milo@ndmath.UUCP (Greg Corson) (01/08/88)
Can anybody suggest how to construct a >>simple<< non-real time video
digitizer which could be attached to a parallel or fast (56k-1m bps)
serial port? I've seen a gadget called DIGIVIEW for the Amiga which
simply connects to the parallel port...it takes awhile to digitize an
image (under a minute usually) but seems to be pretty stable as long
as the input video signal doesn't waver.
I'm thinking the gadget must be pretty simple because the entire DIGIVIEW
hardware fits into a epoxy sealed module about 2x3x3/8 inches in size.
Resolution of the converter is 32 levels (5 bits) and it only handles
Black&white video.
Any hardware hackers out there have a good idea on how something like this
could be built (preferably as inexpensive as possible!). I'd like to
put together something that could be attached to a Mac serial port and
feed in data at around 256kbps or so. I can handle the software if someone
wants to take a whack at the hardware.
As simple as the digiview seems to be I suspect it wouldn't take much to
build one of these...possibly a video ADC and some matching components
would be all that was needed, but then...I don't profess to be a hardware
expert, particularly when it comes to video circuits....so you tell me!
Hope someone can help.
Greg Corson
19141 Summers Drive
South Bend, IN 46637
(219) 277-5306 (weekdays till 6 PM eastern)
{pur-ee,rutgers,uunet}!iuvax!ndmath!milo
ron@topaz.rutgers.edu (Ron Natalie) (01/08/88)
Steve Ciarcia had one in Byte a while back. It was 256x256x8 I think I recall. You can get it in kit form form whatever that company is that capitalizes in turning the Circuit Cellar designs into kits. -Ron
brian@sdcsvax.UCSD.EDU (Brian Kantor) (01/10/88)
One way to do this is rather old technology - there are several on the market that do just this: Use a level detector and a couple of counters to count bits from the horizontal and vertical sync pulses, then when you reach coincidence (use a comparator) with a register for the current-cursor-position (stored in a latch), you use a sample-and-hold and digitize that with a nice slow A/D converter. When the conversion finishes, you store that value and update the current-cursor-position latch to the new screen location you want to digitize. This is slow for doing a whole screen at a high resolution - about 8 seconds or so for 256 x 256 with a 4MHz Z-80 - but it can give you real nice control over what area you want to digitize and it can be really fast if the area is small. The grey-scale resolution is up to you - just use whatever size A/D you want. Faster A/D converters will give you faster frame conversion. Only real drawback is that the video image and digitizer clocks must be rock stable, so real-time work is out unless you have an incredibly fast processor and a flash A/D converter. A couple of years ago we bought a product called the "Digisector" made by The Micro Works in Del Mar, California that works pretty much this way. For about $300, we got a 256x256x6 digitizer that takes in RS170 monochrome video, which I think was a pretty good deal! I'm told they have a new version that can grab and digitize an NTSC frame in colour on an IBM-PC card, but I've not yet tried one. Brian Kantor UCSD Computer Graphics Lab c/o B-028, La Jolla, CA 92093