WO2022247085A1

WO2022247085A1 - Slice compression method based on marking of pixel coordinates of molding region

Info

Publication number: WO2022247085A1
Application number: PCT/CN2021/121485
Authority: WO
Inventors: 王宜怀; 施连敏; 陈琳; 叶柯阳; 何双辰; 朱轩
Original assignee: 苏州大学
Priority date: 2021-05-28
Filing date: 2021-09-28
Publication date: 2022-12-01
Also published as: CN113204527A

Abstract

A slice compression method based on the marking of pixel coordinates of a molding region. The method comprises: parsing a preset STL model, acquiring a model height, and performing slicing according to the STL model, wherein the process of parsing the STL model comprises: acquiring related parameters, including vertex information of triangular patches in the model, and the maximum value and the minimum value of the boundary of the model; obtaining a slice file set by means of OpenGL slices, wherein the slice file set is composed of a plurality of slice files, and each slice file is a multi-row array composed of black pixels and white pixels; traversing each row of pixels in each slice file, determining whether there is a white pixel, adjacent pixels of which comprise a black pixel, in in each row of pixels, and if so, saving coordinates of the white pixel to serve as boundary coordinates of a molding region; and writing the boundary coordinates into a compressed file, so as to obtain a slice compression file set. According to the method, a DPS slice file that is obtained after slicing occupies a small amount of memory space, and the amount of time that is consumed for transmitting the file is quite short.

Description

A Slice Compression Method Based on Pixel Coordinate Marking of Shaped Area

technical field

The invention relates to the technical field of intelligent rapid prototyping, in particular to a slice compression method based on pixel coordinate marking of a forming area.

Background technique

The rapid prototyping technology based on light curing is to project ultraviolet light into the liquid photosensitive resin, so that the resin is continuously cured layer by layer. Digital light processing (DLP) molding technology has problems such as limited molding size, high equipment price and lens distortion that restrict the development of this technology. Therefore, liquid crystal display (LCD) is used as an area selective light transmission device, which can be used to manufacture large and High precision parts. However, the difficult coordination between molding efficiency and molding quality is the main factor limiting the development of LCD molding technology, so it is necessary to find a reconciliation strategy for the two.

After the 3D model is preprocessed and sliced, the slice data is stored in the bitmap file format, which takes up more storage space than the vector file storage format. In order to improve the stability of the system, the molding is controlled offline, so the slices need to be processed before being transferred to the Raspberry In the Pi, 3D model slices often have thousands of layers, and the standard bitmap format is used to store the slice data up to dozens of GB, which not only requires a large storage space on the Raspberry Pi but also consumes transmission time.

technical solution

The purpose of the present invention is achieved through the following technical solutions.

The present invention provides a slice compression method based on the pixel coordinate marking of the forming area, including:

Analyzing the preset STL model, obtaining the height of the model, and slicing according to the STL model; the parsing of the STL model includes: obtaining relevant parameters, including the vertex information of the triangular patch in the model, the maximum value and the minimum value of the boundary of the model;

A slice file set is obtained by OpenGL slicing, the slice file set is composed of a plurality of slice files, and each slice file is a multi-row array composed of black pixels and white pixels;

Traversing each row of pixels of each slice file, judging whether there are white pixels including black pixels among adjacent pixels in the row of pixels, and if so, saving the coordinates of the white pixels as the boundary coordinates of the forming area;

Write the boundary coordinates into the compressed file to obtain a collection of sliced compressed files.

Preferably, the boundary coordinates appear in pairs, and each row of pixels has several pairs of boundary coordinates.

Preferably, the parsing of the STL model includes: obtaining relevant parameters, including vertex information of triangle patches in the model, maximum and minimum values of the boundary of the model.

Preferably, the vertex information includes coordinates and normal vectors of three vertices of the triangle patch.

Preferably, the binary format of the sliced file is stored in bytes, and the ASCII format is stored in plaintext lines.

Preferably, the size of the STL model does not exceed the size of the molding table.

Preferably, further comprising:

Read the sliced file data, process it with OpenGL and display it.

Preferably, a window is first created before slicing, and zoomed according to the size of the LCD display screen;

After reading the model, adjust the viewing angle, use the viewing angle to observe the model view to simulate the intersection of the model and the cross-section, and save the cross-section pixels;

Move the angle of view according to the slice thickness, and save the model slice pixels in this way.

Preferably, further comprising:

The STL model is placed in the coordinate system, the observation point is adjusted to adjust the viewing angle, and the slice direction of the STL model is determined.

Preferably, further comprising:

Adjust the distance between the near plane and the origin of observation along the Z axis to obtain the section of the 3D model, obtain the section pixels, then write the section pixels into the slice file, and repeatedly move the near plane to obtain the slice set.

Beneficial effect

The advantage of the present invention is that: compared with the prior art, the memory occupied by the DPS slicing file obtained after slicing the hand-figure model of the present invention is very small, and the time spent on transferring the file is also very small. It can be seen that the slice compression method designed by the present invention has high practical value in actual work.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention. Also throughout the drawings, the same reference numerals are used to designate the same components. In the attached picture:

Accompanying drawing 1 has shown the flowchart of reading STL file of the present invention.

Accompanying drawing 2 shows the transmission diagram of the three-dimensional model of the present invention.

Accompanying drawing 3 shows the schematic diagram of placement angle of the three-dimensional model of the present invention.

Accompanying drawing 4 shows the sub-model of the Newtonian reflective shell of the present invention and a schematic diagram of slices thereof.

Accompanying drawing 5 shows the schematic diagram of the pixel arrangement of the slice file according to the present invention.

Embodiments of the present invention

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided for more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

Generally speaking, 3D model slice compression uses the characteristics of bitmaps to store the complete information expressed by slices in another file format, which requires this file format to occupy a smaller memory space. In order to ensure the integrity of part molding, the compressed file must be able to restore the original state of the bitmap after parsing, so a lossless compression method should be used. Therefore, the present invention combines the slicing characteristics of the three-dimensional model and the needs of the molding process, and designs a bitmap compression method with a very high compression rate suitable for the light-curing molding system.

1 Implementation process of STL model slicing

The STL model slicing design of the present invention is based on an open source graphics library (Open Graphics Library, OpenGL), this framework contains a series of functions that can manipulate graphics and images, which is convenient for secondary development in 3D processing. The development environment is Qt Creator 4.14.0.

1.1 STL format model analysis

Analyzing the STL model is mainly to obtain relevant parameters, mainly including the vertex information of the triangle patch in the model, the maximum and minimum values of the boundary of the model. The vertex information includes the coordinates and normal vectors of the three vertices of the triangle patch. The binary format of the STL file is stored in bytes, and the ASCII format is stored in plaintext by line. The vertex information of the triangle patch is read and handed over to OpenGL for processing. The reading process is shown in Figure 1.

1.2 STL model slicing

To perform model slicing, you must first obtain the model path, the length and width of the forming table, the pixel width and height of the slice image, and the slice thickness. It should be noted that the size of the model cannot exceed the size of the forming table. After reading the STL file data, it is processed and displayed by OpenGL. Create a window before slicing. Because the actual size of the model may be different from what is displayed on the screen, it needs to be scaled according to the size of the LCD display. After reading the model, adjust the viewing angle, use the viewing angle to observe the model view to simulate the intersection of the model and the cross-section, and save the cross-section pixels. Then move the angle of view according to the slice thickness, and save the model slice pixels in this way. As shown in Figure 2, the 3D model is placed in the coordinate system, and the observation point can be adjusted to adjust the viewing angle and determine which direction to slice from the 3D model. By adjusting the distance between the near plane and the origin of observation along the Z axis, the section of the 3D model can be obtained, and the section pixels can be obtained, and then the section pixels are written into the slice file, and the near plane is moved repeatedly to obtain the slice set.

One point to be noted is that by reading the schematic diagram of the STL model on the forming table, the user can intuitively observe the placement of the model and adjust the position of the model on the forming table. Different placements can directly affect the printing effect, such as As shown in Figure 3. Slicing is from bottom to top, the tip of the model has very little contact with the molding table, and it is difficult to stick to the molding table, so it is necessary to change the appropriate angle to slice. In order to make the release force on the model as uniform as possible during the release process, the center of gravity of the model should be located at the origin of the coordinate axis as much as possible. If the release force on the model is uneven and the molding surface is small, it will lead to release failure.

2 Slice compression methods and parameter markers

In the LCD-based light-curing molding system, the sliced pictures of the 3D model often only have black and white pixels. According to the molding principle, UV ultraviolet light is used to cure the resin through the LCD, and the white pixel area is used to pass through the UV ultraviolet light, which is the molding area. The black area cannot pass through UV ultraviolet light.

2.1 Slice Compression Pixels Based on Coordinate Marking of Imaging Area

Generally speaking, the slice file compression method is to convert the current slice file into a smaller storage form according to the characteristics of the slice file. It is more convenient to store slice pixels in BMP file format after using OpenGL slices, but the BMP file format takes up a lot of memory. If it is converted into a vector file format, the conversion and analysis calculations are complex and time-consuming. Taking the Newton reflective shell as an example, as shown in Figure 4, analyze the slice compression file format designed by the present invention.

1. BMP slice file details

BMP files are used for slice display, and only need three parts of the file format, namely BMP file header, bitmap information header and bitmap pixels. As shown in Table 5-5, the main information of the BMP file header includes a 2-byte bitmap file type flag, a 4-byte bitmap file size, a 4-byte reserved bit, and a 4-byte file header to bitmap pixel. Offset bits, 14 bytes in total. The effective slice data used by the bitmap header includes 4-byte pixel width, 4-byte pixel height, and 2-byte pixel occupancy. The bitmap pixel records the detailed information of the sliced pixels, each pixel occupies 4 bytes of storage, and there are only two forms: 000000ff and ffffffff.

2. Features of BMP slice files

After slicing the 3D model, the slice pixels are obtained, so the slice compression method is designed according to its characteristics. By extracting the characteristics of the slice file, the design requirements of the compressed file can be directly derived. Under the premise of reducing the storage space as much as possible, the information carried in the compressed file and the slice source file must be consistent.

(1) The pixel data of the BMP slice file only contains two types of pixels, that is, black and white pixels. As shown in Figure 4, the forming area is white, and the non-forming area is black.

(2) Due to the high resolution of the image required in the photo-curing molding system, the pixels are usually densely distributed, that is, white pixels and black pixels are basically continuously distributed, and there are rarely a large number of isolated pixels.

(3) The pixel data in the slicing file is completely obtained by slicing the 3D model, and it will neither be added nor damaged arbitrarily. Therefore, only lossless compression mode can be used for slice file compression.

(4) The pixel data of the slice file is stored by row, and the data of a whole row of pixels is stored at a time, and then the data of the next row is stored.

3. Slice file compression

According to the characteristics of the slice file, the slice file compression format is designed. As shown in Figure 5, the pixel arrangement of the slice file, with the row as a basic observation unit, there are only "black and black", "white and white", "black and white" and "white and black" between adjacent pixels, and the "black and black" area indicates the non- Forming area, the "white and white" area indicates the forming area, "white and black" and "black and white" indicate the boundary area between the forming area and the non-forming area, this area can mark the range of the forming area, so only the boundary area needs to be saved to effectively obtain pixels The actual information of the distribution. The slice file compression format is named DPS (Dynamic Print System), that is, dynamic molding system.

The process of DPS slice file compression method is as follows: First, the slice pixels are obtained through OpenGL slices, the slice row pixels are read, and whether there are white pixels in the row pixels, that is, the forming area, as shown in Figure 5. Coordinates (0,2) and (0,4 ). If there is a forming area, save the boundary coordinates of the area, the boundary coordinates appear in pairs, and there are several pairs of boundary coordinates in each row. The slice compression method flow shown in Method 5-2 describes the implementation process of this method in detail. The input data is a collection of slices, slice pixel width and pixel height. The output data is a collection of DPS sliced compressed files. The compression method of the present invention first traverses the slice file set Cn, and then traverses the pixels of each slice. When the row pixels are "white and black" and "black and white", write the coordinates of the white pixels into the DPS file.

DPS slice file restoration is the opposite of compression. When a pair of white pixel coordinates are obtained, only the interval needs to be filled. Although the filling process is time-consuming, the exposure time of each slice is about tens of seconds, which is enough to parse and display the DPS slice file.

2.2 Slice compression storage format

The first essence of the slice compression storage format is to save storage space, which is manifested in that the boundary coordinates occupy less bytes. The resolution of the LCD display screen used in the present invention is 2560x1600. Coordinates occupy 4 bytes of storage space.

As shown in Table 5-6, the slice compression storage format not only stores the boundary coordinates of the slice forming area, but also stores other related forming parameters. The forming parameters change dynamically to match the dynamic forming design.

The DPS slice compression format is a custom file format, which cannot be directly recognized by the system, so it is necessary to restore and fill the slice. Slice restore filling only needs to obtain a set of boundary coordinates each time, and fill the middle of the set of coordinates with white pixels.

2.3 Compression effect analysis

Compare several commonly used slicing file formats, including BMP files, binary files, DPS files, and the ChiTu slicing system with better compression effects. The experimental hardware environment is Windows 10 operating system, and the memory is 64GB. Two STL three-dimensional models were selected as examples to verify the DPS slice compression method of the present invention. The experiments all used a uniform layer thickness of 0.05mm, and the layers of the two three-dimensional models were 715 and 4796 layers respectively.

As shown in Table 5-7, the lion model uses BMP file format slices to occupy a total of 11171.9MB, binary file format slices occupy 349MB, ChiTu slice system slice files occupy 11.5MB, and the DPS slice file format designed by the present invention occupies 1.61MB. Similarly, the DPS slicing file obtained after slicing the hand-made model occupies the smallest memory, and the time spent on transferring the file is also the smallest. It can be seen that the slice compression method designed by the present invention has high practical value in actual work.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims

A slice compression method based on pixel coordinate marking of a molding area, characterized in that it comprises:

Analyzing the preset STL model, obtaining the height of the model, and slicing according to the STL model; the parsing of the STL model includes: obtaining relevant parameters, including the vertex information of the triangular patch in the model, the maximum value and the minimum value of the boundary of the model;

A slice file set is obtained by OpenGL slicing, the slice file set is composed of a plurality of slice files, and each slice file is a multi-row array composed of black pixels and white pixels;

Traversing each row of pixels of each slice file, judging whether there are white pixels including black pixels among adjacent pixels in the row of pixels, and if so, saving the coordinates of the white pixels as the boundary coordinates of the forming area;

Write the boundary coordinates into the compressed file to obtain a collection of sliced compressed files.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 1, it is characterized in that,

The boundary coordinates appear in pairs, and there are several pairs of boundary coordinates in each row of pixels.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 1, it is characterized in that,

The vertex information includes the coordinates and normal vectors of the three vertices of the triangle patch.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 1, it is characterized in that,

The binary format of the slice file is stored by byte, and the ASCII format is stored by line in plaintext.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 1, it is characterized in that,

The size of the STL model does not exceed the size of the molding table.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 1, it is characterized in that, further comprises:

Read the sliced file data, process it with OpenGL and display it.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 6, it is characterized in that,

Create a window first before starting to slice, and scale it according to the size of the LCD display;

After reading the model, adjust the viewing angle, use the viewing angle to observe the model view to simulate the intersection of the model and the cross-section, and save the cross-section pixels;

Move the viewing angle according to the slice thickness, and save the model slice pixels in this way.
A kind of slice compression method based on the pixel coordinate mark of forming area according to claim 7, it is characterized in that, further comprises:

The STL model is placed in the coordinate system, the observation point is adjusted to adjust the viewing angle, and the slice direction of the STL model is determined.
A method for compressing slices based on pixel coordinate marking of a molding area according to claim 8, further comprising:

Adjust the distance between the near plane and the origin of observation along the Z axis to obtain the section of the 3D model, obtain the section pixels, then write the section pixels into the slice file, and repeatedly move the near plane to obtain the slice set.