深入分析梳状滤波器原理Comb-fil.ppt

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).,(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 constant monochrome receivers).,180 degrees,2D comb filter,Important conceptpicture information (y , c) is about the same from line to line . Special case( y - c , y + c ).,y - c,y + c,2c,c,y,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,Vertical detail difference (adjacent lines). Motion difference (adjacent frames). Adaptive comb filter 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.,Mode B (detection (1,3) 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.,Y,Mode D (T1detection (1,3) T3)&(detection (2,3) T2),Which means that detection(2,3) dominates.,Y,Mode D,Conclusion,2D,3D,a