Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2002-10-31
2004-12-07
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S603000, C345S593000, C345S643000, C348S659000
Reexamination Certificate
active
06828982
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “APPARATUS AND METHOD FOR CONVERTING OF PIXELS FROM YUV TO RGB FORMAT USING COLOR LOOK-UP TABLES”, filed in the Korean Industrial Property Office on Jun. 24, 2002 and assigned Serial No. 2002-35313, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for processing video signals, and more particularly to an apparatus and a method for converting pixels from a YUV format to a RGB format using color look-up tables with a small memory capacity.
2. Description of the Related Art
Usually, a RGB format and a YUV format are kinds of color modes for representing colors of pixels of an image in visible media. The RGB format is a mode for separating color signals into color components of R (Red), G (Green), and B (Blue) color, i.e., three primary colors of light used when video display devices such as a CRT (Cathode Ray Tube) or a LCD (Liquid Crystal Display) create colors or images. The YUV format is a mode for separating color signals into a luminance component (Y component) representing a brightness, and chrominance components (U and V components) representing color. Herein, the U component represents a blue color, and the Y component represents a red color.
In order to display colors, the RGB format requires at least three color-difference data, thereby needing a large memory capacity. However, since the RGB format employs the same displaying method as that of the video display device, this mode has excellent color-separation and transmission effects. On the other hand, the YUV format has poorer color-separation and transmission effects than the RGB format, but has an advantage in expressing a large number of colors even using a few color data.
Typically, most graphic cards use the YUV format in processing data. Generally, not only a digital video capturing device such as a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) sensor but also a video decoder with a video compression standard such as a MPEG (Moving Picture Experts Group Standards) 1, 2, 4, or H.261, 263, 26L, or etc. uses an output format in the YUV mode. Therefore, in order to display pixels in the YUV format outputted from the camera or the video decoder in a digital video product device on the CRT or the LCD, the pixels must be converted into the RGB format.
This color model conversion from the YUV format to the RGB format is accomplished by equations representing the relationship between the YUV format and the RGB format. In the equations for converting the pixels between the YUV format and the RGB format, different statistical weight values are respectively distributed to the R, G, and B components according to their sensitivities to human vision. Therefore, various equations are applied according to the distribution methods of the statistical weight values. Among the various equations, four or five equations have been often used. One equation is defined as follows.
R
=1.164*(
Y
−16)+1.596*(
V
−128)
G
=1.164*(
Y
−16)−0.813*(
V
−128)−0.391*(
U
−128)
B
=1.164*(
Y
−16)+2.018*(
U
−128) [Equation 1]
Using the above-described Equation 1, the R, G, and B component values are obtained from hardware-based multipliers and adders. That is, the R and B component values are obtained from two multipliers and one adder, and the G component value is obtained from three multipliers and two adders.
As above-described, the color model conversional operations of Equation 1 are implemented by the hardware. Since the hardware occupies a large space, the hardware is not proper to be employed by a small-sized mobile communication terminal. Further, in multiplication operations of Equation 1, the statistical weight values to the Y, U, and V component values are not integers but decimal fractions with a floating point, thereby complicating the design of the hardware and increasing the size of the hardware chip. Moreover, interfaces between the hardware device for the color model conversion and the camera or video decoder are changed by the kinds of the cameras or video decoders, thereby reducing generalization.
On the other hand, the color model conversional operations of Equation 1 may be implemented by software. However, the statistical weight values to the Y, U, and V component values are also decimal fractions with a floating point, thereby requiring a large number of instructions. These operations impose a heavy burden on a microprocessor of a mobile communication terminal with more limited computing power than a general desktop computer.
MPEG ISO/IEC 13818-2 Section 6.3.6 states a method for converting the statistical weight values of Equation 1 into integers in order to convert a color mode of a mobile communication terminal, as follows.
R
=76309*(
Y
−16)+
crv
*(
V
−128)+32768>>16
G
=76309*(
Y
−16)−
cgu
*(
U
−128)−
cgv
*(
V
−128)+32768>>16
B
=76309*(
Y
−16)+
cbu
*(
U
−128)+32768>>16 [Equation 2]
Herein, crv, cgu, cgv, and cbu are statistical weight values differently given by respective International Standard Organizations. These values are described in the following Table 1.
TABLE 1
International
Standard Organization
crv
cbu
cgu
cgv
No sequence display extension
117504
138453
13954
34903
ITU-R Rec.709(1990)
117504
138453
13954
34903
Unspecified
104597
132201
25675
53279
Reserved
104597
132201
25675
53279
FCC
104448
132798
24759
53109
ITU-R Rec.624-4 System B, G
104597
132201
25675
53279
SMPTE 170M
104597
132201
25675
53279
SMPTE 240M(1987)
117579
136230
16907
35559
As above-described, in Equation 2, the statistical weight values applied to the Y, U, and V component values are integers. Further, since shift operations requiring instructions with a smaller number than the multiplication operations are used, the number of the instructions required in Equation 2 is much smaller than Equation 1.
However, most of microprocessors perform multiplication operations slower than addition or subtraction operations. Further, most of microprocessors perform a table access operations faster than multiplication operations. Moreover, in case an apparatus for converting the color mode is implemented as the above-described hardware, an interface method between a video CODEC for decoding a compressed image and generating Y, U, and V component values and a video display device must be fixed. Thus, when a type of the video CODEC to be used is changed or upgraded, the interface must be amended. Therefore, it is preferable to use color look-up tables instead of multipliers. Many conventional methods for converting a color mode using color look-up tables are known by several documents, e.g., U.S. Pat. No. 5,936,683.
In using the color look-up tables, a necessary memory capacity is determined by the size of the color look-up table. The size of the color look-up table is changed by the number of variables used as indexes. For example, U.S. Pat. No. 5,936,683 discloses color look-up tables using two variables as indexes. In order to use two variables as indexes, since a color look-up table must represent all combinational cases of two variables, the size of the color look-up table becomes larger than that of a color look-up table using one variable as an index. Therefore, it requires that the size of the color look-up table must be reduced by decreasing the number of variables used as indexes.
As the number of color look-up tables increases, a larger memory capacity for storing the color look-up tables is required. Therefore, in order to reduce the memory capacity, it is necessary to decrease the number of the color look-up tables. In the case of Equation 2, if one color look-up table is used for each conversional formula used, the color model conversion can be accomplished by only three color look-up tables. However, in
Bella Matthew C.
Brautigam Alysa N
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