ppmtovtx converts pictures into Videotex (CEPT-3) format.  The Videotex format
is shared with Teletext (Level 1) services such as Ceefax, and Viewdata
services such as Prestel or Minitel.

A Videotex frame is made up of 24 rows of 40 characters.  These characters can
be either printable ASCII characters, mosaic graphics or formatting commands.
The format allows for 8 colours including black, and a graphics resolution of
80x72.  Typically the first row on a Videotex service is a header row showing
the page number and service name, so the actual useable height is reduced to
23 rows, or 69 mosaic pixels.

ppmtovtx expects binary PPM files with a width of 80 pixels.  The height can be
anything up to 72 pixels, and should be divisible by three.  The behaviour of
the program in other cases is undocumented.  The usual height would be 69
pixels, which gives 23 rows of Videotex data.  You can scale pictures to this
size using the following command:

pnmscale -xsize 80 -ysize 69 picture.ppm >scaledpicture.ppm

Where "picture.ppm" is the name of the original file, and "scaledpicture.ppm"
is the destination (NB: the ">" is required).  pnmscale and tools to convert
to and from PPM format files are available in the NetPBM package. (NetPBM is
available from http://netpbm.sourceforge.net and an Amiga port is on Aminet)

You can then convert this into a Videotex frame using:

ppmtovtx scaledpicture.ppm scaledpicture.bin

Where "scaledpicture.ppm" is the input file, and "scaledpicture.bin" is the
output file in raw data format.

There are more options for ppmtocept3:

ppmtovtx <input file> <output file> [options [threshold]]

The output filename should end in ".bin" for a raw format file, or anything
else for an ESC coded file.  The ESC coded files (which I call .vtx format)
can be loaded by PstView amongst others, but .bin format is more widely used.

Options are one or more of {SHAKRGYBMCW} (case sensitive), as follows:

S - Separate mode
    Separates the mosaic graphics pixels.

H - Held graphics mode
    During colour changes the block with the colour change will be a
    duplicate of the previous block.  Probably not very useful.

A - Automatic background colour changes
    Changes the background colour to improve the colour resolution of the
    picture. 

D - Disable black foreground
    Prevents ppmtovtx using the code for black foreground colour (more
compatible)
    Only works with "A" mode enabled.

K - Black background (default)
R - Red background
G - Green background
Y - Yellow background
B - Blue background
M - Magenta background
C - Cyan background
W - White background

It makes no sense to specify more than one of {AKRGYBMCW}.  Later colours
override earlier ones, and in conjunction with A at most only the start of the
first row will be of the specified colour.

=====
History
-------

1.3a (re-release)
* Added OS4 port, no other changes.

1.3
* I have absolutely no idea

1.2 (23.03.2002)
* Added an option to prevent ppmtovtx inserting a code for black foreground
colour.
  Black foreground is not officially supported.  ppmtovtx will use a workaround
instead.

* Defaulted output to use .bin format if an extension was not recognised, rather
than .vtx

1.1 (16.03.2002)
* Fixed a bug where full foreground colour blocks would sometimes be in the
  background colour

* Fixed another bug which caused some of the picture to be in the background
colour
  thus not being visible.

1.0 (07.01.2002)
* First release

=====
Additional notes for included executables:

AmigaOS
-------
Copy the file Amiga/ppmtovtx to somewhere in your path (eg. SYS:C)
You should increase the stack before running this program (issue the
command "STACK 50000")
There seems to be a bug which occasionally causes a Suspend/Reboot requester
when the program exits (if you run it more than once) that I haven't managed to
track down.

DOS/Windows
-----------
Copy the file DOS/PPMTOVTX.EXE to somewhere in your path (usually
C:WINDOWSCOMMAND or C:WINNT)
The compiler I used seems to have caused a bug when writing .bin format data -
occasionally the output includes a code for red text.  I advise recompiling
from the source code if at all possible.

intent/AmigaDE
--------------
Copy the contents of the intent directory to the root of the intent filesystem
(usually c:intent)
No known bugs in this version.

=====
These executable files and source code (in ANSI C) can be freely distributed
provided no money changes hands (excluding reasonable costs for media or
delivery) and the author is acknowledged and this .readme file is included with
the distribution.  The executable MUST NOT be distributed without the source
code, although it is permitted to distribute the source code without any
compiled
binaries.  Modified binaries and source code MUST NOT be distributed without
reasonable contact details for the person who modified them (eg email address).
The author does not accept any responsibility for loss of data or other events
arising from the use of this software.  All use is at your own risk.  Any
changes
made by third parties are their responsibility and not that of the original
author.
The original author retains copyright for the original source and any binary
created using that source code.  Although unlikely, permission to distribute or
use this source code or a resulting executable can be revoked at any time and
without warning.  This licence covers both commercial and non-commercial use. 
If
you do not agree with these terms you must immediately delete this software
package.

-- Chris Young, 13th January 2002
http://www.unsatisfactory.freeserve.co.uk