From e0c6872cf40896c7be36b11dcc744620f10adf1d Mon Sep 17 00:00:00 2001
From: Norbert Preining <norbert@preining.info>
Date: Mon, 2 Sep 2019 13:46:59 +0900
Subject: Initial commit

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+% --- ------------------------------------------------------------------
+% --- halftone.tex
+% --- Format me with LaTeX, print me with an inch of top and left margin
+% --- ------------------------------------------------------------------
+
+\font\halftone=halftone
+
+\def\|#1|{{\tt#1}}
+\def\mmax{M_{\hbox{\scriptsize max}}}
+\def\SYSDEP#1{\marginpar{\scriptsize site\\ specific}}
+\def\TL{{\tt\TeX lase}}
+\def\TV{{\tt\TeX view}}
+\def\VAX{\leavevmode\hbox{V\kern-.12em A\kern-.1em X}}
+\def\VMS{\leavevmode\hbox{V\kern-.06em MS}}
+
+\def\mc{\small}
+\def\FORTRAN{{\mc FORTRAN}}
+
+\nofiles
+\documentstyle[11pt]{article}
+\advance\textheight by 21mm
+
+\title{Halftone Output From \TeX\footnote{Taken from the {\sl \VAX/\VMS\ \TeX\
+       User's Guide}}}
+\author{Dr. Adrian F. Clark\\
+        Department of Electronic Systems Engineering\\
+        University of Essex}
+
+\begin{document}
+\maketitle
+
+\section{Introduction}
+
+This note describes how image data can be converted to a form suitable
+for \TeX\ and then typeset in documents. Pictures are prepared for \TeX\
+in a somewhat different way to normal text---the hard work is done outside
+the \TeX\ input file; incorporating the image into the \TeX\ document is
+then quite straightforward.
+
+The image data must be converted from the binary representation used in Image
+Processing and Pattern Recognition work to a series of characters which \TeX\
+can map into pseudo grey-levels via a special font. A user-callable \FORTRAN\
+\|SUBROUTINE| called \|TEXPIC| is available for this purpose. \|TEXPIC|
+converts a picture held in memory to a text file containing \TeX\ input. (You
+can look at this file if you like, but it is unlikely to make much sense.)
+There are a few additional routines which can be used with \|TEXPIC| to produce
+particular effects: for example, the picture may be plotted as a positive or
+negative image. 
+
+The special font for setting pictures is
+defined to have some 65~grey levels. This does not necessarily imply that all
+the grey levels are distinguishable, nor even that they are strictly monotonic
+on laser printers. However, the quality of the output is certainly adequate for
+run-of-the-mill technical reports. 
+
+An example of an image typeset with \|TEXPIC| and \TeX\ is shown in
+Figure~1. This is the ``girl'' picture from the image database
+distributed by the Signal and Image Processing Institute of the University of
+Southern California, which is widely used to demonstrate image processing
+techniques. This representation is some $64 \times 64$~pixels. 
+
+\begin{figure}
+   \centering
+   \fbox{\input picture\relax}
+   \caption{Example of an Image Typeset using \|TEXPIC| and \TeX}
+\end{figure}
+
+\section{The \|TEXPIC| Routine}
+
+To generate a file containing the image data in a form suitable for input to
+\TeX, you simply invoke \|TEXPIC| from a program. \|TEXPIC| is called as
+follows:
+
+\begin{verbatim}
+    CALL TEXPIC( ARRAY, M, N, FILE )
+\end{verbatim}
+
+\noindent where \|ARRAY| is a \|M| $\times$ \|N| \|REAL| array containing the
+picture to be plotted and \|FILE| is a quoted string or \|CHARACTER| variable
+containing the name of the file to receive the data. If you omit a filetype
+(``extension'') from \|FILE|, \|TEXPIC| will use \|.TEX|. You can call
+\|TEXPIC| as many times as you want from a program; a separate output file will
+be generated for each picture.
+
+Due to problems with the controlling micro-processor in the standard \|LN03|
+printer, pictures with $\|N| > \approx 64$ will come out with white bands
+across them, rendering them effectively useless. However, this problem has been
+overcome on the \|LN03+| device, which can print images up to a full \|A4|
+page in size. 
+
+
+\section{Associated Routines}
+
+\|TEXPIC| normally maximises the contrast of pictures by determining the range
+of grey levels in the image and scaling the output to make use of them. This
+behaviour can be overridden by invoking the routine \|ZRANGE| before \|TEXPIC|.
+\|ZRANGE| requires two \|REAL| arguments, the minimum and maximum grey level
+values to be output: 
+
+\begin{verbatim}
+   CALL ZRANGE( ZMIN, ZMAX )
+   CALL TEXPIC( ARRAY, M, N, FILE )
+\end{verbatim}
+
+\noindent where \|ZMIN| $\le$ \|ZMAX|.
+\|TEXPIC| then uses the supplied extrema, rather than values
+determined from the image, for scaling the data. Values which lie {\em
+outside\/} these extrema are clipped. Hence, if \|ZRANGE| is used with values
+which are outside the values of the pixels in \|ARRAY|, the contrast of the
+data generated by \|TEXPIC| is {\em reduced.\/} The converse is also true. The
+extrema set up by \|ZRANGE| remain in effect until another call is made to
+\|ZRANGE|, superseding the previous limits, or \|ZAUTO| is invoked, which
+restores the default behaviour. 
+
+\|TEXPIC| normally plots positive pictures---i.e.,\ pixels which contain
+low values come out darker than pixels with high values. It can also produce
+negatives, however; you do this by invoking the routine \|DONEG| before
+\|TEXPIC|. Normal, positive picture-plotting is restored by calling \|DOPOS|.
+As with \|ZRANGE| and \|ZAUTO|, \|DOPOS| and \|DONEG| remain in effect until
+explicitly cancelled.
+You can, of course, use the routines in conjunction to produce any
+required effect.
+
+There is a limit, $\mmax$, to the number of pixels that \|TEXPIC| can fit
+across a page of output. For
+pictures with $\|M| \le \mmax$, the data are written out exactly as supplied.
+However, when pictures have $\|M| > \mmax$, the image is interpolated so
+that the data written out form a $\mmax$-pixel image.
+The same interpolation factor is used in both dimensions so that the aspect
+ratio of the picture remains correct. The interpolation technique used is
+a context-sensitive three-point bilinear method due to {\sc
+Smith}.\footnote{There is also a version which uses standard four-point
+bilinear interpolation.} This produces marginally better results in the
+vicinity of edges in the picture.
+
+The default value of $\mmax$ is~256. You can alter this (for example, when
+producing pictures for a document with the text set in narrow columns) by
+invoking \|TEXMAX| before \|TEXPIC|, as follows:
+
+\begin{verbatim}
+   CALL TEXMAX( MV )
+\end{verbatim}
+
+\noindent This sets $\mmax$ to \|MV|. Obviously, $\|MV| \ge 2$.
+
+\|TEXPIC| and the support routines are all to be found in the algorithm
+library, \verb|ESE$LIB:ALG|. \SYSDEP{Location of \\TEXPIC| and utility.}
+There is also a stand-alone program which you can use for images stored in the
+standard formats on disc. This program is \verb"ESE$PROGRAMS:V159". 
+
+
+\section{Inserting the Picture into Your \TeX\ Document}
+
+This is quite easy, although there are a few steps in the process.
+The procedure you follow depends on which macro package you are using with
+\TeX. Most people use ``plain \TeX,'' the default macro package, but \LaTeX\
+is also in widespread use. If you use a customised \TeX\ but don't know exactly
+what is different about it, try the plain \TeX\ procedure.
+
+Whichever version of \TeX\ you use, there are a few things you should know.
+\TeX\ must hold the whole image in memory, so the maximum image size is
+obviously limited to \TeX's memory capacity. Since \TeX\ was designed for
+typesetting rather than image hard-copy, its memory capacity isn't
+large enough to hold dozens of pictures, although it should be adequate
+for reasonable use.
+
+\|TEXPIC| tells \TeX\ to use a special font, a {\em halftone\/} font, for
+setting the picture. You have to tell \TeX\ to load this font. To do this,
+you type the following command at the top of your document:
+
+\begin{verbatim}                                          
+   \font\halftone=halftone
+\end{verbatim}
+
+\noindent This works with both plain \TeX\ and \LaTeX.
+
+We shall now consider the procedure for telling \TeX\ to typeset your picture.
+In the examples that follow, it is assumed that the picture produced by
+\|TEXPIC| is in the file \|PICTURE.TEX|.
+
+\subsection{Procedure for Use with Plain \TeX}
+The first thing you must do is to create an input file for \TeX\ which contains
+the document to be typeset. At the point where you want the picture to
+appear, you type:
+
+\begin{verbatim}
+   \centerline{\input picture}
+\end{verbatim}
+
+\noindent For \TeX{}perts, the image is set as a single \verb|\hbox|.
+  
+The picture can be put into a ``floating'' insert, which will cause the
+picture to be held in \TeX's memory until there is enough free space on
+the page to hold it. For example, to set the picture in a \verb"\midinsert",
+the relevant \TeX\ input would be:
+
+\begin{verbatim}
+   \midinsert
+      \centerline{\input picture}
+   \endinsert
+\end{verbatim}
+
+\noindent This command sequence should be typed between paragraphs,
+when \TeX\ is in `vertical mode.' Typing \verb"\goodbreak" immediately
+before the \verb"\midinsert" may help \TeX's page-breaking mechanism. (In
+practise, you'll probably want to add a title to the picture, too.)
+
+There is one other thing you might want to do and that is to draw a border
+around the picture. You would do this by defining a \TeX\ macro, \|border|,
+as follows:
+
+\begin{verbatim}
+   \def\border#1{\vbox{\hrule\hbox{\vrule\kern3pt
+      \vbox{\kern3pt#1\kern3pt}\kern3pt\vrule}\hrule}}
+\end{verbatim}
+
+\noindent You would then set the picture with
+
+\begin{verbatim}
+   \centerline{\border{\input picture}}
+\end{verbatim}
+
+\noindent instead of simply \verb"\centerline{\input picture}".
+
+\subsection{Procedure for Use with \LaTeX}
+The most sensible way to plot pictures with \LaTeX\ is in the \|figure|
+environment ({\em not\/} the \|picture| environment). This generates
+a ``floating'' figure, which usually surfaces at the top of the following
+page of output. The \verb|\centering| declaration causes the picture to
+be centred in the page.
+
+\begin{verbatim}
+   \begin{figure}
+      \centering
+      \mbox{\input picture\relax}
+      \caption{Figure Title}
+   \end{figure}
+\end{verbatim}
+
+\noindent The \verb|\relax| following the filename in the \verb|\mbox| command
+is required for \LaTeX\ to know where the filename ends. To draw a border
+around your picture, you simply replace the \verb|\mbox| command with
+\verb|\fbox|. 
+
+\section{Producing the Output}
+
+Having inserted the appropriate commands into your document, you run \TeX\ in
+the normal way. If it exits with a ``memory capacity exceeded'' error message,
+you've either tried to set images which are too big or you're holding too
+many in memory at once.  The only solution to this problem is to re-format your
+document. \LaTeX\ users may be able to cure the problem by strategically
+inserting \verb"\clearpage" commands into the manuscript.
+
+You run \TV\ or \TL\ on the \TeX\ output file as normal, although the \TV\
+display bears little relationship to the grey levels produced by \TL. Note that
+you must use \TL\ version~10 to send output to the \|LN03|, since earlier
+versions cannot read the halftone font file. (When you invoke \TL\, it outputs
+a short introductory message which includes its version number.) 
+
+The current version of \TeX\ 2.0 has a larger-than-usual memory capacity,
+\SYSDEP{Size of \TeX's memory.}
+large enough for four $256 \times 256$ images to be held in memory.
+
+\end{document}
-- 
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