Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-03-22
2003-06-10
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
Reexamination Certificate
active
06577320
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to computer graphics and, more particularly, to a method and apparatus for improved texture mapping for three-dimensional computer graphics.
BACKGROUND OF THE INVENTION
In the art of computers, two-dimensional and three-dimensional images are commonly depicted on a display, i.e. computer monitor, with a system including a central processing unit (CPU) that is connected to the display via a video card or the like. The display consists of a large number of pixels(picture elements) which each display a small portion of an image in response to video control signals received from the CPU. These video signals are conventionally manipulated by the video card in order to enhance images depicted on the display.
In particular, video signals received from a CPU typically include information in the form of a predetermined number of bits which are allocated to different components of the pixel with which it is associated. Such components include a Red (R), Green (G), Blue (B), and Alpha (&agr;) component. While the R, G, and B components relate to the intensity of the corresponding color within the pixel, the &agr; component may correspond to various types of information depending on the specific representation that is being employed.
In one representation, the &agr; component corresponds to a “transparency” or “opacity” of the colors within the associated pixel. In such representation, the &agr; component is commonly used for blending purposes. In yet another representation, the &agr; component stores information relating to “coverage” for determining a fraction of how much color is present within the associated pixel. In all of the representations, the &agr; component of the video signals contributes additional information for improving the resultant image.
It should be noted that the amount and allocation of binary information within the various R, G, B, and &agr; components may vary depending on the particular application. In one example wherein 16 bits are provided for each pixel, the R, G, B, and &agr; components may be allocated 5, 6, 5, and 0 bits, respectively, or, in another embodiment, 5, 5, 5, and 1 bits, respectively. In yet another example wherein each pixel has 32 allocated bits, each component (R, G, B, and &agr;) may have 8 bits associated therewith.
With the number of bits allocated for each pixel, information stored therein may be used to generate the resultant image.
FIG. 1
illustrates a pixel
10
corresponding to a small portion of an image
12
on a display
13
. In order to provide a more realistic image, the R, G, and B components of the pixel are desired to accurately reflect a specific texture and lighting. As seen in
FIG. 1A
, this texture and lighting information is usually gathered from a texture pattern grid
14
stored in computer memory in a process conventionally referred to as texture mapping. During texture mapping, information associated with a pixel, or “texel”
16
, from the texture pattern grid
14
stored in computer memory is selected and incorporated into the appropriate pixel
10
within the image
12
. As will be set forth later, this texture mapping may be accomplished in various ways depending on the “representation” of the R, G, B, and &agr; components of the video signals.
For example, “premultiplied”, “postmultiplied”, and “colorkeyed” are all different types of representations of the R, G, B, and &agr; components of the video signals. The premultiplied representation refers to modulating the R, G, and B components with the &agr; component in order to weight the R, G, and B components prior to further processing. In other words, the information associated with the &agr; component is incorporated into the R, G, and B components before any further processing, i.e. filtering, etc. As will soon become apparent, such premultiplication of the components is critical for improving picture quality by way of interpolation.
A specific example of the foregoing texture mapping procedure is shown in FIG.
1
B. As shown, the image to be mapped is referred to as a texture map
20
, and its individual elements are referred to as texels. Texture map
20
is typically described in a rectangular coordinate scheme designated (u, v), and is ordinarily stored in some area of conventional memory, such as, for example, a conventional page-mode dynamic random-access memory (DRAM) or other paged memory. In the example of
FIG. 1B
, four pages
22
,
24
,
26
,
28
are shown, each corresponding to a portion of the image area containing a corresponding portion of texture map
20
.
Surface
30
in three-dimensional space has its own coordinate system (s,t,q). In a typical three-dimensional graphics system, surface
30
may be a primitive object such as a polygon; many such polygons may be defined in three-space to form a three-dimensional object or scene. Each such polygon would be placed in the coordinate system (s,t,q) similar to the surface
30
in FIG.
1
B. Based on the orientation of surface
30
in three dimensions, and on the position and orientation of the “camera,” surface
30
is in turn mapped onto a two-dimensional display grid
40
stored in a frame buffer for display by the computer.
The mapping of surface
30
onto display grid
40
is accomplished by matrix transforms that are well-known in the art. Display grid
40
has coordinate system (x, y) and is typically implemented in an area of memory reserved for video display, such as video random-access memory (video RAM) e.g. VRAM or synchronous graphics random-access memory (SGRAM).
Display grid
40
contains individual elements known as pixels, represented by distinct memory locations in video RAM. Each pixel in some region of display grid
40
maps onto a point on surface
30
and in turn to a point in texture map
20
. Thus, in the example of
FIG. 1B
, point A
xy
of display grid
40
maps onto point A
stq
in the coordinates of surface
30
and to point A
uv
in texture map
20
, or a group of points forming a region in texture map
20
. Each of the mappings among display grid
40
, surface
30
, and texture map
20
may be point-to-point, point-to-region, region-to-point, or region-to-region.
In order to improve picture quality during texture mapping, it is often desired to interpolate between the various texels of the texture pattern grid in order to select the best texture and lighting information that is to be depicted within the pixel of the image. It is important to note that this interpolation, or bilinear interpolation, is permitted only when the various components of the video signals are weighted in the premultiplied representation. Without premultiplication, interpolation of the components of the video signals results in errors and artifacts.
A flowchart depicting the process associated with texture mapping in the premultiplied representation is shown in FIG.
2
. During bilinear interpolation, four texels are first selected (see
FIG. 3
) and the interpolation is subsequently carried out between them for each of the R, G, and B components. With reference to the four selected texels A, B, C, and D of
FIG. 3
, the interpolation proceeds as follows for each of the R, G, and B components:
AB=A
(1−x)+
B
(x)
CD=C
(1−x)+
D
(x)
(
R,G,B
)=
AB
(1−y)+
CD
(y)
Interpolation between the texels affords a “smoother” more realistic resultant image on the display. It should be noted that interpolation need not be limited to merely two dimensions. Three-dimensional interpolation, or trilinear interpolation, may also be carried out. More information on trilinear interpolation may be found by looking to “Pyramidal Parametrics” by Williams, Lance. In Proceedings of SIGGRAPH '83 (July 1983), pp. 1-11 which is incorporated herein by reference in its entirety.
As mentioned earlier, interpolation during texture mapping is not effective when the various components of the video signals take on the postmultiplied and colorkeyed representations. Instead, in the case of postmultiplied represen
Bella Matthew C.
Blackman Anthony
NVIDIA Corporation
Silicon Valley IP Group
Zilka Kevin J.
LandOfFree
Method and apparatus for processing multiple types of pixel... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for processing multiple types of pixel..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for processing multiple types of pixel... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3135851