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Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!rutgers!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga,comp.sys.amiga.hardware,comp.sys.mac.misc
Subject: Re: Fantastic video switcher card being shown at Mac World!
Message-ID: <17433@cbmvax.commodore.com>
Date: 11 Jan 91 23:30:42 GMT
References: <1408@tardis.Tymnet.COM> <1991Jan11.113544.26971@ncsuvx.ncsu.edu>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 50

In article <1991Jan11.113544.26971@ncsuvx.ncsu.edu> hgm@ccvr1.ncsu.edu (Hal G. Meeks) writes:

>I have some literature from RasterOps that advertises a board that will
>capture 8bits in real time. 

One thing to watch out for.  Lots of frame grabbers adverise the capability of
grabbing video at resolution N in real time.  What they often don't talk about
is the fact that they can't actually capture multiple frames that way (I don't
know anything about the RasterOps board itself, only these things in general).

You really have two separate problems.  Some devices, like the DigiView, will
capture an image in non-real time.  They do a very nice job, but are useless
for interactive work.  Then you get the class that will capture an image in
real time, but only to private memory.  These let you take a good snapshot
from a video camera or TV, but don't let you capture moving video.  At the
high end you get devices that allow you to capture multiple frames in real
time and, hopefully, leave a little time on the main CPU to let you do something
interesting with the images as they come through.  "Mandela" for the Live! 
board is an excellent example of this last one.

On a Mac, the big problem would be moving the captured image to some place
it could be processed.  At best, the video capture board will have fully
double buffered memory.  You move one snapshot out while capturing the next.
If the board doesn't support DMA into main Mac memory, you're left with an
effective 2-4MB/s transfer rate, depending on the Mac, to get this stuff out.
If you're capturing images in the Mac internal format, that would leave plenty
of time for CPU interaction.  The only real problem is the amount of memory
needed for this capture on the video board.  If they're selling it for cheap,
it's probably not in the realtime capture class of devices like the Live!
If its $1000 or more, it better be.

Interestingly, the Live! board is a pretty clever design.  Since the levels it
caputures are Amiga resolutions, it never grabs anything more complex than what
the Amiga can deal with.  It doesn't actually have any memory on board, but 
uses the CPU to dump directly to Amiga video memory.  Since it uses the CPU,
it can only grab less than 1/2 the full Amiga non-blocking resolution (which
would be 640x400x2 or 320x400x4), this works.  8-Bitplanes either needs an
awfully fast bus or buffer memory.

>>Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com

>hgm@ccvr1.cc.ncsu.edu	"..now that Mac way of doing things has taken hold, 



-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"Don't worry, 'bout a thing. 'Cause every little thing, 
	 gonna be alright"		-Bob Marley