Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!munnari.oz.au!cluster!metro!natmlab.dap.csiro.au!ditsyda!macuni!mqccsunc!ifarqhar
From: ifarqhar@mqccsunc.mqcc.mq.OZ (Ian Farquhar)
Newsgroups: comp.sys.amiga
Subject: Re: A neat new idea?
Summary: Yes, and an interesting one too...
Keywords: genlocking, interactive windows
Message-ID: <111@macuni.mqcc.mq.oz>
Date: 18 Jan 90 02:41:30 GMT
References: <8269@nigel.udel.EDU>
Sender: news@macuni.mqcc.mq.oz
Reply-To: ifarqhar@mqccsunc.mq.oz (Ian Farquhar)
Organization: Macquarie University, Sydney
Lines: 111

In article <8269@nigel.udel.EDU> SGHYATT%UALR.BITNET@cornellc.cit.cornell.edu (Steve Hyatt) writes:
>To You AMIGA Gurus Everywhere,
>   While thumbing through the campus MAC nuts' fall 89-APDAlog (Information
>Catalog for Apple Programmers and Developers, pg 13-14), I noticed a article
>about a new product for the big apple. Its an onboard TV that fits in the
>corner of the MAC II screen (the 8 color monitor). NOW the reason I'm making
>such a big deal of this is:

[A line accidentally deleted because vi is a pile of $$#@$$E$#$]

>2) Is it feasible? (Surely the AMIGA can do it! ;)

Almost certainly possible, but I would like some heavy financial backing
before I attempted anything like it!

Hmm... initial thoughts.  First, lets assume that you are using PAL (the
REAL television standard).  50 fps at 625 lines.  To
display it on a 640 x 200 screen, we would need to reduce the resolution
somewhat.  Both are fairly easy, and once converted to digital (that may
be the hardest bit - those fast converters are expensive) then it is
either a matter of a few fast TTL, or some custom logic (if you could
make it fast and cheap enough).

The algorythm to convert this is:

  Window height
   ---------   x   current line of source field
     312.5

This give the y coordinate of the current pixel.

The x-coordinate depends on the horizontal resolution of the A/D
converter, but is calculated similarly.

Anti-aliasing - ie. taking into account that a scan line in the window
may consist of several scan lines in the source field - may complicate
matters and would require storage of scan lines temporarily.  Making it
work with interlaced screens would be a real pain in the prosterior.

The hardest part of this is actually writing the finalised field into
chip RAM.  One simple - and quite brute force - method would be to limit
the access of the 68000 across the scan line, which would really pull
the hell out of the performance of the Amiga (many system structures are
in CHIP ram).

You could not clip this against the clipping rectanges nearly fast
enough, so you would have to ensure that it was covered by a foreground
window (sort of like a backdrop window that stays upfront).  This would
allow intuition to clip the lower windows against yours properly.  It
would also have to respond to menu activation by stopping the update so
that the image did not trash meuues (I hate that kludge, CBM!)

Anyone got a better solution?  I am sure that with a bit of thought, and
my hardware manual which is at home, I could come up with a better
system.

Naturally, the fewer bit planes, the easier.  I am assuming that the
screen you are running on is capable of a decent number of bit planes,
or you are willing to put up with a a solarised screen (solarising is
that awful effect with was so overused in the seventies where they
reduced the number of on-screen colors and mucked about with them.  It
looked awful.)

>3) Would not this be the easiest way to digitize something from TV/VCR using a
>   simple screen grabbing program?

Frame rate considerations?  How do you feel about a frame per second..
or less?

>Two of the products suggested for the MAC version were security applications,
>and in-house teleconferenceing.I haven't seen the product first hand but the
>pictures in the article showed screen shots of the ESPN logo & NBC NEWS TODAY.
>I'd love to sit at my terminal writing C code, using a terminal program to
>download, AND watching Gilligans Island reruns... Or the new AMIGA ads for that
>matter!

Security applications?  Sounds like rampant paranoia to me, folks!  Do
they have a camera under the bed so that the mac user can look for
communists (or PC owners - they probably hate them more)?

I remember an issue of Scientific American that had a picture of one of
Bell Lab's development environments.  It has a security system whereby a
picture of the employee was displayed in a small window up the top of
the screen.  If the user did not match the picture...

That is quite a neat idea.  The whole article refered to a small screen
hack called Crabs (I think), which invaded the display and started
munching windows!  Apparently the sight of one attaching a picture was
gruesome.

As for the question of watching television on an Amiga, why not use a 
cheap genlock and just place the image behind your work?
I did this one, though it can be hard to read unless you are clever and
make sure that a window's paper color is not color 0.

The other option is to buy a Toaster (he says, clutching his chest with
helpless laughter).


All hail Saint Fubar, parton saint of computer programmers.

+-----------------------------------+-------------------------------+
|  Ian Farquhar                     | Phone : (02)  805-7420 (STD)  | 
|  Microcomputer Support            |         (612) 805-7420 (ISD)  |
|  Office of Computing Services     | Fax   : (02)  805-7433 (STD)  |
|  Macquarie University  NSW  2109  |         (612) 805-7433 (ISD)  |
|  Australia                        | Also  :       805-7205        |
+-----------------------------------+-------------------------------+
|  ACSNet      ifarqhar@macuni.mqcc.mq.oz			    |
|              ifarqhar@mqccsuna.mqcc.mq.oz         		    |
+-------------------------------------------------------------------+
D