Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Least weight routing
Reexamination Certificate
1999-04-09
2004-02-17
Courtenay, III, St. John (Department: 2126)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Least weight routing
C345S545000
Reexamination Certificate
active
06694379
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of digital video, and, more specifically, to digital video applications in a network environment.
Sun, Sun Microsystems, the Sun logo, Java and all Java-based trademarks and logos are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries. All SPARC trademarks are used under license and are trademarks of SPARC International, Inc. in the United States and other countries. Products bearing SPARC trademarks are based upon an architecture developed by Sun Microsystems, Inc.
2. Background Art
Computers and computer networks are used to exchange information in many fields such as media, commerce, and telecommunications, for example. One form of information that is commonly exchanged is video data (or image data), i.e., data representing a digitized image or sequence of images. A video conferencing feed is an example of telecommunication information which includes video data. Other examples of video data include video streams or files associated with scanned images, digitized television performances, and animation sequences, or portions thereof, as well as other forms of visual information that are displayed on a display device. It is also possible to synthesize video information by artificially rendering video data from two or three-dimensional computer models.
The exchange of information between computers on a network occurs between a “transmitter” and a “receiver.” In video applications, the information contains video data, and the services provided by the transmitter are associated with the processing and transmission of the video data. Typically, one or more applications are located at the receiver to interface with a display unit's local frame buffer. A mutual exclusion lock is implemented to ensure that only one application writes to the frame buffer at a time. A local clip-list, managed by a window manager, is used to identify which portions of the frame buffer correspond to which application.
Unfortunately, the use of locking mechanisms and a local clip-list are inefficient in a distributed, asynchronous networking environment where video applications and window managers may exist on servers (or transmitters) remote from a receiver and its associated frame buffer. To provide a better understanding of computer video technology and its associated drawbacks, a general description of computer graphics and video technology is given below.
General Video Technology
In digital video technology, a display is comprised of a two dimensional array of picture elements, or “pixels,” which form a viewing plane. Each pixel has associated visual characteristics that determine how a pixel appears to a viewer. These visual characteristics may be limited to the perceived brightness, or “luminance,” for monochrome displays, or the visual characteristics may include color, or “chrominance,” information. Video data is commonly provided as a set of data values mapped to an array of pixels. The set of data values specify the visual characteristics for those pixels that result in the display of a desired image. A variety of color models exist for representing the visual characteristics of a pixel as one or more data values.
RGB color is a commonly used color model for display systems. RGB color is based on a “color model” system. A color model allows convenient specification of colors within a color range, such as the RGB (red, green, blue) primary colors. A color model is a specification of a three-dimensional color coordinate system and a three-dimensional subspace or “color space” in the coordinate system within which each displayable color is represented by a point in space. Typically, computer and graphic display systems are three-phosphor systems with a red, green and blue phosphor at each pixel location. The intensities of the red, green and blue phosphors are varied so that the combination of the three primary colors results in a desired output color.
An example of a system for displaying RGB color is illustrated in
FIG. 1. A
frame buffer
140
, also known as a video RAM, or VRAM, is used to store color information for each pixel on a video display, such as CRT display
160
. DRAM can also be used as buffer
140
. VRAM
140
maps one memory location for each pixel location on the display
160
. For example, pixel
190
at screen location X
0
Y
0
corresponds to memory location
150
in VRAM
140
. The number of bits stored at each memory location for each display pixel varies depending on the amount of color resolution required. For example, for word processing applications or display of text, two intensity values are acceptable so that only a single bit need be stored at each memory location (since the screen pixel is either “on” or “off”). For color images, however, a plurality of intensities must be definable. For certain high end color graphics applications, it has been found that twenty-four bits per pixel produces acceptable images.
Consider, for example, that in the system of
FIG. 1
, twenty-four bits are stored for each display pixel. At memory location
150
, there are then eight bits each for the red, green and blue components of the display pixel. The eight most significant bits of the VRAM memory location could be used to represent the red value, the next eight bits represent the green value and the eight least significant bits represent the blue value. Thus, 256 shades each of red, green and blue can be defined in a twenty-four bit per pixel system. When displaying the pixel at X
0
, Y
0
, the bit values at memory location
150
are provided to video driver
170
. The bits corresponding to the red (R) component are provided to the red driver, the bits representing the green (G) component are provided to the green driver, and the bits representing the blue (B) component are provided to the blue driver. These drivers activate the red, green and blue phosphors at the pixel location
190
. The bit values for each color, red, green and blue, determine the intensity of that color in the display pixel. By varying the intensities of the red, green and blue components, different colors may be produced at that pixel location.
Color information may be represented by color models other than RGB. One such color model is known as the YUV (or Y′CbCr as specified in ITU.BT-601) color space which is used in the commercial color TV broadcasting system. The YUV color space is a recoding of the RGB color space, and can be mapped into the RGB color cube. The RGB to YUV conversion that performs the mapping may be defined, for example, by the following matrix equation:
[
Y
′
U
′
V
′
]
=
[
Y
′
Cb
Cr
]
=
[
0.299
0.587
0.114
-
0.169
-
0.331
0.500
0.500
-
0.419
-
0.081
]
·
[
R
′
G
′
B
′
]
The inverse of the matrix is used for the reverse conversion. The Y axis of the YUV color model represents the luminance of the display pixel, and matches the luminosity response curve for the human eye. U and V are chrominance values. In a monochrome receiver, only the Y value is used. In a color receiver, all three axes are used to provide display information.
In operation, an image may be recorded with a color camera, which may be an RGB system, and converted to YUV for transmission. At the receiver, the YUV information is then retransformed into RGB information to drive the color display.
Many other color models are also used to represent video data. For example, CMY (cyan, magenta, yellow) is a color model based on the complements of the RGB components. There are also a variety of color models, similar to YUV, which specify a luminance value and multiple chrominance values, such as the YIQ color model. Each color model has its own color transformation for converting to a common displayable video format such as RGB. Most transformations may be defined with a transform matrix similar to that of the YIQ color space.
Image data is often provided as output of an application executing on a computer system. More than one
Hanko James G.
Northcutt J. Duane
Ruberg Alan T.
Wall Gerard A.
Courtenay III St. John
O'Melveny & Myers LLP
Sun Microsystems Inc.
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