Control device, control method, and program

Abstract

To provide processing for obtaining reflection characteristics of an object when the shape thereof changes.SOLUTION: A control device provided herein is configured to acquire image data obtained by photographing an object placed on conveyance means with a curvature that changes along a conveyance direction of the object, and derives reflection characteristics of the object on the basis of the acquired image data.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a technique for acquiring reflectance characteristics of a target object. [Background technology]

[0002] Conventionally, measurement data of reflection characteristics according to the lighting direction and observation direction has been used to quantitatively evaluate the texture of an object's material. Recent electrophotographic printers have been able to provide high-added-value printed matter in which the color appearance changes depending on the observation angle by using metallic toner and metallic media. Patent Document 1 discloses that the results of color measurement from multiple directions are used to display an image printed using silver toner on a display device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-50488 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, because Patent Document 1 is based on the premise of color matching of a printed matter placed on a flat surface, it has the problem that it cannot accurately measure how the appearance of colors changes when the shape of the printed matter changes.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a process for acquiring the reflection characteristics of an object when the shape of the object changes. [Means for solving the problem]

[0006] In order to solve the above problem, the control device of the present invention is characterized in having an acquisition means for acquiring image data obtained by imaging an object placed on a conveying means whose curvature changes along the conveying direction of the object, and a derivation means for deriving the reflection characteristics of the object based on the image data. Effect of the Invention

[0007] According to the present invention, it is possible to obtain the reflection characteristics of an object when the shape of the object changes. [Brief description of the drawings]

[0008] [Figure 1] Schematic diagram for explaining the reflection characteristics of printed matter [Diagram 2] FIG. 1 is a schematic diagram showing a configuration example of a reflection characteristic acquisition system. [Diagram 3] A block diagram showing an example of the functional configuration of a control device. [Figure 4] Flowchart showing the process in a measurement application [Diagram 5] Flowchart showing a process for acquiring image data [Figure 6] Schematic diagram to explain the measurement principle [Figure 7] 1 is a flowchart showing a process for deriving reflection characteristics. [Figure 8] Schematic diagram for explaining the reflection characteristics of printed matter [Figure 9] FIG. 1 is a schematic diagram for explaining a surface shape of a conveying device; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Each embodiment will be described below with reference to the drawings. Note that the following embodiments do not necessarily limit the present invention. Furthermore, not all of the combinations of features described in each embodiment are necessarily essential to the solution of the present invention.

[0010] [First embodiment] FIG. 1 is a schematic diagram for explaining the reflection characteristics of a printed matter. The horizontal axis indicates the observation angle, and the vertical axis indicates the amount of reflected light. Light incident on a certain printed matter is reflected with a spread in the direction of specular reflection. The spread in the vicinity of the specular reflection changes according to the surface shape of the printed matter. The surface shape of the printed matter changes according to the curvature of the printed matter. When a printed matter is wrapped around a cylindrical shape and displayed, the surface shape of the printed matter changes, and the reflection characteristics of the printed matter also change. Reflection characteristics 101 are an example of the reflection characteristics of a flat printed matter. Reflection characteristics 102 are an example of the reflection characteristics of a printed matter when the same printed matter is folded to change the curvature. It can be seen that reflection characteristics 102 have a larger spread in the vicinity of the specular reflection direction than reflection characteristics 101. In this embodiment, the reflection characteristics of a printed matter are derived based on image data obtained by imaging a printed matter placed on a conveying device whose curvature changes along the conveying direction of the printed matter. This makes it possible to obtain the reflection characteristics of a printed matter when the shape of the printed matter changes.

[0011] 2 is a schematic diagram showing an example of the configuration of a reflection characteristic acquisition system according to this embodiment. An object 201 is an object whose reflection characteristics are to be measured. In this embodiment, the object 201 is a printed matter, but it may be an object other than a printed matter. It is assumed that the reflection characteristics of the object 201 placed on a flat surface are uniform regardless of position. A conveying device 202 is a device for conveying the object 201. The curvature of the conveying device 202 changes along the conveying direction of the object 201. The shape of the object 201 changes along the shape of the conveying device 202 that conveys the object 201.

[0012] The illumination device 203 is a device for irradiating the object 201 with light. The optical system of the illumination device 203 is a non-telecentric optical system. For example, an LED (Light Emitting Diode) can be used as a light source used in the illumination device 203. An LED generally has directional characteristics in which the luminance varies depending on the direction. The imaging device 204 is a device for imaging the object 201 illuminated with light by the illumination device 203. For example, a color camera having a line sensor capable of capturing a one-dimensional image along the conveying direction and capable of acquiring an image in which a signal value linear to the luminance on the object 201 is expressed by a pixel value of 16 bits can be used as the imaging device 204. The sensor of the imaging device 204 is not limited to a line sensor. Furthermore, the imaging device 204 is not limited to a color camera. A monochrome camera, a spectroscopic camera, a multiband camera, or the like may be used as the imaging device 204. The number of bits of the pixel value does not have to be 16 bits. A lens is attached to the imaging device 204, and the optical system of the imaging device 204 is a non-telecentric optical system.

[0013] The control device 205 is a device that controls the transport device 202, the lighting device 203, and the imaging device 204, and performs a series of controls to acquire an image of the object 201. The control device 205 also functions as an image processing device that derives the reflection characteristics of the object 201 based on image data obtained by controlling each device. The control device 205 in this embodiment is a PC (Personal Computer) equipped with a main storage device such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and an auxiliary storage device such as a HDD (Hard Disk Drive) or a flash memory. The transport device 202, the lighting device 203, and the imaging device 204 are each connected to the control device 205 via an interface such as a USB (Universal Serial Bus). The control device 205 is not limited to a PC, and may be a microcomputer or the like incorporated as a part of an image processing device. The function of the image processing device may be provided by a separate device.

[0014] FIG. 3 is a block diagram showing an example of the functional configuration of the control device 205. The input device 301 is a device that accepts operations from a user, and is, for example, a device such as a keyboard or a mouse. The display device 302 is a device that displays the contents input by the user, the imaging conditions, and the imaging results, and is, for example, a device such as a liquid crystal monitor. The control device 205 has an imaging driver 303, an illumination driver 304, a transport driver 305, an input driver 306, a display driver 307, an image acquisition control unit 308, a reflection characteristic derivation unit 309, and a UI management unit 310. The imaging driver 303 is a group of instructions for controlling the imaging device 204, and includes an instruction to be transmitted from the control device 205 to the imaging device 204. The illumination driver 304 is a group of instructions for controlling the illumination device 203, and includes an instruction to turn on and off the light source. The transport driver 305 is a group of instructions for controlling the transport device 202, and includes an instruction to transport the object 201 to a predetermined position. The input driver 306 is a group of instructions for controlling the input device 301. The display driver 307 is a group of commands for controlling the display device 302. The image acquisition control unit 308 is a group of commands for sending commands to the imaging driver 303 and the illumination driver 304 and performing a series of processes for acquiring captured image data. The reflection characteristic derivation unit 309 is a group of commands for deriving the reflection characteristics of the object 201 based on the image data acquired by the image acquisition control unit 308. The UI management unit 310 is a group of commands for a user interface (UI) function for managing information input by a user to the input device 301 and displaying measurement results on the display device 302. The measurement application 311 is a group of commands for linking the commands 303 to 307 and functioning as one measurement application.

[0015] Fig. 4 is a flowchart showing the processing in the measurement application 311. The processing shown in the flowchart in Fig. 4 starts when the user inputs an instruction via the input device 301 and the CPU accepts the input instruction. Hereinafter, each step (process) is represented by adding an S before the reference numeral. In S401, the image acquisition control unit 308 executes a series of processes for acquiring captured image data of the object 201. The process for acquiring the image data will be described in detail later. In S402, the reflection characteristic derivation unit 309 generates reflection characteristic data representing the reflection characteristic of the object 201 based on the captured image data. The process for deriving the reflection characteristic will be described in detail later.

[0016] FIG. 5 is a flowchart showing the process of acquiring image data in S401. In S501, the image acquisition control unit 308 operates the conveying device 202 using the conveying driver 305, and conveys the object 201 to the measurement area and stops it. In S502, the image acquisition control unit 308 uses the illumination driver 304 to turn on the light source of the illumination device 203. In S503, the image acquisition control unit 308 uses the imaging driver 303 to capture the object 201. In S504, the image acquisition control unit 308 uses the illumination driver 304 to turn off the light source of the illumination device 203. In S506, the image acquisition control unit 308 operates the conveying device 202 using the conveying driver 305, and conveys the object 201 and outputs it to the outside of the system. In this embodiment, the captured image data of the object 201 is acquired by the above process.

[0017] FIG. 6 is a schematic diagram for explaining the measurement principle. FIG. 6(a) is a schematic diagram showing the behavior of light at a position 601 of an object 201. An incident direction 602 is the direction in which light is incident on the position 601. A tangent 603 is a tangent at the position 601. A normal direction 604 is a normal direction perpendicular to the tangent 603. An imaging direction 605 is a direction from the position 601 toward the imaging device 204. An angle 606 is an angle between the incident direction 602 and the normal direction 604. An angle 607 between the normal direction 604 and the specular reflection direction 608 is equal to the angle 606. The specular reflection direction 608 is a direction in the same plane as the incident direction 602 and the normal direction 604. An angle 609 is an angle between the specular reflection direction 608 and the imaging direction 605. In order to derive the reflection characteristics of the object 201, it is necessary to obtain information on the reflected light while changing the angle 609. The angle 609 is determined according to the incident direction 602, the normal direction 604, and the imaging direction 605.

[0018] Next, how the incident direction 602, normal direction 604, and imaging direction 605 change depending on the position of the object 201 will be described. FIG. 6(b) is a schematic diagram for explaining the incident direction 610 of light at each position of the object 201. For ease of explanation, six positions on the object 201 will be described, but the number of actual positions is the same as the number of pixels of the imaging device 204. Since the optical system of the light source of the illumination device 203 is non-telecentric, the incident direction 610 of light differs for each position on the object 201. FIG. 6(c) is a schematic diagram for explaining the imaging direction 611 at each position of the object 201. Since the optical system of the lens of the imaging device 204 is non-telecentric, the imaging direction 611 differs for each position on the object 201. FIG. 6(d) is a schematic diagram for explaining the normal direction 612 at each position of the object 201. Since the curvature of the conveying device 202 changes along the conveying direction, the normal direction 612 differs for each position on the object 201.

[0019] Therefore, by using the reflection characteristic acquisition system of this embodiment, it is possible to derive the reflection characteristic while changing the curvature of the object 201. In this embodiment, the optical system of the illumination device 203 is described as being non-telecentric, but it may be telecentric. When the optical system of the illumination device 203 is telecentric, the incident direction of light to the object 201 is constant regardless of the position on the object 201, and the angle 609 is determined according to the normal direction 604 and the imaging direction 605. This makes it possible to derive the reflection characteristic with reduced error in the incident direction of light. The optical system of the lens of the imaging device 204 is described as being non-telecentric, but it may be telecentric like the illumination device 203. When the optical system of the lens of the imaging device 204 is telecentric, the incident direction of light to the object 201 is constant regardless of the position on the object 201, and the angle 609 is determined according to the incident direction 602 and the normal direction 604. This makes it possible to derive the reflection characteristic with reduced error in the imaging direction.

[0020] 7 is a flowchart showing the process of deriving the reflection characteristic in S402. In S701, the reflection characteristic derivation unit 309 reads pixel values ​​J(u) of the captured image of the object 201, and derives reflectance information R(u) as the reflection characteristic for each position of the object 201 according to equation (1). Note that I(u) is the pixel value of the captured image of the perfect diffuse reflection surface.

[0021]

number

[0022] Here, u is an index that specifies a pixel position in an image. If the number of pixels of the imaging device 204 is, for example, 1000, u takes an integer value between 1 and 1000. It can also be said that u represents a position on the object 201. As described above, the geometric conditions such as the incident direction and the imaging direction are different for each position on the object 201. As the perfect diffuse reflecting surface, a medium with high diffusion properties may be used, or a smooth medium such as PET with a highly diffusive paint applied to its surface may be used. The captured image of the perfect diffuse reflecting surface is acquired in advance by performing imaging similar to that of the object 201. Since the captured image of the object 201 and the captured image of the perfect diffuse reflecting surface are captured under the same geometric conditions, the illuminance unevenness of the lighting device 203 and the luminance unevenness of the imaging device 204 can be corrected well.

[0023] In S702, the reflection characteristic derivation unit 309 acquires a normal direction vector N(u) and a curvature C(u) for each position on the object 201. The values ​​of the normal direction vector N(u) and the curvature C(u) are determined in advance for the transport device 202 and stored in a storage device, and are acquired by reading the values. In S703, the reflection characteristic derivation unit 309 acquires an incident direction vector L(u) and an imaging direction vector O(u) for each position on the object 201. The values ​​of the incident direction vector L(u) and the imaging direction vector O(u) are determined in advance for the lighting device 203 and the imaging device 204 and stored in a storage device, and are acquired by reading the values.

[0024] In S704, the reflection characteristic derivation unit 309 derives the incidence angle (θ) for each position of the object 201 based on the normal direction vector N(u), the incidence direction vector L(u), and the imaging direction vector O(u). i (u),φ i (u)) and reflection angle (θ j (u),φ j The reflection characteristic deriving unit 309 also derives the incident angle (θ i (u),φ i (u)) and reflection angle (θ j (u),φ jThe reflectance information R(u) derived in S701 is calculated based on the curvature C(u) obtained in S702, and the curvature C(u) obtained in S703. The calculated reflectance information R(u) .... The calculated reflectance information R(u) is calculated based on the curvature C(u) obtained in S702, and the calculated reflectance information R(u) is calculated based on the curvature C(u) obtained in S703. The calculated reflectance information R(u) is calculated based on the curvature C(u) obtained in S702. The calculated reflectance information R(u) is calculated based on the curvature C(u) obtained in S702. The calculated reflectance information R(u) is calculated based on the curvature C(u) i (u),φ i (u),θ j (u),φ j (u),C(u)).

[0025] In S705, the reflection characteristic derivation unit 309 reads the reflection characteristic information collected in S704, and derives reflection characteristic parameters for each curvature by performing function approximation by a nonlinear least squares method using a reflection characteristic model. The reflection characteristic model used in this embodiment is an improved version of a known reflection characteristic model, and is a reflection characteristic model that takes into account changes in reflection characteristics according to curvature. The known reflection characteristic model is improved so that the spread near the specular reflection direction changes according to the curvature. For example, when a known Torrance-Sparrow model is used, it is the normal distribution term that controls the spread near the specular reflection. The normal distribution term is given by, for example, Equation (2).

[0026]

number

[0027] Here, α is the angle 609, and n is a parameter representing the surface roughness. Therefore, it is sufficient to add an improvement so that the parameter n representing the surface roughness changes according to the curvature C. For example, n=aC+b, where a and b are constants. By comparing the reflection characteristics obtained from the reflection characteristics model improved in this way with the reflection characteristics information generated in S704 and deriving the parameters that minimize the error, it is possible to obtain the reflection characteristic parameters for each curvature.

[0028] In S706, the UI management unit 310 causes the reflection characteristic parameters for each curvature derived by the reflection characteristic derivation unit 309 to be displayed on the display device 302. As a display method, the reflection characteristic parameters may be displayed as numerical values ​​or in a graph format.

[0029] [Other embodiments] In the above-described embodiment, reflection characteristics that differ for each curvature of a printed material are obtained by deriving reflection characteristics based on captured images of the printed material placed on the transport device 202, whose curvature changes along the transport direction of the printed material. In this embodiment, a more suitable surface shape of the transport device 202 will be described.

[0030] Fig. 8 is a schematic diagram for explaining the reflection characteristics of a printed material. The horizontal axis indicates the observation angle, and the vertical axis indicates the amount of reflected light. As described above, light incident on a printed material is reflected with a spread in the specular reflection direction. Under angle condition 801 close to the specular reflection direction, the change in the amount of reflected light is large, and under angle condition 802 far from the specular reflection direction, the change in the amount of reflected light is small. In order to efficiently measure the reflection characteristics of a printed material, it is necessary to perform detailed measurements at angles where the change in the amount of reflected light is large.

[0031] 9 is a schematic diagram for explaining a preferred surface shape of the transport device 202. Normal direction 901 is the normal direction in the region with small curvature, and in the region with small curvature, the change in curvature is made small. Normal direction 902 is the normal direction in the region with large curvature, and in the region with large curvature, the change in curvature is made large. In other words, the surface shape of the transport device 202 is a surface shape in which the change in curvature increases as the curvature increases. This allows detailed measurements to be performed under angle conditions 801 near the specular reflection direction, so that detailed information can be obtained at angles where the change in the amount of reflected light is large.

[0032] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions. [Explanation of symbols]

[0033] 205 Control device 308 Image acquisition control unit 309 Reflection characteristic derivation part

Claims

1. an acquisition means for acquiring image data obtained by capturing an image of an object placed on a conveying means having a curvature that changes along a conveying direction of the object; a derivation means for deriving a reflection characteristic of the object based on the image data; A control device comprising:

2. 2. The control device according to claim 1, wherein the conveying means has a larger change in the curvature as the curvature increases.

3. 2. The control device according to claim 1, wherein an optical system of an illumination means for irradiating the object with light is non-telecentric.

4. 2. The control device according to claim 1, wherein an optical system of the imaging means for imaging the object is non-telecentric.

5. 2. The control device according to claim 1, wherein the deriving means derives the reflection characteristics of the object by using a reflection characteristics model corresponding to the curvature.

6. A program for causing a computer to function as the control device according to any one of claims 1 to 5.

7. Acquiring image data obtained by imaging an object placed on a conveying means having a curvature that changes along a conveying direction of the object; deriving reflectance properties of the object based on the image data; A control method comprising:

8. A conveying means having a curvature that changes along the conveying direction of the object an illumination means for irradiating light onto the object placed on the conveying means; an imaging means for imaging an object illuminated with the light; A derivation means for deriving a reflection characteristic of the object based on image data obtained by capturing an image of the object; A system comprising:

Images