[PD] video analysis

[chris clepper]

>  > - which (cheap!) video-in device should be used?
>
>USB cameras are low-bandwidth and so can't accomodate big resolutions.
>Even if you get 240*320, then if it is YUV-4:2:0, then 2 out of 3 YUV
>color channels are encoded at 120*160 (!!!)

actually using 4:2:0 chroma samples (Cb,Cr) are swapped every other 
line, so each chroma channel is effectively 160*60.  4:2:2 chroma is 
subsampled at a 2:1.  this is really a trivial amount of data loss 
and you look at it everyday and never notice.  DVD  and PAL DV25 is 
4:2:0, NTSC DV is 4:1:1, broadcast TV is 4:2:2 and so is HDTV.  the Y 
is the really critical data as far as clarity goes.  as long as the 
processing is 4:2:2 everything is usually ok.


>We like analog cameras. Find the right shop for buying those (probably not
>"consumer electronics" shops). Then use a capture card such as a PCI
>BTTV. You can get 480*640 @ 30 fps and such.

yet another example of 4:2:2 ;)

cgc