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2006-10-19
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** Using the "ImageWise" Video Digitizer with the TI 99/4A **
=======================================================
by Steve Langguth
For the past year or so, thanks to the authors of a couple of "RLE"
programs, users of the TI 99/4A have been able to view and use high resolution
pictures created by the users of other brands of computers. It was great being
able to take advantage of all of the picture files that could be found on the
various online databases and BBS's. But it also made me realize that something
was missing in the world of the 99/4A. Users of other brands of computers
(even the 8 bit antiques like the Commodore 64 and Atari 800) had access to
video digitizers, and TI users did not. Now, this might not seem like a very
big problem to some users, but to those of us who enjoy working with computer
graphics it was. Notice that I said "was". Finally, users of the TI 99/4A can
digitize images from video cameras and VCR's and put those images into a format
that can be used by the various bitmap mode drawing programs available for our
computer. This article describes how it can be done.
The Hardware
------------
In the May and June 1987 issues of BYTE magazine, Steve Ciarcia (BYTE's
resident hardware genius) described a video digitizing system that he had
developed called the "ImageWise" system. This system is composed of two
parts, a "digitizer/transmitter" and a "receiver/display". Each of these parts
is contained on a separate printed circuit board. You can buy each board
already assembled or in a kit with all the needed components. Or, you can just
buy the printed circuit boards (with an EPROM containing the control software)
and then buy all the other necessary components yourself. I chose to buy the
components myself, and the two parts of the system wound up costing me a total
of about $150 each.
When the boards arrived in the mail, they came with detailed instruction
manuals and parts lists, including the various part numbers for several of the
larger electronics supply companies. Even though I had never attempted a
hardware project before, I had little trouble getting everything put together.
(I DO have a friend next door, who is a 99/4A hardware "genius", so I could
afford to be a little "braver" than I would have been if I had to attempt a
project like this totally by myself!) And once I finally got all the
components soldered into the correct holes (don't ask!!), both boards worked
great.
The digitizer/transmitter (d/t) board is, as the name implies, the part of
the "ImageWise" system that does the digitizing. Unlike some digitizers made
specifically for other computer systems that take several seconds to digitize a
complete image (and therefore require your "subject" to not move or your VCR to
be set to "freeze frame"), the ImageWise d/t board captures a complete image in
1/60th of a second. It accepts video signals from a standard TV camera
(either B&W or color), VCR, laserdisc player, or camcorder, and stores the
picture as 244 lines of 256 pixels with 64 levels of grey scale for each pixel.
The d/t board then converts the stored video image to RS-232 serial data which
can be transmitted to any computer with a RS-232 port or to the ImageWise
receiver/display board.
The receiver/display board (r/d) accepts serial data from the d/t board or
files dowloaded from a computer. It converts this data back into a picture
suitable for display on a composite video input monitor.
Together the two boards allow the user to create a file of digital data
that represent an analog video image, use a computer to manipulate this file,
and then display the newly "manipulated" image. The July and August 1987
issues of BYTE magazine both contain articles describing interesting image
processing techniques that can be performed on files created this way.
The Software
------------
As I stated earlier, each board comes with an EPROM that controls what
that board is doing. But you still need programs for your computer that allow
you to accept the data being sent from the d/t board to the RS-232 and to send
a data file from your computer to the r/d board. Also, if you want to display
the digitized images on your computer monitor, you need a program that converts
the data file into a form that your computer can use. If I was an IBM PC user,
this would have been no problem, because the boards come with a disk containing
programs for the PC that both "grab" and "show" images. But because my little
99/4A is an "orphan", I had to write these programs myself.
To "grab" a digitized image from the d/t board, you simply connect the
DB-25 connector on the board to the RS-232 of the computer. The program needs
to send a one byte code to the board to tell it what resolution to use (the
choices are 256x244, 128x122, and 64x61), then when the program sends to the
board a character >11 (XON), the board "instantly" digitizes the picture and
begins sending it to the computer. (The baud rate being used is selected by a
DIP switch on the board itself.) If the computer must take a "time out" to
write to disk, the program simply sends a character >13 (XOFF) and the board
stops sending until it receives another "XON". The file created by this
program is LARGE. The board sends one byte for each screen pixel. The values
of these bytes range from >00 for black to >3F for a pixel that is white. This
adds up to a file of 246 sectors for each picture digitized. Of course, the
file contains a lot more "data" than 99/4A users can use, because even though
our high resolution screen is 256x192, we only have 15 colors to work with and
each pixel cannot be colored "independently". Perhaps more of this data will
be put to use on the Myarc 9640.
To "show" a digitized image on the r/d board, the process is just reversed.
A file is simply read one record at a time and then sent to the r/d board via
the RS-232. I found that I had to use assembly language to write the "grab"
program, but a very simple Extended Basic program worked fine for the "show"
program.
Finally, because I wanted to use my digitized images on my 99/4A, I wrote
a program that will "convert" the information in the files created by the d/t
board into a picture that can be saved in TI-Artist format. At first I decided
to simply "turn on" a pixel if it was above a certain value and leave it
"turned off" if the value was below the "dividing line". Unfortunately, this
simple method really didn't give as much detail to the pictures as I knew was
possible. After a lot of experimentation I was able to create an "algorithm"
that turns on more pixels in the areas that are supposed to be darker, and less
in the lighter areas. The converted picture has much less resolution than the
original, but it CAN be saved as a TI-Artist picture file (25 sectors), which
can then be modified or printed out.
Summary
-------
The ImageWise video digitizer system is a fairly simple to build,
relatively inexpensive, very powerful video digitizer that CAN be used with the
99/4A. If all you are interested in is digitizing video from a camera or VCR,
all you really need is the digitizer/transmitter board, which can be assembled
for about $150-$175 dollars. To use the digitized images on the 99/4A itself,
you will have to "sacrifice" a lot of the resolution. But because the system
sends its data through a standard RS-232 interface, it will continue to be
compatible as you "upgrade" your graphics capabilities.
If you have any questions that I haven't answered, just leave them on the
message base here on GEnie, or write to me at :
Steve Langguth
2956 South Barnes
Springfield, MO 65804.
Also, if you would be interested in buying the programs I wrote to use
with the ImageWise system and the 99/4A, I will galdly sell them to you for $10
--$11, if I have to supply the disk (hey, I've got to pay for this baby
somehow !!!).
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