Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-11-18
2002-11-05
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
Reexamination Certificate
active
06476819
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the present invention relates to a texture mapping apparatus for carrying out texture mapping adopted as a technique to drastically improve the expression power of a multidimensional computer graphic system. More particularly, the present invention relates to a picture processing apparatus and a method thereof capable of preventing generation of aliasing and excessive resolution deterioration of a picture, and hence, capable of providing high-quality texture mapping by assigning a proper shrinkage factor when pasting a texture of a 2-dimensional picture on a multidimensional figure. In addition, the present invention can be applied to a wide range of applications such as the CAD (Computer Aided Design), designing work and games.
Texture mapping is a technique of pasting a 2-dimensional picture provided in advance on the surface of a figure in an operation to render the figure by means of computer graphics. Such a 2-dimensional picture is referred to hereafter as a texture. By adopting the texture-mapping technique, a high-quality picture can be obtained.
In order to make the following description easy to understand, the basic principle of the texture-mapping technique is briefly explained by referring to
FIGS. 8A
,
8
B,
9
A and
9
B.
FIG. 8A
is a diagram showing a figure, on which a texture is to be pasted, and a coordinate system onto which the figure is mapped. The coordinate system is referred to hereafter as an XY coordinate system
81
.
A triangle
80
represents a polygon. A figure to be rendered is created as a set of a plurality of triangles. 3-dimensional coordinates Sn, Tn and Qn where n=1, 2 and 3 are assigned to the vertexes A, B and C of the triangle
80
respectively. Such 3-dimensional coordinates are referred to hereafter as texture coordinates. A figure for the texture coordinates is omitted. Thus,
FIG. 8A
is a diagram showing the triangle
80
which is expressed in the texture coordinate system and mapped onto the XY coordinate system
81
. Coordinates (s, t, q) of a point D inside the triangle
80
are obtained by linear interpolation of the texture coordinates Sn, Tn and Qn where n=1, 2 and 3 of the vertexes A, B and C.
Texture coordinates such as the coordinates (s, t, q) and (Sn, Tn, Qn) described above are assigned to each of individual triangles constituting a figure being rendered. Thus, the texture coordinates are variables. In addition, the texture coordinates Sn, Tn and Qn where n=1, 2 and 3 assigned to the vertexes A, B and C of the triangle
80
correspond to XY coordinates (X, Y) whereas the texture coordinates (s, t, q) assigned to a pixel inside the triangle
80
correspond to XY coordinates (x, y).
On the other hand,
FIG. 8B
is a diagram showing a 2-dimensional coordinate system of a texture to be pasted on the figure to be rendered as described above. The 2-dimensional coordinate system is referred to as a UV-coordinate system
82
. A texture triangle
83
is a triangle constituting a texture to be pasted on the triangle
80
. The points (A, B, C and D) mapped onto the XY-coordinate system
81
are associated with the points (A′, B′, C′ and D′) of the texture triangle
83
to be posted.
A texture is initially given on the UV coordinate system
82
as a 2-dimensional picture. The texture is then subjected to operations such as a rotation and a movement and finally mapped onto the XY coordinate system
81
. The UV coordinates of the points (A′, B′, C′ and D′) of the texture triangle
83
are expressed in terms of texture coordinates (sn, Tn, Qn where n=1, 2 and 3) and (s, t, q) described above as shown in FIG.
8
B.
In addition,
FIGS. 9A and 9B
are diagrams showing what displacement on the UV coordinate system
82
a component displacement dx of a unit pixel on the XY coordinate system
81
in the X-axis direction corresponds to. As shown in the figure, the component displacement dx in the XY coordinate system
81
corresponds to a component displacement dudx in the U-axis direction and a component displacement dvdx in the V-axis direction on the UV coordinate system
82
. Thus, the component displacement dx on the XY coordinate system
81
corresponds to a resultant displacement e={(dudx)
2
+(dvdx)
2
}
½
on the UV coordinate system
82
. This explanation is also applicable to a component displacement dy in the y-axis direction on the XY coordinate system
81
. dudx described above is a coordinate value of a displacement in the u direction in the UV coordinate system
82
for the change dx in the XY coordinate system
81
. Notation q·q to be used frequently later means processing to multiply q by q where the symbol q represents any quantity. In order to avoid complexity of the explanation, notation q·q is used hereafter.
A MIPMAP filtering technique (Multum In Parvo Mapping) is known as a method to obtain a high-quality picture in a texture mapping process. The MIPMAP filtering technique is described in detail with reference to, such as a publication of Addison Wesley entitled “Advanced Animation and Rendering Techniques,” page 140.
The MIPMAP filtering technique is described by referring to
FIGS. 5
,
6
A,
6
B,
7
A and
7
B as follows.
In order to avoid aliasing caused by information which is dropped when a texture is shrunk and pasted as shown in
FIG. 5
, according to the MIPMAP filtering technique, a plurality of textures completing a filtering process according to the shrinkage factor are prepared in advance. In the example shown in
FIG. 5
, the textures are the original picture, a half picture, a one-fourth picture and a one-eighth picture. One of the textures is to be selected in accordance with the shrinkage factor of pixels. The reason why pictures with compression factors different from each other are prepared in advance is to reduce a load to be borne during the filtering process of the picture.
The texture mapping process adopting the ordinary MIPMAP filtering technique is described as follows.
1) Texture coordinates (S
1
, T
1
, Q
1
), (S
2
, T
2
, Q
2
) and (S
3
, T
3
, Q
3
) are assigned to the three vertexes of the triangle, respectively.
2) Texture coordinates (s, t, q) of each pixel inside the triangle are found by linear interpolation of the texture coordinates (S
1
, T
1
, Q
1
), (S
2
, T
2
, Q
2
) and (S
3
, T
3
, Q
3
) assigned to the three vertexes.
3) The shrinkage factor lod of each pixel inside the triangle is found by using the texture coordinate (s, t, q)
4) Coordinates U=s/q and V=t/q in the UV coordinate system
82
for each pixel inside the triangle are computed.
5) A texture for a given shrinkage factor lod is selected from a plurality of textures prepared in advance. Each position inside a selected texture is referenced by using the coordinates (U, V) in the UV coordinate system
82
.
The shrinkage factor lod of the texture described above indicates how much the original picture is shrunk in the texture mapping process. Different lod values are set for different shrinkage factors as follows.
Shrinkage factor
lod value
1/1
lod = 0
1/2
lod = 1
1/4
lod = 2
1/8
lod = 3
.
.
.
1
lod = log
2
(n)
As an example, the following description explains how to compute the value of lod at texture coordinates (s, t, q) in the triangle, a subject figure to be rendered. In the figure, notations dsdx, dtdx and dqdx denote displacements of s, t and q in the X-axis direction respectively. By the same token, notations dsdy, dtdy and dqdy denote displacements of s, t and q in the Y-axis direction, respectively.
1) Component displacements in the U-axis and V-axis directions of the texture in the UV coordinate system
82
for component displacements dx and dy of a unit pixel in the X-axis and Y-axis directions on the XY coordinate system
81
are found by using Eqs. (1) as follows.
dudx
=(
s·dqdx−q·dsdx
)/
q·q
dvdx
=(
t·dqdx−q·dtdx
)/
q·q
dudy
=(
s·dqdy−q·dsdy
)/
q·q
dvdy
=(
t·dqdy&m
Brier Jeffery
Fulwider Patton Lee & Utecht LLP
Sony Corporation
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