value detection unit and the peak density value detected by the sub-density value detection unit, that is, the second and subsequent densities. The level difference of each density value is calculated by the level difference calculation unit in order from the peak density value side while comparing the value with the value in order, and when the calculated level difference becomes less than or equal to the specified level, it is close to the peak density value. Since the density value on the side is selected by the peak density value selection unit as the true peak density value,
Even if there is an isolated point in the actually read image data, the density difference calculation unit will not be confused by the peak level, and the true peak density value previously selected will be used to determine the appropriate value. It is possible to calculate the density difference.
As a result, the threshold setting unit can appropriately set the threshold value for detecting the document edge based on the density difference calculated by the density difference calculating unit.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image reading unit according to an embodiment.

FIG. 2 is a schematic configuration diagram of a digital copying machine to which the present invention is applied.

FIG. 3 is a conceptual diagram for explaining a document edge detection operation.

FIG. 4 is a comparison diagram of density data obtained at the time of detecting a document edge.

FIG. 5 is a functional block diagram for detecting a document size.

FIG. 6 is a schematic diagram showing a positional relationship of pixels at the time of detecting the document edge.

FIG. 7 is a diagram illustrating the occurrence state of isolated points.

FIG. 8 is a functional block diagram of a density difference calculating unit.

[Explanation of symbols]

2 manuscripts 3 Platen glass 5 exposure lamp 6, 7, 8 reflective mirror 10 CCD image sensor 30 concentration value detecting means 31 Concentration difference calculation means 32 Concentration difference comparison means 33 threshold setting means 34 Document Edge Detection Means 35 pixel interval setting means 311 Main concentration value detector 312 Sub-concentration value detector 313 Level difference calculator 314 Peak concentration value selection section 315 Concentration difference calculation unit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/04-1/207

Claims (4)

(57) [Claims] 1. A document size detection device for detecting the size of a document set in an image reading unit that optically reads image information of a document by detecting the position of the document edge. From the predetermined one line of image data obtained , the density level above the first threshold is
Density difference calculating means for calculating the density difference of the image data for one line when not obtained, and density difference comparing means for comparing the density difference calculated by the density difference calculating means with a prescribed density difference In the comparison result of the density difference comparison means , the calculated
If the density difference is greater than the specified density difference,
The original that has a higher transparency than the
Assuming that the document edge is present, the threshold value for detecting the document edge is referred to as the first threshold value.
A threshold value setting means for setting a second threshold value that is lower than the threshold value, and the document edge detection means set by the threshold value setting means.
Change of image data for one line using the threshold of
A document size detecting apparatus comprising: a document edge detection unit that detects a point and detects the black-and-white change point as the position of the document edge. 2. A predetermined pixel distance from the target pixel
Setting a plurality of comparison pixels, the target pixel and the comparison pixel
To perform document edge detection processing based on data changes between
At this time, in the comparison result by the density difference comparison means,
When the calculated density difference is larger than the specified density difference
Is the pixel interval at the time of detecting the document edge as compared to the case of plain paper document.
2. The document size detecting apparatus according to claim 1, further comprising a pixel interval setting unit that sets a wide range . 3. The density difference calculating means includes a main density value detecting section for detecting a peak density value of the image data of the predetermined one line, and a sub-density detecting section for detecting at least one density value next to the peak density value. The density value detector and the main density value detector are
Therefore, the detected peak concentration value and the sub-concentration value are detected.
The at least one concentration value detected by the
And a level difference calculation unit that sequentially calculates the level difference of the density values between the two ranks from the peak density value side, and when the level difference calculated by the level difference calculation unit falls below a prescribed level. Two orders with the level difference
Using a peak concentration value selecting section for selecting a side of the concentration values near the peak concentration value of the position of the density value as the true peak concentration value, the true peak concentration value selected by the peak concentration value selecting section 3. The document size detecting apparatus according to claim 1, further comprising a density difference calculating unit that calculates the density difference. 4. A document size detection device for detecting the size of a document set in an image reading unit that optically reads image information of the document by detecting the position of the edge of the document. A density difference calculating means for calculating a density difference of the predetermined one line of image data, and a regulation corresponding to a lower limit level of the density difference calculated by the density difference calculating means and the density difference obtained on the plain paper original. If the calculated density difference is larger than the specified density difference in the comparison result of the density difference comparison unit that compares the density difference with the density difference comparison unit, the threshold for document edge detection is set to the first threshold. If the calculated density difference is smaller than the specified density difference, the threshold value for setting the document edge detection threshold value to the second threshold value lower than the first threshold value is set. And a threshold value for detecting the document edge set by the threshold value setting means, the black-and-white change point of the image data for one line is detected, and the black-and-white change point is detected as the position of the document edge. A document size detecting device comprising an edge detecting unit.