Television – Image signal processing circuitry specific to television – Chrominance-luminance signal separation
Reexamination Certificate
2001-12-03
2004-08-03
Hsai, Sherrie (Department: 2614)
Television
Image signal processing circuitry specific to television
Chrominance-luminance signal separation
C348S667000
Reexamination Certificate
active
06771321
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to graphics systems, and more particularly to a method and system for performing PAL luma two line vertical combing.
BACKGROUND OF THE INVENTION
In graphics systems, data for a particular frame includes both luma (luminance) and chroma (chrominance) data. In order to process the graphics data, the luma and chroma are separated. The mechanism used to separate the luma and chroma data depends upon the standard with which the data complies. One such standard is PAL. In PAL, luma and chroma data are carried predominantly at two different frequencies. In PAL, frequencies below 3.1 MHz are assumed to be luma. Thus, one conventional method for separating the luma and chroma data uses a band pass filter to remove the low frequency luma data from the chroma data. However, there is some crosstalk between the luma and chroma data. Consequently, some luma data will exist above 3.1 MHz and some chroma data resides below 3.1 MHz. In order to better separate the luma and chroma data, another process is used.
FIG. 1
depicts a high-level block diagram of a conventional system
10
for separating PAL luma and chroma data. Typically, luma and chroma data are carried predominantly at two different frequencies. The conventional system
10
includes a first line delay
16
and a second line delay
18
, adder
20
, a divide-by-two block
22
and a subtractor
24
. Each line delay
16
and
18
provides a delay equal to one line being processed.
FIG. 2
depicts a conventional method
50
for separating PAL luma and chroma data utilizing conventional three-line combing. The conventional method
50
is generally used by the system
10
. Consequently, the conventional method
50
is described in conjunction with the system
10
. Referring to
FIGS. 1 and 2
, the method
50
and the system
10
assume that the data does not change radically from line to line. Thus, the method
50
and the system
10
approximate data for the current line using a previous line and a next line. A portion of the video signal is separated at the node
11
, via step
51
. Thus, a portion of the video signal is transmitted along the line
12
, while another portion is transmitted along the line
14
. The data is sent through two line delays
16
and
18
, via step
52
. The output of the second delay
18
is data for the previous line. The data at the node
17
between the line delays
16
and
18
is data for the current line. Data taken from the node
11
is data for the next line. The data for the previous, current and next lines are thus present in the system
10
because of the line delays
16
and
18
.
The previous line and next line signals are combined, via step
53
. Step
53
is performed by combining the signal from the line
12
with the signal being output by the second line delay
18
using the combiner
20
. Because the signal from the second line delay
18
is two lines ahead of the signal taken from the node
11
, chrominance data is approximately canceled out when the two signals are combined. The output of the combiner
20
is two times the luma data for the current line. Note that although the output of the combiner
20
is termed twice the luma data for the current line, the output actually approximates the twice luma data for the current line because the previous and next lines were used.
This data is then cut in half, using the divide-by-two block
22
, via step
54
. Thus, the output of the divide-by-two block
22
is the luma data for the current line. The luma data output by the divide-by-two block
22
is considered to be for the current line because data for the current line is taken from the node
17
, between the line delays
16
and
18
.
The luma data is then subtracted from the chroma data for the current line; via step
55
. This step is performed using the subtractor
24
. Consequently, the luma data and the chroma data can be output by the conventional system
10
.
Although the conventional system
10
and method
50
function adequately in most cases, one of ordinary skill in the art will readily recognize that the conventional system
10
and method
50
do not work well at certain rough edges.
FIG. 3
depicts a portion of a frame
60
in a display. The frame
60
includes such a boundary
90
. The boundary
90
is between polygons
70
and
80
. However, the boundary
90
could be between other items. The edge
90
is rough because the polygons
70
and
80
have very different colors. For example, the polygon
70
may be dark, while the polygon
80
may be light. The portion of the polygon
70
shown includes lines
61
,
62
and
63
. The portion of the polygon
80
shown includes lines
64
,
65
and
66
. The edge
90
is between lines
63
and
64
.
Referring to
FIGS. 1-3
, the conventional system
10
and method
50
combine data for a previous line and a next line in order to obtain luma data, which is also used to obtain the chroma data. When line
62
is the current line, taken from node
17
, line
61
is the previous line and line
63
is the next line. Consequently, the luma and chroma data output from the divide-by-two block
22
and the subtractor
24
are as desired. However, when line
63
is the current line taken from the node
17
, line
62
is the previous line and line
64
is the next line. However, line
64
is part of the other polygon
80
, taken from the other side of the edge
90
. Consequently, when the line
64
is combined with the line
62
, the resultant will not be close to the luma data for the current line. This is because the chroma data changes radically due to the boundary
90
. In other words, the assumptions made for performing the conventional three-line combing of the method
50
no longer hold. As a result, the appearance of the frame near the boundary
90
is incorrect.
Accordingly, what is needed is a system and method for separating PAL luma and chroma data while reducing the incongruities introduced around rough boundaries. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for performing combing for PAL luma data. The combing is performed for a display having a plurality of lines. The display is capable of depicting a frame including a horizontal boundary having a top edge and a bottom edge. A top line of the plurality of lines is at the top edge of the horizontal boundary. A bottom line of the plurality of lines is at the bottom edge of the horizontal boundary. The method and system comprise providing a feedback multiplexer, a line delay and a feed forward multiplexer. The feedback multiplexer has a first input, a second input and a first output. The first input is for receiving luma data for a current line. The line delay has a delay input and a delay output, the delay input coupled with the first output. The delay output is coupled with the second input. The feed forward multiplexer has a third input, a fourth input and a second output. The third input is coupled with the delay output. The fourth input is for receiving the luma data for the current line. The feedback multiplexer is controlled to provide fedback luma data from the second input to the first output when the current line is the top line and to provide the luma data for the current line from the first input to the first output otherwise. The feed forward multiplexer is controlled to provide next line luma data from the fourth input to the second output when the current line is the bottom line and to provide the luma data from the current line to the second output otherwise.
According to the system and method disclosed herein, the present invention provides a method and system for performing two-line combing that reduces artifacts of separation of PAL luma and chroma data.
REFERENCES:
patent: 4707732 (1987-11-01), Matono et al.
patent: 5134467 (1992-07-01), Kim
patent: 5526060 (1996-06-01), Raby
patent: 6462790 (2002-10-01), Lowe et al.
Delanghe Brad A.
Movshovich Aleksandr M.
Broadcom Corporation
Hsai Sherrie
Sawyer Law Group LLP
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