Comb Filter - PowerPoint by T44oqFA

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```									Comb Filter
Outline

   Y-C separation
   2D comb filter
   3D comb filter
   conclusion
Comb filter (Y-C separator)
   Separate the incoming composite
video signal into luminance (Y) and
chrominance (C).

(composite)
NTSC composite signal

   Video signal prepared for broadcast
contains two major parts, the
luminance (Y) and chrominance (C).
Basic concept for Y C separate

   1.Frequency- notch , bandpass filter
( in early years ).

   2.Chrominance phase difference-
comb filter ( today ).
Frequency
Luminance & chrominance frequency
Notch/bandpass filter system

   significant overlap , energy go
through.
Chrominance phase difference
   chroma burst reference and the chroma
information is reversed by 180 degrees on
alternate lines (luminance of the system to remain

180 degrees
2D comb filter
   Important concept…picture information (y , c) is
about the same from line to line .
   Special case( y - c , y + c ).

y
y+c

y-c
2c          c
Why we call it a "comb filter"
2D weighting comb filter
   different colors vertically through the picture .
   (1/4,1/2,1/4).
   the transition from one color to another is softened.
Horizontal delay
   analog: glass delay line , CCD .
   digital : memory .
3D comb filter
   compare information in successive frames .(odd)
   perfect separation of Y and C for still frame images
( key advantage over the 2D filter ).
   motion or serious color changes , 3D filter may
perform no better than the 2D filter.
   has to store two frames of video data.
Problems
lines).

1.Detect and select one form.
2.Correction terms.
3.Weighting and sum .
An improved 2D adaptive comb filter

   Overview (mode A,B,C,D)
Mode A (does not perform comb filtering)

   Only when video image has serious
vertical difference.
   Just a bandpass filter.
Mode B (2D weighting with bandpass filter)

   Normal mode ,Y-C can be separated
quite well.
Mode C (2D weighting without bandpass filter)

   Use under that 3 lines are so close.
   Can separate better than B.
Mode D (2D simple comb filter)

   Use under that detection(2,3)
dominates.
Common method for difference detection

   Check Y signal only.
   Switch mode when difference exceeds a
threshold value.
Detection algorithm
   Normal way (upper).
   Special detection (bottom).
   Use these two detections. (T1,T2,T3)
Y           Y

C

Y’

C’
Mode A (detection (1,3) > T3)

   Which means the vertical detail
defference is serious.
   Bandpass filter performs better than
comb filter.
Y
Mode B (detection (1,3) < T3)&(detection (2,3) > T2)

   The mostly encountered situation.
   Use bandpass filter to eliminate
little difference between Y.
Y
Mode C (detection (1,3) < T1)&(detection (2,3) < T2)

   Which means 3 lines have almost
the same Y-C information.
   Mode C better than B.
Mode D                            Y
(T1<detection (1,3) < T3)&(detection (2,3) < T2)

   Which means that detection(2,3)
dominates.                Mode D
Conclusion