JPH10336425A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read an image with a high efficiency by reducing a time required to detect a tilt angle of an original. SOLUTION: An image read by a read means 21 is corrected based on a tilt angle θ of an original D detected by a tilt angle detection means 22 (PS1-PS5) and carried by a carrying means. The image read by the read means 21 is corrected, based on a tilt angle θ of the original, which has already been stored in a tilt angle storage means 24 without detecting the tilt angle θ by the tilt angle detection means 22. Magnification processing is applied to the image read by the read means 21 depending on the tilt angle θ of the original D detected by the tilt angle detection means 22 before data shift processing by a correction means 22 is applied to the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus such as a scanner, a facsimile, a digital copier, and the like, which conveys a document placed on a document table to an image reading position and reads an image of the document. The present invention relates to an image reading apparatus that can correct a conveyed document even if it is tilted.

[0002]

2. Description of the Related Art In an image reading apparatus such as a scanner, a facsimile, a digital copier, or the like, a document placed on a document placing table is transported by a transport means to an image reading position and an image of the document is read. There is a case where the document is conveyed, and when an inclined document is read as it is, for example, when copying (image formation) is performed, there is a possibility that the image may be interrupted.

Therefore, in a conventional image reading apparatus,
The inclination angle of the original is detected by detecting the inclination of the character arrangement from the image information obtained from the inclined original, and the inclination angle of the obtained image information is corrected.

[0004]

In the apparatus described above, it is necessary to read the image information (pre-scan) after setting the document on the reading position in advance in order to detect the inclination angle of the document. Therefore, it takes time to detect the inclination angle, and the efficiency of image reading is reduced. In addition, complicated calculations must be performed in order to detect the inclination of the character arrangement, so that it takes time, and moreover, a large amount of memory is used for calculation, resulting in high costs.

Therefore, the first and second inventions have an object to shorten the time required for detecting the inclination angle of a document and to improve the efficiency of image reading. Another object of the third invention is to reduce the time required for correcting the tilt angle and reduce the cost.

[0006]

The above object can be attained by the following constitution.

According to the first aspect of the present invention, the document placed on the document placing table is transported to the reading position, and the document is recorded on the document transported to the reading position by the transporting device. Reading means for reading the obtained image;
On the way of transporting the document by the transport means, a tilt angle detecting means for detecting a tilt angle of the document being transported, and reading by the reading means based on the tilt angle of the document detected by the tilt angle detecting means. By having a correction unit that corrects the image that has been obtained, the inclination angle is detected while the document is being conveyed, so that it is not necessary to perform prescan to detect the inclination angle of the document, The time required to detect the inclination angle of the document can be reduced, and the efficiency of image reading can be increased.

According to a second aspect of the present invention, there is provided a conveying means for separating one document from a plurality of documents placed on a document table and conveying the document to a reading position; Reading means for reading an image recorded on the document conveyed to the reading position by the means, tilt angle detecting means for detecting a tilt angle of the document on the reading position, and reading of the document detected by the tilt angle detecting means. A tilt angle storage unit that stores a tilt angle, and a correction unit that corrects an image read by the reading unit based on the tilt angle of the document.
Correcting the image read by the reading means on the basis of the inclination angle of the document already stored in the inclination angle storage means without detecting the inclination angle of the document by the inclination angle detection means. Since the tilt angle does not need to be detected each time a plurality of documents are conveyed, the time required to detect the tilt angle of the document is reduced, and the efficiency of image reading is improved. be able to. In the present invention, as a result of diligent study by the present inventors, the inclination angle of the original document changes depending on various conditions such as the paper quality of the original document, the environment and the conditions of the conveying means, but the original document placed on the original table is It is necessary to detect the tilt angle every time a document is conveyed based on the fact that the same paper quality is used and the environment and the conditions of the conveyance means are almost the same, so that it shows the same tilt angle as other documents. Instead, it uses the already detected tilt angle.

Further, according to the third aspect of the present invention, the skew angle detecting means detects the skew angle of the document being conveyed on the path of the document conveyed by the conveying means, thereby detecting the skew of the document. It is not necessary to perform a pre-scan to detect the angle, and the time required to detect the tilt angle of the document can be reduced, and the efficiency of image reading can be improved.

Further, in the invention according to claim 4, the tilt angle detecting means has a plurality of document detecting means arranged in a direction orthogonal to a direction of transporting the document by the transporting means, and By detecting the tilt angle of the document based on the information obtained by the document detection means, the tilt angle of the document can be detected with a simple configuration, which not only reduces the cost but also reduces the tilt angle. Detection efficiency can be improved.

Further, according to a fifth aspect of the present invention, the tilt angle detecting means has a document detecting means in a document conveying direction with respect to at least one of the plurality of document detecting means. By detecting the inclination angle of the document based on the information obtained by the document detection means, the inclination angle of the document can be detected more accurately.

According to a third aspect of the present invention, the transporting means transports the original placed on the original placing table to a reading position, and the transporting means moves relative to the original so that the original is transported. Reading means for reading an image recorded on the document conveyed to the reading position by the means, tilt angle detecting means for detecting a tilt angle of the document on the reading position, and reading of the document detected by the tilt angle detecting means. Correction means for correcting the image read by the reading means by performing data shift processing in accordance with the tilt angle, wherein the data shift processing by the correction means is performed on the image read by the reading means. Before performing the processing, the magnification is changed in accordance with the inclination angle of the document detected by the inclination angle detecting means. It can be the inclination angle correction in a simple manner that Tashifuto to shorten the time required for the inclination angle correction, it is possible to reduce the cost without using a lot of memory. In particular, in the scaling process, the scaling process in the direction of relative movement between the reading unit and the document is performed by changing a relative moving speed according to a tilt angle of the document detected by the tilt angle detecting unit. With the feature, the scaling process in the relative movement direction is not performed by calculation, so that it is possible to further reduce time and cost.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an image reading apparatus 1.
FIG. 2A is a schematic sectional view of FIG. 1A, and FIG.

First, the outline of the image reading apparatus 1 will be described. The document placing table 11 is a unit for placing the document D to be read. The transport unit is a unit that transports a document placed on the document table 11 to a reading position described later. In the present embodiment, the delivery roller pair 12 and the pair of rollers 1
3 and 14, and a transport belt 15 stretched around.
The sending roller pair 12 is a unit that separates and feeds the documents D placed on the document placing table 11 one by one. The transport belt 15 is a unit that transports the document D sent by the delivery roller pair 12 to a reading position while nipping the document D between the document table 17. This reading position is a position for reading the original D conveyed by the conveying means. In this embodiment, since the image reading apparatus 1 reads the original D by the scanning optical system in a state where the original D is stopped, the light transmitting original platen is used. 17 is a predetermined position. In the present embodiment, an image is read while the document D is stopped, but an image reading apparatus that reads the document D while moving the document D may be used. Further, in the image reading apparatus 1 according to the present embodiment, the document D is transported on the basis of the center (the center of the document D transported by the transport unit is set to the center line (sub-scanning direction) of the document table 17). You. This is a method in which the reference is adjusted to the end of the document table 17. If the document D is tilted, at least one image of the document D is read by the reading unit 21 described later.
This is because one corner cannot be read.

The light source 18 is a means for irradiating the original D conveyed to the reading position on the original table 17 and stopped, and is a linear light source extending in the main scanning direction (vertical direction in FIG. 1). is there. The first mirror 19 and the V mirror 20
This is a unit that guides light emitted from the light source 18 and reflected from the document D to the reading unit 21 at the subsequent stage. When reading the image of the document D, the light source 18 and the first mirror are integrated into a sub-scanning direction orthogonal to the main scanning direction (left-right direction in FIG. 1).
And the V mirror 20 moves to the light source 18 and the first
It is configured to move at a moving speed that is 1/2 of the moving speed of the mirror. Although not shown, an image forming unit for forming an optical image of the document D on the reading unit 21 is disposed between the V mirror 20 and the reading unit 21.

The reading means 21 is a means for reading the image of the document D, and is a photoelectric conversion element for photoelectrically converting the light reflected from the document D for each pixel. In the present embodiment, the reading means 21 is a line sensor (line CC) extending in the main scanning direction.
D). Then, the reading unit 21 reads the image of the document in units of one line, and the light source 18, the first mirror 19, and the V mirror 20 move in the sub-scanning direction with respect to the document D stopped at the reading position. The image on the entire surface of the document D can be read. The read image of the document is converted into a digital image signal and supplied to an external device such as an image forming apparatus. The light source 18, the first mirror 1
9, V mirror 20, reading means 21, etc. are called a scanner.

The document D whose entire image has been read by the reading means 21 is conveyed by a conveying belt 15 and discharged onto a discharge tray 16 by a discharge roller (not shown).

In such an image reading apparatus 1, when the original D placed on the original placing table 11 is transported to the reading position by the transport unit, the transport conditions depend on the state of the transport unit, the paper quality of the original D, and the like. May be different in the width direction of the document D (a direction perpendicular to the transport direction of the document D, and in the present embodiment, a direction parallel to the main scanning direction). For this reason, the document D may be conveyed while being tilted (see FIG. 1B), and may not stop at a predetermined reading position at a correct angle. For this reason, in the present embodiment, the inclination angle θ of the document D is detected by the inclination angle detection means 22, and the image read by the reading means 21 is corrected by the correction means based on the inclination angle θ. I have. Hereinafter, this configuration will be described.

First, with respect to the detection of the inclination angle θ of the original by the inclination angle detecting means 22, FIG.
A description will be given based on FIG. 2 showing the detection result of S5 and FIG. 3 showing a functional block diagram of the inclination correction.

The four photosensors PS1 to PS4 are provided below the document table 17 in a direction (main scanning direction) orthogonal to the direction in which the document is conveyed by the conveying means (the main scanning direction in this embodiment). PS4 is arranged on a straight line. The photo sensors PS1 to PS4 are
By arranging them in parallel with each other, the space vacated in the main scanning direction of the reading unit 21 can be used efficiently. Further, a photo sensor PS5 serving as a document detection unit is disposed downstream of the photo sensor PS3 in the conveyance direction (sub-scanning direction) by the conveyance unit. These photo sensors PS
1 to PS5 are means for detecting the end of the document being conveyed by the conveyance means (the end in the conveyance direction, and in the present embodiment, the end on the front end side in the conveyance direction).

In this embodiment, the photo sensor P
The distance between S2-PS3 and the photo sensors PS3-PS5
By arranging the distance between them to be equal,
The calculation of the tilt angle θ is simplified, the calculation speed is improved, and the cost is reduced by simplifying the circuit. Also, when detecting an original by the photo sensors PS1 to PS5,
The light source 18 and the first mirror 19 have a structure that does not move or hinder the detection. In addition, in order to facilitate detection by the photo sensors PS1 to PS5,
It is preferable that the entire surface (or a part) of the transport belt 15 has a density different from the background (white) of the document, for example, black.

While the original D is being conveyed to the reading position by the conveying means, the leading end of the original D is
When the output signal is detected by S1 to PS5, the output signal is detected at the leading end of the document D with a time difference from time t1 to t5 as shown in FIG. Here, the photo sensor PS
2. The tilt angle θ of the document D is detected from the output signal of PS3. That is, the tilt angle θ of the document D is detected by utilizing the fact that the timing difference s between the output signals of the photosensors PS2 and PS3 depends on the tilt angle θ of the document D. Further, in the present embodiment, in order to more accurately detect the tilt angle θ, the document D
Is detected based on the timing difference T between the output signals of the photosensors PS3 and PS5. However, since the transport means is configured to transport the document D at a predetermined transport speed in advance, A predetermined transport speed may be substituted. The timing differences s, T, and the like are measured by a timer or the like (not shown).

The output signals from the photo sensors PS2, PS3 and PS5 are sent to a tilt angle calculator 23, which calculates the tilt angle θ of the document D. That is, by calculating θ = Tan ⁻¹ (s / T), the inclination angle θ of the document D can be obtained.
The obtained tilt angle θ is stored in the tilt angle memory 24 which is a tilt angle storage unit that stores the tilt angle θ.

Note that, in order for the above relationship to be established, the same side of the document D conveyed by the conveying means must pass through the photosensors PS2, PS3, and PS4. This is because if the angle of the document D passes between the photosensors PS2 and PS3, the tilt angle θ cannot be detected only by these signals, and the correct correction of the tilt angle is not performed. Therefore, in the present embodiment, the photo sensors PS1 and PS4 are arranged outside the photo sensors PS2 and PS3. Then, based on the output signals of the photosensors PS1 to PS4, it is detected whether one side of the document D has passed the photosensors PS2, PS3, and PS4. In other words, the inclination angle calculator 23 detects whether or not the condition of t1−t2 = t3−t4 (it does not need to be completely equal and at least both sides have the same sign) is calculated by the tilt angle calculator 23. If this condition is not satisfied, the detection of the inclination angle θ becomes an error, and a display (message) indicating that the conveyance of the document D has failed is displayed on a liquid crystal display (display means) (not shown) provided on an operation panel (not shown). Display and pause image reading.

As described above, in the present embodiment, the detection of the inclination angle θ of the original is performed by detecting the original D being conveyed along the conveyance path of the original D by the conveying means, and based on the result, the original D is detected. The inclination of D is detected. As a result, it is not necessary to perform pre-scan to detect the inclination angle θ of the document D, so that the time required to detect the inclination angle of the document D can be reduced, and the efficiency of image reading can be improved.
Further, in the present embodiment, the plurality of photosensors PS2 and PS3 are arranged in a direction perpendicular to the transport direction of the document D in order to detect the document D. Therefore, the inclination angle θ of the document D is detected with a simple configuration. As a result, not only the cost can be reduced, but also the efficiency of detecting the tilt angle θ can be improved. Further, by disposing the photo sensor PS5 in the transport direction of the document D with respect to the photo sensor PS3, the actual transport speed of the document D can also be accurately detected, and the inclination angle θ of the document D is accurately detected. be able to.

In this embodiment, the photo sensor P
By providing S1 to PS5 below the document table 17, efficient space utilization is achieved, and by calculating the inclination angle θ of the document D at a position close to the reading position, the accurate inclination angle θ is calculated.
Is detected, but the present invention is not limited to this.
, Or between the delivery roller pair 12 and the transport belt 15 along the transport path of the document D by transport means. In the present embodiment, the photo sensors PS1 to PS
5, the leading edge of the document D is detected, but the trailing edge may be detected. In the present embodiment,
The document D is detected using the photosensors PS1 to PS5, but other non-contact switches or contact switches may be used. In other words, any means capable of detecting the document D conveyed by the conveyance means may be used. I just need. Further, the light source 18 and the first mirror 19 are not moved or hindered to a position where the detection is not hindered, and the light source 18 is turned on while the document D is being conveyed by the conveyance unit, and the reading unit 21 is used. The document D may be detected.

Next, correction of an image read by the reading means 21 based on the obtained inclination angle θ will be described.

An affine transformation is generally known as a method for correcting an image read at an inclination angle θ. Since this affine transformation is for performing a 2 × 2 matrix operation, the amount of operation is increased and the memory capacity must be increased. Therefore, in the present embodiment, the calculation amount and the memory proposed by the inventor in Japanese Patent Application No. 9-83794 perform image correction by more economical data shift processing. In this data shift processing, the image information is corrected by shifting the image information in pixel units stored in the image memory 28 as the image storage means as vertical correction or horizontal correction. When the image is corrected by the data shift process, the magnification and the aspect ratio of the document change, so that it is preferable to perform the scaling process independent of the vertical and horizontal directions.

In general, the data shift process and the scaling process are performed such that an image whose aspect ratio is deviated by the data shift process fits the original size when the scaling process is performed after the data shift process. It is easy to think because it can be returned to. On the other hand, when performing the data shift process after performing the scaling process, the aspect ratio caused by the data shifting process is predicted in advance, and the tilt angle of the image read by the scaling process is distorted. The correction process becomes complicated. However, as in this embodiment, relative movement with respect to the original (more specifically, by the scanning optical system,
In an image reading apparatus that reads an image of a document by performing scanning, the magnification in the sub-scanning direction (horizontal) is changed by the relative moving speed (more specifically, the light source 18, the first mirror 19,
This can be easily performed by changing the moving speed of the V mirror 20), and furthermore, it is possible to prevent the image quality from deteriorating due to zooming. Therefore, in the present embodiment, by performing a data shift process after performing a scaling process,
The image read at the tilt angle θ is corrected.

First, the scaling process will be described with reference to FIG. 3 and FIG. 4 showing a document tilted on the document table 17. FIG. 4A is a schematic diagram illustrating a document tilted on the document table 17, and FIG. 4B is a conceptual diagram illustrating an image to be read.
FIG. 4C is a conceptual diagram showing image data after the scaling process. As this scaling process, a scaling process of horizontal (sub-scanning direction): 1 / cos θ times and vertical (main scanning direction): cos θ times is performed.

More specifically, as described above, the inclination angle θ of the document D is detected at the time of conveyance by the conveyance means, and the inclination angle is input to the inclination angle memory 24.
At this time, the document D is placed on the document table 17 while being inclined as shown in FIG. The data of the tilt angle θ stored in the tilt angle memory 24 is first sent to the sub-scanning magnification changing unit 25. The sub-scanning magnification processing unit 25 scans (moves) in the sub-scanning direction by the scanner (in the present embodiment, the light source 18 and the first mirror 1) in accordance with the tilt angle θ.
9, means for changing the horizontal (sub-scanning direction) magnification by changing the moving speed of the V mirror 20). That is, the sub-scanning magnification changing means 25 sets the scanning speed to 1 for the scanning speed at the same magnification.
The scanner is controlled to scan at a scanning speed of / cos θ. Then, the scanner scans the entire surface of the document at a controlled scanning speed (reads by the reading unit 21), thereby generating an image signal scaled by a factor of 1 / cos θ in the sub-scanning direction.

The generated image signals are sequentially inputted to the main scanning magnification processing means 26, and are subjected to main scanning magnification processing (vertical magnification processing).
Receive. The main scanning magnification changing means 26 includes a tilt angle memory 2
4 is a means for performing main-scan scaling processing in accordance with the tilt angle θ stored in step 4. For example, the magnification is changed to cos θ times by linear interpolation or the like.

As described above, when the image recorded on the original D on the original plate 17 is read from the rectangle (see FIG. 4B) by the reading means 21 and subjected to the scaling process, the parallelogram (see FIG. 4 (c)). As the shape changes, the inclination angle also changes as follows (FIG. 4).
(C)).

Angle from horizontal (sub-scanning) direction: θ '= Ta
n ⁻¹ (tan θ · cos ² θ) Angle from the vertical (main scanning) direction: θ ″ = Tan ⁻¹ (tan
θ / cos ² θ) As described above, the image signal that has been subjected to the scaling process is multi-valued by the multi-value processing unit 27. As a method of multi-leveling, it is preferable to use a multi-leveling method of compressing an image size in order to enable processing with a small memory capacity, for example, an error diffusion method or a dither method. If so, this multi-value processing means may be omitted. Then, the image signal subjected to the multi-value processing is temporarily stored in an image memory 28 which is an image storage unit for storing image data. Then, the inclination of the image is corrected by the data shift process.

By the way, the image data output from the scanner covers almost the entire surface of the document table 17, but extracts an area corresponding to the document D therein (in the case of a copier, it is located at a correct position on a predetermined sheet). In order to perform printing, it is necessary to know where the document area in the image data should be corrected so as to start from the beginning of the corrected document area. Therefore, before correcting the inclination of the image, it is necessary to accurately grasp the size of the document D, the document reference point, and the head of the document area after the inclination correction. Here, the “document reference point” refers to a corner of the document D which is read first when an image is read by the reading unit 21.
The “head of the document area after correction” is a position corresponding to the head of the document area of the image data after the inclination correction, and as shown in FIG. 4C, the document reference point is set to (xs, ys). ),
The head of the document area after the skew correction is represented as (xt, yt). By the way, the original reference point (the corner of the original D) is used for the inclination correction.
Is corrected to be at the top of the corrected document area. The area shown by the broken line in FIG. 4C is the area of the document after the inclination correction.

To grasp these, the image memory 28
The edge portion of the document D is detected from the image data stored in the document D, and the size of the document D, the document reference point, and the head of the document area after the inclination correction can be obtained.

However, based on the image data stored in the image memory 28, the size of the document D, the document reference point, and
In order to obtain the head of the document area after the inclination correction, a processing time for performing the calculation is required. Therefore, by detecting and estimating these by the following method, it is possible to obtain them in a short time.

First, detection and estimation of the size of the document D will be described. The size of the document D may be detected by size detection means (not shown). That is, when a document is placed on the document table 11, the width of the document (a direction perpendicular to the transport direction) is detected, and the length of the document D (the transport direction) is determined while being transported by the transport unit. A method of detecting and detecting the size of the document from the detected width and length, and a method of detecting the size of the document D by placing the document D on the document table 17 using a non-contact type switch (not shown). The size of the document may be detected.

Next, the estimation of the head of the document area after the inclination correction will be described. If the size of the document D is known, the head (xt, yt) of the document area after the inclination correction can be obtained. That is, the head (xt, y
t) is located a / 2 below the center of the document table 17 (the dashed line shown in FIG. 4A). In this equation, a is the width of the document D in the main scanning direction, and is 210 mm for A4R (for reference, A4R
Is 297 mm in the sub-scanning direction).
It is located 105 mm below the center of the document table 17. In the following description, the head of the original area after the inclination correction is set as the origin ((xt, yt) =
(0,0)).

When the present embodiment is mounted on a copying machine, information of "copy size", which is the size of the transfer paper set from an operation panel (not shown), is estimated as the size of the document D, and the tilt is further determined. In the following calculation including the head of the corrected document area, the copy size may be handled as the size of the document D. This is because, in the case of a copying machine, a copy size that matches the original D is used (so-called, same size), or the original D is adjusted to match the copy size.
It is better to use the copy size in order to perform the scaling process on the image information (the magnification may be performed simultaneously with the sub-scanning scaling process or the main scanning scaling process).

Next, the estimation of the document reference point will be described. The document reference point is estimated based on the size of the document D and the inclination angle θ. In order to obtain the document reference point, first, the length L and the angle φ from the center point (the intersection of the diagonal lines) of the document D to the corner are obtained. Since L is half the length of the diagonal, L = ^1/2 × (a ² + b ² ) ^1/2 . Also, the angle φ from the center line (see FIG. 4A)
Is φ = Tan ⁻¹ (a / b). Since L and φ are values dependent only on the size of the document D, L and φ calculated in advance for each paper size are stored in the memory, and L and φ are directly read from the memory based on the size of the document D. Is also good.

When L and φ are determined, the original reference position (xs,
ys) can be obtained by the following equation.

Xs = 0, ys = a / 2−Lsin (φ−
θ) × cos θ where the right side of ys is multiplied by cos θ
As described above, the image data is transferred to the main scanning
This is because the image has undergone the scaling process (according to the inclination angle θ of the document D).

As described above, by obtaining the size of the document D, the document reference point, and the head of the document area after the inclination correction by detection and estimation, the image data can be detected before being stored in the image memory 28. In addition to immediately performing the data shift processing described later, when performing vertical correction (correction in the main scanning direction) in the data shift processing first, when storing image data in the image memory 28, The vertical correction can be performed simultaneously during the shift processing (that is, before the original D is read by the reading unit 21, the original reference position and the head of the original area after the inclination correction are known in advance. Can be stored in the memory), and the efficiency can be further improved.

Next, the data shift processing will be described. The data shift process is a process for correcting an image read by the reading unit 21 based on the document tilt angle θ stored in the tilt angle memory 24. This is performed by shifting the image data stored in the image memory 28 by the inclination correcting means 29 as the correcting means.
That is, the inclination correcting means 29 is means for correcting the inclination by performing data shift on the image memory 28.
In accordance with the tilt angle θ stored in the tilt angle memory 24, the amounts (movement amounts, I and J, respectively) for moving each pixel in the vertical direction (main scanning direction) and the horizontal direction (sub scanning direction) are obtained. The inclination of the image is corrected by moving each pixel based on the movement amount. Hereinafter, the details will be described. In the following description, the case where the horizontal correction is performed after the vertical correction is described, but the reverse may be performed.

First, the vertical correction will be described with reference to FIG. 5 schematically showing the vertical correction. FIG. 5A is a diagram schematically showing image data (original document) before vertical correction.
FIG. 5B is a diagram schematically showing image data (original document) after the vertical correction, and FIGS. 5C and 5D are diagrams schematically showing the data shift of the vertical correction.

In FIG. 5A, a straight line AB parallel to one side of the document and including the document reference point (xs, ys) is defined as a “head of the document area after tilt correction” parallel to the sub-scanning direction (x direction). That is, the image data is shifted (moved) in the vertical (main scanning) direction so as to be aligned (matched) with a straight line CD including the origin. At this time, no shift (movement) is made in the horizontal (sub-scanning) direction. The vertical shift (movement) amount I can be expressed as I = ys−x · tan θ ′ where an arbitrary point in the image data is (x, y). In FIG. 5, downward when I <0,
Move upward when I> 0. Note that θ ′ is a function of θ as described above.

Therefore, the movement amount I is a function of x,
Since it does not depend on y, data having the same y has the same movement amount I, and the image data before the vertical correction is obtained by grouping pixels (pixels separated by x) in the main scanning direction as shown in FIG. In this case, the image memory 28 is simply shifted on the image memory 28 in accordance with the movement amount I so as to be as shown in FIG. 5D, that is, a simple movement in the main scanning (y, vertical) direction is performed, and a plurality of pixels are collectively performed. The movement amount I can be calculated and calculated for each group of pixels separated by x.

The image data after the vertical correction is shown in FIG.
(B). Incidentally, the angle δ between the oblique side and the main scanning direction in the image data after the vertical correction (FIG. 5B)
Is expressed by a function of θ as in the following equation.

Δ = Tan ⁻¹ (1 / (1 / tan θ ″ + tan θ ′)) = Tan ⁻¹ (1 / (cos ² θ (1 / tan θ + tan θ))) Next, the lateral correction is schematically illustrated. 6A shown in Fig. 6. Fig. 6A shows the state before the horizontal correction (after the vertical correction).
FIG. 6 is a diagram schematically showing image data (original) of FIG.
(B) shows image data (original) after horizontal correction (after inclination correction)
FIG. 6C and FIG. 6D are diagrams schematically illustrating the data shift of the horizontal correction.

In FIG. 6A, the image data is shifted (moved) in the x direction (sub-scanning direction, also called horizontal direction) so that the oblique side becomes vertical. At this time,
No shift (movement) is made in the vertical (main scanning) direction. The lateral shift (movement) amount J is given by J = −y · tan δ, where (x, y) is an arbitrary point in the image data. In FIG. 6, the camera is moved to the left when J <0, and to the right when J> 0.

Therefore, the movement amount J is a function of y,
Since the data does not depend on x, the data having the same x has the same movement amount J, and the image data before the horizontal correction is obtained by grouping the pixels (pixels divided in y) in the sub-scanning direction as shown in FIG. 6 (d) according to the movement amount J, that is, a simple movement in the sub-scan (x, horizontal) direction is required, and a plurality of pixels are collectively performed. The movement amount J can be calculated for each group of pixels separated by y.

As described above, based on the tilt angle θ stored in the tilt angle memory 24, the image data of the document D stored in the image memory 28 is subjected to data shift processing for shifting by the tilt correcting means. , The inclination can be corrected. That is, by vertical correction and horizontal correction,
Tilt correction can be performed by moving (shifting) pixels on the memory in units of y (main scanning, vertical) or x (sub-scanning, horizontal) collectively, and the total amount of movement i, j is small. Specifically, in the case of image data of x × y pixels, it is sufficient to calculate the amount of movement x + y times, and the number of operations is reduced as compared with the calculation of the amount of movement x × y times of the affine transformation. The time required for the tilt angle correction can be reduced without performing complicated calculations, and the cost can be reduced without using much memory.

The inclination angle θ of the original D changes depending on various conditions such as the paper quality of the original D, the environment and the conditions of the conveying means, but the original D placed on the original mounting table 11 has the same paper quality. Since the conditions of the environment and the conveying means are almost the same, the inclination angle θ is the same as that of the other document D. That is,
As for one set of originals D placed on the original mounting table 11, the inclination angle θ of the originals D (one original out of one set of originals) associated with the conveyance means is reproducible. Therefore, every time the document D is transported by the transport means, the tilt angle θ of the document D is determined by the tilt angle detecting means 22.
In other words, the inclination angle detecting means 2
2, the image read by the reading unit 21 can be corrected based on the tilt angle θ of the document D already stored in the tilt angle memory 24 without detecting the tilt angle of the document D due to 2. Therefore, since it is not necessary to detect the tilt angle θ each time a plurality of documents D are transported, the time required to detect the tilt angle θ of the document D is reduced, and the efficiency of image reading is improved. Can be.

For example, for the first document D, the inclination angle θ is detected, the detected inclination angle θ is stored in the inclination angle memory 24, the inclination is corrected, and the original document D is placed on the original placing table 11. For the other original D (the second and subsequent originals), the inclination angle θ
May not be detected, and the inclination may be corrected based on the inclination angle θ stored in the inclination angle memory 24. Further, every n sheets of the document D conveyed by the conveying means (where n is The inclination angle θ may be detected at any integer, which may be set by a user from an operation panel or the like (not shown). Further, in the case of the document D that is frequently used, the tilt angle θ is set in advance from an operation panel or the like (not shown) and stored in the tilt angle memory 24, based on the tilt angle θ stored in the tilt angle memory 24. The inclination of the image read by the reading unit 21 may be corrected.

[0056]

According to the first aspect of the present invention,
It is not necessary to perform a pre-scan to detect the inclination angle of the document, so that the time required for detecting the inclination angle of the document can be reduced, and the efficiency of image reading can be improved.

According to the second aspect of the present invention, since it is not necessary to detect the inclination angle each time a plurality of originals are conveyed, the time required for detecting the inclination angle of the original is reduced. However, it is possible to improve the efficiency of image reading.

Further, according to the third aspect of the present invention, it is not necessary to perform a pre-scan to detect the inclination angle of the original, the time required to detect the inclination angle of the original is reduced, and the image reading speed is improved. Efficiency can be improved.

Further, according to the fourth aspect of the present invention, the inclination angle of the document can be detected with a simple configuration, and not only the cost can be reduced, but also the efficiency of the inclination angle detection can be improved.

Further, according to the fifth aspect of the present invention, the inclination angle of the document can be detected more accurately.

According to the third aspect of the present invention, the tilt angle can be corrected by a simple method called data shift without performing a complicated operation, and the time required for the tilt angle correction can be reduced. The cost can be reduced without using a lot of memory.

Further, in the invention according to claim 7, since the scaling process in the relative movement direction is not performed by calculation, it is possible to further reduce the time and cost.

[Brief description of the drawings]

FIG. 1A is a schematic cross-sectional view of an image reading apparatus, and FIG.

FIG. 2 is a diagram showing detection results of photosensors PS1 to PS5.

FIG. 3 is a functional block diagram of tilt correction.

FIG. 4 is a diagram illustrating a document tilted on a document table.

FIG. 5 is a diagram schematically illustrating vertical correction.

FIG. 6 is a diagram schematically illustrating horizontal correction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading apparatus 11 Document mounting table 12 Sending roller pair (conveying means) 15 Conveying belt (conveying means) 17 Document table 18 Light source 21 Reading means 22 Tilt angle detecting means 23 Tilt angle calculating section 24 Tilt angle memory (Tilt angle storing means) 25 Sub-scanning magnification change processing means 26 Main scanning magnification change processing means 28 Image memory 29 Tilt correction means (correction means) D Document PS1 to PS5 Photo sensor (Document detection means)

Claims (7)

[Claims] A transport unit configured to transport a document placed on a document table to a reading position; a reading unit configured to read an image recorded on the document transported to the reading position by the transport unit; An inclination angle detecting means for detecting an inclination angle of the document being conveyed on the way of the original document being conveyed by the conveying means; and a reading means for reading the document based on the inclination angle of the document detected by the inclination angle detecting means. An image reading device comprising: a correction unit configured to correct an image. 2. A transport unit for separating one document from a plurality of documents placed on a document table and transporting the document to a reading position, and recording on the document transported to the reading position by the transport unit. Reading means for reading the read image, tilt angle detecting means for detecting a tilt angle of the document on the reading position, tilt angle storing means for storing the tilt angle of the document detected by the tilt angle detecting means, Correction means for correcting the image read by the reading means based on the inclination angle of the document stored in the storage means, wherein the inclination angle detection means does not detect the inclination angle of the document, An image reading apparatus, wherein an image read by the reading means is corrected based on a tilt angle of a document already stored in a storage means. 3. The image reading apparatus according to claim 2, wherein the tilt angle detecting means detects a tilt angle of the document being conveyed on the way of the document being conveyed by the conveying means. 4. The tilt angle detecting means has a plurality of document detecting means arranged in a direction orthogonal to a direction in which the document is conveyed by the conveying means, and based on information obtained by the plurality of document detecting means. The image reading apparatus according to claim 1, wherein an inclination angle of the document is detected by using the image reading apparatus. 5. An image forming apparatus according to claim 1, wherein said tilt angle detecting means has a document detecting means in a document conveying direction with respect to at least one of the plurality of document detecting means, and information obtained by these document detecting means is provided. The image reading apparatus according to claim 4, wherein the inclination angle of the document is detected based on the following. 6. A transport unit for transporting a document placed on a document table to a reading position, and recording on the document transported to the reading position by the transport unit by moving relative to the document. Reading means for reading the read image, tilt angle detecting means for detecting a tilt angle of the document on the reading position, and performing data shift processing according to the tilt angle of the document detected by the tilt angle detecting means. Correction means for correcting the image read by the reading means, wherein the inclination angle detection means detects the image read by the reading means before performing the data shift processing by the correction means. An image reading apparatus that performs a scaling process in accordance with a tilt angle of a scanned document. 7. The resizing process in the relative movement direction between the reading unit and the document in the resizing process is performed by changing a relative moving speed in accordance with a tilt angle of the document detected by the tilt angle detecting unit. The image reading apparatus according to claim 6, wherein the image reading is performed.