Visual registration guide overprint method and system for a deformable print substrate

Abstract

This invention discloses a visual positioning-guided overprinting method and system for easily deformable printing substrates, belonging to the field of digital printing and image registration technology. The method includes an offline preparation stage and an online working stage: In the offline stage, a reference image is established in two ways: first, mapping the actual deformed image to a standard return image; second, establishing a pixel-by-pixel mapping relationship between a regular color image and the actual image to generate a grayscale image; based on this, artwork design is performed. In the online stage, the visual system acquires images of the substrate in real time, calculates deformation parameters, and performs inverse transformation compensation on the design artwork to generate a deformed printing image matching the current deformation, achieving high-precision overprinting. This invention is applicable to multi-color overprinting, varnish overprinting, and hot stamping positioning processes for easily deformable materials such as textiles, plastic films, and paper, and has advantages such as wide applicability, high editing efficiency, flexible design sources, and high overprinting accuracy.

Description

Technical Field

[0001] This invention relates to the field of digital printing and image registration technology, specifically to a visual positioning and guidance overprinting method and system for easily deformable printing carriers. Background Technology

[0002] In the field of digital printing, ensuring precise alignment of patterns is a key technical challenge when using easily deformable printing substrates (such as textiles, flexible packaging films, and specialty papers) for multi-color overprinting or secondary processes (such as varnish overprinting and hot stamping). Due to the elasticity of the material itself, tension changes during transport, or the influence of environmental temperature and humidity, the substrate is prone to non-linear deformation, resulting in the subsequent printed pattern not accurately aligning with the already printed base image.

[0003] For example, the invention patent CN114905864B discloses an adaptive and precise positioning printing method for textile fabric deformation. This method calculates deformation parameters by acquiring fabric images and extracting characteristic yarns, and then deforms the original print image. This method mainly targets the adaptive correction of the yarn structure characteristics of textile fabrics, achieving good results. However, this method primarily focuses on online real-time correction and lacks sufficient support for the front-end artwork creation stage. The invention patent CN114905864B also discloses a precise digital printing method for fabrics using a digital printing machine. This method acquires the original pattern template on the fabric, performs secondary design on the original template to obtain the target pattern, and then adjusts the target pattern by identifying the deviation between the feature points on the fabric to be printed and the original template. This method achieves secondary design based on existing finished fabrics, but its processing mainly relies on the original template acquired from the fabric.

[0004] The aforementioned existing technologies still have certain limitations: First, their application scope is mainly limited to textiles with obvious yarn structures, and it is difficult to extract effective feature parameters for carriers with irregular textures or obvious anisotropy, such as soft packaging plastics and paper; second, for artworks with long return units or large-format deformations, designers find it difficult to efficiently restore the actual deformed images to standard design drafts using general image editing software, resulting in low editing efficiency; finally, when the design source is a regular design drawing (color illustration) from the fabric weaving process rather than an actual photograph, how to efficiently establish the mapping relationship between the design drawing and the actual deformed image to reduce the development workload of large return patterns still needs optimization. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a visual positioning and overprinting method and system for easily deformable printable carriers that has a wider range of applications, higher editing efficiency, and better positioning accuracy.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A visual positioning and overprinting method for easily deformable printing substrates, used for secondary processing or multi-color overprinting of substrates, includes the following steps: S1: Obtain a reference image of the area to be printed; the reference image is obtained through one of the following two methods: Method A: Collect real-world images of the surface of the carrier, and use a semi-automatic mapping tool to map the deformed real-world images into undistorted standard restored images; Method B: Obtain the design pattern of the rule as a color image, collect a real photo of the surface of the carrier, and establish a pixel-by-pixel mapping relationship between the color image and the real photo using offline software tools to obtain a gray image that is pixel-by-pixel aligned with the color image; S2: Based on the reference image, design and draw in image editing software to generate the original design draft; S3: Real-time image acquisition of the substrate in the area to be printed on the printing production line; If method A is used, the first comprehensive deformation field between the current image of the carrier and the standard retracement image is calculated; If method B is used, then the mapping relationship file between the current carrier image and the grayscale image is calculated; S4: Based on the deformation parameters calculated in step S3, perform inverse transformation compensation on the original design drawing to generate a deformed printing drawing that matches the actual deformation of the current load-bearing object, and output it to the printing mechanism for printing.

[0008] Furthermore, the semi-automatic mapping tool in method A of step S1 has a mapping algorithm that includes: correcting the nonlinearly deformed real-shot image into a regular rectangular standard image by using thin-plate spline interpolation or perspective transformation algorithm based on user-marked feature points or feature grids.

[0009] Furthermore, in step S1, method B, establishing the mapping relationship between the color image and the actual photograph includes: selecting several feature points on the color image and generating multiple repeating patterns through continuous printing; identifying the corresponding feature points on the actual photograph; calculating the positional deviation between the two sets of feature points, and generating the pixel-by-pixel mapping relationship.

[0010] Furthermore, the carrier is textiles, flexible packaging plastic film, or paper; the secondary process is color ink layer overprinting, transparent varnish layer overprinting, or cold foil stamping with adhesive for positioning printing.

[0011] Furthermore, in step S3, if method B is adopted, it specifically includes: The image ImgReal of the current carrier is acquired using an industrial camera; image features are extracted from ImgReal and matched with grayscale features prepared offline; transformation parameters from grayscale coordinates to the coordinates of the current real-shot image are calculated, and the mapping relationship file is generated.

[0012] Furthermore, in step S4, if method B is adopted, applying the mapping relationship file to the color image means: according to the transformation parameters recorded in the mapping relationship file, the regular color image is distorted in accordance with the actual deformation of the current load.

[0013] Furthermore, it also includes the step of establishing a deformation database: storing the deformation field or mapping relationship file obtained from each calculation along with its corresponding substrate batch and process parameters for retrieval of the pre-deformation model during subsequent production of the same batch.

[0014] A visual positioning-guided overprinting system for implementing the method as described in any of the above claims includes: The offline processing module is used to perform the offline benchmark establishment steps and generate standard repositioning images or color-grayscale benchmark pairs; An image acquisition module is installed on the printing production line to acquire images of the substrate in the area to be printed. The deformation calculation module, connected to the image acquisition module, is used to perform online deformation calculation steps and calculate the deformation parameters of the current load-bearing image; The image deformation module, connected to the deformation calculation module, is used to perform inverse transformation compensation on the original design drawing according to the deformation parameters to generate a deformed printing image; A printing actuator, connected to the image warping module, is used to print the warped image onto a substrate.

[0015] The beneficial effects of this invention are: (1) Wide range of applications: This invention is not limited to the extraction of yarn features in textiles. Through visual comparison (comparison of real photos and standard photos), it is applicable to all easily deformable materials, solving the problem of extracting feature parameters from textureless materials such as plastics and paper.

[0016] (2) High front-end editing efficiency: By introducing semi-automatic mapping software, the pain point of general software being unable to efficiently process long-return deformed images is solved. Designers no longer need to design directly on deformed real-life images, but can first "restore" the standard image in the software before designing, which improves the accuracy and efficiency of artwork production.

[0017] (3) Flexible and diverse design sources: This invention not only supports secondary design based on real-shot images, but also supports starting from the regular design patterns (color images) during fabric weaving. By establishing the mapping relationship between color images and gray images, the regular design patterns can be directly utilized, which greatly reduces the workload of developing large-scale pattern reversal.

[0018] (4) Good compatibility of multi-process overprinting: It is not only suitable for color printing, but also for secondary positioning overprinting of various processes such as varnish and hot stamping, and can achieve high-precision registration between multiple printing process layers. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of mapping a real-shot image to a standard repositioned image in this invention; Figure 3 This is a schematic diagram illustrating the establishment of the mapping relationship between color images and grayscale images in this invention; Figure 4 This is a schematic diagram of the principle of integrated deformation field solution and inverse transformation compensation in this invention; Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0020] Embodiment 1 of the present invention: The substrate is a stretchable PE flexible packaging film, which requires printing colored patterns on the film first, and then overprinting a layer of high-gloss varnish on specific areas.

[0021] like Figure 2 and 4 As shown, the visual positioning and overprinting method for easily deformable printed substrates includes the following steps: S1: Offline Preparation Phase Image acquisition is performed on the surface of the substrate to be printed to obtain a real-shot image; the real-shot image is imported into a semi-automatic mapping tool software, and feature points or feature regions are marked on the real-shot image and bound to a preset regular grid or standard template. Using image thin plate spline interpolation or perspective transformation algorithm, the real-shot image with nonlinear deformation is mapped into a standard return image without deformation and output. Due to tension fluctuations in the film roll on the production line, the pattern after the first printing may be stretched or skewed. Specifically, a real-life image (ImgRaw) of the film with the printed color pattern is captured using a line scan camera and imported into semi-automatic mapping software. A complete repositioning unit of the pattern is selected in the software. The software automatically identifies the unit edges or allows manual clicking at the four corner points. Based on these control points, the software automatically pulls the distorted unit back into a standard rectangular unit using a thin-plate spline interpolation algorithm, outputting a standard repositioning image (ImgStd).

[0022] S2: Design Draft Production Using the standard repositioned image ImgStd as the bottom reference layer, the coverage area of ​​the varnish layer is designed in Photoshop to generate the original design artwork ImgDesign, which precisely defines where the varnish should cover the pattern.

[0023] S3: Online Work Phase When the film roll undergoes its second varnish printing process, another vision system captures a real-time image (ImgReal) of the film in the area to be printed at the front of the varnish printhead. The image processing unit extracts features of the color pattern in ImgReal (such as the edges of specific color blocks) and compares them with the previously stored ImgStd, calculating the first comprehensive deformation field (DFF) of ImgReal relative to ImgStd in the X-axis, Y-axis, and rotational directions. For example, if it is found that the current film is stretched by 2% compared to ImgStd, the deformation field records the offset of each pixel.

[0024] S4: Adaptive Image Warping and Overlay The overprint control system acquires the ImgDesign and the deformation field DFF, and performs inverse transformation compensation on the ImgDesign; that is, based on the value of the DFF, the ImgDesign is pre-distorted into an image ImgPrint that is the opposite of the film's deformation state. For example, if the film is stretched, the ImgDesign is pre-compressed. Then, the ImgPrint drives the printhead to print, and the originally deformed film receives a pre-distorted pattern in reverse, the two cancel each other out, and finally, visually, the varnish layer and the underlying color pattern are registered.

[0025] Embodiment 2 of the present invention: This embodiment is applicable to secondary printing design on fabrics with existing regular woven patterns, and is especially suitable for the development of large repeating patterns.

[0026] like Figure 3 and 4 As shown, the visual positioning and overprinting method for easily deformable printed substrates includes the following steps: S1: Offline Preparation Phase The regular design pattern of the fabric weaving process is obtained as a color image. Using offline software tools, a pixel-by-pixel mapping relationship is established between the color image and the actual photograph of the substrate surface using manual marking or intelligent image processing algorithms. The actual photograph is mapped onto the regular color image coordinate system to obtain a gray image that is pixel-by-pixel aligned with the color image. This color image and gray image are used as the reference image pair for online work.

[0027] Specifically, the regular design pattern during the fabric weaving process is captured as a ColorImg image. This pattern is a regular, undistorted original design. Due to tension variations during weaving, the pattern on the actual produced fabric may be distorted. A real-world image of the actual fabric, RealFabImg, is captured using a line scan camera.

[0028] In the offline software tool, the operator selects several feature points (such as vertices and intersections of a flower pattern) on the color image (ColorImg), and the software automatically generates multiple feature point sets for repeating patterns through continuous printing. Simultaneously, the corresponding feature points are identified on the real-image (RealFabImg). By calculating the positional deviation between the two sets of feature points, a pixel-by-pixel mapping relationship is established from the color image coordinate system to the real-image coordinate system, generating a grayscale image (GrayImg) that is pixel-by-pixel aligned with the color image. At this point, the offline setup is complete: the color image (ColorImg, the rule design draft) and the grayscale image (GrayImg, the real-image mapping version aligned with the color image) serve as the reference image pair.

[0029] S2: Design Draft Production Designers can perform secondary designs based on the ColorImg image, such as filling in colors within existing floral outlines or adding new decorative elements, to generate the original design draft ImgDesign. Because the ColorImg image is regular in shape, designers can easily perform operations such as continuous printing and copying, greatly improving the design efficiency of large-scale pattern layouts.

[0030] S3: Online Work Phase During the secondary printing process on the production line, the vision system acquires the fabric image CurrentImg of the area to be printed in real time. The processing unit performs feature matching between CurrentImg and the offline prepared grayscale image GrayImg, calculates the transformation parameters from the grayscale image coordinates to the coordinates of the current real-shot image, and generates a mapping file mapping_file.

[0031] S4: Adaptive Image Warping and Overlay The control system acquires the color image (ColorImg) and the mapping file (mapping_file), applies the mapping relationship to the color image, and generates a second deformed print image (ImgPrint) that matches the actual deformation of the current fabric. The originally regular color image is distorted according to the current fabric deformation, so that the printed pattern can be accurately aligned with the existing weave pattern on the fabric. Then, the ImgPrint drives the printhead to print onto the fabric.

[0032] In this embodiment, designers only need to design on regular color images without having to process complex images after deformation. When working online, grayscale images are used as a bridge to calculate deformation parameters in real time and deform the color images accordingly, achieving high-precision overprinting of the design patterns.

[0033] The easily deformable printing substrate involved in this invention can be one of textiles, flexible packaging plastic film and paper; the secondary process can be one of color ink layer overprinting, transparent varnish layer overprinting and cold hot foil adhesive positioning printing.

[0034] A visual positioning-guided overprinting system for implementing the methods described above includes: The offline processing module is used to perform the offline benchmark establishment steps and generate standard repositioning images or color-grayscale benchmark pairs; An image acquisition module is installed on the printing production line to acquire images of the substrate in the area to be printed. The deformation calculation module, connected to the image acquisition module, is used to perform online deformation calculation steps and calculate the deformation parameters of the current load-bearing image; The image deformation module, connected to the deformation calculation module, is used to perform inverse transformation compensation on the original design drawing according to the deformation parameters to generate a deformed printing image; A printing actuator, connected to the image warping module, is used to print the warped image onto a substrate.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0036] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0037] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A visual positioning and guided overprinting method for easily deformable printing substrates, used for secondary processing or multi-color overprinting of substrates, characterized in that, Includes the following steps: S1: Obtain a reference image of the area to be printed; the reference image is obtained through one of the following two methods: Method A: Collect real-world images of the surface of the carrier, and use a semi-automatic mapping tool to map the deformed real-world images into undistorted standard restored images; Method B: Obtain the design pattern of the rule as a color image, collect a real photo of the surface of the carrier, and establish a pixel-by-pixel mapping relationship between the color image and the real photo using offline software tools to obtain a gray image that is pixel-by-pixel aligned with the color image; S2: Based on the reference image, design and draw in image editing software to generate the original design draft; S3: Real-time image acquisition of the substrate in the area to be printed on the printing production line; If method A is used, the first comprehensive deformation field between the current image of the carrier and the standard retracement image is calculated; If method B is used, then the mapping relationship file between the current carrier image and the grayscale image is calculated; S4: Based on the deformation parameters calculated in step S3, perform inverse transformation compensation on the original design drawing to generate a deformed printing drawing that matches the actual deformation of the current load-bearing object, and output it to the printing mechanism for printing.

2. The visual positioning and overprinting method for easily deformable printable carriers according to claim 1, characterized in that: The semi-automatic mapping tool in step S1, method A, has a mapping algorithm that includes: correcting the nonlinearly deformed real-shot image into a regular rectangular standard image based on user-marked feature points or feature grids through thin-plate spline interpolation or perspective transformation algorithms.

3. The visual positioning and guidance overprinting method for easily deformable printing carriers according to claim 1, characterized in that: In step S1, method B, establishing the mapping relationship between the color image and the real-shot image includes: selecting several feature points on the color image and generating multiple repeating patterns through continuous printing; identifying the corresponding feature points on the real-shot image; calculating the positional deviation between the two sets of feature points, and generating the pixel-by-pixel mapping relationship.

4. The visual positioning and overprinting method for easily deformable printed carriers according to claim 1, characterized in that: The carrier is textiles, flexible packaging plastic film, or paper; the secondary process is color ink layer overprinting, transparent varnish layer overprinting, or cold hot foil stamping with adhesive for positioning printing.

5. The visual positioning and overprinting method for easily deformable printed carriers according to claim 1, characterized in that: In step S3, if method B is used, it specifically includes: The image ImgReal of the current carrier is acquired using an industrial camera; image features are extracted from ImgReal and matched with grayscale features prepared offline; transformation parameters from grayscale coordinates to the coordinates of the current real-shot image are calculated, and the mapping relationship file is generated.

6. The visual positioning and guidance overprinting method for easily deformable printing carriers according to claim 1, characterized in that: In step S4, if method B is adopted, applying the mapping relationship file to the color image means: according to the transformation parameters recorded in the mapping relationship file, the regular color image is distorted in accordance with the actual deformation of the current load.

7. The visual positioning and guidance overprinting method for easily deformable printable carriers according to claim 1, characterized in that: It also includes the step of establishing a deformation database: storing the deformation field or mapping relationship file obtained from each calculation along with its corresponding substrate batch and process parameters for retrieval of the pre-deformation model during subsequent production of the same batch.

8. A visual positioning guided overprinting system for implementing the method as described in any one of claims 1 to 7, characterized in that, include: The offline processing module is used to perform the offline benchmark establishment steps and generate standard repositioning images or color-grayscale benchmark pairs; An image acquisition module is installed on the printing production line to acquire images of the substrate in the area to be printed. The deformation calculation module, connected to the image acquisition module, is used to perform online deformation calculation steps and calculate the deformation parameters of the current load-bearing image; The image deformation module, connected to the deformation calculation module, is used to perform inverse transformation compensation on the original design drawing according to the deformation parameters to generate a deformed printing image; A printing actuator, connected to the image warping module, is used to print the warped image onto a substrate.

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