Image reading device and image reading method

Abstract

To prevent adverse effects on images when extracting a feature amount of a subject or a background part from at least one of a visible image and an invisible image.SOLUTION: An image reading device comprises: an illumination part which irradiates a subject with visible light and invisible light; an imaging part which receives the visible light and invisible light reflected by the subject and captures a visible image and an invisible image; a background part which is provided within an imaging range of the imaging part; and an image processing part which detects a feature amount of the subject or the background part from at least one of the visible image and the invisible image. The background part is configured such that reflectance of a specific wavelength of the visible light is set to be equal to or greater than visible light lower limit value reflectance that defines a lower limit of the reflectance of the visible light, and reflectance of a specific wavelength of the invisible light is set to be equal to or less than invisible light upper limit reflectance that defines an upper limit of the reflectance of the invisible light.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image reading device and an image reading method. [Background technology]

[0002] Conventionally, image processing techniques have been devised for image reading devices that correct the inclination and position of a document or cut out the document to its size based on edges between the document and the background detected from a read image.

[0003] Furthermore, Patent Document 1 discloses a technique for extracting feature amounts from a visible image and an invisible image in order to detect double feeding of documents. Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in a conventional image reading device, for the above image processing, an invisible light low reflection portion that has low reflectivity to invisible light is provided in the background portion, thereby enabling edge detection between the document and the background.

[0005] However, when the reflectance of the low invisible light reflectance portion to invisible light is reduced, the reflectance of the visible light is generally also reduced. When the reflectance of the visible light is reduced in this manner, there are problems in that the background of the document becomes dark, which affects image processing functions such as blank page detection, and when the background remains in the image, the image becomes unnatural.

[0006] The present invention has been made in consideration of the above, and aims to prevent adverse effects on an image when extracting features of a subject or background from at least one of a visible image and an invisible image. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the present invention provides an illumination unit that irradiates a subject with visible light and invisible light, an imaging unit that receives the visible light and invisible light reflected by the subject and captures a visible image and an invisible image, a background unit provided within the imaging range of the imaging unit, and an image processing unit that detects features of the subject or the background unit from at least one of the visible image and the invisible image, wherein the background unit has a reflectance of a specific wavelength of visible light that is equal to or greater than a visible light lower limit reflectance that defines a lower limit of the reflectance of visible light, and has a reflectance of a specific wavelength of invisible light that is equal to or less than an invisible light upper limit reflectance that defines an upper limit of the reflectance of invisible light. Effect of the Invention

[0008] According to the present invention, it is possible to prevent adverse effects on an image when extracting features of a subject or background from at least one of a visible image and an invisible image. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a device configuration of an image reading device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of the reading unit. [Diagram 3] FIG. 3 is a block diagram showing electrical connections between the various components constituting the image reading device. [Figure 4] FIG. 4 is a diagram showing differences in spectral reflection characteristics due to media in the imaging section. [Diagram 5] FIG. 5 is a diagram illustrating an example of the difference between a visible image and an invisible image. [Figure 6] FIG. 6 is a block diagram showing the functional configuration of the image processing unit. [Figure 7] FIG. 7 is a diagram showing the definition of the reflectance of the background portion. [Figure 8] FIG. 8 is a diagram showing the difference in read images depending on the reflectance of the background. [Figure 9] FIG. 9 is a diagram showing an example of subject edge detection. [Figure 10] FIG. 10 is a diagram showing an example of correction of the inclination and position of a document. [Figure 11] FIG. 11 is a diagram showing the definition of the reflectance of the background portion according to the second embodiment. [Figure 12] FIG. 12 is a diagram showing an example of visible light being mixed into an invisible light image sensor. [Figure 13] FIG. 13 is a diagram showing the definition of the reflectance of the background portion according to the third embodiment. [Figure 14] FIG. 14 is a diagram showing an example of automatic level correction (ALC). [Figure 15] FIG. 15 is a diagram showing the difference in read images depending on the reflectance of the background portion with respect to invisible light. [Figure 16] FIG. 16 is a diagram showing the definition of the reflectance of the background portion according to the fourth embodiment. [Figure 17] FIG. 17 is a diagram showing differences in read images due to differences in visible light reflectance of the background portion. [Figure 18] FIG. 18 is a diagram showing the definition of the reflectance of the background portion according to the fifth embodiment. [Figure 19] FIG. 19 is a diagram showing the definition of the reflectance of the background portion according to the sixth embodiment. [Figure 20] FIG. 20 is a diagram showing the definition of the reflectance of the background portion according to the seventh embodiment. [Figure 21] FIG. 21 is a diagram showing the definition of the reflectance of the background portion according to the eighth embodiment. [Figure 22] FIG. 22 is a diagram showing the definition of the reflectance of the background portion according to the ninth embodiment. [Figure 23] FIG. 23 is a diagram showing a modified example of the image reading device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of an image reading device and an image reading method will be described in detail with reference to the attached drawings. In the following, the term "visible" refers to a wavelength range of visible light (visible wavelength range), and "invisible" refers to a wavelength range other than visible light, such as infrared light or ultraviolet light.

[0011] (First embodiment) Fig. 1 is a diagram showing an example of the device configuration of an image reading device according to a first embodiment. Fig. 1 shows the configuration of an image reading device 1 provided in an image forming device generally called a multifunction peripheral / printer / product (MFP) having at least two functions of a copy function, a printer function, a scanner function, and a facsimile function. Here, the configuration of an image reading device including a reading unit is shown, but the reading device and the image reading device may be provided separately from the reading unit.

[0012] A reader body 10 of the image reading device 1 has a contact glass 11 on its upper surface. The image reading device 1 has a light source 13, a first carriage 14, a second carriage 15, a lens unit 16, a sensor board 17, and the like inside the reader body 10. In Fig. 1, the first carriage 14 has the light source 13 and a reflecting mirror 14-1, and the second carriage 15 has reflecting mirrors 15-1 and 15-2.

[0013] Light from the light source 13 is irradiated onto the object to be read, and the light reflected from the object to be read is reflected by mirror 14-1 of the first carriage 14 and mirrors 15-1 and 15-2 of the second carriage 15 and enters lens unit 16, and an image of the object to be read is formed on the light receiving surface of sensor board 17 from lens unit 16. Sensor board 17 has imaging unit 40 which is a line sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary MOS), and the image of the object to be read formed on the light receiving surface in imaging unit 40 is sequentially converted into electrical signals. Reference white plate 12 is a white density reference member which is read to correct for changes in the amount of light from light source 13 and variations in pixels (pixel circuits) of imaging unit 40.

[0014] The image reading device 1 includes a control board in the reading device main body 10, and controls each part of the reading device main body 10 and each part of the ADF 20 to read the reading target in a predetermined reading method. The reading target is, for example, a recording medium on which characters, pictures, etc. are formed. In the following, this recording medium is referred to as an original. The original corresponds to the "subject" and will be described as paper or a transparent sheet (such as an overhead projector sheet) as an example, but is not limited to these.

[0015] The image reading device 1 is equipped with an ADF (Automatic Document Feeder) 20 on top of the reading device main body 10. The image reading device 1 reads the original 100 by a sheet-through method using the ADF 20. The ADF 20 is an example of a "conveying section." In the configuration shown in FIG. 1, the image reading device 1 separates the original 100 one by one from a stack of originals on a tray 21 of the ADF 20 using a pickup roller 22, conveys the original 100 to a conveying path 23, reads the surface of the original 100 to be read at a reading position of the reading section, and discharges the original 100 to a paper output tray 25. The original 100 is conveyed by the rotation of various conveying rollers 24.

[0016] In the image reading device 1, for example, with the first carriage 14 and the second carriage 15 moved to and fixed at a predetermined home position, the original 100 passes between the reading window 19 and the background section 26 of the reading unit. The reading window 19 is a slit-shaped reading window provided in a part of the contact glass 11. The background section 26 is a member located opposite the reading window 19. While the original 100 passes through the reading window 19, the reading unit irradiates light from the light source 13 onto a first surface (front or back surface) of the original 100 facing the reading window 19, and receives the reflected light with the imaging unit 40 on the sensor board 17 to read the image.

[0017] Here, the light source 13, the background section 26, the optical system (mirror 14-1, mirrors 15-1 and 15-2, lens unit 16, etc.) that guides the reflected light from the original 100 to the imaging section 40 of the sensor board 17, and the imaging section 40 will be described as a reading section (first reading section). The configuration of the reading section will be described again with reference to FIG. 3.

[0018] When reading both sides of the document 100, for example, an inversion mechanism that inverts the document 100 is provided. The image reading device 1 is provided with an inversion mechanism to invert the document 100 and read the second side of the document 100 at the reading position (reading window 19) of the reading unit. The second side may be read by other configurations, such as a second reading unit, instead of the inversion mechanism. For example, after the document 100 passes through the reading window 19, the second side of the document 100 is read by a reading unit (second reading unit) that has a reading sensor provided on the back side of the document 100. In this case, a member located opposite the reading sensor corresponds to the background unit 26 (see FIG. 2).

[0019] The configuration of the image reading device 1 of this embodiment also allows flatbed scanning. Specifically, the ADF 20 is lifted to expose the contact glass 11, and the original 100 is placed directly on the contact glass 11. Then, the ADF 20 is lowered to its original position, and the rear surface of the original 100 is pressed by the lower part of the ADF 20. In the flatbed method, the original 100 is fixed, so scanning is performed by moving the carriage (first carriage 14, second carriage 15) side relative to the original 100. The first carriage 14 and the second carriage 15 are driven by a scanner motor 18, and scan the original 100 in the sub-scanning direction. For example, the first carriage 14 moves at a speed V, and at the same time, the second carriage 15 moves in conjunction with it at a speed 1 / 2V, half that of the first carriage 14, to read the first surface of the original 100 on the contact glass 11 side. In this case, the lower part of the ADF 20 (the member that holds the original 100 from the rear side) corresponds to the background part 26 (see FIG. 2).

[0020] In this example, the first carriage 14, the second carriage 15, the lens unit 16, the sensor board 17, etc. are shown separately, but these may be provided separately or as an integrated sensor module.

[0021] 2 is a diagram for explaining an example of the configuration of the reading unit 30. As an example, the configuration and transport mechanism of the reading unit 30 (first reading unit) that reads the first side of the document 100 is shown. As shown in FIG. 2, the document 100 is transported by various transport rollers 24 and passes between the reading position (reading window 19) of the contact glass 11 and the background portion 26.

[0022] The reading unit 30 has a background unit 26 as a set, and when the light source 13 is turned on, while the original 100 passes through the reading window 19, the reflected light of the light source 13 from the first side of the original 100 facing the reading window 19 is received by the imaging unit 40 on the sensor board 17 via the path shown by the dotted line in Figure 2, and the image is read.

[0023] The configuration of the reading unit is not limited to the configuration of the first reading unit, and may be modified as appropriate according to the configuration of the image reading device, such as a method of reading with a contact type image sensor like the second reading unit.

[0024] As shown in FIG. 2, the light source 13 of this embodiment is composed of a visible light source 13a and an invisible light source 13b, and is an illumination unit that irradiates a subject with visible light and invisible light. The visible light source 13a irradiates a subject and a background 26 with visible light. The invisible light source 13b irradiates a subject and a background 26 with invisible light. It is effective to use infrared light as the invisible light source 13b. Generally, the visible light wavelength range is 380 to 750 nm, and the range beyond 750 nm is considered to be the infrared wavelength range, which is the invisible light wavelength range.

[0025] Fig. 3 is a block diagram showing electrical connections of the components constituting the image reading device 1. As shown in Fig. 3, the image reading device 1 includes a control unit 41, a light source driving unit 42, and an image processing unit 43 in addition to the above-mentioned imaging unit 40 and light source 13. The control unit 41 controls the imaging unit 40, the light source driving unit 42, and the image processing unit 43. The light source driving unit 42 drives the light source 13 under the control of the control unit 41. The imaging unit 40 transfers a signal to the image processing unit 43 arranged in a subsequent stage.

[0026] The imaging unit 40 includes an invisible light image sensor 40b that functions as an invisible image reading unit, and a visible light image sensor 40a that functions as a visible image reading unit. The imaging unit 40 receives visible light and invisible light reflected by a subject, and captures a visible image and an invisible image. More specifically, the invisible light image sensor 40b obtains an invisible image (an image in the invisible light wavelength region) by reading invisible reflected light from a subject, which is a part of invisible light. The visible light image sensor 40a obtains a visible image (an image in the visible light wavelength region) by reading visible reflected light from a subject, which is a part of visible light. The invisible light image sensor 40b and the visible light image sensor 40a are sensors for a reduced optical system, such as a CMOS image sensor.

[0027] The visible light image sensor 40a and the invisible light image sensor 40b may be integrated into one body. This allows for a smaller structure and closer reading positions for visible light and infrared light, making it possible to extract and restore lost information with high accuracy. In other words, there is no image shift caused by multiple readings, and positional correction can be performed with high accuracy.

[0028] The image processing unit 43 executes various image processes according to the intended use of the image data. The image processing unit 43 may be realized by either hardware or software.

[0029] Here, Fig. 6 is a block diagram showing the functional configuration of the image processing unit 43. As shown in Fig. 6, the image processing unit 43 includes a feature amount detection unit 431. The image processing unit 43 detects a feature amount of the subject or background portion 26 from at least one of the visible image and the invisible image obtained by the reading device main body 10, using the feature amount detection unit 431. An example of the feature amount is an edge between the background portion 26 and the document 100.

[0030] Here, differences in spectral reflection characteristics due to the medium in the imaging section 40 will be described.

[0031] Fig. 4 is a diagram showing differences in spectral reflectance characteristics due to media. Fig. 4 is a diagram showing the spectral reflectance characteristics of paper type A and paper type B, which are two types of plain paper that are generally used as documents and are targets of reading by image reading device 1, and background portion 26. In Fig. 4, the dashed-dotted line graph is a graph of the spectral reflectance characteristics of plain paper (paper type A), the dotted line graph is a graph of the spectral reflectance characteristics of plain paper (paper type B), and the solid line graph is a graph of the spectral reflectance characteristics of background portion 26.

[0032] As can be seen from FIG. 4, in the visible wavelength range, the reflectance of background portion 26, which is a white background, is higher than that of plain paper, but in the near-infrared (NIR) wavelength range, the reflectance of background portion 26 is lower than that of plain paper (paper type A and paper type B).

[0033] Here, Fig. 5 is a diagram showing an example of the difference between a visible image and an invisible image. As shown in Fig. 5, images with different feature amounts are obtained using visible light and invisible light. Therefore, if the image to be detected is set in advance as either a visible image or an invisible image depending on the type of subject and the type of background portion 26, it is easy to obtain the desired feature amount.

[0034] For example, in the example shown in Figure 5, since the invisible image of paper type A has a greater difference in spectral reflectance characteristics from the background portion 26 than the visible image, the feature detection target can be set to the invisible image, and conversely, the visible image can be set for paper type B.

[0035] Next, the definition of the reflectance of the background portion 26, which is a feature of this embodiment, will be described.

[0036] FIG. 7 is a diagram showing the definition of the reflectance of the background portion 26. A background portion with low reflectance for invisible light has been proposed in the past. However, the necessary reflectance for visible light has not been defined in the past, and there is a possibility that side effects will be caused in a normal visible image. Therefore, in this embodiment, as shown in FIG. 7, for the background portion 26, the reflectance of a specific wavelength of visible light is equal to or higher than the lower limit reflectance of visible light, and the reflectance of a specific wavelength of invisible light is equal to or lower than the upper limit reflectance of invisible light. This will be described in detail below.

[0037] Here, FIG. 8 is a diagram showing the difference due to the reflectance of the background portion 26. FIG. 8(a) shows a read image when the reflectance of the background portion 26 is high, and FIG. 8(b) shows a read image when the reflectance of the background portion 26 is low. In this embodiment, a visible light lower limit reflectance indicating the lower limit of the reflectance of visible light for a specific wavelength of visible light and an invisible light upper limit reflectance indicating the upper limit of the reflectance of invisible light for a specific wavelength of invisible light are defined. By increasing the reflectance of visible light and decreasing the reflectance of invisible light, an image as shown in FIG. 8(a) is obtained with visible light. On the other hand, with invisible light, the color difference between the original 100 and the background portion 26 becomes large, making the background stand out, and in the case of a white original with high transmittance, the image becomes dark due to the influence of the background, resulting in an image as shown in FIG. 8(b).

[0038] In the case of visible images, they are often output to users, and since normal paper is white, it is often required that the document and background appear white. For this reason, it is generally not desirable for the entire image to be dark, as in Figure 8(b). This will also affect functions such as blank page detection and automatic color selection (ACS).

[0039] Conversely, in the case of an invisible image, in order to realize a function that utilizes the difference from a visible image, it is desirable to be able to reduce the reflectance of the background as shown in FIG. 8(b).

[0040] Fig. 9 is a diagram showing an example of detecting edges of a subject, and Fig. 10 is a diagram showing an example of correcting the inclination and position of a document. For example, as shown in Fig. 9, when extracting an edge between a background portion 26 and a document 100 from an image, it is preferable to reduce the reflectance of the background portion 26 and use an invisible image. Also, as shown in Fig. 10, when correcting the inclination and position of a document and cutting out a document image, it is preferable to reduce the reflectance of the background portion 26 and use an invisible image.

[0041] Thus, according to this embodiment, in order to obtain the desired optical characteristics when extracting the feature amount of the subject or background from at least one of the visible image and the invisible image, the upper and lower limits of the background reflectance are set for a specific visible light wavelength and a specific invisible light wavelength, thereby preventing adverse effects on the image. Specifically, the visible image can be kept at a certain level of brightness as before, while the invisible image can be darkened to detect the edge between the document 100 and the background 26, thereby preventing side effects on the image processing function, etc.

[0042] (Second embodiment) Next, a second embodiment will be described.

[0043] The second embodiment differs from the first embodiment in that an upper limit of visible light reflectance is set for the background portion 26. In the following description of the second embodiment, the description of the same parts as in the first embodiment will be omitted, and only the parts different from the first embodiment will be described.

[0044] Here, Fig. 11 is a diagram showing the definition of the reflectance of background portion 26 according to the second embodiment. As shown in Fig. 11, in this embodiment, it is specified that the reflectance of a specific wavelength of visible light is equal to or higher than the minimum visible light reflectance and the reflectance of a specific wavelength of invisible light is equal to or lower than the maximum invisible light reflectance, and further, the reflectance of a specific wavelength of visible light is equal to or lower than the maximum visible light reflectance. The reason for setting the maximum visible light reflectance for background portion 26 is as follows.

[0045] If the document is fixed, such as when scanning with the flatbed method, it can be scanned by irradiating visible light and invisible light at different times. On the other hand, if the document moves, such as when scanning with the sheet-through method using the ADF20, it cannot be scanned in the same position unless it is scanned by irradiating visible light and invisible light at the same time.

[0046] Here, Fig. 12 is a diagram showing an example of visible light being mixed into invisible light image sensor 40b. When an original moves, such as when the original is read by a sheet-through method using ADF 20, some visible light components may be mixed into the invisible image, as shown in Fig. 12. When the reflectance of visible light in background portion 26 is too high, the amount of visible light components mixed in increases, and even the invisible image may become closer to the image shown in Fig. 8(a) than to the image shown in Fig. 8(b).

[0047] Therefore, in this embodiment, the amount of visible light mixed into the invisible image is reduced by setting an upper limit of the visible light reflectance of the background portion 26. This makes it possible to maintain the luminance of the invisible image low.

[0048] Thus, according to this embodiment, in order to increase reading productivity, when visible light and invisible light are turned on simultaneously to read the visible and invisible components, in the case where a certain amount of visible light is mixed into the invisible components, if the reflectance to visible light is too high, it is possible to eliminate the possibility that it becomes difficult to obtain a reading difference between the original 100 and the background portion 26 in the invisible image.

[0049] (Third embodiment) Next, a third embodiment will be described.

[0050] The third embodiment differs from the first and second embodiments in that a lower limit invisible light reflectance is provided for the background portion 26. In the following description of the third embodiment, the description of the same parts as those in the first and second embodiments will be omitted, and only the parts different from the first and second embodiments will be described.

[0051] Here, Fig. 13 is a diagram showing the definition of the reflectance of the background portion 26 according to the third embodiment. As shown in Fig. 13, in this embodiment, it is specified that the reflectance of a specific wavelength of visible light is equal to or higher than the lower limit reflectance of visible light, the reflectance of a specific wavelength of invisible light is equal to or lower than the upper limit reflectance of invisible light, and in addition to the reflectance of a specific wavelength of visible light being equal to or lower than the upper limit reflectance of visible light, the reflectance of a specific wavelength of invisible light is equal to or higher than the lower limit reflectance of invisible light. The reason for setting the lower limit reflectance of invisible light for the background portion 26 is as follows.

[0052] In a typical image reading device, the reference white board 12 is read in order to obtain reference data for the read value of the imaging unit 40 .

[0053] Fig. 14 is a diagram showing an example of automatic level control (ALC). As shown in Fig. 14, when reading with the ADF 20, in order to improve reading productivity, there are cases where the reference white board 12 is not read directly, but the background portion 26 is read to predict the read value of the reference white board 12. In this case, if the read value of the background portion 26 is too small, the resolution becomes coarse, and the error between the actual read value of the reference white board 12 and the predicted value tends to become larger accordingly.

[0054] Here, Fig. 15 is a diagram showing the difference in the read image depending on the reflectance of the background portion 26 to invisible light. Fig. 15(a) shows the read image when the reflectance of the background portion 26 is high, and Fig. 15(b) shows the read image when the reflectance of the background portion 26 is low. As shown in Fig. 15(b), when the reflectance of the background portion 26 to invisible light is too low, the original background becomes darker than Fig. 15(a), particularly for highly transparent originals, making characters difficult to recognize. For example, this becomes a problem when characters that are not visible in visible images and only react to invisible light are read as invisible images and output as the final image.

[0055] Therefore, in this embodiment, a lower limit of invisible light reflectance of the background portion 26 is set, thereby making it possible to improve image quality by suppressing reading errors and to improve the legibility of characters.

[0056] As described above, according to this embodiment, it is possible to improve image quality by suppressing reading errors, and to improve the legibility of characters.

[0057] (Fourth embodiment) Next, a fourth embodiment will be described.

[0058] The fourth embodiment differs from the first to third embodiments in that the difference between the maximum and minimum values ​​of the reflectance of multiple wavelengths of visible light in the background portion 26 is set to be equal to or less than a visible light reflectance difference upper limit that specifies the upper limit of the difference. In the following explanation of the fourth embodiment, explanations of the same parts as the first to third embodiments will be omitted, and only differences from the first to third embodiments will be explained.

[0059] Here, Fig. 16 is a diagram showing the definition of the reflectance of background portion 26 according to the fourth embodiment. As shown in Fig. 16, in this embodiment, for background portion 26, a plurality of wavelengths are selected from the visible range (wavelengths of approximately 380 to 750 nm), and the difference between the maximum and minimum values ​​of the reflectance of the plurality of wavelengths of visible light is set as the visible light reflectance difference. By setting this visible light reflectance difference between the maximum and minimum values ​​of the reflectance of the plurality of specific wavelengths of visible light to be equal to or less than the visible light reflectance difference upper limit that defines the upper limit of the difference, a background portion image with low saturation is obtained.

[0060] Here, FIG. 17 is a diagram showing the difference in the read image depending on the visible light reflectance difference of the background portion 26. FIG. 17(a) shows the read image when the visible light reflectance difference of the background portion 26 is small, and FIG. 17(b) shows the read image when the visible light reflectance difference of the background portion 26 is large. When the visible light reflectance difference of the background portion 26 is small, as shown in FIG. 17(a), the color is difficult to appear in the background portion 26. On the other hand, when the visible light reflectance difference of the background portion 26 is large, the color difference between the original 100 and the background portion 26 becomes large, so that the background stands out, and the background portion 26 appears yellowish, for example, as shown in FIG. 17(b). In addition, in the case of a white original with high transmittance, the original skin is also colored due to the influence of the background.

[0061] Therefore, in this embodiment, by setting an upper limit on the visible light reflectance difference of the background portion 26, it is possible to prevent coloring of the original and background portion and to avoid affecting the blank paper detection function, the automatic color selection (ACS) function, and the like.

[0062] In this way, according to this embodiment, side effects on the color tone of a visible image can also be prevented.

[0063] (Fifth embodiment) Next, a fifth embodiment will be described.

[0064] The fifth embodiment differs from the first to fourth embodiments in that the upper limit invisible light reflectance for the background portion 26 is specified for 850 nm and is set to 55% or less. In the following explanation of the fifth embodiment, explanations of the same parts as the first to fourth embodiments will be omitted, and only differences from the first to fourth embodiments will be explained.

[0065] Here, Fig. 18 is a diagram showing the definition of the reflectance of the background portion 26 according to the fifth embodiment. As shown in Fig. 18, in this embodiment, the upper limit invisible light reflectance of the background portion 26 is defined for 850 nm which is the representative wavelength of the near-infrared sensor, and the upper limit invisible light reflectance is set to 55% or less.

[0066] The upper limit of the invisible light reflectance is set to 55% or less because if the upper limit is exceeded, the edge between the subject and the background 26 will not be removed, and there is a high possibility that the position and inclination correction and size cut-out of the subject will not function properly.

[0067] The upper limit invisible light reflectance may be changed depending on the system, and is specified as a value that allows sufficient edge capture between a specific document 100 and the background portion 26. The specific value depends on the type of document that is specified, and the image characteristics such as S / N and MTF of the acquired image. For documents, it is advisable to specify the value based on the expected document basis weight, ream weight, and ISO opacity.

[0068] As described above, according to this embodiment, by detecting the edge between the document 100 and the background portion 26, it is possible to utilize the detection for correcting the positional inclination of the document and for cutting out the size.

[0069] (Sixth embodiment) Next, a sixth embodiment will be described.

[0070] The sixth embodiment differs from the first to fifth embodiments in that the background portion 26 is specified to have a visible light lower limit reflectance of 550 nm, and the visible light lower limit reflectance is set to 55% or more. In the following explanation of the sixth embodiment, explanations of the same parts as the first to fifth embodiments will be omitted, and only differences from the first to fifth embodiments will be explained.

[0071] Here, Fig. 19 is a diagram showing the definition of the reflectance of the background portion 26 according to the sixth embodiment. As shown in Fig. 19, in this embodiment, the visible light lower limit reflectance of the background portion 26 is defined for 550 nm, which is the representative wavelength of the sensor for the visible range G component, and the visible light lower limit reflectance is set to be 55% or more.

[0072] The reason why the lower limit of visible light reflectance is set to 55% or more is that if it is below the lower limit, image processing functions such as the blank page detection function and ACS function will not operate normally, and there is a possibility that, for example, a white document will be mistakenly detected as not being blank.

[0073] The visible light lower limit reflectance may be changed depending on the system, and is specified as the value at which image processing functions such as the blank page detection function and ACS function operate normally for a specific document. The specific value depends on the type of document specified, the S / N ratio of the acquired image, image characteristics such as MTF, and the judgment threshold of the image processing function. For documents, it is recommended to specify the basis weight, ream weight, and ISO opacity of the expected document.

[0074] As described above, according to this embodiment, it is possible to prevent contamination of the document / background of a visible image, and to prevent side effects on the blank page detection function, ACS function, and the like.

[0075] (Seventh embodiment) Next, a seventh embodiment will be described.

[0076] The seventh embodiment differs from the first to sixth embodiments in that the upper visible light reflectance limit for the background portion 26 is set at 550 nm and is set to 99% or less. In the following description of the seventh embodiment, the description of the same parts as those of the first to sixth embodiments will be omitted, and only the parts different from the first to sixth embodiments will be described.

[0077] Here, Fig. 20 is a diagram showing the definition of the reflectance of the background portion 26 according to the seventh embodiment. As shown in Fig. 20, in this embodiment, the upper limit of the visible light reflectance of the background portion 26 is defined for 550 nm, which is the representative wavelength of the sensor for the visible range G component, and the upper limit of the visible light reflectance is set to be 99% or less.

[0078] The upper limit of visible light reflectance is set to 99% or more because, if the upper limit is exceeded, when sensing is performed by simultaneously irradiating visible light and invisible light, the edge between the subject and background 26 cannot be obtained, and correction of the position and inclination of the subject and size cut-out may not function properly.

[0079] The visible light upper limit reflectance may be changed depending on the system, and is specified as a value that allows sufficient capture of the edge between a specific document 100 and the background portion 26 even when sensing is performed by simultaneously irradiating visible light and invisible light. The specific value depends on the type of document to be specified, the amount of visible light mixed into the invisible light image sensor 40b, and the image characteristics such as the S / N and MTF of the acquired image. For documents, it is advisable to specify the document based on the expected basis weight, ream weight, and ISO opacity.

[0080] As described above, according to this embodiment, by detecting the edge between the document 100 and the background portion 26, it is possible to utilize the detection for correcting the positional inclination of the document and for cutting out the size.

[0081] (Eighth embodiment) Next, an eighth embodiment will be described.

[0082] The eighth embodiment differs from the first to seventh embodiments in that the background portion 26 has a lower limit invisible light reflectance of 850 nm set to 1% or more. In the following description of the eighth embodiment, the description of the same parts as the first to seventh embodiments will be omitted, and only the parts different from the first to seventh embodiments will be described.

[0083] Here, Fig. 21 is a diagram showing the definition of the reflectance of the background portion 26 according to the eighth embodiment. As shown in Fig. 21, in this embodiment, the lower limit invisible light reflectance of the background portion 26 is defined for 850 nm which is the representative wavelength of the near-infrared sensor, and the lower limit invisible light reflectance is set to be 1% or more.

[0084] The lower limit of the invisible light reflectance is set to 1% or more because if it is below the lower limit, the reading estimation error of the reference white board 12 in the ADF 20 will be large, which may result in abnormal brightness of the output image or make it impossible to read characters in the invisible image of the document.

[0085] The invisible light lower limit reflectance may be changed depending on the system, and is specified as a value at which the estimated reading error of the reference white board 12 is sufficiently small and the characters in the invisible image of the document can be sufficiently identified. The specific value depends on the allowable value of the estimated reading error of the reference white board 12 and the type of document (characters) to be specified. For the document, it is recommended to specify it based on the expected document basis weight, ream weight, ISO opacity, and character font and size.

[0086] In this way, according to this embodiment, it is possible to prevent side effects on ALC (Automatic Level Control). Also, according to this embodiment, when an invisible image is output, it becomes possible to distinguish between the background and the text, and it is possible to prevent an effect on a function that uses the distinction between the background and the text.

[0087] Ninth embodiment Next, a ninth embodiment will be described.

[0088] The ninth embodiment differs from the first to eighth embodiments in that the upper limit of the visible light reflectance difference is specified for 450 / 550 / 600 nm for the background portion 26, and the upper limit of the visible light reflectance difference is set to 44% or less. In the following explanation of the ninth embodiment, explanations of the same parts as the first to eighth embodiments will be omitted, and only differences from the first to eighth embodiments will be explained.

[0089] Here, Fig. 22 is a diagram showing the definition of the reflectance of the background portion 26 according to the ninth embodiment. As shown in Fig. 22, in this embodiment, the upper limit of the visible light reflectance difference of the background portion 26 is defined for 450 / 550 / 600 nm, which are the representative wavelengths of the sensor for the visible range RGB components, and the upper limit of the visible light reflectance difference is set to 44% or less. This range is determined from the difference between the above-mentioned upper limit of the visible light reflectance (99% or less) and the lower limit of the visible light reflectance (55% or more).

[0090] The upper limit of the visible light reflectance difference is set to 44% or less because, if the upper limit is exceeded, image processing functions such as the blank page detection function and the ACS function will not operate normally, and there is a possibility that, for example, a black and white document image will be mistakenly detected as a color image.

[0091] The upper limit of the visible light reflectance difference may be changed depending on the system, and is specified as the value at which image processing functions such as the blank page detection function and ACS function operate normally for a specific document. The specific value depends on the type of document specified, the image characteristics such as the S / N and MTF of the acquired image, and the judgment threshold of the image processing function. For documents, it is recommended to specify the document based on the expected basis weight, ream weight, and ISO opacity.

[0092] As described above, according to this embodiment, it is possible to prevent contamination of the document / background of a visible image, and to prevent side effects on the blank page detection function, ACS function, and the like.

[0093] In the above embodiment, an example is given in which the image reading device of the present invention is applied to a multifunction device having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function. However, the image reading device can be applied to any image reading device provided in a copier, printer, scanner device, facsimile device, etc.

[0094] In the above-mentioned embodiments, the image reading device 1 is applied as the image reading device, but the present invention is not limited to this. The definition of an image reading device is that it is sufficient if it is a device that can obtain a reading level, such as a line sensor of a life-size optical system (contact optical system: CIS method) shown in Fig. 23(a), even if it does not read an image. The device shown in Fig. 23(a) reads information of multiple lines by moving the line sensor or the original.

[0095] Furthermore, the image reading device can also be applied to a bill transport device shown in FIG. 23(b) and a white line detection device for an automated guided vehicle (AGV) shown in FIG. 23(c).

[0096] The object of the paper money transport device shown in Fig. 23(b) is a paper money. The feature amount detected by the paper money transport device is used for correction processing of the image itself. That is, the paper money transport device shown in Fig. 23(b) recognizes the inclination of the paper money by edge detection, and performs skew correction using the recognized inclination.

[0097] The subject of the white line detection device for an automated guided vehicle shown in FIG. 23(c) is a white line. The feature value output by the white line detection device for an automated guided vehicle can be used to determine the moving direction of the automated guided vehicle. That is, the white line detection device for an automated guided vehicle recognizes the inclination of the white line area by edge detection, and determines the moving direction of the automated guided vehicle using the recognized inclination. In addition, the white line detection device for an automated guided vehicle can also perform a post-processing correction of the moving direction according to the position and orientation of the automated guided vehicle. For example, in the case of an automated guided vehicle, it is also possible to perform a process such as stopping the drive when a thickness different from a known thickness of a white line is detected.

[0098] Although several embodiments and modifications of the present invention have been described above, these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. Each of these embodiments and modifications is included in the scope and gist of the invention, and is included in the scope of the invention and its equivalents described in the claims.

[0099] For example, aspects of the present invention are as follows. <1> an illumination unit that irradiates a subject with visible light and invisible light; an imaging unit that receives visible light and invisible light reflected by the subject and captures a visible image and an invisible image; A background portion provided in an imaging range of the imaging portion; an image processing unit that detects a feature amount of the subject or the background from at least one of the visible image and the invisible image; Equipped with the background portion has a reflectance of a specific wavelength of visible light equal to or higher than a lower limit visible light reflectance that defines a lower limit of the reflectance of visible light, and has a reflectance of a specific wavelength of invisible light equal to or lower than an upper limit invisible light reflectance that defines an upper limit of the reflectance of invisible light; 1. An image reading apparatus comprising: <2> the background portion has a reflectance of a specific wavelength of visible light equal to or lower than an upper limit reflectance of visible light that defines an upper limit of the reflectance of visible light; Characterized by <1> 2. The image reading apparatus according to claim 1 . <3> The background portion has a reflectance of a specific wavelength of invisible light equal to or higher than a lower limit invisible light reflectance that defines a lower limit of the reflectance of invisible light. Characterized by <1> or <2> 2. The image reading apparatus according to claim 1 . <4> the background portion sets a difference between a maximum value and a minimum value of reflectance of a plurality of specific wavelengths of visible light to a visible light reflectance difference upper limit that specifies an upper limit of the difference; Characterized by <1> Or <3> 13. The image reading device according to claim 12, <5> The illumination unit irradiates infrared light as the invisible light, The imaging unit captures an infrared image as the invisible image. Characterized by <1> Or <4> 13. The image reading device according to claim 12, <6> the image processing unit detects an edge between the subject and the background as a feature amount of at least one of the visible image and the invisible image; The background portion has an upper limit invisible light reflectance of 55% or less when the specific wavelength is 850 nm. Characterized by <1> Or <5> 13. The image reading device according to claim 12, <7> the image processing unit detects a luminance of the subject as a feature amount of the visible image; The background portion has a visible light lower limit reflectance of 55% or more when the specific wavelength is 550 nm. Characterized by <1> Or <6> 13. The image reading device according to claim 12, <8> the image processing unit detects an edge between the subject and the background as a feature amount of at least one of the visible image and the invisible image; The background portion has an upper limit visible light reflectance of 99% or less when the specific wavelength is 550 nm. Characterized by <2> Or <7> 13. The image reading device according to claim 12, <9> the image processing unit detects a luminance of the background portion as a feature amount of the invisible image, The background portion has a lower limit invisible light reflectance of 1% or more when the specific wavelength is 850 nm. Characterized by <3> 2. The image reading apparatus according to claim 1 . <10> the image processing unit detects a saturation of the subject as a feature amount of the visible image; The background portion has a visible light reflectance difference upper limit of 44% or less when the specific wavelengths are 450, 550, and 600 nm. Characterized by <4> 2. The image reading apparatus according to claim 1 . <11> an illumination unit that irradiates a subject with visible light and invisible light; an imaging unit that receives visible light and invisible light reflected by the subject and captures a visible image and an invisible image; A background portion provided in an imaging range of the imaging portion; an image processing unit that detects a feature amount of the subject or the background from at least one of the visible image and the invisible image; An image reading method for an image reading device comprising: the background portion has a reflectance of a specific wavelength of visible light equal to or higher than a lower limit visible light reflectance that defines a lower limit of the reflectance of visible light, and has a reflectance of a specific wavelength of invisible light equal to or lower than an upper limit invisible light reflectance that defines an upper limit of the reflectance of invisible light; 13. An image reading method comprising: [Explanation of symbols]

[0100] 1 Image reader 13 Lighting Department 40 Imaging unit 26 Background section 43 Image Processing Section [Prior art documents] [Patent documents]

[0101] [Patent Document 1] Patent Publication No. 2022-059526

Claims

1. an illumination unit that irradiates a subject with visible light and invisible light; an imaging unit that receives visible light and invisible light reflected by the subject and captures a visible image and an invisible image; a background portion provided in an imaging range of the imaging portion; an image processing unit that detects a feature amount of the subject or the background from at least one of the visible image and the invisible image; Equipped with the background portion has a reflectance of a specific wavelength of visible light that is equal to or greater than a lower limit visible light reflectance that defines a lower limit of the reflectance of visible light, and a reflectance of a specific wavelength of invisible light that is equal to or less than an upper limit invisible light reflectance that defines an upper limit of the reflectance of invisible light; An image reading device characterized by:

2. the background portion has a reflectance of a specific wavelength of visible light equal to or less than an upper limit of visible light reflectance that defines an upper limit of the reflectance of visible light; 2. The image reading device according to claim 1, wherein:

3. the background portion has a reflectance of a specific wavelength of invisible light that is equal to or higher than a lower limit reflectance of invisible light that defines a lower limit of the reflectance of invisible light; 3. The image reading device according to claim 2, wherein:

4. the background portion sets a difference between a maximum value and a minimum value of reflectance of a plurality of specific wavelengths of visible light to be equal to or less than an upper limit of visible light reflectance difference that defines an upper limit of the difference; 4. The image reading device according to claim 3, wherein:

5. the illumination unit irradiates infrared light as the invisible light, The imaging unit captures an infrared image as the invisible image.

2. The image reading device according to claim 1, wherein:

6. the image processing unit detects an edge between the subject and the background as a feature amount of at least one of the visible image and the invisible image; the background portion has an upper limit invisible light reflectance of 55% or less when the specific wavelength is 850 nm; 2. The image reading device according to claim 1, wherein:

7. the image processing unit detects the luminance of the subject as a feature amount of the visible image; the background portion has a visible light lower limit reflectance of 55% or more when the specific wavelength is 550 nm; 2. The image reading device according to claim 1, wherein:

8. the image processing unit detects an edge between the subject and the background as a feature amount of at least one of the visible image and the invisible image; the background portion has an upper limit of visible light reflectance of 99% or less when the specific wavelength is 550 nm; 3. The image reading device according to claim 2, wherein:

9. the image processing unit detects the luminance of the background portion as a feature amount of the invisible image; the background portion has a lower limit invisible light reflectance of 1% or more when the specific wavelength is 850 nm; 4. The image reading device according to claim 3, wherein:

10. the image processing unit detects saturation of the subject as a feature amount of the visible image; the background portion has a visible light reflectance difference upper limit of 44% when the specific wavelengths are 450, 550, and 600 nm; 5. The image reading device according to claim 4, wherein:

11. an illumination unit that irradiates a subject with visible light and invisible light; an imaging unit that receives visible light and invisible light reflected by the subject and captures a visible image and an invisible image; a background portion provided in an imaging range of the imaging portion; an image processing unit that detects a feature amount of the subject or the background from at least one of the visible image and the invisible image; An image reading method for an image reading device comprising: the background portion has a reflectance of a specific wavelength of visible light that is equal to or greater than a lower limit visible light reflectance that defines a lower limit of the reflectance of visible light, and a reflectance of a specific wavelength of invisible light that is equal to or less than an upper limit invisible light reflectance that defines an upper limit of the reflectance of invisible light; An image reading method comprising:

Images