JPH09282484A - Picture composing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the expressive and real video of a gaseous material by leaving an overlapped numerical value as it is when the value Z (a view point coordinate value) of the gaseous object is closer to a view point than a face defining object and setting the numerical value to be a specific value when the value Z is distant. SOLUTION: A minimum graphic element expressing the gaseous object is read from a picture memory 5. Luminance fl is inputted to a smoothing filter circuit 7. The value Z fz and the value Z fz of the face defining object are compared by a comparing circuit 8. A selector 9 selects the overlapped number (m) as it is when the gaseous object is at the front face of the face defining object and selects zero or a prescribed value (n) when it is at the rear based on the comparing result. The overlapped number smoothed by a smoothing filter 10 is transformed to a prescribed radioscopy coefficient through a storage element 11 and respectively multiplied by the luminance gl of the gaseous object after smoothing, by the luminance sl of the face defining object in multipliers 12a and 12b. After then, these are added by an adder 13 to obtain a composite image.

Description

Detailed Description of the Invention

The present invention relates to a hardware circuit and a volume rendering thereof for dynamically visualizing a natural phenomenon such as a fog or a cloud-like object in a three-dimensional space by computer graphics. .

[Prior Art] Many shape models for displaying three-dimensional objects by computer graphics are curved surfaces or solid models. By calculating reflections or shadows between light sources or objects on these surfaces, , Producing realistic images. Most of these use a rendering technique called ray tracing or radiocity method. Unlike the object display method such as this curved surface model, expressing a natural phenomenon such as fog or cloud requires a lot of calculation time because it requires calculation of shape complexity, dynamic change, irregular reflection, etc. doing. It is also necessary to combine these gaseous objects with the curved surface model in three-dimensional space. From this point of view, the computer graphics display by the hardware of the gaseous object as the volume rendering has been applied to Japanese Patent Application No. 7-20.
There were few examples other than the circuit shown in 1251, and it was generated only by software. On the other hand, in Japanese Patent Application No. 7-201251, as a method for more realistically displaying a gaseous object such as a brushing effect, smoothing filtering is performed on the number of overlapping primitives and the viewpoint coordinate value Z, and then the surface definition object Then, the Z value is determined, and the luminance and the perspective are calculated only for the primitive having the Z value closer to the viewpoint than the surface object, and the primitive and the surface defining object are combined. In this method, when the presence of primitives is coarse, the Z value after smoothing is significantly reduced, and the primitive moves to the back of the surface defining object, and some gaseous objects exist in front of the surface defining object. Even if I was doing it, there was a phenomenon that it was not displayed. The purpose is to provide a continuous and appropriate transparent feeling depending on the density and position of a surface-defining object surrounded by a gaseous object. In the present invention, two methods are introduced in order to effectively obtain this effect. First, after generating a gas-like object (primitive) having a Gaussian distribution, for each coordinate point of each primitive, a primitive having a Gaussian distribution around that point is generated. Furthermore, a third primitive is generated with the point of the second primitive thus generated as the center. By repeating the above processing, a gas-like object figure having a hierarchical structure is constructed. As a result, an image of a gaseous object having a locally high density can be expressed by increasing the density of the lower hierarchy higher than that of the upper hierarchy, and filtering this reduces the coarse particle image. The other method is to directly compare the Z values of a gaseous object and a surface-defining object directly without filtering the Z value as in the conventional method, and if the Z value of the gaseous object is closer to the viewpoint than the surface-defining object. , The overlap value is left as it is, while if it is far away, it is set to a specific value, for example, zero, and then these overlap numbers are filtered.At the position where this overlap number exists, the primitive corresponding to that overlap number is set. It is assumed that it exists, and the transparency for the surface defining object is determined using this value and the primitive brightness. This method is different from the conventional method in that the presence or absence of the display of the gaseous object is not determined by the Z value of the primitive, but the concentration distribution is averaged by averaging the number of overlaps. It has the characteristic that a change in brightness can be obtained. As a result, according to the present invention, it is possible to provide a more realistic and realistic image than the display based on the Z value.

[Means for Solving the Problem] A surface defining object is one of shape models that define an object by a polyhedron. As shown in Japanese Patent Application No. 7-201251, the transmissivity must be calculated in order to synthesize a gaseous object and a plane-defining object. As this method, first, the surface defining object and the gas-like object are stored in the image memory, respectively, and at this time, the hidden surface is erased independently. In the process of storing primitives in the image memory, if there is a primitive already stored at that location at the time of writing to the memory, the Z value (distance from the viewpoint) of the primitive is compared, and the information closer to the viewpoint is compared. Is stored in the image memory.
Therefore, only one primitive closest to the viewpoint is always stored in the image memory. At this stage of hidden surface elimination, the number of overlaps is counted each time when a primitive already exists and overlaps. From the number of overlaps, although only the coordinate values closest to the viewpoint are stored in the image memory, the density of the primitives forming the gaseous object in the three-dimensional space with respect to the viewpoint axis can be known. 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 dense distribution, the permeability will be reduced if a gaseous object is present in front of the surface defining object. In synthesizing a surface-defining object and a gas-like object, first, the gas-like object and the surface-defining object are individually stored in an image memory, and each has two kinds of data (image (color or brightness) information and Z value). In addition to this, the gaseous object has an overlapping number for each primitive (pixel). When the drawing of the gaseous object and the surface-defined object is completed, the image and the Z value (including the number of overlaps of the gaseous object) are taken over from the respective image memories by the scanning procedure for the display device and sequentially read. When these images are simply combined by using the number of overlaps like alpha blending, a mottled spot-like pattern of primitives is formed on the curved surface of the surface-defining object in a gas-like object consisting of scattered primitives. This is a result in which the scattered state is emphasized in the case of a few primitives. Smoothing filtering is necessary to eliminate this spot shape. On the other hand, in a group of point groups simply based on one Gaussian distribution, the positioning of the points becomes coarse, and the effect of the filter cannot be obtained so much. Therefore, it is effective to generate a point group having a Gaussian distribution centered on each point based on the Gaussian distribution hierarchically to make it locally high density, and then perform filtering. In Japanese Patent Application No. 7-201251, 3 × 3 smoothing filtering is applied to each of luminance, Z value and the number of overlaps when a gaseous object is read out as serial data from an image memory. On the contrary,
In the present invention, the Z value is directly compared without filtering. If the primitive is closer to the viewpoint than the surface defining object, the number of overlaps is given to the filter circuit as it is. On the other hand, if it is far away, it is changed to a specific smaller value and then given to the filter circuit. As a result, the number of overlaps after smoothing changes depending on the anteroposterior relationship with the view axis with respect to the surface defining object. That is, the number of overlaps decreases when many primitives are located on the rear surface of the surface object, and increases when the primitives are in front.
The present invention considers that there is a gaseous primitive at every projected coordinate (perpendicular to the view axis) for which there is an overlap number due to smoothing (value is not zero), and this value and its already smoothed Color blending is performed by taking into consideration the transmittance with respect to the surface based on the brightness of the primitive. This method is easier to control the transmittance than the conventional method. This transmittance is determined by the reciprocal of the overlap number. Therefore, in Japanese Patent Application No. 7-201251,
When the surface definition object is located in the gaseous object space, some of the gaseous primitives are deleted by their Z value, and some are displayed because the gaseous object is simply deleted when it is far from the surface. Whereas, in the present invention, the presence of primitives is located by smoothing regardless of the presence or absence of Z values. The Z value is used only to determine the number of overlaps, ie the transmittance.

[Embodiment] FIG. 1 shows an example of a gaseous substance generating circuit of the present invention. In FIG. 1, a random number and a Gaussian distribution circuit 1 generate a predetermined number of primitives for a gaseous object, and at this stage the primitives are composed of three-dimensional coordinate points. The circuit 2 is a random number and Gaussian distribution circuit like the circuit 1. The circuit 3 is also the same. The coordinate value A of the first primitive output from the circuit 1 becomes the base value (center point) of the primitive coordinate value B output from the circuit 2 after being added by the reference point P0 and the adder 4a,
The adder 4b positions the second primitive at P0 + A + B. This value is added to the primitive coordinate value C output from the circuit 3 by the adder 4c. Therefore, the position of the primitive is P0 + A + B + C in the three layers. A point group having locality can be configured by independently defining the distribution ratio and the density in each of the circuits 1 to 3. FIG. 2 is a circuit related to the present invention. The primitive generated in FIG.
It is stored in the image memory 5 as brightness and three-dimensional coordinate values. When writing data to the image memory 5,
The hidden surface removal and the number of overlaps are counted by the hidden surface removal circuit 6. The brightness (fl) and the Z value (f stored in the image memory 5
z) and the number of overlaps (m) are read in the scanning procedure in synchronization with the video frequency of the display device. The luminance (fl) of this data is input to the smoothing filter circuit 7 and smoothed. The Z value (fz) is the Z value (s
z) is compared for each pixel in the comparison circuit 8, and the comparison result is given to the selector 9. Based on the comparison result, the selector 9 selects the zero or a predetermined value (n) when the gaseous object is on the front surface of the surface-defining object while keeping the overlapping number (m) as it is. This selected number of overlaps is added to the second smoothing filter 10. The smoothed overlap number is converted into a predetermined perspective coefficient through the storage element 11, and is multiplied by the brightness (gl) of the smoothed gaseous object and the brightness (sl) of the surface defining object by the multipliers 12a and 12b, respectively. After these, adder 1
3 is added to obtain the composite image.

[Effect] By implementing the hardware of the present invention,
Gaseous objects and surface-defining objects can be synthesized at high speed in three-dimensional space, enabling real-time display, which is essential for drawing virtual reality systems.

[Brief description of drawings]

FIG. 1 is a primitive generation circuit of the present invention.

FIG. 2 is a circuit diagram showing a gaseous object display of the present invention.

[Explanation of symbols]

 1-3 random number and Gaussian distribution circuit 4a-4c adder 5 image memory 6 hidden surface removal 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)

[Claims] 1. A circuit for generating a natural phenomenon object having a gas-like shape as a computer graphic image and synthesizing the same with a surface defining object in a three-dimensional space,
The minimum graphic element that represents a gaseous object is defined as a primitive. This primitive consists of three-dimensional coordinate values and brightness, and is generated using the first random number and probability distribution function circuit. As a reference point
Furthermore, the first means having at least two levels of this hierarchical process for generating the primitive by the second random number and the probability distribution function circuit, and the density and distribution rate of the probability distribution function in each hierarchy are defined independently. The second means for generating the shape of the gaseous object and the hidden surface removal processing when storing the primitives in the image memory, and the means for counting the overlapping primitives on the same viewpoint coordinate axis, in the image memory Of the stored primitive information, the primitive brightness is smoothed by adding a smoothing filter, while the viewpoint axis coordinate values of the primitive and the surface definition object are compared, and the coordinate value of the primitive is the surface definition object for the viewpoint. Set the number of overlaps of the primitives to a predetermined value for each farther or forward After that, the third means for smooth filtering, and the transparency value for the surface defining object is determined from the number of smoothing overlaps obtained by the above processing, and after the transparency value is multiplied by the brightness of the primitive and the surface defining object, respectively. An image synthesizing circuit having a fourth means for synthesizing to add a surface defining object and a gaseous object.