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1986-06-19
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VIDTEX GRAPHICS
Several CompuServe services offer graphics using the VIDTEX graphics
protocol. There are three types of graphics: semigraphics 4, medium, and high
resolution. Most services offer high and (occasionally) medium resolution graphics
and this document describes those two modes and how to access them with FLASH
terminal program (currently the only ST terminal program offering VIDTEX graphics).
If you have a terminal program that does not support VIDTEX graphics you can
still download a VIDTEX graphics picture and view it using a program to convert
it to DEGAS compatible format. DGEN.TOS in Data Library 3 is such a program.
The program PICSW6.PRG (in Data Library 4) also allows you to convert VIDTEX
graphics picture to a variety of formats. If you want to create a VIDTEX graphics
picture, then the program RGEN.TOS, also in Data Library 3 allows you to do so.
FLASH terminal program will save the VIDTEX picture as a DEGAS compatible
picture for you if you hit the <INSERT> key while the picture is on your screen.
You will get the prompt 'Filename' and you should type in the full filename
(including drive and pathname if applicable) and hit enter. If you change your
mind and don't wish to save the picture, hit <escape>, then return. Note that if
you are using a monochrome monitor that FLASH saves the picture as a DEGAS
high resolution picture and if you are using a color monitor it's saved as a
LOW resolution picture. Therefore you should use the proper extensions to
the filename e.g. .PI3 for monochrome and .PI1 for color.
WHAT ARE VIDTEX GRAPHICS
Medium and high resolution VIDTEX graphics are identical except for their
resolution. 'High' resolution graphics are 256 by 192 pixels and 'medium'
resolution graphics are exactly half that (128 x 96 pixels). The VIDTEX
'pixels', however, are always scaled appropriately so that the picture you
see on your ST screen is square and is the full height of the screen (minus
one 'text' line). Current VIDTEX pictures do not have color information in
them, so you see the identical picture whether you have a color or
monochrome monitor. i.e. 'high' and 'medium' resolution as used in VIDTEX
does NOT mean the same as 'high' (monochrome) and 'medium' (color) resolutions
on the ST.
High and medium resolution VIDTEX pictures are encoded using a method
called 'run length encoded characters' or RLE. What that means is that the
pictures are in a compressed format If you view or download a vidtex picture
from one of the Data Libraries here on CompuServe, you will see the phrase
"/graphic:rle" next to the filename. This means that CompuServe has stored the
picture in the correct format and will allow you to view it on-line correctly.
If you produce your own VIDTEX picture using one of the programs in the Data
Library, then when you upload it, you MUST specify that it is and RLE type
picture. For example, if you use xmodem protocol to upload it you are asked if
the file is binary, ascii or RLE graphics. Always answer RLE graphics if you
are uploading a VIDTEX picture so that others can view it properly on line.
ERROR MESSAGES
If you are using a terminal program that does not have the VIDTEX graphics
protocol OR if you are using FLASH terminal program and you are not in VIDTEX
mode both in FLASH and on CompuServe, then you will receive error messages
from CompuServe. There are also certain other circumstances in which you will
receive error messages. CompuServe will warn you that your terminal is not
VIDTEX compatible, and ask you if you still want to proceed to view the
picture on-line. Assuming your terminal program supports VIDTEX, or you wish
to capture the picture for off-line conversion, simply answer Y to the question
and CompuServe will proceed to send the VIDTEX picture. When the VIDTEX picture
has been fully displayed you will hear the terminal bell ring. Hit the
return key when you have finished looking at the picture and CompuServe will
then send your terminal the code to erase the picture.
There is one service in CompuServe that offers 'price-volume' graphs
of stock. It sends a special control character to FLASH to ask if it is
VIDTEX compatible. The current version of FLASH does not respond to that
character so you will recieve an error message. You may ignore the error
message, and as long as FLASH is in VIDTEX mode, the picture will be displayed
correctly.
Users have also reported that if they are logged in to CompuServe in
7-bits parity, they will also get the error message because it appears that
CompuServe changes to 8-bits, no parity before displaying a VIDTEX picture.
You can either ignore the error message or visit the DEFALT section of
CompuServe and change your parity setting to ZERO. Note that CompuServe keeps
separate settings for 300 baud and 1200 baud, so if you change the setting
at 300 baud and later log on at 1200 baud, you will have to make the changes
again.
When using FLASH terminal program with no parity, the message
'User ID:' when you log on may appear garbled. You can set the 'strip-bit'
on so that the message appears normal - or you can just type in your user ID
anyway and not worry about it. You can even leave FLASH in 8-bits no parity
and log on to CompuServe with 'strip-bit' on. As long as you leave the 'strip-bit'
on, FLASH will strip out (and ignore) the parity bit.
There are two ways you can tell CompuServe that you have a VIDTEX
compatible terminal. One way is to visit the DEFALT section of CompuServe
(GO DEFALT) and pick the selection "Changing your terminal type". Select the
VIDTEX option and CompuServe will send a special sequence that will determine
if your terminal is really VIDTEX compatible. Then, when you exit this section
you will be asked if you wish to make the change permanent or for this session
only - the choice is yours. The other way of telling CompuServe that your
terminal is VIDTEX compatible is to type the command SET TTY VIDTEX at any
"!" (exclamation mark) prompt on CompuServe. Note that you cannot issue this
command from within one of the SIGS or Forums.
IMPORTANT!
BEFORE you use either method with FLASH you must set FLASH to VIDTEX type
also. You can do this either by hitting the <INSERT> key, then typing in
MO VI <return> or by holding down the <ALTERNATE> key and pressing the letter
M. This will cause an alert box to appear and you will see the current terminal
type with a thick outline. Use the mouse to click on VIDTEX and FLASH is now
set to VIDTEX.
GARBAGE pictures
VIDTEX graphics are very sensitive to line noise. Even a single extra
character will throw the picture out of sync. If you have a noisy connection
with CompuServe, then your best bet is to download the picture with xmodem
protocol (assuming the picture is in one of the Data Libraries) and convert
it to DEGAS format off-line using one of the programs mentioned above. If you
are using FLASH and wish to abort viewing the picture, hit a control-C to tell
CompuServe to stop sending the picture, then hit the undo key to take FLASH out
of the VIDTEX graphics mode.
Where to find VIDTEX pictures
A number of SIGS on CompuServe have VIDTEX pictures in their Data
Libraries for on-line viewing or downloading. Ones that we are aware of
at this time include ATARI8, ATARI16, ARTSIG, and MAUG (Macintosh users group).
You can find VIDTEX pictures on-line in HHA (Hollywood Hall of Art)
which has digitized pictures of many movie stars. The FBI has posted VIDTEX
pictures of the 'ten most wanted fugitives' on-line in the FBI section called
TEN (GO TEN). Weather maps are available for on-line viewing in the AWX-4
(GO AWX-4) section of CompuServe and stock market graphs may be obtained in
the securities (GO SECURITIES and pick the Price-volume graph selection)
area. NOTE: There is a fee for both the maps and the stock market graphs.
In the stock market area there is no fee for graphing HRB (H and R Block)
to allow you to test your terminal without incurring a charge. As mentioned
above, you may get a warning message in this area if you are using FLASH.
You may ignore the message.
FURTHER READING
If you want more technical information about the VIDTEX protocol, then
go to the VIDTEX (GO VIDTEX) section on CompuServe and browse through the
technical library section.
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