Computer graphics processing and selective visual display system – Computer graphics processing – Three-dimension
Reexamination Certificate
1998-10-28
2001-08-07
Zimmerman, Mark (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Three-dimension
C345S419000
Reexamination Certificate
active
06271850
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image generation apparatus, an image generation method, an image generation program recording medium, an image composition apparatus, an image composition method, and an image composition program recording medium. Particularly, the present invention relates to an image generation apparatus and an image generation method for generating an image from shape data comprising coordinate values representing a three-dimensional shape, and an image generation program recording medium. The present invention also relates to an image composition apparatus and an image composition method for compositing a generated image and a photo image, and an image composition program recording medium.
BACKGROUND OF THE INVENTION
In recent years, three-dimensional computer graphics techniques for generating a three-dimensional image seen from an arbitrary point based on shape data of an object represented by three-dimensional coordinates have been extremely important in fields such as article design or simulation of physical events. Further, techniques for compositing an image generated by the use of the three-dimensional computer graphics techniques, and a photo image have been effective in fields of video production such as television broadcasting, cinema, and the like. A description will now be given of an image generation apparatus and an image composition apparatus which have been employed for such use, according to a prior art.
First, a description will be given of an image generation apparatus for generating an image based on three-dimensional shape data. A general image generation apparatus illustrated herein according to the prior art, handles an object to be displayed as a plane polygon (in many cases “triangle”) called “polygon ”, and uses shape data described as three-dimensional coordinates.
FIG. 17
is a block diagram showing an image generation apparatus according to a prior art. Turning to
FIG. 17
, this image generation apparatus comprises a shape data buffer
1701
, a pixel generating unit
1702
, a Z buffer
1103
, a frame buffer
1704
, and an image display
1705
. The shape data buffer
1701
holds shape data input to the image generation apparatus. As mentioned previously, the shape data is described as the three-dimensional data representing the polygon. The pixel generating unit
1702
sequentially reads shape data for each polygon held in the shape data buffer
1701
, divides the read data in display pixel units, and finds a display color of each display pixel as a pixel value (R, G, B). The pixel generating unit
1702
performs an operation according to a formula considering a view point, to find a depth value (Z value) indicating a position on a display screen as depth in the direction of line of sight.
Algorithms for deciding the value of the pixel to be generated, includes “flat shading” in which all the pixels belonging to the same polygon have the same value, and “smooth shading” for calculating a value for each pixel belonging to the same polygon according to a formula considering environmental capabilities such as a light source, and the like. The flat shading is a simple algorithm, arid Therefore reduces processing burden. However, since the flat shading makes it difficult to obtain a display image having smooth and fine shades, the smooth shading is generally used to obtain a realistic and high-quality image. Such processing is described in detail in “Computer Graphics PRINCIPLES AND PRACTICES, Foley, by van dam, Feiner, Hughes, ADDISON-WESLEY PUBLISHING COMPANY (1990)”.
The pixel generating value unit
1702
is implemented by software by using a general-purpose processor, although it may be implemented by dedicated hardware. Moreover, the dedicated hardware is commonly implemented by an IC (integrated circuit). In this case, the IC includes a control function for reading data from the frame buffer
1704
which is mentioned later, and a D/A conversion function. The Z buffer
1703
and the frame buffer
1704
in
FIG. 17
hold the depth value (Z value) and the pixel value (R, G, B), respectively. The Z buffer
1703
holds Z values of display pixels and the frame buffer
1704
holds pixel values (R, G, B) of the display pixels.
In computer graphics process which handles a display object as a polygon, “hidden-surface” process which prevents an invisible part or an invisible object seen from a certain view point from being displayed, improves reality. The image generation apparatus uses a “hidden-surface” method termed a “Z buffer method”. In the process according to the Z buffer method, a Z value of a polygon previously processed is held in the Z buffer, which is compared to a Z value of a polygon to be processed, to decide whether or not the polygon to be processed is positioned in front, thereby deciding whether or not the polygon should be displayed. In the image generation apparatus in
FIG. 17
, comparison is made between the Z value of the polygon generated by the pixel generating unit
1702
and the Z value of the corresponding pixel of the previously processed polygon held in the Z buffer
1703
. When the Z value of the polygon is smaller that that of the pixel, the Z value held in the Z buffer is replaced by the Z value of the polygon, and then the value held in the frame buffer
1704
is replacedby the pixel value of the polygon. A smaller Z value indicates a smaller depth, and therefore the above processing can display the polygon to be seen from a certain view point and can eliminate the polygon which cannot be seen therefrom without being displayed.
For the hidden-surface method, algorithms other than the Z buffer method is possible. For example, there is a conventional “depth sorting method”. In the depth sorting method, all the polygons are rearranged in the order of depth, and then pixel values of the polygons are written to a frame buffer (in increasing or decreasing order of depth). An advantage of this method is that a memory as a buffer (Z buffer) for holding depth values is dispensed with. However, processing amount of rearrangement is greatly increased with an increase in the number of polygons, since “order” of the number of polygons n is n
2
or n×log n. The Z buffer method is suitable for handling many polygons rather than the depth sorting method. To obtain high-speed by the concurrent execution of such processing, the-Z buffer method is effective, because it can perform individual processing in parallel for each polygon.
In general, the image display
1705
is a CRT (cathode ray tube) monitor, and displays an image generated by the image generation apparatus. In some uses of the image generation apparatus, a monitor or the like as the image display
1705
may be replaced by video editing equipment.
When the shape data, i.e., the three-dimensional coordinates are input to the image generation apparatus so constructed, the shape data is first held in the shape data buffer
1701
. The pixel generating unit
1702
reads shape data for each polygon from the shape data buffer
1701
, and generates the pixel value and the depth value as mentioned previously. The pixel generating unit
1702
makes a comparison between the generated Z value and the Z value of the corresponding pixel of the previously processed polygon, and then rewrites a content of the Z buffer
1703
when the generated value is smaller.
After rewriting, the generated pixel value (R, G, B) is output to the frame buffer
1704
, followed by rewriting a content thereof.
The pixel values held in the frame buffer
1704
are read in the order of the corresponding pixels, and displayed on the image display
1705
. Alternatively, the pixel values may be first subjected to D/A conversion process and then output to the image display
1705
.
The prior art image generation apparatus is thus capable of generating an image which can be displayed in a three-dimensional manner, by the use of the Z buffer which performs hidden-surface method according to the Z buffer method.
Disadvantages of the Z buffer method are that “anti aliasing”
Abe Minobu
Kida Mitsuteru
Kobayashi Tadashi
Nishimura Akio
Matsushita Electric - Industrial Co., Ltd.
Vo Cliff N.
Wenderoth , Lind & Ponack, L.L.P.
Zimmerman Mark
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