Comb Filter
Outline
Y-C separation 2D comb filter 3D comb filter 2D adaptive comb filter conclusion
Comb filter (Y-C separator)
Separate the incoming composite video signal into luminance (Y) and chrominance (C).
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)
1.Frequency- notch , bandpass filter ( in early years ).
2.Chrominance phase differencecomb filter ( today ).
Frequency
Luminance & chrominance frequency
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
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)
Reference
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)
( 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.
(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
The mostly encountered situation. Use bandpass filter to eliminate
little difference between Y.
Y
Mode C (detection (1,3) < T1)&(detection (2,3) < T2)
constant[ monochrome receivers]).
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.
ference (adjacent lines).
Motion difference (adjacent frames).
Adaptive comb filter 1.Detect and select one form. 2.Correction terms. 3.Weighting and sum .
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
dominates.
Mode D
Conclusion
2D,3D,adaptive 2D.
Academic : adaptive 2D comb filter (less gate count ,more strategy).
Earn money : 3D/2D switch (best performance ,largest area)
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
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)