[PD] video analysis

chris clepper cclepper at artic.edu
Tue Mar 25 20:13:58 CET 2003


>Ok, according to that I had it right. if Y is 240*320, then U is 120*160
>and V is 120*160. There's no 60*160 involved...

if both U and V are 1/2 the samples of Y then the format is 4:2:2. 
4:2:0 looks like*:

row1 : YYUYYU
row1 : YYVYYV
row3 : YYUYYU
row4 : YYVYYV

for every 4 Y samples there are two samples of U or V and they 
alternate every row.  the 0 means that the U and V are both 
vertically and horizontally subsampled unlike 4:2:2 (YUYV) or 4:1:1 
(YYUYYV), which are only horizontally subsampled. so effectively 
there are only 1/2 the vertical samples of U and V in 4:2:0.  how 
those are reconciled into 4:2:2 is left to the decoding/decompression 
method.  UV data can be either copied or averaged or some sort of 
interpolation can take place....

>... unless you have interlacing as well (which I assume is *not* the case.
>I know incoming video is, but isn't that deinterlaced before the input
>card gives a frame ?)

if the incoming video is interlaced then the interlacing might always 
be a factor.  depending on the computer format you are using for 
storage the fields could be kept intact rather than deinterlaced 
progressive images, a raw DV stream for example keeps the fields.

*the page Marc Lavallée linked to http://www.fourcc.org/fccyuv.htm 
lists the 4:2:0 formats as planar but that might not be the way 4:2:0 
is actually stored in DV.  anyone know for certain if DV stores 
packed or planar data?  i'm fairly certain that it's packed.  another 
link: http://www.dvcentral.org/DV-Beta.html

cgc





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