Capturing 640x480 - interlace --> ugly result

[victor_diago]

Hi all.

im about to finalize the mpeg montage way, just solving a little delay problems with that, trying to go from 2 sec delay to 200 ms one !


but i have a question to you all..

i work with cheap bttv 4 inputs x 1 bt878 cards.

when try to capture at 640x480 it interlaces image... and i see all shaking like an earthquake. i know there is a fix made that discards some frames. but my question is : why do this happen, and there is a way to make it better without need to drop many frames ? i work at 5 fps each camera, so there will be no problem to only drop 10 frames (the chipset support 30), but i would like to have bigger images..

thanks in advance !

victor diago

[lazyleopard]

The drop-a-frame kludge just gives the chip time to be sure it's looking at one camera, and to sort out which is the even half-frame and which the odd. (If all the cameras were perfectly synchronised this wouldn't be necessary, and you'd only have to throw away the half-frame that was in progress when the chip was switched, but in reality...) If the even and odd frames are swapped you get the most horrible jagglies on non-horizontal lines.

The other problem with interlacing is that there's a 1/50th (or 1/60th) second difference between the two half-frames. Anything moving fast enough to have shifted in that time is going to appear as a doubled image. There's not a lot you can do about that.

Ref: http://www.zoneminder.com/forums/viewtopic.php?t=1546
and: http://www.zoneminder.com/forums/viewtopic.php?t=3303