JP3733493B2 - Image composition circuit - Google Patents

Description

The present invention relates to a hardware circuit for generating an object having a gaseous shape such as a fog or a cloud in a three-dimensional space by computer graphics and dynamically visualizing the object, and its volume rendering. .
[0001]
[Conventional technology]
Many shape models that display three-dimensional objects by computer graphics are curved or solid models, and by generating reflections and shadows between light sources or objects on these surfaces, real images can be generated. Yes. Many of these use rendering techniques called ray tracing or radiosity methods. Unlike object display methods such as this curved surface model, expressing natural phenomena such as fog and clouds requires calculation of complex shapes, dynamic changes, diffuse reflection, etc., and requires a lot of calculation time. is doing. In addition, a process for synthesizing these gaseous objects with a curved surface model in a three-dimensional space is also necessary. From this point of view, there are almost no examples of the computer graphics display by the hardware of the gaseous object as volume rendering until today, except for the circuit shown in Japanese Patent Application No. Hei 7-201251, which is generated only by software. It was. On the other hand, in Japanese Patent Application No. Hei 7-202511, as a method for displaying a gaseous object more realistically, such as a brushing effect, the number of primitives and the viewpoint coordinate value Z are smoothed and filtered, respectively, and then a surface defining object is obtained. The Z value is determined for the object, and the luminance and the transparency are calculated only for the primitive whose Z value is closer to the viewpoint than the surface object, and is combined with the surface definition object. In this method, if the presence of primitives is rough, the Z value after smoothing will decrease significantly and will move behind the surface definition object, and some gaseous objects will be present in front of the surface definition object. Even if it was doing, the phenomenon which is not displayed has occurred. The purpose is to provide a continuous and appropriate transparency according to the density and position when a gaseous object surrounds a surface-defining object. In the present invention, two methods are introduced in order to effectively obtain this effect. One is to generate a gaseous object (primitive) having a Gaussian distribution, and then generate a primitive having a Gaussian distribution around the coordinate point of each primitive. Further, a third primitive is generated around the point of the second primitive thus generated. By repeating the above process, a gaseous object figure having a hierarchical structure is formed. As a result, it is possible to express an image of a gaseous object having a high density locally by raising the density of the lower hierarchy higher than that of the upper hierarchy, and filtering this reduces the coarse particle image.
The other method does not filter the Z value as before, but first compares the Z value of the gaseous and surface-defined objects directly, and if the Z value of the gaseous object is closer to the viewpoint than the surface-defined object , Leave the overlap value as is, but if it is far away, set it to a specific value, for example, zero, and then filter these overlap numbers, where there is a primitive corresponding to that overlap number. It is assumed that it exists, and the transparency for the surface definition object is determined using this value and the primitive luminance. Unlike the conventional method, this method means that the concentration distribution is averaged by averaging the number of overlaps, rather than determining whether or not a gaseous object is displayed based on the Z value of the primitive. It has a feature that changes in luminance can be obtained. As a result, in the present invention, it is possible to provide a realistic video with a greater expressiveness than the display based on the Z value.
[0002]
[Means for solving problems]
A surface definition object is one of shape models that define an object by a polyhedron.
As shown in Japanese Patent Application No. 7-202511, the transmittance must be calculated in order to synthesize a gaseous object and a surface-defined object. In this method, first, the surface definition object and the gaseous object are stored in the image memory, and at this time, the hidden surface is deleted independently. In the process of storing a primitive in the image memory, if there is a primitive already stored at that location when writing to the memory, the Z value (distance from the viewpoint) of the primitive is compared, and information closer to the viewpoint Is stored in the image memory. Therefore, only one primitive closest to the viewpoint is always stored in the image memory. At this hidden surface removal stage, if there are already primitives and they overlap, the number of overlaps is counted each time. Although only the coordinate value closest to the viewpoint is stored in the image memory, the density in the three-dimensional space with respect to the viewpoint axis of the primitive constituting the gaseous object can be known from the number of overlaps. That is, when the number of overlaps is large, the number of primitives per unit area (XY plane) is large, resulting in a high-density distribution.
In a high-density distribution, when a gaseous object exists in front of a surface-defining object, the transmittance decreases. In the synthesis of the surface definition object and the gaseous object, first, the gaseous object and the surface definition object are individually stored in the image memory, and each has two kinds of data, that is, image (color or luminance) information and Z value. In addition to this, a gaseous object has an overlapping number for each primitive (pixel). When the drawing of the gaseous object and the surface-defining object is finished, the image and the Z value (including the overlapping number of the gaseous object) are taken over from the respective image memories and sequentially read out. If the number of overlaps is used for alpha blending to simply synthesize an image, a gaseous object composed of scattered primitives can form a mottled spot-like pattern of primitives on the curved surface of the surface defining object. This is the result of emphasizing scattered states, especially for a few primitives.
Smoothing filtering is necessary to eliminate this spot shape. On the other hand, in a collection of point groups based on a single Gaussian distribution, the positioning of the points is coarse and the filter effect is not very good. For this reason, it is effective to perform filtering after generating a point group consisting of a Gaussian distribution centered on each point based on a Gaussian distribution and making it locally high in density.
In Japanese Patent Application No. 7-202511, 3 × 3 smoothing filtering was applied to each of luminance, Z value, and number of overlaps when a gaseous object was read out as serial data from the image memory. On the other hand, in the present invention, Z values are compared as they are without filtering. If the primitive is closer to the viewpoint than the surface definition object, the number of overlaps is directly given to the filter circuit.
On the other hand, if it is far away, it is changed to a specific smaller value and then applied to the filter circuit.
As a result, the number of overlaps after smoothing changes depending on the context with respect to the viewpoint axis with respect to the surface definition object.
That is, when many primitives are located on the rear surface of a planar object, the number of overlaps decreases, and when it is in front, increases. The present invention assumes that there is a gaseous primitive in all projected coordinates (perpendicular to the viewing axis) where there is an overlap number due to smoothing (the value is not zero) and this value is already smoothed Color blending is performed in consideration of the transmittance with the surface from the luminance of the primitive. This method is easier to control the transmittance than the conventional method. This transmittance is determined by the reciprocal of the number of overlaps.
Therefore, in Japanese Patent Application No. 7-202511, the gaseous object is simply deleted when it is far from the surface with respect to the viewpoint. Therefore, when the surface definition object is located in the gaseous object space, the gaseous primitive In the present invention, the existence of a primitive is positioned by smoothing regardless of the presence or absence of a Z value, while some are deleted by the Z value and others are displayed. The Z value is only used to determine the number of overlaps, ie the transmittance.
[0003]
[Example]
An example of the gaseous object generation circuit of the present invention is shown in FIG.
In FIG. 1, a predetermined number of primitives are generated from a gaseous object by a random number and Gaussian distribution circuit 1, and at this stage, the primitives are constituted by three-dimensional coordinate points. The circuit 2 is a random number and Gaussian distribution circuit like the circuit 1. The circuit 3 is the same. The coordinate value A of the first primitive output from the circuit 1 is added to the reference point P0 by the adder 4a, and then becomes the base value (center point) of the primitive coordinate value B output from the circuit 2, and the adder 4b. The second primitive is positioned at P0 + A + B.
This value is added to the primitive coordinate value C output from the circuit 3 by the adder 4c. Therefore, in the third hierarchy, the position of the primitive is P0 + A + B + C. By defining the distribution ratio and density independently in each of the circuits 1 to 3, a point group with locality can be configured.
FIG. 2 is a circuit relating to the present invention. The primitive generated in FIG. 1 is stored in the image memory 5 as luminance and three-dimensional coordinate values after predetermined processing. When writing data to the image memory 5, hidden surface removal and the number of overlaps are counted by the hidden surface removal circuit 6. The brightness (fl), Z value (fz), and number of overlaps (m) stored in the image memory 5 are read out in a scanning procedure in synchronization with the video frequency of the display device. Of this data, the luminance (fl) is input to the smoothing filter circuit 7 and smoothed. The Z value (fz) is compared with the surface definition object for each pixel in the comparison circuit 8 and the comparison result is given to the selector 9. The selector 9 selects the overlap number (m) as it is when the gaseous object is in front of the surface-defining object based on the comparison result, and selects zero or a predetermined value (n) when it is on the rear surface. This selected number of overlaps is added to the second smoothing filter 10. The smoothed number of overlaps is converted into a predetermined perspective coefficient through the storage element 11, and multiplied by the smoothed brightness (gl) of the gaseous object and the brightness (sl) of the surface-defined object by the multipliers 12a and 12b, respectively. Then, these are added by the adder 13 to obtain a composite image.
[0004]
[effect]
By implementing the hardware of the present invention, a gaseous object and a surface-defined object can be synthesized at high speed in a three-dimensional space, and real-time display indispensable for drawing a virtual reality system becomes possible.
[Brief description of the drawings]
FIG. 1 Primitive generation circuit of the present invention FIG. 2 Gaseous object display circuit of the present invention
1-3 Random number and Gaussian distribution circuit 4a-4c Adder 5 Image memory 6 Hidden surface elimination circuit 7 Smoothing filter circuit 8 Comparison circuit 9 Selector 10 Smoothing filter circuit 11 Storage element 12 Multiplication circuit 13 Addition circuit

Claims (1)

A circuit that generates a natural phenomenon object composed of a gaseous shape as a computer graphic image and synthesizes it in a three-dimensional space with a surface definition object.
The minimum graphic element that represents a gaseous object is defined as a primitive. This primitive consists of three-dimensional coordinate values and luminance, and is generated using the first random number and probability distribution function circuit. A first means having at least two or more levels of this hierarchical process for generating a primitive by means of a second random number and a probability distribution function circuit as a reference point;
A second means for generating the shape of the gaseous object by independently defining the density and distribution rate of the probability distribution function in each layer;
When storing primitives in the image memory, if there is a hidden surface removal process and a primitive that overlaps on the same viewpoint coordinate axis, the primitive luminance of the primitive information stored in the image memory is a smoothing filter. In addition to smoothing, the viewpoint axis coordinate values of the primitive and the surface definition object are compared, respectively, and the primitive overlaps with respect to the viewpoint with respect to the viewpoint, respectively, far away from or in front of the surface definition object. A third means for smooth filtering after setting the number to a predetermined value;
The transparency value for the surface definition object is determined from the smoothing overlap number obtained by the smoothing filtering, and the transparency value is multiplied by the primitive and the surface definition object luminance, respectively, and then added to each other to add the surface definition object and the gaseous object. And a fourth means for synthesizing the image.

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