JP3761835B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly uses an image reading apparatus used as an image forming apparatus such as a copying machine, a printer, and a facsimile, or used as a network scanner connected to another computer via a network, and the image reading apparatus. The present invention relates to an image forming apparatus provided as a major component.
[0002]
[Prior art]
2. Description of the Related Art As an image reading apparatus used in an image forming apparatus such as a copying machine, a printer, a facsimile, or the like, a system in which a sheet-like document is moved relative to a light source is known.
[0003]
In such an image reading apparatus, a bar-shaped light source is used, a reading line is set parallel to the longitudinal direction (main scanning direction), and the document is moved in a direction perpendicular to the reading line (sub scanning direction). Let Then, light is emitted from the light source to the image surface of the moving document, and the reflected light when the image surface passes through the reading line is received to sequentially read the images on the image surface.
[0004]
Accordingly, when the document is conveyed obliquely (skewed) and the image passes obliquely through the reading line, the image is read obliquely. In the above-described image forming apparatus such as a copying machine, when image formation is performed based on an image read obliquely in this way, there is an image defect that an image is formed obliquely on a recording material. appear.
[0005]
Techniques for preventing such image defects are disclosed in, for example, Japanese Patent Application Laid-Open No. 8-151401 (the former) and Japanese Patent Application Laid-Open No. 6-188109 (the latter).
[0006]
In both of these, two sensors for detecting the leading edge of the document are arranged so that the positions in the sub-scanning direction are the same and the positions in the main scanning direction are different. When the document is skewed, the time (timing) for the leading edge of the document to reach the two sensors is shifted. The skew amount (tilt angle) is calculated from this time difference and the document transport speed. The skew of the original is mechanically corrected according to the inclination angle. In the former, two conveying rollers are individually arranged on a line parallel to the reading line, and a speed difference is provided to the two conveying rollers according to the calculated inclination angle to correct the skew of the document. Yes. On the other hand, in the latter case, a long conveying roller parallel to the reading line and an opposing roller pressed against the reading line are arranged, and the pressing force of the opposing roller at both ends of the conveying roller is changed according to the calculated inclination angle. By changing the relative position of the axis of the transport roller, a difference is provided in the transport force of the document at both ends of the transport roller, thereby correcting the skew of the document. The latter also discloses a technique for rotating read image information based on an inclination angle.
[0007]
[Problems to be solved by the invention]
Such a conventional image reading apparatus requires two sensors in order to detect the leading edge of the document, and the configuration is complicated accordingly. In addition, in order to correct the skew of the document, a difference in speed between the two transport rollers (the former) or a difference in transport force between the ends of the long transport roller (the latter) can be forced. Since the skew is mechanically corrected by rotating it, the document may be damaged. Further, mechanical correction has a problem that it is difficult to perform high-precision correction.
[0008]
Therefore, the present invention provides an image reading apparatus that has a simple configuration and can accurately detect and correct the inclination of the original image based on the skew of the original without damaging the original. And an object of the present invention is to provide an image forming apparatus including such an image reading apparatus.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, image input means for reading a document image of a sheet-like document, image processing means for processing image data read by the image input means, and image data sent from the image processing means are stored. The present invention relates to an image reading apparatus including a data storage means. The image reading apparatus includes a filtering unit that detects image data about an edge of the document from image data stored in the data storage unit and performs edge enhancement, and an inclination angle of the edge after edge enhancement And an inclination correction processing means for correcting the image data sent from the image processing means based on the image data about the inclination angle of the edge sent from the inclination detection means. Preparation ing. The image data on the edge of the document on which the filtering unit performs edge enhancement is read by the image input unit as a shadow generated by obliquely irradiating the edge of the document with light from a light source. Is a thing It is characterized by that.
[0010]
The invention of claim 2 relates to the image reading apparatus of claim 1. And this image reading device In The image input unit includes a light source that irradiates the document image on a reading line set along a main scanning direction, and a conveying unit that relatively moves the document in a multi-scanning direction with respect to the reading line. It is a feature.
[0011]
The invention according to claim 3 relates to the image reading apparatus according to claim 2. The image reading apparatus is characterized in that the edge of the document whose tilt angle is to be detected is the leading edge or the trailing edge when the moving direction of the document is used as a reference.
[0012]
The invention according to claim 4 relates to an image forming apparatus including an image reading unit and an image output unit that forms an image on a recording material based on image data read by the image reading unit. In this image forming apparatus, the image reading unit is the image reading apparatus according to any one of claims 1 to 3.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
FIG. 1 is a block diagram showing a functional configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, an image forming apparatus 1 includes an image input unit 2 that reads an image of a document, an image processing unit 3 that performs image processing on image data read by the image input unit 2, and an image process. Data storage means 4 for storing the image data, filtering means 5 for detecting and filtering image data on the edge of the document from the image data stored in the data storage means 4, Inclination detection means 6 for detecting the inclination angle of the edge, inclination correction processing means 7 for performing inclination correction processing based on image data sent from the inclination detection means 6, and sent from the inclination correction processing means 7 And image output means 8 for forming an image on a recording material such as copy paper based on the image data. Note that the image reading apparatus according to the present embodiment can be configured by removing the image output unit 8 from the configuration of the image forming apparatus 1 described above.
[0015]
FIG. 2 is a longitudinal sectional view showing the mechanical configuration of the entire image forming apparatus 1 as viewed from the front side (side operated by the user). Assuming that the entire image forming apparatus main body 9 is shown in FIG. 1, the image input unit 2 is disposed on the upper part of the image forming apparatus main body 9. The printed circuit board 10 disposed on the left side of the image forming apparatus main body 9 corresponds to the image processing unit 3, the data storage unit 4, the filtering unit 5, the tilt detection unit 6, and the tilt correction processing unit 7. The remaining part of the image forming apparatus main body 9 corresponds to the image output unit 8.
[0016]
Among these, as shown in FIG. 3, the image input means 2 includes a document conveying section (conveying means) 11, a document detecting section 12, an image reading section 13, and an A / D conversion section (not shown). ing.
[0017]
Among these, the document transport section 11 includes a document presser 14 for pressing the document D transported in the direction of the arrow A in the figure from above, and a document front upper portion disposed on the most upstream side in the document transport direction. A roller 15, a document lower front roller 16, a document middle upper roller 17 disposed downstream thereof, and a document rear upper roller 18 and document rear lower roller 19 disposed further downstream thereof. ing. A document guide 20 for guiding the document D is formed on the upstream side of the document retainer 14 described above. The document upper roller 17 has a white outer peripheral surface and is used for shading correction.
[0018]
The document detection unit 12 is disposed on the upstream side of the document front upper roller 15 to detect the leading edge of the document D, and is disposed on the downstream side of the document front upper roller 15 to detect the trailing edge of the document D. And a rear end detection sensor 22.
[0019]
The image reading unit 13 includes a contact image sensor. The contact glass 23 sandwiches the document D between the document upper roller 17, the light source 24 that irradiates the image surface of the document D from below, and the image surface. The SELFOC lens array 25 through which the reflected light passes and a photoelectric element (not shown) that converts the received light into an electrical signal. As the light source 24 described above, a rod-shaped xenon lamp that is long in the main scanning direction (the direction along the front end of the document D) is used. A reading line L that is long in the main scanning direction is formed at the contact portion between the contact glass 23 and the upper middle roller 17 in the document. The document D is read when it passes through the reading line L in the direction of arrow A (sub-scanning direction).
[0020]
The A / D converter converts analog data input from the photoelectric element into digital data.
[0021]
In the image input unit 2 described above, the rotation and stop timings and rotation speeds of the rollers of the document conveying unit 11 and the blinking timing of the light source 24 are controlled by the control unit provided in the printed circuit board 10 described above. ing.
[0022]
Next, the operation of the image input unit 2 having such a configuration will be described. In the following description, it is assumed that the document image starts slightly inside the leading edge of the document D and ends slightly inside the trailing edge of the document D. The leading edge from the leading edge of the document D to the leading edge of the document image is defined as the leading edge margin, and the trailing edge from the trailing edge of the document D to the trailing edge of the document image is defined as the trailing edge margin.
[0023]
The image input unit 2 reads the document image by the image reading unit 13 at a predetermined timing detected by the document detection unit 12 while conveying the document D by the document conveyance unit 11.
[0024]
That is, the document D is conveyed in the direction of arrow A while being guided by the document guide 20 of the document retainer 14. When the leading edge of the document D is detected by the leading edge detection sensor 21, rotation of each roller is started by the control means. Then, before the leading edge of the document image reaches the reading line L, the light source 24 is turned on and reading is started. Here, the time t1 from when the leading edge of the document D is detected by the leading edge detection sensor 21 to when it reaches the reading line L, the distance between the leading edge detection sensor 21 and the reading line is x, and the conveyance speed of the document D is v. Is calculated as t1 = x / v. Therefore, the leading edge of the document image reaches the reading line L with a delay corresponding to the leading edge margin from t1. The document D is sequentially read by the image reading unit 13 when the document image passes the reading line L. When the trailing edge of the document D is detected by the trailing edge detection sensor 22, the light source 24 is turned off after the trailing edge of the document image passes the reading line L. Here, the time t2 from when the trailing edge of the document D is detected by the trailing edge detection sensor 22 to when the document D reaches the reading line L is determined when the distance between the trailing edge detection sensor 22 and the reading line L is y. Calculated as t2 = y / v. Therefore, the trailing edge of the document image reaches the reading line L before t2 by a time corresponding to the trailing edge margin. After the image reading, after the trailing edge of the document D passes through the document back upper roller 18, each roller is stopped, and the image reading is completed. In this way, an image is formed on the recording material by the image output means 8 based on the image data read by the image input means 2.
[0025]
The image processing means 3 performs image processing such as density conversion processing, scaling processing, filter processing, and gradation processing on the digital data converted by the A / D conversion unit, and stores the processed image data as data This is sent to the means 4. Note that the filter processing in the image processing means 3 has the same function as the Softone filter attached to the lens of the camera in principle. This filter process is a process using an electrical filter instead of the above-mentioned Softone filter in order to express an image softly, and is performed on the entire image. On the other hand, the filtering process by the filtering means 5 which is a feature of the present invention is different from the above, and emphasizes black streaks (shadow portions) corresponding to the edge of the document D as described later. .
[0026]
The data storage unit 4 is a part for storing image data after image processing by the image processing unit 3.
[0027]
The filtering means 5, the inclination detection means 6, and the inclination correction processing means 7 will be described in detail later.
[0028]
The image output means 8 corresponds to a printer, and as shown in FIG. 2, a recording material supply unit 26 that supplies a recording material on which an image is formed, and an image formation that forms an image on the supplied recording material. Part 27. Of these, the image forming unit 27 exposes the surface of the photosensitive drum 28 to be rotated, the charging unit 30 that uniformly charges the surface of the photosensitive drum 28 to a predetermined polarity and potential, and electrostatically exposes the surface of the charged photosensitive drum 28. An exposure unit 31 that forms a latent image, a developing unit 32 that develops a toner image by attaching toner to the electrostatic latent image, and a toner image formed on the photosensitive drum 28 are supplied from the recording material supply unit 26. A transfer unit 33 for transferring to a recording material and a fixing unit 34 for fixing a toner image on the recording material are provided.
[0029]
In this image output means 8, the image data that is the basis when the exposure means 31 forms an electrostatic latent image on the photosensitive drum 28 is a document image read by the image input means 2 described above.
[0030]
Therefore, when the document D read by the image input means 2 is skewed, the inclined electrostatic latent image is written on the photosensitive drum 28 by the exposure means 31, and naturally the final output image ( The toner image is also inclined with respect to the recording material, resulting in an image defect.
[0031]
As techniques for eliminating such image defects, the techniques described in the prior art are known.
[0032]
However, according to the conventional example, the configuration is complicated, the original is damaged, and the image shift cannot be corrected with high accuracy.
[0033]
Therefore, the present invention has a simple configuration and can reliably detect and correct the inclination of the original image based on the skew of the original without damaging the original.
[0034]
By the way, it is generally known that unnecessary black streaks are formed on a portion corresponding to the leading edge and the trailing edge of the document D on a copy in a copying machine or a printer. In the present embodiment, as shown in FIG. 4, a shadow due to the thickness of the document D is likely to occur at the trailing edge D1 of the document D. While the document D is conveyed in the direction of arrow A and the document image is read, the light emitted from the light source 24 is reflected by the image surface of the document D and enters the SELFOC lens array 25. However, before and after the trailing edge D1 of the document D passes through the reading line L, the light from the light source 24 is blocked by the trailing edge D1 of the document D and is not incident on the SELFOC lens array 25. That is, the reflectance of the portion corresponding to the trailing edge D1 is different from the reflectance of the document upper roller 17 or the document D (generally, the reflectance is low), and thus appears as a black streak on the copy. The black streaks appear darker and thicker as the thickness of the document D increases.
[0035]
Since such black streaks should preferably not appear on the copy, conventionally, they tend to be erased without being particularly used. In the present invention, this black streak is actively used to detect the skew (tilt angle) of the document.
[0036]
This will be described in detail below with reference to the flowchart of FIG.
[0037]
First, the original image of the original D is read by the image input means 2 (step S1). The reading of the document D is performed by the image input unit 2 as described above. In the present invention, the turn-off timing of the light source 24 is changed in order to read the rear end D1 of the document D. The light source 24 is turned off after the trailing edge of the document D has passed the reading line L. Since the time from when the trailing edge detection sensor 22 detects the trailing edge D1 of the document D to when the trailing edge D1 passes the reading line L is t2 = y / v, t2 + Δt with some allowance. Later, the light source 24 is turned off. Thus, the rear end D1 of the document D is positively read by the image input unit 2.
[0038]
The read image data is converted from analog image data to digital image data in the A / D converter (step S2).
[0039]
The digitally converted image data is sent to the image processing means 3 to perform the image processing as described above.
[0040]
The image data after the image processing is stored in the data storage unit 4 (step S3).
[0041]
The filtering means 5 detects image data for the trailing edge D1 of the document D from the image data stored in the data storage means 4, and filters the image data to enhance the shadow corresponding to the trailing edge D1. (Step S4).
[0042]
In step S4, first, detection of the rear end D1 can be performed by detecting the coordinates of the black pixel corresponding to the rear end D1 with reference to the coordinates of the printed circuit board 10, for example. The original image and the above-described black pixel can be distinguished by comparing the coordinates of both.
[0043]
As image enhancement, the most representative edge enhancement is performed. In general, the edge point (edge) has a property that the density rapidly changes, and the presence or absence of the edge point can be examined by obtaining a density gradient in the vicinity of the edge point. A Sobel filter and a Prewitt filter are known as methods for approximating the differential of the first derivative utilizing this property.
[0044]
In the present invention, these filters can be used. However, as a more preferable method, a Laplacian filter that approximates the second-order derivative by difference is used. This Laplacian filter detects a peak of density change.
[0045]
The Laplacian filter includes a 4-direction Laplacian filter shown in FIG. 6A and an 8-direction Laplacian filter shown in FIG. Among these, the former is a differential filter that approximates a second-order derivative in the vicinity of 4, and is based on the pixels in the four directions, up, down, left, and right, with the median corresponding to the pixel of interest as “4”. On the other hand, the latter is a differential filter that approximates a second-order derivative in the vicinity of 8 and is based on a total of 8 pixels, in which four pixels in the oblique direction are further added to the pixels in the four directions described above.
[0046]
Hereinafter, an example using the 8-direction Laplacian filter of FIG. 6B will be described.
[0047]
The 8-direction Laplacian filter multiplies the nine pixel values of the top, bottom, left, and right centered on a certain target pixel by coefficients as shown in FIG. 6B, and uses the sum of the results as a new pixel value. Adopted.
[0048]
This will be described in more detail with a specific example shown in FIGS. Of these figures, FIG. 7A shows the density of nine pixels before applying the 8-direction Laplacian filter, and FIG. 7B shows the density of nine pixels after applying.
[0049]
For example, if the density of the image data is expressed by 8 bits, it becomes 0 to 255. In the 8-bit image data, it is assumed that the center pixel is “100” as shown in FIG. 7A, and the upper, lower, left, and right 8 are all “50”. Although not shown in the figure, it is assumed that 16 pieces of image data around eight pieces of “50” image data are also “50”.
[0050]
The 8-direction Laplacian filter shown in FIG. 6B is applied to such image data. First, the center “100” is set as a target pixel, and the filter is applied so that the center “8” of the 8-direction Laplacian filter matches this. As a result, the density A of the target pixel is calculated as follows.
[0051]
A = 100 × 8 + {50 × (−1) × 8} = 400
Here, since the maximum density is “255”, anything exceeding this is set to “255”.
[0052]
Accordingly, the density of the pixel of interest after applying the 8-direction Laplacian filter becomes “255”, which is “100” before the application. That is, as shown in FIG. 7B, the density of the central pixel is “255”.
[0053]
Next, the pixel above the central pixel in FIG. The density of this pixel of interest is “50”, and the center “8” of the 8-direction Laplacian filter of FIG. As a result, the density B of the target pixel is calculated as follows.
[0054]
B = 50 × 8 + {100 × (−1) + 50 × (−1) × 7} = − 50
Here, since the lowest density is “0”, everything below this is set to “0”.
[0055]
Therefore, the density of the target pixel after applying the 8-direction Laplacian filter becomes “0” when it is “50” before applying. That is, as shown in FIG. 7B, the density of the pixel immediately above the center pixel is “0”.
[0056]
The remaining seven “50” pixels around the central “100” pixel in FIG. 7A are similarly calculated by applying an 8-direction Laplacian filter to obtain “0”.
[0057]
As a result of the above, by applying an 8-direction Laplacian filter to the nine pixels in FIG. 7A, as shown in FIG. 7B, the central pixel has the same degree of “255” and the surrounding eight pixels. A new pixel having a pixel density of “0” can be obtained.
[0058]
As can be seen by comparing these figures, the density difference between the central pixel and the surrounding pixels was “50 (= 100−50)” before applying the 8-direction Laplacian filter. After the call, “255 = (255-0)”. That is, the density difference is emphasized by applying the 8-direction Laplacian filter.
[0059]
By applying the 8-direction Laplacian filter to the image data corresponding to the trailing edge D1 of the document D, the image data of this portion can be emphasized (sharpened).
[0060]
In the above description, an example in which an 8-direction Laplacian filter is used as a filter for sharpening image data has been described. However, in the present invention, image data at the edge of the document D including the trailing edge D1 is effective. Of course, any other filter can be used as long as it can be sharpened.
[0061]
Thus, the image data in which only the image data corresponding to the trailing edge D1 of the document D is sharpened is returned to the data storage means 4 and stored (step S5).
[0062]
The image data stored in the data storage means 4 is sent to the inclination detection means 6, and the inclination detection means 6 recognizes the continuity of the black pixels corresponding to the trailing edge D1 of the original D, and reads the inclination angle of the original D, that is, the reading. The angle of the trailing edge D1 of the document D with respect to the line L is detected (step S6). At this time, since the black pixel corresponding to the rear end D1 is sharpened by the filtering means 5 described above, it can be reliably detected with high accuracy.
[0063]
On the other hand, the image data stored in the data storage unit 4 is temporarily returned to the image processing unit 3, and the black pixel corresponding to the trailing edge D1 of the document D is converted into a white pixel in the image data, and black stripes are formed on the copy. Is sent to the inclination correction processing means 7 so as not to be output.
[0064]
In the inclination correction processing means 7, the whole image data sent from the image processing means 3 is rotated in accordance with the inclination angle sent from the inclination detection means 6 to perform inclination correction processing (step S 7). . Note that the tilt correction means 7 may be one that performs software processing using a CPU or the like, or one that uses dedicated hardware.
[0065]
The image data thus subjected to the tilt correction processing is sent to the exposure means 31 of the image output means 8, and based on this, an electrostatic latent image is formed on the photosensitive drum 28 by the exposure means 31.
[0066]
Therefore, even when the document D when being read by the image input means 2 is tilted and the document image is input while being tilted, the electrostatic latent image formed on the photosensitive drum 28 is in a normal state, that is, The original D is formed in the same manner as when the original is conveyed without being skewed and the original image is read. The final copy output image (toner image) is also formed at a normal position with respect to the recording material.
[0067]
According to the present embodiment, it is not necessary to use a dedicated sensor for detecting the skew of the document, so that the configuration can be simplified. In addition, since the document D itself is not forcibly rotated, for example, by providing a difference in the transport speed of the two rollers that transport the document D to correct the tilt angle of the image, the document is not damaged. In addition, highly accurate correction can be performed. Furthermore, since the black streak corresponding to the trailing edge of the document is once sharpened by filtering, the inclination angle can be detected more reliably.
[0068]
In the above embodiment, since the rear end D1 is more likely to be shadowed at the front end and the rear end D1 of the document D, the rear end D1 is detected. When a configuration is adopted in which a shadow is likely to appear, the tip may be detected.
[0069]
In the above description, the configuration in which the document D is moved with respect to the light source 24 has been described as an example. Conversely, the present invention can also be applied to a configuration in which the light source is moved with respect to the document D. .
[0070]
Further, although the outer peripheral surface of the upper roller 17 in the document that acts as a back when the document D is irradiated by the light source 24 is white, it can be replaced with, for example, silver with a mirror finish. That is, as long as the trailing edge D1 or the leading edge of the document D can be detected based on the difference in reflectance, an arbitrary color may be used for the back.
[0071]
Further, for example, a release mode that does not perform the tilt correction process may be selected by the user's selection. For example, when the original image itself is tilted with respect to the trailing edge of the original and it is desired to easily correct it on the copy, the original may be read while being inclined. If a release mode is provided, this can be realized easily.
[0072]
In addition, the present invention is characterized in that it detects the edge (front end, rear end, left end, right end) of a sheet-like recording material without providing a special mechanism or device. Therefore, the configuration for moving the document relative to the reading line is not necessarily essential. That is, for example, the document may be placed on the platen glass so as not to move, and the light source for irradiating it may be placed so as not to move. In such a case, for example, if the document image is read by irradiating the document with a plurality of light sources, any edge of the document is positively detected before the document is read. For this purpose, some of the plurality of light sources may be thinned and irradiated with light so that a shadow due to an edge is easily produced intentionally.
[0073]
In the above description, the example in which the density conversion means 5 for sharpening the portion corresponding to the trailing edge D1 of the document D is provided separately from the image processing means 3 has been described. The image processing means 3 may be included.
[0074]
【The invention's effect】
As described above, the image reading apparatus according to the present invention actively detects the edge of the document by the document input unit, emphasizes the detected edge by the filtering unit, and then responds to the inclination angle of the edge. Thus, the image data is corrected, so that it is possible to accurately detect and correct the inclination of the document image based on the skew of the document without damaging the document, although the configuration is simple.
[0075]
In addition, since the image forming apparatus according to the present invention includes the above-described image reading device, the final image on the recording material is normal with no inclination even when the document is skewed at the time of reading the document image. Can be.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a mechanical configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing a mechanical configuration of the entire image forming apparatus according to the exemplary embodiment of the present invention as seen from the front side.
FIG. 3 is an enlarged longitudinal sectional view showing a schematic configuration of image input means of the image reading apparatus according to the embodiment of the present invention.
FIG. 4 is a diagram schematically illustrating how a shadow is formed on the edge of the document.
FIG. 5 is a flowchart showing an inclination correction operation.
FIG. 6A is a diagram showing a four-direction Laplacian filter.
(B) is a figure which shows an 8-direction Laplacian filter.
FIG. 7A is a diagram illustrating an example of the density of image data of nine pixels before applying an 8-direction Laplacian filter;
(B) is a figure which shows the density | concentration of the image data after applying an 8-direction Laplacian filter to nine pixels of (a).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image input means, 3 ... Image processing means, 4 ... Data storage means, 5 ... Filtering means, 6 ... Inclination detection means, 7 ... Inclination correction processing means, 8 ...... Image output means, 11 ... Conveyance means, 24 ... Light source, D ... Original, D1 ... Document edge (rear edge), L ... Reading line

Claims (4)

Image input means for reading a document image of a sheet-like document, image processing means for processing image data read by the image input means, and data storage means for storing image data sent from the image processing means An image reading apparatus provided,
Filtering means for detecting image data about the edge of the document from image data stored in the data storage means to enhance edge points, and inclination detecting means for detecting an inclination angle of the edges after edge point enhancement. If, e Bei and tilt correcting means for correcting, based an image data transmitted from said image processing means into image data for the tilt angle of the edge that has been sent from said tilt sensing means,
The image data about the edge of the document on which the filtering unit performs edge enhancement is obtained by reading the shadow generated by obliquely irradiating the edge of the document with light from the light source by the image input unit. image reading apparatus characterized by certain.   The image input unit includes a light source that irradiates the document image on a reading line set along a main scanning direction, and a conveying unit that relatively moves the document in a multi-scanning direction with respect to the reading line. The image reading apparatus according to claim 1, wherein:   3. The image reading apparatus according to claim 2, wherein an edge of the document whose inclination angle is to be detected is a leading edge or a trailing edge when the moving direction of the document is used as a reference. In an image forming apparatus comprising: an image reading unit; and an image output unit that forms an image on a recording material based on image data read by the image reading unit.
The image forming apparatus according to claim 1, wherein the image reading unit is the image reading apparatus according to claim 1.

Images