Image analysis – Image enhancement or restoration – Image filter
Reexamination Certificate
1998-09-15
2001-05-22
Rogers, Scott (Department: 2624)
Image analysis
Image enhancement or restoration
Image filter
C382S275000
Reexamination Certificate
active
06236763
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a computer controlled filter system and pipeline architecture to detect and remove noise artifacts in signals in real time, primarily but not limited to video signals.
2. Brief Description of the Prior Art
Advances in technology have made it possible to store electrical signals and primarily electrical video signals digitally, such as on a compact disk (CD) read only memory (ROM). For many purposes, in order to store a sufficient amount of digital information on a CD ROM, it is generally necessary to compress the digital data. This is accomplished by removing data which is unnecessary or redundant as well as removing data which will not dramatically affect the quality of the reproduced video and/or audio, it being understood that the term “quality” can vary in accordance with personal desires or specified requirements. At present, data can be extracted from a CD ROM at a maximum data rate of about 1.5 megabits per second. This is a very low data rate and is generally insufficient for providing acceptable quality live video. For this reason, even with the most advanced compression techniques presently available, noise is introduced into the decompressed signal. This noise or picture degradation, in part, appears as fuzziness along the edges of the moving objects in the picture. Therefore, in order to improve the quality of the picture and/or sound, it is necessary to filter the decompressed signals by identifying and eliminating or minimizing the amount of noise causing the picture and/or sound degradation. This has presented a problem in the prior art.
SUMMARY OF THE INVENTION
The above described problem is minimized in accordance with the present invention.
Briefly, to filter noise from a display having a pixel matrix of x rows and y columns of pixels, initially a small subgroup of a matrix of pixels from m rows and n columns of the x rows and y columns, the rows and columns preferably being consecutive and odd in number, are chosen from the matrix. These m×n pixels are sampled in a number of different configurations, all of which include the same center pixel with each configuration preferably including the same number of pixels. The configurations preferably extend in as many different directions as possible such as, for example, each diagonal, a vertical line through the center pixel of the chosen pixels, a horizontal line through the center pixel of the chosen pixels and the center pixel and the four pixels on the vertical and horizontal lines therethrough which are immediately adjacent the center pixel, it being understood that other possible configurations are also acceptable and form a part of this invention. After the first m×n pixels are tested in a manner to be described hereinafter, the testing procedure moves over one column and selects the m×n pixels from the same m rows and columns numbered one pixel over (n+1), this being repeated until all of the columns have been reached and included in the testing. Thereafter the testing will select the first n columns and m rows starting with the row numbered one pixel down (m+1) and proceed across the columns in the same manner as described above until the last column has been reached. The test procedure then selects the first n columns and rows starting with the row numbered two pixels down (m+2) and continues in this manner until the last row has been reached. At this point in time there is adequate compensation for each of the pixels of the matrix except possibly for a small fringe about the perimeter of the matrix. All of the data obtained from this testing procedure is stored.
The testing procedure consists of four steps: finding the direction of minimal noise, mosquito noise filtering, vertical noise filtering, and horizontal noise filtering. After the configurations to be tested are chosen, the direction which has the minimum noise content is determined by finding the intensity contrast (IC) in each of the configuration directions. This is accomplished by testing each of the configurations and determining which of the configurations has the minimum intensity contrast (difference between maximum and minimum pixel values in the configuration). The configuration having the minimum intensity contrast is the one of minimum noise. If it is assumed that each configuration has (2k+1) pixels characterized as t
1
, t
2
, ... t
k
, P (the center pixel of the configuration) , t
k+1
, t
k+2
, . . . t
2k
, the intensity contrast of configuration i is determined as:
IC
(
i
)=max (t
1
, t
2
, . . . p, . . . t
2k−1
, t
2k
)−min (
t
1
, t
2
, . . . p, . . . t
2k−1
, t
2k
).
i.e., IC(i)=maximum pixel difference in configuration i. The configuration with the minimum IC value (called IC
m
) is selected, that is, IC
m
=minimum (IC(1), IC(2), IC(3), . . . ). A weighed mean (WM) of the pixels in this configuration of minimum intensity contrast IC
m
is then computed. The weighed mean can be computed by, for example, using the equation:
WM
=(
t
1
×w
1
+t
2
×w
2
+. . . +p×w
p
+. . . +t
2k
×w
2k
) &Parenclosest;÷(
w
1
+w
2
+. . . +w
p
+. . . +w
2k
)
where (w
1
, w
2
, . . . , w
p
, . . . , w
2k
) are the (2k+1) weights used in computing WM. The weights should be chosen such that pixels closer to the center pixel p will use higher weights and those which are farther away from p will use lower weights. The sum of the absolute value of the difference (SA) between the weighed mean (WM) and the pixels in the selected configuration is computed by:
SA
m
=abs
(
WM−t
1
)+
abs
(
WM−t
2
)+. . . +
abs
(
WM−p
) +. . . +
abs
(
WM+t
2k
)
where abs(x) is the absolute value of x. The same formula can be used to compute SA value for other configurations (e.g., SA(1) for configuration 1, SA(2) for configuration 2, etc.).
The SA
m
value is then saturated to an 8 bit quantity (i.e., if SA
m
is larger than 255, then it is set to 255) followed by a right-shift of three bits (equivalent to divide by 8) to provide a five bit value which ranges from 0 to 31. The resulting value is then used as an index to fetch one of the 32 filter coefficient pairs from a filter coefficient table. The jth row in the filter coefficient table contains the values (qtabP(j), qtabP_ml(j)). The values of qtabp() and qtabP
13
ml() are shown in the following Table:
qtabP()
qtabP_m1()
0.00000000
1.00000000
0.00000000
1.00000000
0.00000000
1.00000000
0.00000000
1.00000000
0.00000000
1.00000000
0.16406250
0.83593750
0.40625000
0.59375000
0.55859375
0.44140625
0.65625000
0.34375000
0.72656250
0.27343750
0.77734375
0.22265625
0.81640625
0.18359375
0.84375000
0.15625000
0.86718750
0.13281250
0.88281250
0.11718750
0.89843750
0.10156250
0.91015625
0.08984375
0.92187500
0.07812500
0.92968750
0.07031250
0.93750000
0.06250000
0.94140625
0.05859375
0.94921875
0.05078125
0.95312500
0.04687500
0.95703125
0.04296875
0.96093750
0.03906250
0.96093750
0.03906250
0.96484375
0.03515625
0.96875000
0.03125000
0.96875000
0.03125000
0.97265625
0.02734375
0.97265625
0.02734375
0.98046875
0.01953125
Note that qtabP(j)+qtabP
13
ml(j)=1.0 for all j. These selected filter coefficients (suppose the jth row has been selected) are used as filter coefficents in the mosquito noise filter which filters the center pixel p by providing an output MFout, where
MFout=QTABP
(
j
)*
p+qtabP
13
ml
(
j
)*
WM.
The output of the mosquito filter is then filtered by a vertical cross filter which, if turned on by the cross
13
V
13
on signal, provides an output VFout, where
VFout
=(3*
MFout+Vavg
)/4,
and Vavg=average of the neighboring pixels of p in the vertical configuration. If the vertical cross filter is not turned on (the control signal cross
13
V
13
on is off), then
VFout=MFout.
If the control signal cross
13
H
13
on is on, then HFout, the output of the horizon
Wong Yiwan
Yamaguchi Hirohisa
Brady III Wade James
Rogers Scott
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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