~F8TVFONT PRIMER - (draft).

	TVFONT is on the system, and can be  run by typing "R TVFONT"
at  a III display console.  At present, III  #23 is next  to a camera
setup for making  fonts.   The process of  making a new  XGP font  or
altering an old one will be explained in six steps:

	1.  Raster input:	get a video image or an old font.
	2.  Contouring:	 	make polygons.
	3.  Polygon editing:	delete, scale, position and alter.
	4.  Polygon I/O:	save and restore polygons.
	5.  Font output:	make new font and output font file.

	Complexity arises in  that there is  more than one way  to do
each  step, there are  default arguments  and switchs which  the user
may alter, there are ways  to save and restore intermediate  results,
and  there  are  quite a few  different  display  modes  and  display
diagonostics.  The TVFONT command scanner resembles  that of TVED and
E;  (as well  as  CRE  and  GEOMED); the  command  scanner  types  an
asterisk "*"  when it is  in its top  most listen loop  waiting for a
single command character.  The command character  may be modified  by
the META and CONTROL  keys which will be abbreviated as  "α", "β" and
"ε"  for CONTROL, META, and  META-CONTROL respectively. Many commands
in turn require arguments such as numbers or file names.  Finally the
"X"  command   waits  for  an   extended  command  name   of  several
characters, which is called an extended command.

	This first  explanation will present  a way  of making a  new
font  using the fewest  commands.

Raster Input and Contouring:

	1.	"T"	take television picture.
	2.	"H"	Display histogram of television picture.
	3.	"C24"	Cut at intensity level 24.

	Get the  Font Camera  looking at  a single  letter in a  font
book. Use  a black piece of paper with a square  cut out as a mask to
isolate the letter. The "T"  command will take a television  picture.
The "H" command  will display a histogram of  the television picture,
showing how  many points of the image were 0 intensity, (total black)
and how many points of the image were 77  intensity, (total white). A
picture of a black glyph  on a white background surrounded by a black
mask should yield a  histogram with two peaks.

	Next the "C" command followed by an  octal number followed by
a  carriage return; contours the  image at the  given octal intensity
cut threshold.    That is  all  the points  of  the image  above  the
threshold  are inside  of  a polygon.   The  intensity  value of  the
lowest valley  between the two peaks of the histogram is probably the
best cut value (and is  probably the octal number 24 or 30).  The cut
command, will display the polygons that are made.
~I1973,800;F8- 43 -