Document reading device

Abstract

To ensure accurate document size detection.SOLUTION: An image forming device 1 includes: a document end candidate detection part 211 that detects, as a candidate position of a document end, a position of a concentration change point on the most downstream side in a conveyance direction at which an image density is equal to or higher than a threshold value at each of a plurality of positions in a main scanning direction on the basis of the concentration change indicated by image data obtained by reading by a reading part 51, and further detects, as a document end candidate, an image formed by a group of pixels continuous in the main scanning direction at the candidate position; and a document size detection part 212 that performs size detection processing of detecting a document size of the image data in the main scanning direction on the basis of the image of the document end candidate when the detected image of the document end candidate is composed of one image that extends in the main scanning direction and is present at the same position in the conveyance direction.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a document reading device, and more particularly to a technique for detecting the size of a document. [Background technology]

[0002] Some document reading devices detect the shadow formed on the document edge by irradiating the document with light, and then detect the document size from the detected shadow (see, for example, Patent Documents 1 to 3 listed below). Some document reading devices are equipped with an automatic document feeder, such as a DP (Document Processor) or an ADF (Auto Document Feeder), that automatically reads the image of a document placed on a document tray. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3584658 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-285585 [Patent Document 3] Japanese Patent Application Publication No. 2019-022010 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for improved productivity, and automatic document feeders are also required to read document images at high speeds. To read document images at high speeds, it is necessary to increase the amount of light irradiated onto the document compared to low or medium speed readings.

[0005] However, if the amount of light irradiated onto the document is increased, the image of the shadow created by the light irradiating the document edge, which is included in the document image obtained by document reading, becomes thinner. If the document is thin, it is difficult to create a shadow, especially at the document edge, and the image becomes thinner. If the image of the shadow becomes thinner, the document size cannot be detected correctly, and there is a risk that the output image will differ from the document size.

[0006] The present invention has been made in view of the above circumstances, and has as its object to ensure accurate detection of the document size. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an original reading device comprising: an original tray on which an original is placed; a transport unit that transports the original placed on the original tray; a reading unit having a light source that irradiates light onto the original being transported by the transport unit and that reads an image of the original in a main scanning direction perpendicular to the transport direction by irradiating the light onto the original being transported by the transport unit; an original end candidate detection unit that detects, based on density changes indicated by image data read by the reading unit, positions of density change points furthest downstream in the transport direction where image density is equal to or greater than a predetermined threshold at each of a plurality of positions in the main scanning direction as original end candidate positions, and further detects, at each candidate position, an image formed by a group of pixels that are continuous in the main scanning direction; and an original size detection unit that, when the image of the original end candidate detected by the original end candidate detection unit consists of a single image extending in the main scanning direction and located at the same position in the transport direction, performs size detection processing to detect the original size of the image data in the main scanning direction based on the image of the original end candidate. [Effects of the Invention]

[0008] When all the document edge candidates indicating the shadows of the document edges are the same, the document edge candidates (i.e., images indicating the shadows of the document edges) are not interrupted and the document size in the main scanning direction can be correctly detected from the document edge candidates, but when they are interrupted, it becomes difficult to accurately detect the document size from the document edge candidates.

[0009] According to the present invention, when the image of the document end candidate consists of a single image extending in the main scanning direction, the document size in the main scanning direction is detected based on the image of the document end candidate, so that document size detection is performed only when accurate document size detection is possible, thereby ensuring accurate document size detection. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view showing the appearance of an image forming apparatus including a document reading device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a functional block diagram illustrating a main internal configuration of the image forming apparatus. [Figure 3] 1A and 1B are diagrams each showing a schematic view of a part of the internal configuration of a document feeding section and a document reading section that constitute the document reading device. [Figure 4] FIG. 2 is a functional block diagram illustrating a main internal configuration of the document reading device. [Figure 5] 10A and 10B are diagrams showing an example of an image represented by image data that has been subjected to binarization processing. [Figure 6] FIG. 1A is a diagram for explaining possible positions of an edge of a document, and FIGS. 1B and 1C are diagrams for explaining possible edges of a document. [Figure 7] FIG. 10 is a diagram illustrating document edge candidates. [Figure 8] 10 is a flowchart illustrating an example of processing performed by a control unit in the document reading device. [Figure 9] FIG. 10 is a diagram showing an example of a document edge candidate; [Figure 10] 10A and 10B are diagrams showing examples of document edge candidates. [Figure 11] 10A to 10C are diagrams showing an example of an image change when the threshold value is lowered in a stepwise manner. DETAILED DESCRIPTION OF THE INVENTION

[0011] An original reading device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the exterior of an image forming apparatus equipped with an original reading device according to a first embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic diagram of the main internal configuration of the image forming apparatus. The image forming apparatus 1 is a multifunction peripheral having multiple functions, such as a copy function, a printer function, a scanner function, and a facsimile function, and is configured to include a control unit 10, an original feeding unit 6, an original reading unit 5, an image forming unit 12, a paper feeding unit 14, an operation unit 47, a network interface unit 91, and a storage unit 8. The original reading device 20 is an automatic document feeder (DP) or automatic document feeder (ADF), and is disposed above the main body of the image forming apparatus 1. The original reading device 20 is configured to include the original feeding unit 6 and the original reading unit 5.

[0012] The document feed unit 6 is configured to be openable and closable by a hinge or the like (not shown) on the top surface of the document reading unit 5, and functions as a document pressing cover when reading a document placed on a platen glass (not shown). The document feed unit 6 also includes a document placement tray 61 on which documents are placed, a pair of document guides 62 provided on the document placement tray 61, and a document discharge tray 63 provided below the document placement tray 61. The document feed unit 6 supplies documents placed on the document placement tray 61 to the document reading unit 5 one by one and discharges the documents to the document discharge tray 63. The document guide 62 is movable in the document width direction, which is perpendicular to the document transport direction, and regulates the position of the document in the width direction.

[0013] The document reading unit 5 includes a scanner and the like, and reads the document fed from the document feeding unit 6 or reads the document placed on the platen glass. The document reading unit 5 is also capable of sequentially reading multiple document images sent from the document feeding unit 6.

[0014] The following describes an image forming operation performed by the image forming apparatus 1. The image forming unit 12 is equipped with a photosensitive drum, charging device, exposure device, developing device, and primary transfer device for each color, and is a mechanism for forming an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt. The image forming unit 12 forms a toner image on recording paper fed from the paper feed unit 14 based on image data generated by a document reading operation, image data stored in an image memory, etc., and image data received from a computer connected via a network, to create a printed matter.

[0015] The fixing unit 13 is a fixing device equipped with a heat roller, a pressure roller, and a drive mechanism for rotating these rollers. The fixing unit 13 heats and presses the recording paper on which the toner image has been formed by the image forming unit 12 at the nip between the two rollers, fixing the toner image to the recording paper. The recording paper that has been fixed is then discharged to the discharge tray 151.

[0016] The paper feed unit 14 includes a paper feed cassette 141, a pickup roller that picks up recording paper from the paper feed cassette and feeds it to the image forming unit 12, a transport roller, a transport path, and a rotation drive mechanism for each roller.

[0017] The operation unit 47 includes various hard keys that are operated by the user, and receives instructions from the user, such as an instruction to execute an image forming operation, regarding various operations and processes that the image forming apparatus 1 can execute in response to the operation of the hard keys.

[0018] The operation unit 47 includes a display unit 473 that displays operation guides and the like to the operator. The operation unit 47 also receives input of instructions from the user based on the user's operation (touch operation) on the screen displayed on the display unit 473 via a touch panel that the display unit 473 has.

[0019] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. When the operator touches a button or key displayed on the screen, the touch panel receives an instruction associated with the touched position. In this case, the touch panel functions as an operation unit.

[0020] The network interface unit 91 is a communication interface for transmitting and receiving various data to and from an external device (for example, a personal computer) within a local area or on the Internet.

[0021] The storage unit 8 is a large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various control programs and the like.

[0022] The control unit 10 includes a processor, a RAM (Random Access Memory), a ROM (Read Only Memory), and a dedicated hardware circuit. The processor may be, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit). The control unit 10 includes a control unit 100.

[0023] The control unit 10 functions as the control unit 100 by the operation of the processor in accordance with a control program stored in the storage unit 8. However, the control unit 100 can also be configured by a hardware circuit, without relying on the operation in accordance with the control program by the control unit 10. Unless otherwise stated below, the same applies to each embodiment.

[0024] The control unit 100 is responsible for overall operational control of the image forming apparatus 1. The control unit 100 is connected to the document feed unit 6, the document reading unit 5, the image forming unit 12, the fixing unit 13, the paper feeding unit 14, the operation unit 47, the network interface unit 91, and the storage unit 8, and performs drive control of each of these units and executes various processes required for image formation by the image forming apparatus 1. For example, the control unit 100 controls the operation of the image forming unit 12 to execute a copy job in which an image indicated by image data of a document obtained by reading the document by the document reading unit 5 is formed on a recording medium.

[0025] The following describes the case where a document is read by the image forming apparatus 1. The document reading unit 5 optically reads an image of a document supplied to the document reading unit 5 by the document feeding unit 6 or a document placed on the platen glass, and generates image data. The image data generated by the document reading unit 5 is stored in an image memory (not shown) or the like.

[0026] 3(A) and (B) are diagrams that schematically show part of the internal configuration of the document feeding unit 6 and the document reading unit 5 that make up the document reading device 20. FIG. 3(A) shows a high-speed model, and FIG. 3(B) shows a low-speed or medium-speed model.

[0027] The document feed unit 6 includes a transport unit 64 that transports the document M placed on a document placement tray 61 (FIG. 1), and a shading roller 65. The document reading unit 5 includes a reading unit 51 that includes light sources 52 and 53 that irradiate light (shown by dashed lines) onto the document M transported by the transport unit 64, and a reading sensor 54. The number of light sources is smaller for low-speed or medium-speed machines than for high-speed machines.

[0028] The transport section 64 includes a pair of transport rollers 641 and a pair of discharge rollers (not shown). The pair of transport rollers 641 transports the original M placed on the original placement tray 61 and guides the original M to a position between the shading roller 65 and the reading sensor 54 (image reading position). The original M passes through the image reading position and is discharged onto the original discharge tray 63 (FIG. 1) by a discharge roller (not shown).

[0029] The reading unit 51 has light sources 52 and 53, which irradiate light onto the original M being transported by the transport roller pair 641, and reads the image of the original M with a reading sensor 54 in a main scanning direction SD (direction from the front to the back of the paper in FIG. 3) perpendicular to the document transport direction CD. The light sources 52 and 53 are, for example, LEDs, and are arranged to extend in the main scanning direction SD. The reading sensor 54 is, for example, a CIS (Contact Image Sensor), and is arranged to extend in the main scanning direction SD.

[0030] At the image reading position, light source 52 illuminates original document M in a direction oblique to the conveying direction CD, from the upstream side to the downstream side in the conveying direction CD. On the other hand, light source 53 at the image reading position illuminates original document M in a direction oblique to the conveying direction CD, from the downstream side to the upstream side in the conveying direction CD. Note that, as shown in the example in Figure 3(A), if there are light sources on both the upstream and downstream sides of the image reading device, shadows on the edges of the original document are less likely to appear, so the light intensity ratio of light sources 52 and 53 is set to about 70 for downstream light source 53 compared to 100 for upstream light source 52, making it easier for shadows to appear on the edges of the original document.

[0031] 4 is a functional block diagram showing a schematic diagram of the main internal configuration of the document reading device 20. The document reading device 20 includes a control unit 21, a transport unit 64, a reading unit 51, and a storage unit 22. The control unit 21 includes a processor, RAM, ROM, and a dedicated hardware circuit. The processor is, for example, a CPU, ASIC, or MPU. The control unit 21 includes a control unit 210, a document edge candidate detection unit 211, and a document size detection unit 212.

[0032] The control unit 21 functions as a control unit 210, a document edge candidate detection unit 211, and a document size detection unit 212 by operation of the processor in accordance with a control program or the like stored in a storage unit 22 consisting of a non-volatile memory or the like. Note that in this embodiment, the document reading device 20 is described as having the control unit 21. However, the document reading device 20 may not have the control unit 21, and the control unit 10 of the image forming device 1 may also function as the control unit 21. In this case, the document reading device 20 will have the control unit 210, document edge candidate detection unit 211, and document size detection unit 212 that are provided in the control unit 10 of the image forming device 1 as part of the document reading device 20.

[0033] The control unit 210 is responsible for overall operational control of the document reading device 20. The control unit 210 is connected to the conveying unit 64, the reading unit 51, and the storage unit 22, and performs drive control of each of these units. For example, the control unit 210 acquires image data of the document M, and outputs the acquired image data to the control unit 10 provided in the main body of the image forming apparatus 1. The control unit 210 also outputs data indicating the document size (main scanning direction and conveying direction) and inclination of the document M conveyed from the document placement tray 61 to the image forming apparatus 1.

[0034] Based on density changes indicated by the image data obtained by reading by the reading unit 51, the document edge candidate detection unit 211 detects, as document edge candidate positions, the positions of density change points in the image data most downstream in the transport direction CD where the image density is equal to or greater than a predetermined threshold value TH at each of a plurality of positions in the main scanning direction SD. Furthermore, the document edge candidate detection unit 211 detects, as document edge candidate positions, images formed by groups of pixels that are continuous in the main scanning direction SD at the candidate positions. When reading the document M by the reading unit 51, the document is read at each position in the transport direction CD of the document M by the scanning line of the reading sensor 54 extending in the main scanning direction SD. The images im1 read at each position by the scanning line of the reading sensor 54 are aligned in the transport direction CD to generate image data obtained by reading the document M. The main scanning direction SD in the image data is the direction in which the images im1 obtained by a single reading by the scanning line extend and are aligned in the image data. The transport direction CD in the image data is the direction perpendicular to the direction in which the images im1 extend and are aligned.

[0035] When the image of the document end candidate detected by the document end candidate detection unit 211 consists of one image extending in the main scanning direction SD, the document size detection unit 212 performs size detection processing to detect the document size in the main scanning direction SD of the image data based on the image of the document end candidate.

[0036] In addition, the document size detection unit 212 detects the document size of the document M in the transport direction CD based on a signal from an optical sensor (not shown) that detects the passage of the leading and trailing ends of the document during transport, based on the time from when the leading end of the document passes to when the trailing end of the document passes, and the transport speed of the document.

[0037] Next, the operation of the document reading device 20 for detecting the document size in the main scanning direction SD will be described. Since image density information (brightness information) is required to detect the image of the shadow formed at the document edge in the transport direction CD in the image data obtained by document reading by the document reading unit 5, for example, the document edge candidate detection unit 211 performs image processing such as binarization on the image data obtained by reading by the reading unit 51 in order to clarify the boundary between the shadow (dark part) formed at the document edge and the background (bright part).

[0038] For example, if the image data obtained by the reading unit 51 represents a color (RGB) image, the document end candidate detection unit 211 performs YUV conversion on the image data to create a monochrome image. The document end candidate detection unit 211 performs filtering (e.g., Sobel filtering) on ​​the monochrome image to reduce noise and enhance edges, and then binarizes the monochrome image based on a predetermined threshold value TH. If the threshold value TH is set too high, shadows caused by document edges cannot be detected. Conversely, if the threshold value TH is set too low, noise will be detected. Therefore, an appropriate value for the threshold value TH is determined in advance through experiments, etc. For example, the threshold value TH is set to 32 for pixel values ​​0 to 255 (8 bits) that can be used for monochrome images. In addition, the document end candidate detection unit 211 preferably performs expansion / contraction processing on the binarized image data to improve the continuity of the shadow image caused by the document edge and minimize discontinuities in the image representing the document edge shadow in the main scanning direction SD.

[0039] 5(A) and (B) are diagrams showing an example of an image represented by image data obtained by scanning by the scanning unit 51 and subjected to the above-mentioned binarization process, etc. The black images shown in FIGS. 5(A) and (B) are parts where the density is less than the threshold value TH, and the white images are parts where the density is equal to or greater than the threshold value TH, and represent shadows of the document edges, etc. In the image shown in FIG. 5(A), the shadows of the document edges are clearly visible, but in the image shown in FIG. 5(B), the image representing the shadows of the document edges is interrupted at various positions in the main scanning direction SD.

[0040] Here, when the document end candidate detection unit 211 performs document end candidate detection on the image shown in Figure 5(B), it detects positions CP1 to CP15 as candidate document end positions, which are the density change points (points where the image changes from black to white) most downstream in the conveying direction CD that are equal to or greater than the threshold value TH at each of multiple positions P1 to P15 that divide the image reading range of the reading unit 51 into 16 in the main scanning direction SD, as an example shown in Figure 6(A).

[0041] Furthermore, the document end candidate detection unit 211 detects, as a document end candidate, each image formed by a group of pixels that are continuous in the main scanning direction SD at candidate positions CP1 to CP15. As shown in the example in Figure 6(B), at document end candidate position CP3, the document end candidate detection unit 211 detects, as a document end candidate, an image consisting of a distance D3 that is formed by a group of pixels that are continuous in the main scanning direction SD at candidate position CP3.

[0042] FIG. 6C shows the document edge candidates detected at each of the document edge candidate positions CP1 to CP15, and the distances D1 to D15 (excluding distance D14) between each document edge candidate. As shown in FIG. 6C, the same (single) document edge candidate is detected at document edge candidate positions CP12 and CP14, and its length is distance D12. Note that the document edge candidate detection unit 211 excludes line segments that do not reach a predetermined size (e.g., 20 mm) from the document edge candidates. This prevents small particles such as dust from being included in the document edge candidates.

[0043] Also, as shown in Figure 7, if the image showing the shadow of the document edge is not interrupted at each position in the main scanning direction SD, the same (single) document edge candidate, i.e., a document edge candidate consisting of one image extending in the main scanning direction, will be detected at the document edge candidate positions CP1 to CP15, and its length will be a distance D21.

[0044] In this case, the document size in the main scanning direction SD can be accurately calculated based on the positions (position coordinates) of both ends in the main scanning direction SD of this document end candidate L21. However, if there are multiple document end candidate images in the main scanning direction SD detected by the document end candidate detection unit 211 (FIG. 6A), the images showing the document end shadows are interrupted at each position in the main scanning direction SD, making it difficult to accurately detect the length of the image data in the main scanning direction SD based on the length of each document end candidate in the main scanning direction SD.

[0045] Therefore, when the image of the document end candidate detected by the document end candidate detection unit 211 consists of a single image extending in the main scanning direction SD that exists at the same position in the conveying direction CD, the document size detection unit 212 detects the document size in the main scanning direction SD of the image data obtained by document reading based on the image of the document end candidate.

[0046] Next, a process for detecting the size of the document in the main scanning direction SD by the document reading device 20 will be described with reference to the flowchart shown in FIG.

[0047] The document end candidate detection unit 211 performs image processing such as binarization on the image data obtained by reading by the reading unit 51 (S1), detects the density change point on the downstream side in the conveying direction CD that is equal to or greater than the threshold value TH at each of the multiple positions P1 to P15 as a document end candidate position (S2), and detects the image formed by a group of consecutive pixels in the main scanning direction SD at each candidate position as a document end candidate position (S3).

[0048] The document size detection unit 212 then determines whether the document edge candidate images detected by the document edge candidate detection unit 211 are located at the same position in the transport direction CD and consist of a single image extending in the main scanning direction SD (S4). If the document size detection unit 212 determines that the document edge candidate images detected by the document edge candidate detection unit 211 are connected in the main scanning direction SD at the same position in the transport direction CD and consist of a single image extending in the main scanning direction SD (an example is shown in FIG. 7) (YES in S4), the document size detection unit 212 detects the distance from one end to the other end as the document size in the main scanning direction SD based on the positions (position coordinates) of both ends of the document edge candidate images in the main scanning direction SD (S5). Furthermore, the document size detection unit 212 calculates the skew of the document M based on the positions in the transport direction SD of both ends of the document edge candidate (S6). Furthermore, based on the signal from the optical sensor that detects the passage of the leading and trailing edges of the original document during transport, the document size detection unit 212 detects the size of the original document M in the transport direction CD based on the time from when the leading edge of the original document passes to when the trailing edge of the original document passes, and the transport speed of the original document (S7). After this, the process ends. Data indicating the original document size in the main scanning direction SD and the transport direction CD and the inclination of the original document M are output by the control unit 10 from the control unit 210.

[0049] On the other hand, if the document size detection unit 212 determines that the images of the document edge candidates detected by the document edge candidate detection unit 211 are not connected in the main scanning direction SD at the same position in the transport direction CD but are interrupted, and do not form a single image extending in the main scanning direction SD (NO in S4), it determines that the document size detection is an error (S8). In this case, the document size detection unit 212 detects the document size in the main scanning direction SD based on signals from unillustrated optical sensors that detect the positions of the document guides 62, which are moved in accordance with the position of the edge of the document M in the main scanning direction SD placed on the document placement tray 61 (S9). After the process of S9, the document size in the transport direction CD is detected in S7. Then, the process ends. Data indicating the document sizes in the main scanning direction SD and the transport direction CD are output by the control unit 210 to the control unit 10.

[0050] In the first embodiment, when the image of the document edge candidate consists of a single image extending in the main scanning direction at the same position in the conveying direction CD, the document size in the main scanning direction is detected based on the image of the document edge candidate. Therefore, accurate document size detection is performed only when accurate document size detection is possible, ensuring accurate document size detection. Furthermore, when the image of the document edge candidate is not formed of a single image extending in the main scanning direction, the document size in the main scanning direction based on the image of the document edge candidate is not detected. This prevents inaccurate document size detection and inappropriate output images.

[0051] Next, a second embodiment of the process for detecting the size of a document in the main scanning direction SD by the document reading device 20 will be described. The second embodiment differs from the first embodiment in that the document size in the main scanning direction SD is detected based on the document end candidate even when the image of the document end candidate is not formed by a single image extending in the main scanning direction.

[0052] In the second embodiment, when the image of the document end candidate is not formed by a single image extending in the main scanning direction SD, but is made up of multiple images extending in the main scanning direction SD that are located at the same position in the conveying direction CD, the document size detection unit 212 detects the document size in the main scanning direction SD based on the image of the document end candidate that is closest to one end in the main scanning direction SD and the image of the document end candidate that is closest to the other end.

[0053] 9, if document end candidates L1 to L5 exist in the main scanning direction SD, among the document end candidates L1 to L5, the document end candidate located at the end on one side (the left side in FIG. 9) in the main scanning direction SD is document end candidate L1, and the document end candidate located at the end on the other side is document end candidate L5. In this case, the document size detection unit 212 detects positions L1_L and L5_R, which are the outer ends of the document end candidates L1 and L5, and detects the distance from positions L1_L to L5_R as the document size in the main scanning direction SD.

[0054] Next, a third embodiment of the process for detecting the size of a document in the main scanning direction SD by the document reading device 20 will be described. The third embodiment differs from the second embodiment in that, as shown in the example of Fig. 10(A), when an image showing the shadow of a document edge is interrupted at each position in the main scanning direction SD, the document edge candidate detection unit 211 changes the predetermined threshold value TH to a lower value, making it easier for the image showing the shadow of the document edge to appear.

[0055] If the document edge candidate image is not formed by a single image extending in the main scanning direction, but is composed of multiple images extending in the main scanning direction SD and located at the same position in the transport direction CD, the document edge candidate detection unit 211 stores the document edge candidate with the longest length in the main scanning direction SD as the document edge reference line.The document edge candidate detection unit 211 then changes the threshold value TH to a lower value until the document edge candidate images are detected as a single image extending in the main scanning direction SD and located at the same position in the transport direction SD.The document size detection unit 212 then detects the document size in the main scanning direction SD based on the document edge candidate image consisting of the single image whose position in the transport direction CD coincides with the position of the stored document edge reference line.

[0056] The document size detection unit 212 may calculate the linear components of the document end candidate by linear interpolation from the position coordinates of both ends of the document end candidate as the document end reference line, and detect the document size in the main scanning direction SD based on the image of the document end candidate consisting of the one image having the same linear components as the calculated linear components.

[0057] As shown in Figure 10(A), when document end candidates L1 to L5 exist, the document end candidate detection unit 211 stores the longest document end candidate L4 among them as the document end reference line, and as shown in the example in Figure 10(B), detects document end candidate L11 by changing the threshold value TH to a lower value until the document end candidates L1 to L5 are all connected at a position in the conveying direction CD that is the same as the document end reference line.

[0058] For example, the document end candidate detection unit 211 gradually lowers the threshold value TH, and if the initial value is 32, it first lowers it by eight steps to set the threshold value TH to 24, and if the document end candidates are still not connected, it lowers it another eight steps to set the threshold value TH to 16. However, if the document end candidates are not connected even after lowering the threshold value TH to the predetermined lower limit, the document end candidate detection unit 211 stops changing the threshold value TH.

[0059] 11A to 11C are diagrams showing examples of images obtained when the threshold value TH is gradually lowered. In image G1 shown in FIG. 11A, the document edge candidates (document edge shadows) are disconnected in the main scanning direction SD. In image G2 shown in FIG. 11B, the document edge candidates are partially connected in the main scanning direction SD. In image G3 shown in FIG. 11C, the document edge candidate detection unit 211 gradually lowers the threshold value TH until image G1 shown in FIG. 11A becomes image G3 shown in FIG. 11C.

[0060] When the document size detection unit 212 sets the threshold value TH in this way and obtains a document end candidate L11 as shown in Figure 10 (B), it detects the document size based on the positions of both end portions L11_L, L11_R of the document end candidate L11.

[0061] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. Furthermore, in the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 11 are merely one embodiment of the present invention, and it is not intended that the present invention be limited to these configurations and processing. [Explanation of symbols]

[0062] 1. Image forming device 20 Document reader 51 Reading unit 61 Document tray 64 Transport section 211 Document edge candidate detection unit 212 Original size detection unit

Claims

1. a document tray on which documents are placed; a conveying unit that conveys the document placed on the document placement tray; a reading unit that has a light source that irradiates light onto the document being transported by the transport unit, and that irradiates light onto the document being transported by the transport unit and reads an image of the document in a main scanning direction perpendicular to the transport direction; a document end candidate detection unit that detects, based on density changes indicated by image data obtained by reading by the reading unit, positions of density change points on the most downstream side in the conveying direction where image density is equal to or greater than a predetermined threshold at each of a plurality of positions in the main scanning direction as document end candidate positions, and further detects, at the candidate positions, images formed by pixel groups that are continuous in the main scanning direction; a document size detection unit that performs size detection processing to detect the document size in the main scanning direction of the image data based on the image of the document end candidate when the image of the document end candidate detected by the document end candidate detection unit consists of a single image extending in the main scanning direction that is located at the same position in the transport direction.

2. The document size detection unit When the document edge candidate image is made up of a plurality of images that are present at the same position in the transport direction and extend in the main scanning direction, 2. The document reading device according to claim 1, wherein the document size in the main scanning direction is detected based on an image of the document edge candidate closest to one end in the main scanning direction and an image of the document edge candidate closest to the other end in the main scanning direction.

3. The document edge candidate detection unit When the document edge candidate image is made up of a plurality of images extending in the main scanning direction, Among the images of the document edge candidates, the one having the longest length in the main scanning direction is stored as a document edge reference line; changing the threshold value to a lower value until the images of the document edge candidates are detected as a single image that is present at the same position in the transport direction and extends in the main scanning direction; The document reading device according to claim 1, wherein the document size detection unit performs a size detection process to detect the document size in the main scanning direction based on an image of the document edge candidate consisting of the one image whose position in the transport direction coincides with the position of the document edge reference line.

Images