Multi-layer superposition treatment process for special printed image

Abstract

The invention discloses a special printing multi-layer superposition treatment process which comprises the following steps: S1, pretreating a rock surface, cleaning and acquiring three-dimensional coordinate data; s2, software simulation and parameter calculation are carried out, three-dimensional morphology and color layer distribution are analyzed, patterns are disassembled, and superposition parameters are calculated; s3, spraying a bottom gold coating, namely spraying matte gold pigment for four times by adopting an interval spraying method; s4, carrying out local whitening treatment according to parameters without covering the bottom golden color; s5, coloring treatment: coloring by using six color pigments on the basis of shrinkage and expansion coefficients; s6, real-time detection and adjustment, wherein the digital camera and the image sensor are used for obtaining images and adjusting the spraying state in real time; and S7, curing and quality inspection: coating a nano coating material after ultraviolet curing, and performing quality inspection. By accurately analyzing the morphology and color distribution of the rock, the spraying state is adjusted in real time, the printing precision and quality are ensured, the color expressive force is improved, the problems of color mixing and fault are reduced, and high-precision image printing of the irregular surface of the natural rock is achieved.

Description

Technical Field

[0001] The invention relates to the application field of stone printing, in particular to a special printing multi-layer superposition processing process. Background Art

[0002] Stone imprinting technology has a wide range of applications in decoration, handicraft production and other fields. The early stone imprinting technology was relatively simple, but with the continuous increase in market demand, the technology has also been gradually developed.

[0003] The most common stone surface printing process is the mechanical embossing "gold plate" technology, which first colors and then directly gilds (embossing). The mechanical embossing "gold plate" technology has the advantages of high production efficiency and good consistency on the flat stone surface, and has become the mainstream process. However, this method can only be used for purely flat rock surfaces after manual polishing. The natural rock slabs formed by hammering from the whole rock have uneven surfaces and no regularity, so the embossing effect is poor and cannot meet the printing needs of high-end handicrafts such as Buddha statues and murals. For this reason, a special printing multi-layer superposition processing process is proposed. Summary of the Invention

[0004] The present invention provides the following technical solution: a special printing multi-layer superposition processing process, comprising the following steps: S1 rock surface pretreatment: First, the rock surface to be processed is cleaned, and the three-dimensional coordinate data of the rock surface is obtained using a three-dimensional laser scanner and optical interferometry technology; S2 software simulation and parameter calculation: Using software simulation technology, the three-dimensional morphology of the rock surface and the distribution of each color layer obtained in step S1 are analyzed. The pre-designed printed pattern is decomposed into multiple layers according to the expansion and contraction coefficients of the edges of the printed strokes of each layer. At the same time, the color distribution and superposition parameters of each layer are calculated using color space conversion technology to simulate the preparation process. S3 bottom gold coating spraying: Use matte gold pigment and spray it on the rock surface four times using the interval spraying method to form the bottom gold coating; S4 local whitening treatment: According to the distribution and superposition parameters of each color layer calculated in step S2, local whitening is performed without covering the gold color at the bottom during the local whitening; S5 cover color processing: Beginning to implement the color covering process, performing the color covering process based on the shrinkage coefficient and expansion coefficient obtained in step S2, and using six color pigments for the color covering process; S6 real-time detection adjustment: During the spraying process, digital cameras and image sensors are used to obtain rock images in real time. The color depth of each layer is analyzed based on the acquired images, and the spraying status is adjusted in real time according to the different color depths. S7 curing and quality inspection: After spraying, the print is irradiated with an ultraviolet curing lamp, and after curing, a transparent nano-coating material is used to coat the surface of the print. Finally, quality inspection is carried out to complete the rock print processing.

[0005] Preferably, when cleaning the rock surface in step S1, a soft nylon brush is used to perform preliminary cleaning along the rock texture direction to remove larger particles of dust and loose impurities, and then a soft cloth is soaked in a neutral detergent solution with a pH value of 7-8 to wet it, and then the rock surface is wiped. After wiping with the detergent, the rock surface is rinsed with plenty of clean water, and finally the rock surface is wiped dry with an absorbent cloth.

[0006] Preferably, in step S2, the software simulation technology first digitizes the printed pattern when analyzing the distribution of each color layer, converts the pattern into a pixel matrix, and for each pixel in the pixel matrix, classifies it according to its color value to determine the color layer to which it belongs, and when analyzing the influence of the three-dimensional morphology of the rock surface on the distribution of the color layer, calculates the actual spraying distance of each area according to the three-dimensional coordinate data, and adjusts the distribution weight of the color layer in the area according to the calculated actual distance.

[0007] Preferably, the specific operation of the interval spraying method in step S3 is as follows: after the first spraying, wait for 10-15 minutes to allow the gold pigment to initially dry and form a certain adhesion, and in the second spraying, the movement speed of the nozzle is set to be faster than the first, and the third and fourth spraying are carried out in accordance with the above-mentioned interval spraying method, and the waiting time between each spraying is gradually shortened.

[0008] Preferably, in step S4, piezoelectric on-demand inkjet technology is used when whitening, the nozzle hole of the piezoelectric on-demand inkjet technology is 0.2-0.3 mm, and a 0.05-0.1 mm gradient transition zone is set at the edge of the whitening area using translucent milky white ink.

[0009] Preferably, in step S5, the six color pigments used in the covering color include the standard four colors of cyan, magenta, yellow and black, and two transition colors of warm gray and cold gray, and when spraying the standard four colors, the concentration of the sprayed pigment is high and the movement speed of the nozzle is fast, while when spraying the transition colors, the concentration of the sprayed pigment is low and the movement speed of the nozzle is slow.

[0010] Preferably, the digital camera in step S6 has a pixel of 20 million to 40 million pixels, and when analyzing the color depth of each layer of the image, a multi-region analysis method is adopted, that is, the acquired rock image is divided into small areas, and the color depth in each small area is analyzed separately. For areas with too dark colors, the amount of pigment deposition is reduced by reducing the pigment flow of the spraying equipment and increasing the moving speed of the nozzle, while for areas with too light colors, the pigment flow is increased and the moving speed of the nozzle is reduced to control the area.

[0011] Preferably, the power of the ultraviolet curing lamp in step S7 is 50-100 watts, the irradiation distance between the ultraviolet curing lamp and the rock is between 10-20 centimeters, and the irradiation time of the ultraviolet curing lamp on the rock is 10-15 minutes.

[0012] Preferably, the thickness of the nano coating material applied in step S7 is 5-10 microns, and the coating of the nano coating material is performed by spraying, and the nozzle is perpendicular to the printed surface at a distance of 15-20 cm.

[0013] Preferably, the ambient temperature of each process step in steps S1-S7 is 18-25 degrees Celsius, and the ambient humidity of each process step is 40%-60%.

[0014] In summary, compared with the prior art, the present invention provides a special printing multi-layer superposition processing process, which has the following beneficial effects: 1. The present invention uses a three-dimensional laser scanner and optical interferometry technology to obtain three-dimensional coordinate data of the rock surface, and uses software simulation technology to analyze the three-dimensional morphology of the rock surface and the distribution of each color layer. At the same time, the printed pattern is disassembled according to the expansion and contraction coefficients of the printed stroke edges. The color distribution and superposition parameters are calculated with the help of color space conversion technology. The position and distribution of each layer of color can be accurately determined, thereby reducing errors when multiple layers are superimposed. In addition, a digital camera and image sensor are used to obtain rock images in real time during the spraying process. The spraying state is adjusted based on the image analysis of the color depth of each layer. Color deviation or unevenness that may occur during the spraying process can be corrected in a timely manner, further ensuring the accuracy of image printing, improving the quality of printing irregular rocks, and achieving high-precision image printing on irregular surfaces of natural rocks. 2. The present invention uses matte gold pigment for spraying the bottom gold coating in the S3 bottom gold coating spraying and S4 local whitening treatment steps, and then performs local whitening according to the accurately calculated color layer distribution and superposition parameters, so that the golden bottom layer and the white local area form a sharp contrast, laying a color foundation for subsequent covering color treatment. At the same time, in the S5 covering color treatment step, by using the shrinkage coefficient and the expansion coefficient as the basis and using the standard four colors and two transition colors for covering color, the visual graininess can be reduced, and the color transition of the finished product can be made smoother, smoother and more natural. The gold line is smooth and delicate, without white edges, and the texture is flat, avoiding the problems of color mixing and color discontinuity, thereby improving the color expression of the printed image. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the process implementation of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] See also Figure 1 , the present invention provides a technical solution, a special printing multi-layer superposition processing process, comprising the following steps; S1 rock surface pretreatment: First, the rock surface to be processed is cleaned, and the three-dimensional coordinate data of the rock surface is obtained using a three-dimensional laser scanner and optical interferometry technology. The specific implementation process of obtaining the three-dimensional coordinate data is as follows; First, place the three-dimensional laser scanner in a suitable position to ensure full coverage of the rock surface to be measured. The positioning of the device should be stable to ensure that there is no error during the measurement process due to device shaking or other factors. Turn on the three-dimensional laser scanner and let the laser beam scan the rock surface according to a certain scanning mode. After the laser beam reflects on the rock surface, the scanner obtains part of the three-dimensional information of the rock surface according to the information of the reflected light. During this process, the scanner gradually scans the entire rock surface to construct a preliminary three-dimensional model of the rock surface, and simultaneously or subsequently uses optical interferometry. Optical interferometry obtains more accurate microscopic topographic information of the rock surface by analyzing the interference phenomenon of light. It can supplement the parts that may be missed or not accurate enough by three-dimensional laser scanning, and further improve the three-dimensional coordinate data of the rock surface. The data obtained by three-dimensional laser scanning and optical interferometry are integrated to form complete three-dimensional coordinate data of the rock surface. These data will accurately describe the shape, undulation and other characteristics of the rock surface, providing important basic data for subsequent special impression multi-layer superposition processing technology; When cleaning the rock surface, use a soft nylon brush to perform a preliminary sweep along the rock grain direction to remove larger particles of dust and loose impurities. Then, soak a soft cloth in a neutral detergent solution with a pH value of 7-8 and wipe the rock surface. After wiping with the detergent, rinse the rock surface with plenty of clean water. Finally, wipe the rock surface dry with an absorbent cloth. The above process, due to the soft texture of the soft nylon brush, sweeps along the rock grain direction, effectively removing larger particles of dust and loose impurities while minimizing scratches or other damage to the rock surface. This helps maintain the integrity of the rock surface, which is crucial for subsequent printing processing, because any damage to the rock surface may affect the quality and effect of the print. Cleaning in the direction of the rock grain can clean along the natural structure of the rock surface, which can more thoroughly remove dust and impurities. Furthermore, following the grain direction of the rock surface does not disrupt the original microstructure, facilitating coating adhesion and even color distribution in subsequent processes. A neutral detergent solution with a pH of 7-8 effectively removes dirt from the rock surface without causing corrosion or other chemical damage due to pH issues. This gentle cleaning method ensures surface stability during the cleaning process, providing an excellent foundation for subsequent measurement and printing. Thoroughly removing dirt from the rock surface improves the adhesion of subsequent coatings. For example, during the gold basecoat spraying process, a clean rock surface facilitates better adhesion of the gold pigment, resulting in a stronger, more uniform basecoat. In multi-layer overlay printing, good adhesion is crucial for accurate and long-lasting color reproduction across the layers. Flushing the rock surface with plenty of clean water can thoroughly remove detergent residue. Detergent residue can affect subsequent processes. For example, during 3D laser scanning and optical interferometry, residual detergent can interfere with measurement results. During the coating spraying process, residual detergent can affect pigment adhesion or cause uneven color mixing. S2 software simulation and parameter calculation: Using software simulation technology, the three-dimensional morphology of the rock surface and the distribution of each color layer obtained in step S1 are analyzed. The pre-designed printed pattern is decomposed into multiple layers according to the expansion and contraction coefficients of the edges of the printed strokes of each layer. At the same time, the color distribution and superposition parameters of each layer are calculated using color space conversion technology to simulate the preparation process. When analyzing the distribution of each color layer, the printed pattern is first digitized and converted into a pixel matrix. For each pixel in the pixel matrix, it is classified according to its color value to determine the color layer to which it belongs. When analyzing the influence of the three-dimensional topography of the rock surface on the distribution of the color layers, the actual spraying distance of each area is calculated based on the three-dimensional coordinate data, and the distribution weight of the color layer in the area is adjusted according to the calculated actual distance. The specific process of the above method is as follows; Digitalization of the print pattern: First, the pre-designed print pattern is processed and converted into a pixel matrix. This step is to be able to analyze and process the pattern digitally so that the color layer information of each part can be determined later; Color layer classification: Each pixel in the pixel matrix is ​​classified according to its color value. For example, pixels with similar color value ranges may be classified into the same color layer. By determining the color layer to which each pixel belongs, the distribution of different color layers in the printed pattern can be preliminarily obtained; Calculate the actual spraying distance of each area: Based on the three-dimensional coordinate data of the rock surface obtained in S1, calculate the actual spraying distance of each area on the rock surface. Since the rock surface is irregular, the distance between different areas and the nozzle is different. The three-dimensional coordinate data can be used to determine these distance information. Adjust color layer distribution weights: Based on the calculated actual spraying distance of each area, adjust the distribution weights of the color layers in that area. For example, if an area is far from the print head, you may need to increase the distribution weights of certain color layers in that area to ensure that these colors can be adequately covered during actual spraying, thereby ensuring the accuracy of the final printed color. Coefficient-based pattern decomposition: The printed image is broken down into multiple layers based on the expansion and contraction coefficients of the stroke edges of each layer. Taking into account that the edges of different color layers may expand or contract due to various factors (such as ink diffusion) during the actual printing process, these coefficients are used to decompose the complete printed image into multiple layers suitable for multi-layer overlay printing. Color space conversion: Perform color space conversion from the original color space to a color space suitable for printing analysis (for example, from a common display color space to a print color space), thereby facilitating more accurate analysis and calculation of color information; Calculate the color distribution of each layer: In the converted color space, combined with the previously determined influence of the rock surface topography on the color layer distribution and the information of each layer after pattern decomposition, calculate the distribution of each color layer in different areas of the rock surface. This includes determining the proportion and coverage of each color in different areas; Calculate overlay parameters: Based on the information obtained from color space conversion and the distribution of each layer's colors, calculate the parameters for overlaying different color layers. These parameters cover the order in which different color layers are overlaid, the mixing method during overlay (e.g., complete coverage, partial mixing, etc.), and other content, thereby simulating the entire print preparation process to accurately determine the position and distribution of each color layer and reduce errors when overlaying multiple layers; S3 bottom gold coating spraying: Matte gold pigment was selected and sprayed on the rock surface four times using the interval spraying method to form the bottom gold coating. The specific operation of the interval spraying method is as follows: after the first spraying, wait for 10-15 minutes to allow the gold pigment to initially dry and form a certain adhesion. When spraying the second time, the movement speed of the nozzle was set faster than the first time. The third and fourth spraying times were carried out according to the above interval spraying method, and the waiting time between each spraying was gradually shortened. S4 local whitening treatment: Based on the distribution and superposition parameters of each color layer calculated in step S2, local whitening is performed, and the gold color at the bottom is not covered during the local whitening. Piezoelectric drop-on-demand inkjet technology is used for the whitening. The nozzle aperture of the piezoelectric drop-on-demand inkjet technology is 0.2-0.3 mm, and a 0.05-0.1 mm gradient transition zone is set at the edge of the whitening area using translucent milky white ink. S5 cover color processing: A capping process is started, and capping is performed based on the shrinkage coefficient and the expansion coefficient obtained in step S2. Six color pigments are used for capping during the process. The six color pigments used in the capping process include the standard four colors of cyan, magenta, yellow, and black, and two transition colors of warm gray and cool gray. When spraying the standard four colors, the pigment concentration is high and the movement speed of the nozzle is fast. When spraying the transition colors, the pigment concentration is low and the movement speed of the nozzle is slow. S6 real-time detection adjustment: During the spraying process, a digital camera and image sensor are used to acquire rock images in real time, and the color depth of each layer is analyzed based on the acquired images. The spraying status is adjusted in real time according to the different color depths. The digital camera has a pixel of 20 million to 40 million pixels. At the same time, when analyzing the color depth of each layer of the image, a multi-region analysis method is adopted, that is, the acquired rock image is divided into small areas, and the color depth in each small area is analyzed separately. For areas with too dark colors, the amount of pigment deposition is reduced by reducing the pigment flow of the spraying equipment and increasing the movement speed of the nozzle. For areas with too light colors, the pigment flow is increased and the movement speed of the nozzle is reduced to control the amount of pigment deposition. S7 curing and quality inspection: After spraying, the printed image is irradiated with an ultraviolet curing lamp, and after curing, a transparent nano-coating material is applied to the printed image surface. Finally, a quality inspection is performed to complete the rock printing process. The power of the ultraviolet curing lamp is 50-100 watts, the irradiation distance between the ultraviolet curing lamp and the rock is between 10-20 cm, the irradiation time of the ultraviolet curing lamp on the rock is 10-15 minutes, and the thickness of the coated nano-coating material is 5-10 microns. The nano-coating material is applied by spraying, and the nozzle is perpendicular to the printed image surface at a distance of 15-20 cm. The ambient temperature for each process step in steps S1-S7 is 18-25 degrees Celsius, and the ambient humidity for each process step is 40%-60%. This processing environment is ideal because the physical properties of rock are relatively stable at an ambient temperature of 18-25 degrees Celsius. When using 3D laser scanners and optical interferometry to obtain 3D coordinate data of rock surfaces, a stable temperature helps reduce minor deformations caused by thermal expansion and contraction, thereby improving the accuracy of the measurement data. Furthermore, this temperature range facilitates optimal cleaning effects of cleaning agents when cleaning rock surfaces. For example, the chemical activity of cleaning agents is relatively stable within this temperature range, enabling more effective dirt removal. The physical properties of cleaning tools such as soft nylon brushes also remain stable, making initial cleaning operations more efficient. Furthermore, matte gold pigment achieves a good balance between drying speed and adhesion at an ambient temperature of 18-25 degrees Celsius. Within this temperature range, the gold pigment's volatility is moderate, preventing excessively high temperatures from drying too quickly, resulting in an uneven coating, and neither excessively low temperatures from drying too slowly, impacting subsequent processes. At the same time, the optimal temperature helps the gold pigment bond better to the rock surface, forming a solid underlying gold coating. Within this temperature and humidity range, the rock's water absorption and expansion are minimal, minimizing the impact on the print quality. Furthermore, the paint drying speed during the spraying process and the chemical reaction rate during the curing process are ideal. If the ambient temperature is too high, the paint dries too quickly, potentially leading to uneven distribution and cracking. If the temperature is too low, the paint dries too slowly, prolonging the process and potentially affecting its adhesion. Humidity has a similar impact: excessively high humidity can dilute the paint or impair its adhesion to the rock surface, while excessively low humidity can cause the paint to dry too quickly and fly, polluting the environment and causing pigment waste.

[0018] This solution uses a three-dimensional laser scanner and optical interferometry technology to obtain three-dimensional coordinate data of the rock surface, and uses software simulation technology to analyze the three-dimensional morphology of the rock surface and the distribution of each color layer. At the same time, it decomposes the printed pattern according to the expansion and contraction coefficients of the printed stroke edges, and uses color space conversion technology to calculate the color distribution and overlay parameters. It can accurately determine the position and distribution of each layer of color, thereby reducing errors when multiple layers are superimposed. In addition, during the spraying process, a digital camera and image sensor are used to obtain rock images in real time, and the spraying status is adjusted according to the image analysis of the color depth of each layer. The color deviation or unevenness that may occur during the spraying process can be corrected in time, further ensuring the accuracy of image printing and improving the quality of printing irregular rocks.

[0019] This solution uses matte gold pigment for the base gold spraying in the S3 base gold spraying and S4 local whitening treatment steps, and then performs local whitening according to the precisely calculated color layer distribution and superposition parameters, so that the golden base layer and the white local area form a sharp contrast, laying a good color foundation for the subsequent cover color treatment. At the same time, in the S5 cover color treatment step, by using the standard four colors and two transition colors based on the shrinkage coefficient and expansion coefficient for cover color, the visual graininess can be reduced, and the color transition of the finished product can be smoother and more natural. The gold line is smooth and delicate, without white edges, and the texture is flat, avoiding the problems of color mixing or color discontinuity, thereby improving the color expression of the printed image.

[0020] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0021] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A special printing multi-layer superposition processing process, characterized in that: The following steps are involved: S1 rock surface pretreatment: First, the rock surface to be processed is cleaned, and the three-dimensional coordinate data of the rock surface is obtained using a three-dimensional laser scanner and optical interferometry technology; S2 software simulation and parameter calculation: Using software simulation technology, the three-dimensional morphology of the rock surface and the distribution of each color layer obtained in step S1 are analyzed. The pre-designed printed pattern is decomposed into multiple layers according to the expansion and contraction coefficients of the edges of the printed strokes of each layer. At the same time, the color distribution and superposition parameters of each layer are calculated using color space conversion technology to simulate the preparation process. S3 bottom gold coating spraying: Use matte gold pigment and spray it on the rock surface four times using the interval spraying method to form the bottom gold coating; S4 local whitening treatment: According to the distribution and superposition parameters of each color layer calculated in step S2, local whitening is performed without covering the gold color at the bottom during the local whitening; S5 cover color processing: Beginning to implement the color covering process, performing the color covering process based on the shrinkage coefficient and expansion coefficient obtained in step S2, and using six color pigments for the color covering process; S6 real-time detection adjustment: During the spraying process, digital cameras and image sensors are used to obtain rock images in real time. The color depth of each layer is analyzed based on the acquired images, and the spraying status is adjusted in real time according to the different color depths. S7 curing and quality inspection: After spraying, the print is irradiated with an ultraviolet curing lamp, and after curing, a transparent nano-coating material is used to coat the surface of the print. Finally, quality inspection is carried out to complete the rock print processing.

2. A special printing multi-layer superposition processing process according to claim 1, characterized in that: In step S1, when cleaning the rock surface, a soft nylon brush is used to perform preliminary cleaning along the rock texture direction to remove larger particles of dust and loose impurities, and then a soft cloth is soaked in a neutral detergent solution with a pH value of 7-8 to wet it and wipe the rock surface. After wiping with the detergent, the rock surface is rinsed with plenty of clean water and finally dried with an absorbent cloth.

3. The special printing multi-layer superposition processing process according to claim 1, characterized in that: In step S2, the software simulation technology first digitizes the printed pattern when analyzing the distribution of each color layer, converts the pattern into a pixel matrix, and classifies each pixel in the pixel matrix according to its color value to determine the color layer to which it belongs. When analyzing the influence of the three-dimensional morphology of the rock surface on the distribution of the color layer, the actual spraying distance of each area is calculated based on the three-dimensional coordinate data, and the distribution weight of the color layer in the area is adjusted according to the calculated actual distance.

4. The special printing multi-layer superposition processing process according to claim 1, characterized in that: The specific operation of the interval spraying method in step S3 is as follows: after the first spraying, wait for 10-15 minutes to allow the gold pigment to initially dry and form a certain adhesion. During the second spraying, the movement speed of the nozzle is set to be faster than the first spraying. During the third and fourth spraying, the interval spraying method is used, and the waiting time between each spraying is gradually shortened.

5. The special printing multi-layer superposition processing process according to claim 1, characterized in that: In step S4, piezoelectric drop-on-demand inkjet technology is used for whitening, the nozzle hole of the piezoelectric drop-on-demand inkjet technology is 0.2-0.3 mm, and a 0.05-0.1 mm gradient transition zone is set at the edge of the whitening area using translucent milky white ink.

6. The special printing multi-layer superposition processing process according to claim 1, characterized in that: In step S5, the six color pigments used in the covering color include the standard four colors of cyan, magenta, yellow and black, and two transition colors of warm gray and cold gray. When spraying the standard four colors, the concentration of the sprayed pigments is high and the movement speed of the nozzle is fast, while when spraying the transition colors, the concentration of the sprayed pigments is low and the movement speed of the nozzle is slow.

7. The special printing multi-layer superposition processing process according to claim 1, characterized in that: The digital camera in step S6 has a pixel of 20 million to 40 million pixels, and when analyzing the color depth of each layer of the image, a multi-region analysis method is adopted, that is, the acquired rock image is divided into small areas, and the color depth in each small area is analyzed separately. For areas with too dark colors, the amount of pigment deposition is reduced by reducing the pigment flow of the spraying equipment and increasing the moving speed of the nozzle, while for areas with too light colors, the pigment flow is increased and the moving speed of the nozzle is reduced to control the area.

8. The special printing multi-layer superposition processing process according to claim 1, characterized in that: The power of the ultraviolet curing lamp in step S7 is 50-100 watts, the irradiation distance between the ultraviolet curing lamp and the rock is between 10-20 cm, and the irradiation time of the ultraviolet curing lamp on the rock is 10-15 minutes.

9. The special printing multi-layer superposition processing process according to claim 1, characterized in that: The thickness of the nano coating material applied in step S7 is 5-10 microns. The nano coating material is applied by spraying, and the nozzle is perpendicular to the printed surface at a distance of 15-20 cm.

10. The special printing multi-layer superposition processing process according to claim 1, characterized in that: The ambient temperature of each process step in steps S1-S7 is 18-25 degrees Celsius, and the ambient humidity of each process step is 40%-60%.

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