(no subject)

Jason Williams (streak@ccwf.cc.utexas.edu)
Thu, 15 Jan 1998 14:38:56 -0600 (CST)


On Thu, 15 Jan 1998, Rolf Hemmerling wrote:
> Remember, because many refs are not compatible with color videos,

Those are becoming fewer and fewer now that there's a freeware alternative
to the White Pine reflector...
From=20http://ccwf.cc.utexas.edu/cgi-bin/cgiwrap/streak/scan?age=3D0

35 are Cornell reflectors ; 134 are White Pine or Brian Godette's Enhanced
reflectors

A few of those listed as Cornell are Enhanced Reflectors with the
NO-GENERAL-REFMON option set.

> So the CPU burden for the color cams is not lower if You send b/w to the
> ref, because the cameras send color all the time to the PC.

I don't quite buy this...if you can select a grayscale mode then it should
communicate in B&W with the computer.

> In fact, if
> You send b/w to the ref, there is an additional translation burden for
> converting color to b/w data to be sent to the ref).

If you look at it that way, there's also a burden on the B&W Quickcam
converting 6 bit grayscale to 4 bit grayscale.

> O.k., each frame sent to the ref is worth less KBytes if it is b/w and
> not color,

Hmm..the misconception that B&W vid consumes less bandwidth than color.
From=20what I understand (though I could be wrong), B&W uses a completely
different method of transmission. The Cornell codec uses differences in
frames.. MJPEG sends complete frames with smeared pixels (Dale Paul
explained it much better than me a few days ago).

> but the
> real limit for video transfers are the 28.8/33.6/64K limitations of Your
> Internet connection. So with b/w sending, You may get higher frame
> rates, but the burden is less.

If you use ANY parallel port camera, the CPU load is going to be much much
higher than if you had used a capture card. The capture card has hardware
compression and not the limited bandwidth of a parallel port. A parallel
port camera uses software compression (I believe).

True, the frame rate limitation (15 fps for the Quickcam) isn't the
bottleneck..but the internet connection is. (Assuming 28.8kbps modem)

> For Cu-SEEME, be glad if You transmit 1 frame per second on a heavy ref,
> so the Internet transfer is not the special CPU burden, it is the same
> for all cams (You can=B4t send more than 28.8/33.6/64K if you have a 28.8
> or 33.6 analog connection or 64K ISDN connection, that=B4s it)

True, the FPS limitation is the internet connection generally..but the CPU
load also prevents you from doing OTHER CPU intensive processes (such as
audio compression). It's NOT the same for all cameras....a camera
attached to a capture card doesn't have the same CPU load. Talk to other
capture card owners :)

--
streak@ccwf.cc.utexas.edu    * Jason Williams -- Austin, Tx.  |     |
streak@mail.utexas.edu       * University of Texas at Austin  | ___ |
streak@cs.utexas.edu         * BS Computer Science             \_|_/
*************** http://ccwf.cc.utexas.edu/~streak/ **************|