JP2001092987A - Image data processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a cross generic polygon list at high speed by efficiently performing cross generic discrimination in ray tracing. SOLUTION: When generating the cross generic polygon list of respective voxels 3 with an accelerating method based on the spatial division of ray tracing, the cross generic discrimination is performed by executing work for painting out the polygon 1 with voxels 3 for the unit of each polygon while using a 3DDDA algorithm and the identifier of that polygon 1 is added to the cross generic polygon list of voxels 5 used for painting out the polygon 1. Thus, in the case of cross generic discrimination, idle voxels can be excluded from the target of processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data processing method for generating a high-quality image of a three-dimensional object or the like by using a ray tracing method or a Z-buffer = Guro shading method in a computer system.

[0002]

2. Description of the Related Art Three-dimensional computer graphics (C)
As a general method of expressing a curved surface in G), a method of approximating a three-dimensional figure by a plurality of polygons is known.
These polygons are called polygons, and three-dimensional figures are drawn on a screen such as a CRT screen by projecting the polygons onto a two-dimensional image.

[0003] When an image is generated by a ray tracing method, that is, a ray tracing method, a high-quality image including reflection and transmission can be generated, but an extremely enormous processing time is required. Means for reducing the time are desired. Ray tracing provides high quality images,
Since an enormous amount of processing time is required to determine the intersection between a ray and an object, a high-speed algorithm for determining the intersection is essential.

Conventionally, a space division method has been used as a high-speed algorithm. The space is divided into cuboids called voxels, and a list of objects that each voxel intersects and encompasses in each voxel is generated and stored in advance. When actually performing ray tracing, instead of determining the intersection of the target ray and all objects, find the voxel through which the ray passes, and in the voxel unit, add the The intersection is determined only for the included object. This reduces the number of intersection judgments,
High-speed image generation becomes possible.

On the other hand, when generating an image by the Z-buffer method, the brightness is calculated for each polygon. However, in the case of the Gouraud shading method used for the Z-buffer method, the luminance is calculated only for the vertices based on some illuminance model. Since the brightness of the remaining polygon inside points is obtained by interpolation between vertices, an image can be generated in a short processing time. However, since a shadow created by an object cannot be expressed, some means of shadowing is desired to generate a more realistic image.

In order to generate an image with a shadow by the Z-buffer method, a shadow polygon method is used in which a virtual object consisting of a black polygon is regarded as being present in a range where the shadow exists, and the target polygon is hidden. A shadow feeler method that uses an algorithm called at the time of calculating the brightness at each point of a polygon and determines whether the polygon intersects with the vector connecting the point and the light source and determines whether the point is a shadow. Is generally used.

In the shadow feeler method, the intensity of transmitted light attenuated by an object is determined using the light transmittance of an object between a light source and a point on the polygon, and the intensity of light reaching the point on the polygon is determined. This is a method of calculating strength. First, a point on a polygon whose luminance is to be determined is determined, and a vector connecting the point and the light source is determined. A polygon that intersects this vector is examined, and the intensity of light from the light source is calculated assuming that light having an intensity corresponding to the light transmittance of the intersecting polygon reaches that point. The following formula (1) is a basic calculation formula used in the shadow feeler method. Light intensity reaching a point on the polygon = light intensity of light source × {P ₁ × P ₂ ×... P _n ×... _PN } (1) where P _n is _n from the light source This is the light transmittance of the intersection polygon that intersects the third. The above equation (1) represents a case where it intersects with N polygons.

FIG. 4A is a schematic diagram showing a digital straight line generated by DDA. FIG. 4B is a schematic diagram showing a digital straight line generated by line drawing. When determining the intersection between the line of sight and the object, 3D
An algorithm called ifferential analyzer) is used. 3DDDA generates a three-dimensional digital straight line. A digital straight line according to 3DDDA is different from a digital straight line generated by line segment drawing, for example, a digital straight line when a straight line is displayed on a display. 3DD
The digital straight line by DA is a row of all the voxels through which the base straight line passes. Does not constitute

[0009]

SUMMARY OF THE INVENTION In the ray tracing method,
Although the ray tracing process is sped up by adopting the high-speed algorithm of the space division type, preprocessing for the ray tracing process, that is, time for generating an intersection comprehensive polygon list for each voxel is required. The intersection inclusion polygon list is for determining which polygon the voxel intersects or encompasses, and records the distribution of the polygons before performing the processing by the ray tracing method.

For example, the space is divided into N voxels,
If there are M rendering target polygons in that space, simply performing the intersection comprehensive determination for each voxel requires N × M determination processes. When N and M become large, the time required for the process of the intersection comprehensive determination becomes too long to be ignored.
Many voxels are often empty voxels that do not contain polygons, and the more voxels the more empty voxels. Since such an empty voxel is ignored in the subsequent ray tracing method, it is useless to perform the cross-overall inclusion determination of the empty voxel.

On the other hand, when the shadow polygon method is used in the Z-buffer method, calculations such as derivation of a polygon shape and determination of a position before and after a real object are required. In addition, when the shadow feeler method is performed, there is a problem that shadow determination by intersection determination must be performed at each point on a polygon. In any case, it takes time to perform the shadowing process by the luminance calculation.

In view of the above-mentioned conventional problems, the present invention provides an image data processing method capable of generating an intersection inclusion polygon list at a high speed in a ray tracing method by excluding empty voxels from processing objects and performing intersection inclusion judgment. It is intended to provide.

Further, the present invention has been made in view of the above-mentioned conventional problems, and provides an image data processing method capable of calculating the vertex luminance of a polygon in the Z-buffer method in consideration of the influence of the shadow of another polygon. The purpose is.

[0014]

In order to achieve the above-mentioned object, according to the present invention, in generating an intersection comprehensive polygon list of each voxel performed as preprocessing of the space division method, 3DDD is used.
A digital straight line is generated using A, and the polygon is filled with voxels. It is determined that the voxel used to fill the polygon intersects or covers the polygon, and the polygon is added to the voxel intersection inclusion polygon list used to fill the polygon.

That is, according to the present invention, a step of dividing a space containing an object approximated by a polygon into a plurality of voxels, and a step of dividing each of the sides constituting a target polygon into a digital image comprising the plurality of voxels. Generating a straight line by 3DDDA; and obtaining an intersection between the boundaries of the plurality of voxels and the respective sides;
Adding an identifier of the target polygon to the intersection comprehensive polygon list of the voxels constituting the digital straight line, arbitrarily selecting one vertex of the target polygon, and selecting the selected vertex Generating, by 3DDDA, a new digital straight line composed of the plurality of voxels with respect to a line segment connecting the intersection and the intersection, and adding the identifier to an intersection comprehensive polygon list included in the voxels constituting the new digital straight line And an image data processing method.

To achieve the above object, according to the present invention, in the Z-buffer method, the vertex luminance is calculated in consideration of the light transmittance of an object that blocks light from a light source obtained using the shadow feeler method. Then, the luminance of the vertices is interpolated using the Gouraud shading method to calculate the luminance of a point on the polygon.

That is, according to the present invention, a step of calculating a vector between each vertex of a target polygon and a light source in an object approximated by a polygon, and a step of determining an intersection between the vector and a surrounding polygon Calculating the intensity of light from the light source reaching each of the vertices according to the light transmittance of the polygon determined to intersect; and calculating the luminance of each of the vertices based on the intensity of light. And calculating the brightness at a point inside the target polygon by interpolating the brightness at each of the vertices.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> An image data processing method according to the present invention will be described below with reference to the drawings. 2D in two-dimensional space to simplify the description
The DDA (2D Digital Differential Analyzer) will be described. Hereinafter, 2DDDA is simply referred to as DDA (Digital
Differential Analyzer). Further, as will be described later, expansion from a two-dimensional space to a three-dimensional space is easy.

FIG. 1 is a flowchart illustrating a first embodiment of the image data processing method according to the present invention.
FIG. 3 is a schematic diagram showing polygons in a space divided by voxels. Now, assume that the target polygon is an N-gon. In step S101, FIG.
(FIG. 3 depicts the case where N = 5), as shown in FIG.
According vertex transitions clockwise, assign V _n such that the value of the exponent is increased. Also, the sides of the polygon 1 of interest is a line segment connecting the vertex V _{n + 1} next to the positive direction in the clockwise direction with respect to V _n, polygons 1 of interest
Is represented by a line segment L (n, n + 1). However, if n = N, V _{N + 1} = V ₁ . Also, as shown in FIG. 3, it is assumed that the plane including the target polygon 1 is divided into voxels by S × S, and that there are S ² voxels 3.

In step S103, digital straight lines are generated by DDA for N line segments L (n, n + 1) from n = 1 to N. As a result, the N sides constituting the target polygon 1 can be represented by digital straight lines. At this time, in the process of DDA,
The intersection between the line segment L (n, n + 1) and the boundary of the voxel 3 is also determined at the same time.

FIG. 5 shows a line segment L (n, n + 1) and a voxel 3
FIG. 4 is a schematic diagram showing an intersection C (n, q) with the boundary of FIG. In step S105, it will be represented line L (n, n + 1) obtained in the DDA processing the intersection of the boundary voxel 3 from the forward close to V _n intersection C (n, q) and. Here, q is a reference number of each intersection, and q is a natural number.
Thus, the intersection C (n, q) for n = 1 to N
Is required.

The jagged line generated by DDA is a collection of voxels that comprise the line L (n, n + 1) a just proportion connecting the vertex V _{n + 1} vertices V _n. That is, one side of the target polygon 1 is constituted by the voxels 5 constituting the digital straight line as shown in FIG. 4A, and the voxel 5 constituting the digital straight line is constituted by the voxel 5 constituting the digital straight line. Because it includes, step S10
At 7, the identifier of the target polygon 1 is added to the intersection comprehensive polygon list of each voxel 5 constituting the digital straight line. However, if the identifier of the target polygon 1 already exists in the list, it is not necessary to perform the process of adding the identifier of the target polygon 1 to the intersection comprehensive polygon list. It is necessary to set an identifier of a polygon in advance so that one polygon can be specified from a plurality of polygons.

In the above embodiment, the processing of each step is collectively performed on all the sides of the target polygon 1. However, for each side, steps S103 to S10 are performed.
7 can be performed. That is, first, a digital straight line is generated by 3DDDA for the line segment L (1, 2), and the identifier of the target polygon 1 is added to the intersection comprehensive polygon list of the voxels 5 constituting the digital straight line. Next, the same processing is performed for the line segment L (2, 3). Then, by changing the target side, the line segment L
Step S1 for all sides up to (N, 1)
It is also possible to perform the processing of 03 to S107.

Next, in step S109, one vertex of the target polygon 1 is arbitrarily selected. Now, consider the case where the vertex _Vm is selected, for example. However, 1 ≦ m ≦ N
It is. In step S111, the line segment L (m-1,
m) and all C except points on the line segment L (m, m + 1)
(N, q) with respect to a line segment connecting the the vertex V _m, to produce a digital linear with DDA. That is, n ≠ m−1,
a m C (n, q) with respect to a line segment connecting the vertex V _m, to produce a digital linear with DDA. Then, in step S113, the identifier of the target polygon 1 is added to the intersection comprehensive polygon list of the voxels 5 constituting the digital straight line generated in step S111. However, as in the case of step S107, if the identifier of the same polygon already exists in the intersection comprehensive polygon list, it is not necessary to perform the process of adding the identifier. By the above steps S101 to S113,
It becomes possible to check all voxels 3 including a certain polygon 1 to be processed.

The line segment L (m-1, m) and the line segment L
(M, m + 1) points on is identical to the line segment connecting the segments and C (m, q) connecting the C (m-1, q) and V _m and the V _m. Therefore, already in step S107, the line segment L
Since the work of adding the identifier of the target polygon 1 to the intersection inclusion polygon list of the voxels including (m-1, m) and the line segment L (m, m + 1) is performed, n = m in step S111. -1 and C (n, n = m
For the line segment connecting q) and a V _m, it is not necessary to generate a digital line.

Further, by performing the above steps in units of polygons, intersection determination between polygons and voxels can be performed for all polygons in the three-dimensional space.
An intersection comprehensive polygon list can be created for all voxels.

In the above embodiment, a polygon in a two-dimensional space is considered for the sake of simplicity, and a plane including the polygon is divided into voxels by S × S. The polygon is embedded in a three-dimensional space. However, for a polygon in an actual three-dimensional space, a digital straight line may be generated with respect to the side of the polygon using 3DDDA, and the same process as in the above embodiment may be performed. Therefore, it is easy to expand the voxel two-dimensional space to the three-dimensional space, and the case of actually processing polygons in the three-dimensional space is the same as the above-described two-dimensional space embodiment.

When the target polygon 1 is an N-sided polygon, it is also possible to divide the N-sided polygon into triangles and then perform the processing from step S113. In this case, the process of dividing the N-sided polygon into triangles is a process performed instead of step S111. Consider dividing the N polygon into triangles, and in each triangular polygon after division,
An identifier of a voxel passing through a line segment connecting the intersection C (n, q) on the side connecting the two vertices and a vertex different from the two vertices is added to the intersection comprehensive polygon list.

<Second Embodiment> FIG. 2 is a flowchart for explaining a second embodiment according to the image data processing method of the present invention.

When calculating the brightness at the vertices, first, in step S201, a vector from each vertex of the target polygon 11 to the light source 13 is calculated. Next, in step S203, an intersection between the vector calculated in S201 and surrounding polygons constituting the image is determined. This is to determine whether there is another polygon between the light source 13 and each vertex of the target polygon 11, as shown in FIG. If it is determined in step S203 that there is a polygon 15a, b that intersects the vector, a shadow feeler method is used that considers that light having an intensity corresponding to the light transmittance of the surrounding polygon 15a, b reaches the vertex. In step S205, the light source 1 at each vertex
The light intensity is calculated from Equation (3) according to Equation (2).

Light intensity reaching the apex of the polygon = light intensity of light source × {P ₁ × P ₂ ×... × P _n ×... × P _N } (2) where P _n is light from the light source Is the light transmittance of the polygon 15 that intersects nth. The above equation (2) represents a case where the polygon intersects with N polygons. The light transmittance of each polygon is given in advance as data unique to each polygon. If it is determined in step S203 that they do not intersect, it is considered that the light intensity at the vertex is equal to the light intensity of the light source. When calculating the light intensity at the vertices using the equation (2), the light attenuation may be considered according to the distance between each vertex and the light source.

FIG. 6 shows polygons 15a and 15b intersecting a vector connecting the vertices of the target polygon 11 and the light source 13.
FIG. 3 is a schematic diagram showing an example in which is present. It is assumed that there is a polygon 15a having a transmittance P ₁ = a and a polygon 15b having a transmittance P ₂ = b on a vector connecting one vertex V ′ of the target polygon 11 and the light source. In this case, the intensity F 'of light reaching the vertex V' from the light source 13 is as follows. F ′ = light source intensity × a × b

The light intensity at each vertex calculated by the equation (2) in step S205 is equal to the light source 1 reaching the vertex.
3 is the intensity of the incident light. In step S207, the luminance at each vertex is calculated by substituting the obtained intensity of the incident light from the light source into a luminance calculation model formula for calculating diffuse reflection, specular reflection, and the like. Further, in step S209, by performing interpolation calculation by the Gouraud shading method using the calculated vertex luminance, it is possible to calculate the luminance at an arbitrary point on the polygon.

Further, in the case of the Z-buffer method, generally, luminance calculation using the light transmittance of a polygon is not performed. Therefore, in the case of simplified data in which the light transmittance of the polygon is not defined, if the light transmittance of the polygon is all 0, the intensity of the transmitted light is 0, and the intersection with one polygon can be detected. At this point, the remaining intersection determination becomes unnecessary, and a reduction in processing time can be expected.

[0035]

As described above, according to the present invention, in the generation of the intersection comprehensive polygon list of each voxel to be performed as preprocessing of the space division method, the polygon is filled with the voxel for each polygon using the 3DDDA algorithm. Perform the work, determine that the voxel used for filling the polygon intersects or is inclusive with the polygon, and add the identifier of the polygon to the intersection inclusion polygon list of the voxel used for filling the polygon, It is not necessary to perform useless intersection comprehensive determination for an empty voxel that does not include a polygon as in the related art, and the processing time can be reduced. Also, according to the present invention, in generating the intersection comprehensive polygon list of each voxel, the 3DDDA algorithm processing function which is also required in the ray passing voxel determination performed at the time of ray tracing by the space division method is used. Increase in size can be avoided.

As described above, according to the present invention, in the Z-buffer method, the vertex luminance is calculated in consideration of the light transmittance of an object that blocks light from the light source obtained by the shadow feeler method. Since the brightness of vertices is interpolated using the Gouraud shading method to calculate the brightness of points on the polygon, the processing time can be reduced compared to the conventional shadow feeler method, and the conventional Gouraud shading The luminance calculation can be performed with higher precision than the method.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a first embodiment of an image data processing method according to the present invention.

FIG. 2 is a flowchart illustrating a second embodiment of the image data processing method according to the present invention.

FIG. 3 is a schematic diagram showing polygons in a space divided by voxels.

FIG. 4 is a schematic diagram showing a digital straight line generated by DDA and a digital straight line generated by line segment drawing.

FIG. 5 is a schematic diagram showing an intersection C (n, q) between a line segment L (n, n + 1) and a boundary of a voxel 3;

FIG. 6 is a schematic diagram showing an embodiment in which a polygon exists on a vector connecting a vertex of a target polygon and a light source.

[Description of Signs] 1, 11 Target polygon 3 Voxel 5 Voxel constituting digital straight line 13 Light source 15 Polygon that intersects vector from each vertex of target polygon 11 to light source 13

Claims (2)

[Claims] 1. A step of dividing a space containing an object approximated by a polygon into a plurality of voxels, and generating a digital straight line constituted by the plurality of voxels by 3DDDA for each side constituting a target polygon. Determining the intersection of the boundary of each of the plurality of voxels and each of the sides, and adding the identifier of the target polygon to the intersection comprehensive polygon list of the voxels constituting the digital straight line, Arbitrarily selecting one vertex of the target polygon; and, regarding a line segment connecting the selected vertex and the intersection, a new digital straight line composed of the plurality of voxels is created in 3D.
An image data processing method, comprising: generating by the DDA; and adding the identifier to the intersection comprehensive polygon list included in the voxels constituting the new digital straight line. 2. An object approximated by a polygon,
Calculating a vector between each vertex of the target polygon and the light source; determining an intersection between the vector and a surrounding polygon; and determining each of the vertices according to the light transmittance of the polygon determined to intersect. Calculating the intensity of the light from the light source that reaches, and calculating the luminance of each vertex based on the intensity of the light, by interpolating the luminance at each vertex. Calculating the luminance at a point inside the target polygon.