Image processing method based on surface structural color and display / hidden state conversion method thereof

Abstract

The invention belongs to the technical field of flexible micro-nano optical element processing and information display / hiding, and discloses a surface structure color-based image processing method and a display / hiding state transition method thereof, and the method comprises the following steps: 1, predicting the pixel hue information of a displayed color picture through numerical calculation, calculating the wavelength value corresponding to a pixel, and calculating the pixel hue information according to the wavelength value; cutting process parameters corresponding to cutting pixels on the surface of the metal mold are determined according to the flexible material stretching rate and the grating parameters; 2, an elliptical vibration cutting process is adopted, a designed grating structure is machined on the surface of the metal mold to serve as a mother set, and a metal surface micro / nano structure is reprinted through a flexible material monomer polymerization curing process; and step 3, adjusting and controlling the wavelength of the structured light by stretching the flexible optical element and changing the spacing of the gratings, realizing the change of the structured light from a visible range to an invisible / invisible visible range, and realizing the display / hidden state conversion of an image. According to the method provided by the embodiment of the invention, the display / hidden state conversion of the color image on the surface of the flexible optical element is successfully realized.

Description

Technical Field

[0001] The present application belongs to the field of flexible micro-nano optical element processing and information display / hidden technology, and in particular, relates to an image processing and display / hidden state transition method based on surface structural color. Background Art

[0002] Among the many performance indicators of metal materials, the ultimate deformation and Young's modulus are two important parameters. The ultimate deformation refers to the maximum deformation that a material can undergo under the action of an external force, while the Young's modulus reflects the elastic properties of the material when it is subjected to force. Generally speaking, the ultimate deformation of metal materials is small, not exceeding 15% at most. This is because the bonding force between metal atoms is strong, and the arrangement structure between atoms is not easy to change under the action of external force. Therefore, when metal materials are subjected to external force, their ultimate deformation is relatively small. This characteristic makes metal materials have high stability when subjected to force and are not easily stretched. On the other hand, the Young's modulus shows a large value in metal materials, which reflects the amount of strain of the material when it is subjected to force. The Young's modulus of metal materials is large, which means that when subjected to external force, metal materials can produce a small amount of strain and are difficult to deform. Therefore, it is difficult to achieve a change in the surface structure period based on material deformation on the metal surface, and further change the wavelength and pattern of the structured light.

[0003] Therefore, this conversion process can be achieved by using flexible materials based on macromolecules. However, the surface processing and coloring of flexible materials still faces many challenges, mainly due to their high elasticity, easy deformation and low surface energy. During the processing, the material is easily deformed by external forces, which affects the processing accuracy of the micro-nano structure; at the same time, inks and coatings are difficult to adhere firmly to flexible materials with low surface energy, resulting in uneven coloring, weak adhesion, and difficulty in changing color with stretching deformation. In addition, flexible materials are sensitive to heat, which limits the application of high-temperature processing technology. Special processes and technologies are developed for the surface processing and coloring of flexible materials and the use of their easy stretching and deformation characteristics to achieve variable, high-quality, and durable image display / hiding effects. Summary of the invention

[0004] In order to solve the above problems, the purpose of this application is to propose an image processing method based on surface structural color and its visible / invisible state transformation method. The geometric parameters of the surface structure are accurately calculated using simulation software to achieve fine processing of the image. During the processing, flexible materials are used to replicate micro / nano structures. The grating spacing is changed by stretching the flexible optical element, and then the wavelength of the structured light is regulated to achieve the change of the visible / invisible state of the image. Through this technology, the tensile deformation of the flexible material can be accurately controlled, and the dynamic regulation of the visible / invisible state of the image can be achieved without changing the color of the material itself. It provides a new method for the processing of color-changing micro-nanostructure optical elements and image visibility / invisibility, which has important scientific research significance and application value for promoting the development of advanced optical manufacturing technology, broadening the application scope of structural color images, and deepening the understanding of the mechanism of material morphology change.

[0005] To achieve the above object, the technical solution adopted by the present invention is: The image processing method based on surface structural color and the visible / hidden state transformation method thereof include the following steps: Step 1: Use numerical calculation to predict the pixel tone information of the color image, calculate the wavelength value corresponding to the pixel, and determine the cutting process parameters corresponding to the pixel on the surface of the metal mold according to the elongation rate of the flexible material and the grating parameters; Step 2: Using an elliptical vibration cutting process, a designed grating structure is processed on the surface of a metal mold as a master, and a flexible material monomer polymerization and curing process is used to reprint the micro / nano structure on the metal surface; Step 3: By stretching the flexible optical element and changing the grating spacing, the wavelength of the structured light can be adjusted to achieve the change of the structured light from visible to invisible / invisible to visible range, thereby realizing the conversion of the image's visible / hidden state.

[0006] Preferably, in step 1, according to the image analysis module and the wavelength calculation module in the numerical calculation process, the method for calculating the wavelength of the structured light of each pixel of the image to be displayed includes: Step 111: Decompose the input color image into pixel levels through the image analysis module, extract the hue information of each pixel, and convert it into corresponding numerical data; Step 112: using a wavelength calculation module, according to the numerical data and in combination with preset optical parameters, calculate the wavelength value corresponding to each pixel point;

[0007] in, is the hue value of the image, is the wavelength value corresponding to the hue.

[0008] Step 113, output and store the calculated structured light wavelength value of each pixel, so that these data can be used in subsequent steps to accurately process the grating structure, and the structured light wavelength required for each pixel of the image to be displayed can be accurately determined, providing reliable data support for subsequent flexible material processing and image display / hiding control.

[0009] Preferably, in step 1, the method for verifying whether the image can successfully achieve visible / hidden conversion before and after stretching includes: Step 121: To ensure that the image can be correctly displayed after stretching, first determine the parameters for forming a grating on the cutting surface: ; In the formula, is the grating spacing, is an integer of the diffraction order, and are the incident light angle and The angle of the diffracted beam is is the wavelength of the diffracted light; Step 122: To ensure that the image can be correctly displayed after stretching, after the spacing is determined, the cutting speed required for each pixel can also be given, that is: ; In the formula, is the tool cutting rate, is the tool vibration frequency; Step 123, to ensure that the image can be correctly displayed after stretching, the formed grating structure is determined by simulating the cutting process; after the cutting speed is determined, the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory; Among them, the elliptical vibration trajectory is: ; In the formula, , are the displacement of the cutting tool relative to the metal mold in the X and Z directions as time t changes, , are the amplitudes of the elliptical vibration in the X and Z directions, is the phase difference of vibration displacement in X and Z directions; Step 124: To ensure that the image can be correctly displayed after stretching, the diffraction spectrum is determined through the surface grating structure, and the variation curve of the diffraction light intensity of each pixel with the wavelength can be analyzed; Step 125: To ensure that the image can be correctly displayed after stretching, after parsing the light intensity corresponding to each pixel, the three-color XYZ formula in the CIE 1931 color space can be used to achieve accurate reproduction of the image; After the three-color coordinates are determined, the pre-processed color image can be reproduced using specific program codes in the simulation software; Step 126. To ensure that the image can be correctly hidden before stretching, firstly, according to the image that is visible under the stretching state, the image parameters hidden in the initial state are analyzed. For the corresponding wavelength of the image before stretching deformation, according to the uniform deformation mechanism of the medium, the grating constant in the stretched state should be calculated and divided by the stretching rate to obtain the grating constant in the undeformed state. Then, the above steps are followed in sequence to reproduce whether the image is hidden after stretching.

[0010] Preferably, in step 2, a method for processing a high-resolution structural color image on the surface of a metal mold using an elliptical vibration cutting process is as follows: Step 211, debug and process according to the principle, select appropriate metal material as the mold base, and ensure that it has good mechanical properties and surface finish; Step 212, using a high-precision elliptical vibration cutting device, according to the preset image data, accurately controlling the cutting path and depth to form a micro-nano structure; after determining the cutting speed by the grating constant of the image before stretching and formula (3), the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory to ensure that the structure size and shape meet the design requirements; Step 213, installing a high-performance diamond tool on an ultrasonic elliptical vibration generator capable of generating a precise elliptical vibration trajectory; Step 214, installing the ultrasonic elliptical vibration generator on the linear drive to achieve efficient cutting operation; Step 215: To ensure the parallelism between the cutting motion and the workpiece surface, an inclined workbench is used and the workpiece is fixed on a three-axis nanopositioning workbench with nanometer positioning. class Excellent positioning resolution and repeatability to precisely control cross feed and cutting depth; Step 216, the tertiary motion generator is used to generate elliptical vibration at the tool tip, and two orthogonal vibration modes are realized at the same ultrasonic frequency through coupling resonance modes, thereby obtaining the elliptical tool trajectory in formula (4); Step 217: Perform quality assessment on the generated structural color image through optical detection equipment to ensure that it meets the expected visual effect.

[0011] Preferably, in step 2, the method of reprinting the color image structure on the surface of the metal mold with the liquid flexible material comprises: Step 221, using a mold release spray before pouring the glue into the mold; Step 222, preparing a release agent, and mixing the flexible material and the curing agent in a certain proportion; Step 223, degassing to remove bubbles in the release agent, and then spraying the release agent; Step 224, pouring glue on the metal mold; Step 225, placing the flexible material into a drying oven for baking; Step 226: The flexible material is formed and peeled off.

[0012] During the process of molding and stripping the flexible material, ensure gentle movements to avoid unnecessary damage to the mold and the flexible material; After the flexible material is printed, the micro-nano grating structure and coloring effect on its surface are characterized and analyzed using detection instruments.

[0013] Preferably, in step 226, an atomic force microscope and a scanning electron microscope are used to analyze the morphology, size and distribution consistency of the micro-nano grating structure in the colored area of ​​the surface; a spectrometer is used to measure visible light waves under darkroom conditions to evaluate the structural color effect caused by the micro-nano grating structure.

[0014] Preferably, in step 3, the method of performing a stretching experiment with a flexible template to observe the change in the color image structure includes: Step 301, prepare stretching test equipment, select a suitable stretching machine, and ensure that it can provide a stable stretching rate and force, fix the flexible template on the fixture of the stretching machine, and ensure that the template will not deviate during the stretching process; Step 302: Set stretching parameters, set stretching rate and determine the final length of stretching.

[0015] Step 303, start the stretching machine, start stretching the flexible template and observe the color image changes on the flexible template in real time, and record key data; Step 304: after reaching the preset stretching length, stop stretching, keep the template state unchanged, and use a microscope or a high-resolution camera to shoot the color image on the flexible template to record the image changes after stretching; Step 305: After the color image change observation is completed, the tension of the stretching machine is released, allowing the flexible template to rebound to its original state, and the recovery of the color image of the template after the tension is released is observed and recorded to verify the reversibility of the structural color change.

[0016] Step 306: If necessary, repeat steps 221 to 225 to verify the repeatability and reliability of the experimental results.

[0017] The beneficial effects of using the present invention are: (1) The present invention successfully achieves accurate replication of the color image structure on the surface of a metal mold through the method provided in the embodiment, proving the effectiveness of the method in replicating micro / nano grating structures and laying a technical foundation for the mass production of color image structures.

[0018] (2) The stretching experimental method in the embodiment allows intuitive observation of the changes in the color image structure on the flexible template during the stretching process, provides an experimental means for studying the relationship between material morphology changes and structural color, and reveals the law of structural color changes with deformation.

[0019] (3) This method has high versatility and repeatability, and is suitable for the processing and experimentation of different metal molds and flexible materials. It ensures the reliability and stability of the experimental results and provides a practical technical path for research and application in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of an image processing and stretching visible / invisible transformation method based on surface structural color provided in an embodiment of the present application is shown; Figure 2 The embodiment of the present invention shows the analysis of the change of the wavelength and diffraction intensity of a certain pixel of a color image; Figure 3 A comparison diagram between an original image before processing and a reproduced image provided in an embodiment of the present application is shown; Figure 4 A schematic diagram of the processing flow provided by an embodiment of the present application is shown; Figure 5 The flexible material surface obtained by replication provided by the embodiment of the present application is shown; Figure 6 A schematic diagram of realizing visible / invisible transition of an image after template stretching provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the technical solution more clear, the technical solution is further described in detail below in conjunction with specific implementation methods. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the technical solution.

[0022] Embodiment 1

[0023] See also Figure 1 , Figure 1 The flowchart of the image processing and stretching display / hidden evolution method based on surface structural color provided by an embodiment of the present application is shown, and the method includes: S101, using numerical calculation to predict the pixel tone information of the displayed color image, calculating the wavelength value corresponding to the pixel, and determining the cutting process parameters corresponding to the cutting pixel on the surface of the metal mold according to the elongation rate of the flexible material and the grating parameters.

[0024] S102, using elliptical vibration cutting technology, the designed grating structure is processed on the surface of the metal mold as a master, and the micro / nano structure on the metal surface is reproduced using the flexible material monomer polymerization and curing process.

[0025] S103, by stretching the flexible optical element, changing the grating spacing, thereby regulating the wavelength of the structured light, achieving the change of the structured light from visible to invisible / invisible to visible range, and realizing the conversion of the visible / hidden state of the image.

[0026] Embodiment 2: A method for calculating the wavelength of structured light of each pixel of a to-be-visible image according to the image analysis module and the wavelength calculation module in the numerical calculation process includes: Step 201: Decompose the input color image into pixel levels through the image analysis module, extract the hue information of each pixel, and convert it into corresponding numerical data.

[0027] Step 202: Utilize the wavelength calculation module to calculate the wavelength value corresponding to each pixel point according to the numerical data and the preset optical parameters.

[0028]

[0029] in, is the hue value of the image, is the wavelength value corresponding to the hue.

[0030] Step 203, output and store the calculated structured light wavelength value of each pixel, so that these data can be used in subsequent steps to accurately process the grating structure, and the structured light wavelength required for each pixel of the image to be displayed can be accurately determined, providing reliable data support for subsequent flexible material processing and image display / hiding control.

[0031] Embodiment 3: A method for verifying whether an image can be successfully converted between visible and invisible before and after stretching includes: Step 301: To ensure that the image can be correctly displayed after stretching, first determine the parameters of the grating formed on the cutting surface: ; In the formula, is the grating spacing, is an integer of the diffraction order, and are the incident light angle and The angle of the diffracted beam is is the wavelength of the diffracted light.

[0032] Step 302: To ensure that the image can be correctly displayed after stretching, after the spacing is determined, the cutting speed required for each pixel can also be given, that is: ; In the formula, is the tool cutting rate, is the tool vibration frequency.

[0033] Step 303: To ensure that the image can be correctly displayed after stretching, the formed grating structure is determined by simulating the cutting process. After the cutting speed is determined, the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory.

[0034] Among them, the elliptical vibration trajectory is: ; In the formula, , are the displacement of the cutting tool relative to the metal mold in the X and Z directions as time t changes, , are the amplitudes of the elliptical vibration in the X and Z directions, is the phase difference between the vibration displacements in the X and Z directions.

[0035] Step 304: To ensure that the image can be correctly displayed after stretching, the diffraction spectrum is determined through the surface grating structure, and the variation curve of the diffraction intensity of each pixel with the wavelength can be analyzed, such as Figure 2 Shown is the spectral intensity corresponding to a pixel.

[0036] Step 305: To ensure that the image can be correctly displayed after stretching, after parsing the light intensity corresponding to each pixel, the three-color XYZ formula in the CIE 1931 color space can be used to achieve accurate reproduction of the image.

[0037] After the three-color coordinates are determined, the pre-processed color image can be reproduced using specific program codes in the simulation software. Figure 3 A comparison between the pre-displayed image and the reproduced image after stretching is shown.

[0038] Step 306: To ensure that the image can be correctly hidden before stretching, firstly, according to the image that is visible under the stretching state, the image parameters hidden in the initial state are analyzed. For the corresponding wavelength of the image before stretching deformation, according to the uniform deformation mechanism of the medium, the grating constant in the stretched state should be calculated and divided by the stretching rate to obtain the grating constant in the undeformed state, and then the above steps are followed in sequence to reproduce whether the image is hidden after stretching.

[0039] Embodiment 4: Method for processing a high-resolution structural color image on the surface of a metal mold using an elliptical vibration cutting process: Step 401: Debug and process according to the principle, select appropriate metal material as the mold base to ensure that it has good mechanical properties and surface finish. The workpiece material can be stainless steel, or one or more metals such as brass, aluminum, iron, etc. The diffraction spectrum will also change due to the different metal materials.

[0040] Step 402: Using a high-precision elliptical vibration cutting device, the cutting path and depth are precisely controlled according to the preset image data to form a micro-nano structure. After the cutting speed is determined by the grating constant of the image before stretching and formula (3), the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory to ensure that the structure size and shape meet the design requirements.

[0041] Step 403: Install a high-performance diamond tool on an ultrasonic elliptical vibration generator that can generate a precise elliptical vibration trajectory.

[0042] Step 404: Install the ultrasonic elliptical vibration generator on the linear drive to achieve efficient cutting operation.

[0043] Step 405: To ensure the parallelism between the cutting motion and the workpiece surface, an inclined workbench is used and the workpiece is fixed on a three-axis nanopositioning workbench with nanometer positioning. class Excellent positioning resolution and repeatability for precise control of cross feed and cutting depth.

[0044] Step 406: The tertiary motion generator is used to generate elliptical vibrations at the tool tip, and two orthogonal vibration modes are realized at the same ultrasonic frequency by coupling the resonance modes, thereby obtaining the elliptical tool trajectory in formula (4).

[0045] Step 407: Perform quality assessment on the generated structural color image by optical detection equipment to ensure that it meets the expected visual effect.

[0046] By using the method of the fourth embodiment, a high-resolution structural color image is successfully processed on the surface of the metal mold. The micro-nano grating structure in the image has a uniform period, appropriate depth and good surface quality, providing a high-quality mold foundation for subsequent reprinting through flexible materials.

[0047] Example 5: A method for reprinting a color image structure on the surface of a metal mold using a liquid flexible material. In this process, polydimethylsiloxane (PDMS) is used as an example for demonstration: Step 501: Before preparation, it should be noted that the mold needs to be hydrophobic, otherwise it will be difficult to peel off, and a release agent spray needs to be used before pouring the glue.

[0048] Step 502: The flexible material and the curing agent are mixed in proportion. The flexible material here includes but is not limited to PDMS.

[0049] Step 503: degassing to remove bubbles.

[0050] In this step, a vacuum drying oven and a vacuum pump or a centrifuge may be used first. In fact, a centrifuge is generally used for PDMS sheets of smaller weight. The tiny bubbles that appear after standing can be blown away with an air pump.

[0051] At the same time, in the process of drawing vacuum to remove bubbles in the vacuum drying oven, if the vacuum extraction speed is too fast, it is necessary to ensure that the PDMS does not overflow. Once the bubbles are removed, the vacuum needs to be turned off in time and the PDMS needs to be baked to fix the shape.

[0052] Step 504: pour glue on the metal mold.

[0053] In this step, it needs to be poured evenly on the mold surface. If bubbles appear, they can be removed with a steel needle.

[0054] Step 505: Place the PDMS in a drying oven for baking.

[0055] In this step, the specific baking time and temperature need to be determined according to the specific requirements of the experiment to ensure that the desired effect is achieved. After baking, the mold is cooled to room temperature, and the PDMS mold can be formed and ready for use.

[0056] Step 506: PDMS molding and peeling.

[0057] In this step, first prepare some tools, such as spade-shaped tweezers, etc. During the operation, ensure that the movements are gentle to avoid unnecessary damage to the mold and PDMS.

[0058] Next, place the PDMS mold on a flat surface. At this time, if you need to cut the PDMS, pay attention to the parallelism between the cutter and the template and keep them tangent to avoid experimental errors.

[0059] After PDMS printing, the micro-nano grating structure and coloring effect on the surface are characterized and analyzed using detection instruments, specifically: Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to analyze the morphology, size and distribution consistency of the micro-nano grating structure in the colored area of ​​the surface. At the same time, a spectrometer was used to measure the visible light waves under dark room conditions to evaluate the structural color effect caused by the micro-nano grating structure.

[0060] Through the method of the fifth embodiment, the color image structure on the surface of the metal mold is successfully copied into the liquid PDMS, and a solid PDMS template is formed through the curing process, thereby obtaining a PDMS template having the same color image structure as the surface of the metal mold. Figure 5 , in order to facilitate subsequent stretching and observation experiments.

[0061] Embodiment 6: Method for observing the structural changes of a color image by conducting a stretching experiment using a flexible template: Step 601: Prepare stretching test equipment.

[0062] In this step, select a suitable stretching machine and ensure that it can provide a stable stretching rate and force.

[0063] At the same time, the flexible template is fixed to the clamp of the stretching machine to ensure that the template will not deviate during the stretching process.

[0064] Step 602: Set stretching parameters.

[0065] In this step, the stretching rate is set and the final length of the stretch is determined according to the experimental purpose.

[0066] Step 603, start the stretching machine, start stretching the flexible template and observe the color image changes on the flexible template in real time, and record key data. The schematic diagram of the image change during the stretching process is as follows: Figure 6 shown.

[0067] Step 604: After reaching the preset stretching length, stop stretching and keep the template state unchanged.

[0068] In this step, a color image is taken on the flexible template using a microscope or a high-resolution camera to record the image changes after stretching.

[0069] Step 605: After the color image change observation is completed, the tension of the stretching machine is released to allow the flexible template to rebound to its original state.

[0070] In this step, the recovery of the color image of the template after releasing the tension is observed and recorded to verify the reversibility of the structural color change.

[0071] Step 606: If necessary, repeat steps 501 to 505 to verify the repeatability and reliability of the experimental results.

[0072] For the entire processing process reference Figure 4 , which describes the general process from elliptical vibration cutting of metal surface to flexible material imprinting surface.

[0073] The above contents are only preferred embodiments of the present invention. For ordinary technicians in this field, many changes can be made in the specific implementation methods and application scopes based on the ideas of the present technical content. As long as these changes do not deviate from the concept of the present invention, they all fall within the scope of protection of this patent.

Claims

1. An image processing method based on surface structural color and a method for changing the visible / hidden state thereof, characterized in that: The following steps are included: Step 1: Use numerical calculation to predict the pixel tone information of the color image, calculate the wavelength value corresponding to the pixel, and determine the cutting process parameters corresponding to the pixel on the surface of the metal mold according to the elongation rate of the flexible material and the grating parameters; Step 2: Using an elliptical vibration cutting process, a designed grating structure is processed on the surface of a metal mold as a master, and a flexible material monomer polymerization and curing process is used to reprint the micro / nano structure on the metal surface; Step 3: By stretching the flexible optical element and changing the grating spacing, the wavelength of the structured light can be adjusted to achieve the change of the structured light from visible to invisible / invisible to visible range, thereby realizing the conversion of the image's visible / hidden state.

2. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 1, characterized in that: In step 1, according to the image analysis module and the wavelength calculation module in the numerical calculation process, the method for calculating the wavelength of the structured light of each pixel of the image to be displayed includes: Step 111: Decompose the input color image into pixel levels through an image analysis module, extract the hue information of each pixel, and convert it into corresponding numerical data; Step 112: using a wavelength calculation module, according to the numerical data and in combination with preset optical parameters, calculate the wavelength value corresponding to each pixel point; ； in, is the hue value of the image, is the wavelength value corresponding to the hue; Step 113, output and store the calculated structured light wavelength value of each pixel, so that these data can be used in subsequent steps to accurately process the grating structure, and the structured light wavelength required for each pixel of the image to be displayed can be accurately determined, providing reliable data support for subsequent flexible material processing and image display / hiding control.

3. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 1, characterized in that: In step 1, the method of verifying whether the image can successfully achieve visible / hidden conversion before and after stretching includes: Step 121: To ensure that the image can be correctly displayed after stretching, first determine the parameters for forming a grating on the cutting surface: ； In the formula, is the grating spacing, is an integer of the diffraction order, and are the incident light angle and The angle of the diffracted beam is is the wavelength of the diffracted light; Step 122: To ensure that the image can be correctly displayed after stretching, after the spacing is determined, the cutting speed required for each pixel can also be given, that is: ； In the formula, is the tool cutting rate, is the tool vibration frequency; Step 123, to ensure that the image can be correctly displayed after stretching, the formed grating structure is determined by simulating the cutting process; after the cutting speed is determined, the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory; Among them, the elliptical vibration trajectory is: ； In the formula, , are the displacement of the cutting tool relative to the metal mold in the X and Z directions as time t changes, , are the amplitudes of the elliptical vibration in the X and Z directions, is the phase difference of vibration displacement in X and Z directions; Step 124: To ensure that the image can be correctly displayed after stretching, the diffraction spectrum is determined through the surface grating structure, and the variation curve of the diffraction intensity of each pixel with the wavelength can be analyzed; Step 125: To ensure that the image can be correctly displayed after stretching, after parsing the light intensity corresponding to each pixel, the three-color XYZ formula in the CIE 1931 color space can be used to achieve accurate reproduction of the image; After the three-color coordinates are determined, the pre-processed color image can be reproduced using specific program codes in the simulation software; Step 126. To ensure that the image can be correctly hidden before stretching, firstly, according to the image that is visible under the stretching state, the image parameters hidden in the initial state are analyzed. For the corresponding wavelength of the image before stretching deformation, according to the uniform deformation mechanism of the medium, the grating constant in the stretched state should be calculated and divided by the stretching rate to obtain the grating constant in the undeformed state. Then, the above steps are followed in sequence to reproduce whether the image is hidden after stretching.

4. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 3, characterized in that: In step 2, a method for processing a high-resolution structural color image on the surface of a metal mold using an elliptical vibration cutting process is as follows: Step 211, debug and process according to the principle, select appropriate metal material as the mold base, and ensure that it has good mechanical properties and surface finish; Step 212, using a high-precision elliptical vibration cutting device, according to the preset image data, accurately controlling the cutting path and depth to form a micro-nano structure; after determining the cutting speed by the grating constant of the image before stretching and formula (3), the cutting tool can process the metal surface according to the elliptical vibration cutting trajectory to ensure that the structure size and shape meet the design requirements; Step 213, installing a high-performance diamond tool on an ultrasonic elliptical vibration generator capable of generating a precise elliptical vibration trajectory; Step 214, installing the ultrasonic elliptical vibration generator on the linear drive to achieve efficient cutting operation; Step 215, to ensure the parallelism of the cutting motion with the workpiece surface, a tilted workbench is used, and the workpiece is fixed on a three-axis nanopositioning workbench, which has nanometer-level positioning resolution and repeatability to accurately control the lateral feed and cutting depth; Step 216, the tertiary motion generator is used to generate elliptical vibration at the tool tip, and two orthogonal vibration modes are realized at the same ultrasonic frequency through coupling resonance modes, thereby obtaining the elliptical tool trajectory in formula (4); Step 217: Perform quality assessment on the generated structural color image through optical detection equipment to ensure that it meets the expected visual effect.

5. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 1, characterized in that: In step 2, the method of reprinting the color image structure on the surface of the metal mold with the liquid flexible material includes: Step 221, using a mold release spray before pouring the glue into the mold; Step 222, preparing a release agent, and mixing the flexible material and the curing agent in a certain proportion; Step 223, degassing to remove bubbles in the release agent, and then spraying the release agent; Step 224, pouring glue on the metal mold; Step 225, placing the flexible material into a drying oven for baking; Step 226, the flexible material is formed and peeled off; During the process of molding and stripping the flexible material, ensure gentle movements to avoid unnecessary damage to the mold and the flexible material; After the flexible material is printed, the micro-nano grating structure and coloring effect on its surface are characterized and analyzed using detection instruments.

6. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 5, characterized in that: In step 226, an atomic force microscope and a scanning electron microscope are used to analyze the morphology, size and distribution consistency of the micro-nano grating structure in the colored area of ​​the surface; a spectrometer is used to measure visible light waves under dark room conditions to evaluate the structural color effect caused by the micro-nano grating structure.

7. The image processing method based on surface structural color and the visible / hidden state conversion method thereof according to claim 1, characterized in that: In step 3, the method of performing a stretching experiment using a flexible template to observe a change in the color image structure includes: Step 301, prepare stretching test equipment, select a suitable stretching machine, and ensure that it can provide a stable stretching rate and force, fix the flexible template on the fixture of the stretching machine, and ensure that the template will not deviate during the stretching process; Step 302: Set the stretching parameters, set the stretching rate and determine the final length of the stretching: Step 303, start the stretching machine, start stretching the flexible template and observe the color image changes on the flexible template in real time, and record key data; Step 304: after reaching the preset stretching length, stop stretching, keep the template state unchanged, and use a microscope or a high-resolution camera to shoot the color image on the flexible template to record the image changes after stretching; Step 305: After the color image change observation is completed, the tension of the stretching machine is released, allowing the flexible template to rebound to its original state, and the recovery of the color image of the template after the tension is released is observed and recorded to verify the reversibility of the structural color change: Step 306: If necessary, repeat steps 221 to 225 to verify the repeatability and reliability of the experimental results.

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