KR100795600B1 - A medium which can be read by a computer, storing a table structure for a modified marching cube method adapted for volume ray casting - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer readable medium recording a table structure for a marching cube method modified for the volume ray projection method, wherein the eight voxels are transparent to each of the eight voxels constituting a cell. An index table for which a value is determined; And a side-table using a result value of the index table as an input value and having an output value of information on the 12 sides constituting the cell in response to the input value. Characterized by the medium being present.

In particular, in the table structure, the side-table includes a first field including information on the number of triangles included in the case corresponding to the input value, for the address corresponding to each input value, and the input value. In the case of, and includes a second to thirteenth field, each of which includes information on the twelve sides constituting the cell, each of the second to thirteenth field is associated with each side to which it corresponds Thus, a first subfield and a second subfield each including information about two vertices constituting the side, and a third subfield indicating which of the two vertices constituting the side is transparent. It characterized by including the.

When using the method according to the present invention, even if all the sample points of the transparent cells belong only to the transparent region, it is possible to jump, thereby improving the rendering speed without degrading the image quality.

Marching Cube, Volume Ray Projection, Voxel, Cell, Transparent Cell, Opaque Cell, Translucent Cell, Space Jump, Resampling Filter, Table Structure, Index Table, Side Table, Field, Subfield

Description

A computer-readable medium that records a table structure for the marching cube method modified to fit the volume ray projection method.

1 shows an example of a translucent cell in a two-dimensional plane.

2A is a diagram showing a floor chart according to a conventional volume ray projection method.

Figure 2b is a view showing a floor chart according to the volume ray projection method proposed in the present invention.

3 is a view for explaining a method of determining whether a resampling step is required in a translucent cell according to the volume ray projection method proposed in the present invention.

4 is a diagram illustrating 15 cases of a polygon generating method used in a conventional marching cube method.

5 is a view showing the structure of a table used in the conventional marching cube method.

FIG. 6 is a view illustrating only eight cases corresponding to cases required for the volume ray projection method proposed in the present invention among polygon generation methods used in the conventional marching cube method. FIG.

7 shows the structure of a table modified to conform to the modified marching cube method according to the invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer readable medium recording a table structure for a marching cube method modified to fit the volume ray projection method. More specifically, the marching cube method used in the surface rendering method of volume rendering techniques is a direct volume. A table structure optimized for the marching cube method, which is modified to apply to the volume ray projection method, is modified to apply to the volume ray projection method, which is one of the rendering techniques. A computer readable medium.

The volume rendering technique is a technique of extracting and visualizing meaningful information from volume data. Volume data may be represented by a voxel (voxel, volume element), and a cube structure composed of eight voxels is called a cell. The case where all eight voxels constituting the cell are transparent among the cells is called a transparent cell, and the case where all eight voxels are opaque is called a nontransparent cell. In addition, a cell in which both transparent and opaque ones of the eight voxels constituting the cell exist is called a semi-transparent cell. 1 shows an example of a translucent cell in a two-dimensional plane. As shown in FIG. 1, the translucent cell includes both transparent and opaque regions.

Volume rendering techniques include surface rendering techniques and direct volume rendering techniques. The marching cubes method is a representative method of surface rendering techniques, and is a method of expressing volume data in a mesh form. The marching cube method will be described in more detail below. The direct volume rendering technique is a technique of directly rendering volume data without reconstructing it into a mesh form, and the most typical method is volume ray casting.

The volume ray projection method fires a virtual ray from a pixel and then leaps when the ray is placed in a transparent cell, and when the ray is placed in an opaque cell or translucent cell, the current sample point is actually on the surface or inside of the object of interest. In order to accurately determine whether or not, the density value is estimated by using a resampling filter, and then a color value is obtained by shading. As a resampling filter, trilinear interpolation is widely used in volume ray projection. Since it is composed of seven linear interpolations, it is possible to calculate the exact density value, but there is a problem that it is slow due to the large amount of calculation.

In addition, the space-leaping algorithms previously proposed as direct volume rendering techniques can rapidly leap to transparent cells to speed up the rendering process, but both transparent and opaque regions exist for the semi-transparent cells. Therefore, it was not possible to know whether the sample point belongs to the transparent region or the opaque region, and thus, the density value was inferred using the resampling filter as in the opaque cell. However, among the semi-transparent cells, as illustrated in FIG. 1, although all sample points belong to only transparent regions, rendering processing speed may be increased by leap. However, this is not possible in conventional space hopping techniques.

The present invention has been proposed to solve the above problems, by modifying the marching cube method that is used in the surface rendering technique of the volume rendering technique by applying to the volume ray projection method, which is one of the direct volume rendering techniques, Likewise, if all the sample points of the semi-transparent cells belong to the transparent area, we propose a method that can speed up the rendering process. For this purpose, the table structure optimized for the existing marching cube method is changed to apply the volume ray projection method. An object of the present invention is to propose a computer-readable medium that records a table structure that is optimized for a marching cube method modified to fit.

According to a feature of the present invention for achieving the above object, a computer-readable medium recording a table structure for the marching cube method modified to fit the volume ray projection method,

After firing a virtual ray from a pixel, the ray leaps when placed in a transparent cell, and when the ray lies in an opaque or translucent cell, a resampling filter to determine exactly whether the current sample point is actually on or inside the object you want. A computer-readable medium recording a table structure for a marching cube method modified for the volume ray projection method of estimating density values using

An index table whose value is determined according to whether each of the eight voxels is transparent to the eight voxels constituting the cell, and

A side-table which uses the result value of the index table as an input value and has information about the 12 sides constituting the cell as output values in response to the input value.

Including,

The side-table, for the address corresponding to each input value,

A first field including information on the number of triangles included in the case corresponding to the input value;

Second to thirteenth fields each of which includes information about twelve sides constituting the cell when the input value corresponds to the input value;

Including;

Each of the second to thirteenth fields may be associated with each side to which it corresponds.

A first subfield and a second subfield each including information on two vertices constituting the side;

A third subfield indicating which of the two vertices constituting the side is transparent

It characterized by including the.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2A is a diagram illustrating a floor chart according to a conventional volume ray projection method. As shown in FIG. 2A, according to the conventional volume ray projection method, first, a virtual ray is emitted from a pixel (s110), and then a space jump is performed on transparent cells (s120). Trilinear interpolation determines whether the sample point is transparent or opaque (S130). If the sample point is transparent, it moves to the next sample point (s170), but if it is opaque, shading and accumulation is performed (s140), and if the opacity is 1.0 ('yes' in s150), the color value is returned ( s160). If the opacity is not 1.0, that is, no in step S150, the process moves to the next sample point (S170).

2B is a diagram illustrating a floor chart according to the volume ray projection method proposed in the present invention. As shown in Fig. 2B, the volume ray projection method proposed in the present invention basically includes the same steps as the conventional volume ray projection method (the corresponding or identical steps in Figs. 2A and 2B are denoted by the same reference numerals). However, after the space jump to the transparent cells (s120), it is not determined whether the corresponding sample point is transparent through trilinear interpolation, but instead of the sample point and the hexahedron (for the cell including the sample point to be investigated currently, In-out inspection of all triangles created using the cube method, with an in-out test, indicates that the sample point is inside the cube (ie in the opaque region) or outside the cube (ie in the transparent region). (S180), if the sample point is outside the hexahedron, it moves to the next sample point immediately without trilinear interpolation (s190) to improve the processing speed of the volume rendering. If it is determined in step s180 that the sample point is inside the hexahedron, it is determined whether the sample point is transparent through trilinear interpolation as in the conventional volume ray projection method.

3 is a view for explaining a method of determining whether a resampling step is required in a translucent cell according to the volume ray projection method proposed in the present invention. Although it should be shown in three dimensions in reality, it is shown in two dimensions for ease of understanding. Referring to FIG. 3, since the sample point s1 is placed in the transparent cell, the sample point s1 may proceed through the leap according to the conventional space leaping technique (step s120 of FIG. 2b). When the ray is placed in the translucent cells such as s2, s3, s4, and s5, it is determined whether the resampling filter is applied through an in-out test with the hexahedral region. Since the sample points s2, s3, and s4 place the sample points outside the cube, they move to the next sample point immediately without resampling (steps s180 and s190 in FIG. 2b). On the other hand, since the sample point s5 has a sample point inside the cube, it is necessary to further determine whether the sample point belongs to the transparent region or the opaque region by applying a resampling filter (steps s180 and s130 to s170 of FIG. 2b). ). As described above, according to the present invention, the sample points of the semi-transparent cells that exist outside the hexahedron and belong to the transparent region can be leaped to the next sample point without further investigation, thereby increasing the processing speed. Enable improvement.

Next, referring to FIGS. 4 to 7, a comparison of the existing marching cube method and the modified marching cube method newly proposed by the present invention will be described.

The marching cube method is a representative technique of surface rendering among volume rendering techniques. A single value-surface (polygon is created by connecting boundary points where state changes occur between voxels). Fast value approximation). The marching cube method considers eight adjacent voxels constituting a cube (cube) as one cell, and generates a polygon for each cell constituting the volume. The state of each cell can be expressed in 256 cases depending on whether 8 voxels are inside or outside, and this is reduced to 15 cases in consideration of symmetry, and the polygon generation method has 15 indices. The marching cube method is a method of creating a surface using a reference table at high speed. 4 is a diagram illustrating 15 cases of a polygon generating method used in a conventional marching cube method.

5 is a view showing the structure of a table used in the conventional marching cube method. As shown in FIG. 5, the existing marching cube method uses two tables, an index table (a table located at the top of FIG. 5) and an edge table (a table located at the bottom right of FIG. 5). . The index table is composed of 8 bits corresponding to each of the eight voxels constituting the cell, and corresponding bits are 0 or 1 according to the transparency of the density values of each of the eight voxels. It is a structure that can be determined. The data structure of these tables is very optimized for the existing marching cube method because it stores the geometric information of the generated triangles. However, since the method according to the present invention needs to quickly calculate the intersection of the cube, it is necessary to change the existing table structure. Hereinafter, the marching cube method modified according to the needs of the present invention with reference to FIGS. 6 and 7 and The table structure used here will be explained.

Referring back to FIG. 4, all of the existing marching cube methods use 15 polygon generation methods. However, in the marching cube method modified according to the present invention, it is not necessary to use all 15 of these methods, and the cases that need to be excluded are as follows. In the first case, it is noted that trilinear interpolation is composed of seven linear interpolations, except that the number of linear interpolations when generating a cube that surrounds triangles generated by marching cubes is seven or more times. This is because, if the number of linear interpolations is more than seven times, applying this method may rather slow down the speed. Cases 7, 10 and 13 in FIG. 4 correspond to this case, which requires 9, 8 and 12 linear interpolations, respectively. In the second case, the hexahedron surrounding the triangles created by the marching cube covers the entire cell. This is because, in this case, the result of the in-out inspection of the cube and the sample point always includes the sample point inside the cube area (that is, it always appears to require trilinear interpolation). Cases 9, 11 and 14 in FIG. 4 correspond to this case. Finally, the third case excludes the case 0 in FIG. 4. This is because in this case, after the leap with the existing space leap technique. Except for the three cases described above, Fig. 6 shows a method for generating polygons in eight cases of marching cubes for use in the volume ray projection method according to the present invention. The shaded portions in FIG. 6 represent the generated cubes. In the marching cube method according to the present invention, the number of cases to be considered in the polygon generating method is not only changed, but the structure of the table to be used is also changed. The structure of the table changed according to the needs of the present invention will be described below with reference to FIG. 7.

7 is a view showing the structure of the table modified to be suitable for the modified marching cube method according to the present invention. Although not shown in FIG. 7, the same table structure as that shown in FIG. 5 is used in the table structure modified according to the present invention. That is, even in the table structure modified according to the present invention, 8 bits corresponding to each of the 8 voxels constituting the cell are configured so that corresponding bits become 0 or 1 according to the transparency of the density values of the 8 voxels. Therefore, we use an index table with a structure that can determine the index on the side table. The difference between the table structure modified according to the present invention and the existing table structure is that a side table composed of 13 fields is used as shown in FIG. 7. The first field of the thirteen fields stores information on the number of triangles included in a value corresponding to a value of an index table. In an embodiment of the present invention shown in FIG. The number of triangles included in the case can be known by knowing the number of cases in the marching cube. For example, if the value of the index table is 1, it corresponds to 1, so the value of '1' is stored in the first field. If the value of the index table is 30, the value is '12'. do. In the method according to the present invention, a value of '-1' is stored in the first field when it is not used. In this case, the process proceeds directly to step S130 in FIG. 2B to perform trilinear interpolation. The remaining 12 fields of the 13 fields store information on the 12 sides constituting the cell, each of which includes three subfields. The three subfields may include first and second subfields each of which includes information about two vertices constituting the side (for example, a position of an intersection of a cube), and one of two vertices constituting the side. It consists of a 3rd subfield which shows whether a side is transparent (namely, the orientation information of a cube).

In one embodiment according to the present invention, the first and second subfields store the position of the voxel with respect to the position of the intersection of the hexahedron among the information on the vertices, which is not the geometric information of the triangles but the position information of the intersections in the present method. Because it is necessary. In addition, the third subfield stores directional information of a cube, which can be understood that only an intersection point exists between both voxels with only the first and second subfields, and a cube is located between the intersection points from the left voxel of both voxels. This is because it is not known whether or not there is a cube or a cube exists between the intersection points from the right voxel.

For example, case 1 of FIG. 6 will be described. Case 1 creates one cube with intersections on sides 0, 4, and 8. First, referring to the side 0, the side is composed of voxels 0 and 1, forming a cube between the intersection point from the voxel 0. Looking at the information on the side 0 of the row corresponding to the value 1 of the index table in Figure 7 is (0, 1, 0), which is composed of voxel 0 and 1, the cube is formed between the intersection from the left voxel (Indicated by '0'), which corresponds to side 0 of 1 in the case described above. Similarly, in the case of side 4 of case 1, the side is composed of voxels 0 and 2, and a cube is formed between the intersection points from voxel 0, which is information about side 4 of the row corresponding to value 1 of the index table of FIG. Matches (0, 2, 0). The value of the table is determined in the same manner for the case 8 as well as for each of the remaining cases.

As an exception, if two or more intersections are located on each axis, and the values of the third subfield are the same (that is, the cubes are in the same direction), you must create a cube that surrounds all the triangles that are created. Therefore, the maximum and minimum values should be considered. In this case, when the third subfield is '0', a maximum value among two or more intersection points of the same axis is selected, and when the third subfield is '1', a minimum value is selected. As another exceptional case, the case where the hexahedral region covers all the specific axes of the cell can be considered. In this case, (-1, -1, -1) is set in the subfield because it does not need to be considered separately.

Experiment and result

Athlon this experiment to demonstrate the effectiveness of the table structure proposed for how the modified marching cubes to meet the volume light projection method, and this suggests that the present invention AMD's 64x2 ^TM 4200+ central processing unit (CPU Athlon 64x2 ^TM 4200+) And a PC with 2GB of main memory. Six experimental data were used, and the sizes are shown in Table 1 below.

data size data size head 512 × 512 × 450 engine 512 × 512 × 512 Cerebral artery 512 × 512 × 512 kettle 512 × 512 × 356 teeth 512 × 512 × 322 Bonsai 512 × 512 × 512

Since the method according to the present invention is a method for selectively leaping and accelerating translucent cells, there is a need for a conventional space leaping technique for effectively leaping empty space. For this purpose, the distance map data structure and hierarchical maximum-minimum octree data structure are used. Table 2 shows the percentage of improvement in rendering speed when using the method according to the invention after fixing the viewpoint.

head Cerebral artery teeth engine kettle Bonsai Average Case 1 18.8 23.0 21.5 20.5 22.0 24.1 22 Case 2 16.8 19.6 18.1 18.9 20.1 21.7 19

In Table 2, Case 1 uses the distance map data structure as a space leap technique, and Case 2 uses the hierarchical maximum-minimum octree. As can be seen in Table 2, when using the method according to the invention it was possible to improve the speed of about 20% compared to the existing method. In addition, as a result of comparing the pixel values of the image before and after applying the method according to the present invention, it was confirmed that there was no difference, which means that there was no deterioration of the image quality by the method according to the present invention. In conclusion, when the method according to the present invention is used, the rendering speed can be improved without degrading the image quality.

The present invention described above may be variously modified or applied by those skilled in the art, and the scope of the technical idea according to the present invention should be defined by the following claims.

According to the present invention, the marching cube method, which is used in the surface rendering method of the volume rendering method, is modified and applied to the volume ray projection method, which is one of the direct volume rendering methods, and for this purpose, the table structure optimized for the existing marching cube method is changed. By suggesting a table structure optimized for the marching cube method modified to fit the volume ray projection method, even if all the sample points of the semi-transparent cells belong only to the transparent area, the rendering process can be improved by leaping. It does not cause any deterioration in image quality.

Claims (3)

After firing a virtual ray from a pixel, a cube structure consisting of eight voxels, which are transparent cells (three-dimensional pixels), is called a cell. When the eight voxels are all transparent, they are placed in a transparent cell, and they leap, and the ray is a nontransparent cell (the case where all eight voxels constituting the cell are opaque is called an opaque cell) or a semi-transparent cell (semi-). When placed in a transparent cell (the case where both transparent and opaque voxels are present) is called a translucent cell. A computer readable medium recording a table structure for the marching cube method modified for the volume ray projection method of estimating a value, An index table whose value is determined according to whether each of the eight voxels is transparent to the eight voxels constituting the cell, and A side-table which uses the result value of the index table as an input value and has information on the 12 sides constituting the cell as output values in response to the input value. Including, The side-table, for the address corresponding to each input value, A first field including information on the number of triangles included in the case corresponding to the input value; Second to thirteenth fields each of which includes information about twelve sides constituting the cell when the input value corresponds to the input value; Including; Each of the second to thirteenth fields may be associated with each side to which it corresponds. A first subfield and a second subfield each including information on two vertices constituting the side; A third subfield indicating which of the two vertices constituting the side is transparent A computer-readable medium having recorded thereon the table structure comprising a. The method of claim 1, In the field corresponding to the side that does not need to be considered in the modified Marching Cube algorithm among the 12 sides constituting the cell, a value of (-1, -1, -1) is set. Readable media. The method of claim 1, And the first field includes information on the number of triangles included by storing which one of the fifteen types of marching cubes is included.

Images