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Date: Mon, 24 Aug 2020 18:44:51 +0200
Subject: New upstream version 1.0.31

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-\documentclass[11pt]{report}
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-
-\title{\huge SANE Standard Version 1.06}
-\author{}
-\date{2008-05-03}
-
-\makeindex
-
-\begin{document}
-
-\newcommand{\filename}[1]{{\tt #1}}
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-
-\maketitle
-\tableofcontents
-\listoffigures
-\listoftables
-
-
-\chapter{Preface}
-
-The SANE standard is being developed by a group of free-software
-developers.  The process is open to the public and comments as well as
-suggestions for improvements are welcome.  Information on how to join
-the SANE development process can be found in Chapter
-\ref{chap:contact}.
-
-The SANE standard is intended to streamline software development by
-providing a standard application programming interface to access
-raster scanner hardware.  This should reduce the number of different
-driver implementations, thereby reducing the need for reimplementing
-similar code.
-
-
-\section{About This Document}
-
-This document is intended for developers who are creating either an
-application that requires access to raster scanner hardware and for
-developers who are implementing a SANE driver.  It does not cover
-specific implementations of SANE components.  Its sole purpose is to
-describe and define the SANE application interface that will enable
-any application on any platform to interoperate with any SANE backend
-for that platform.
-
-The remainder of this document is organized as follows.
-Chapter~\ref{chap:intro} provides introductional material.
-Chapter~\ref{chap:environ} presents the environment SANE is designed
-for.  Chapter~\ref{chap:api} details the SANE Application Programmer
-Interface.  Chapter~\ref{chap:net} specifies the network protocol that
-can be used to implement the SANE API in a network transparent
-fashion.  Finally, Chapter~\ref{chap:contact} gives information on how
-to join the SANE development process.
-
-\subsection{Typographic Conventions}
-
-Changes since the last revision of this document are highlighted
-like this:
-
-% \begin{changebar}
-%   Paragraphs that changed since the last revision of the documention
-%   are marked like this paragraph.
-% \end{changebar}
-
-\chapter{Introduction}\label{chap:intro}
-
-SANE is an application programming interface (API) that provides
-standardized access to any raster image scanner hardware.  The
-standardized interface allows to write just one driver for each
-scanner device instead of one driver for each scanner and application.
-The reduction in the number of required drivers provides significant
-savings in development time.  More importantly, SANE raises the level
-at which applications can work.  As such, it will enable applications
-that were previously unheard of in the UNIX world.  While SANE is
-primarily targeted at a UNIX environment, the standard has been
-carefully designed to make it possible to implement the API on
-virtually any hardware or operating system.
-
-SANE is an acronym for ``Scanner Access Now Easy.''  Also, the hope is
-that SANE is sane in the sense that it will allow easy implementation
-of the API while accommodating all features required by today's
-scanner hardware and applications.  Specifically, SANE should be broad
-enough to accommodate devices such as scanners, digital still and
-video cameras, as well as virtual devices like image file filters.
-
-\section{Terminology}
-
-An application that uses the SANE interface is called a SANE {\em
-  frontend}.  A driver that implements the SANE interface is called a
-SANE {\em backend}.  A {\em meta backend\/} provides some means to
-manage one or more other backends.
-
-
-\chapter{The SANE Environment}\label{chap:environ}
-
-SANE is defined as a C-callable library interface.  Accessing a raster
-scanner device typically consists of two phases: first, various
-controls of the scanner need to be setup or queried.  In the second
-phase, one or more images are acquired.
-
-Since the device controls are widely different from device to device,
-SANE provides a generic interface that makes it easy for a frontend to
-give a user access to all controls without having to understand each
-and every device control.  The design principle used here is to
-abstract each device control into a SANE {\em option\/}.  An option is
-a self-describing name/value pair.  For example, the brightness
-control of a camera might be represented by an option called
-\code{brightness} whose value is an integer in the range from 0 to
-255.
-
-With self-describing options, a backend need not be concerned with
-{\em presentation\/} issues: the backend simply provides a list of
-options that describe all the controls available in the device.
-Similarly, there are benefits to the frontend: it need not be
-concerned with the {\em meaning\/} of each option.  It simply provides
-means to present and alter the options defined by the backend.
-
-
-\section{Attaching to a SANE backend}
-
-The process through which a SANE frontend connects to a backend is
-platform dependent.  Several possibilities exist:
-\begin{itemize}
-
-\item {\bf Static linking:} A SANE backend may be linked directly into
-  a frontend.  While the simplest method of attaching to a backend, it
-  is somewhat limited in functionality since the available devices is
-  limited to the ones for which support has been linked in when the
-  frontend was built.  But even so static linking can be quite useful,
-  particularly when combined with a backend that can access scanners
-  via a network.  Also, it is possible to support multiple backends
-  simultaneously by implementing a meta backend that manages several
-  backends that have been compiled in such a manner that they export
-  unique function names.  For example, a backend called \code{be}
-  would normally export a function called \code{sane\_read()}.  If
-  each backend would provide such a function, static linking would
-  fail due to multiple conflicting definitions of the same symbol.
-  This can be resolved by having backend \code{be} include a
-  header file that has lines of the form:
-  \begin{quote}
-\begin{verbatim}
-#define sane_read be_sane_read
-\end{verbatim}
-  \end{quote}
-  With definitions of this kind, backend \code{be} will export
-  function name \code{be\_sane\_read()}.  Thus, all backends will
-  export unique names.  As long as a meta backend knows about these
-  names, it is possible to combine several backends at link time and
-  select and use them dynamically at runtime.
-
-\item {\bf Dynamic linking:} A simpler yet more powerful way to
-  support multiple backends is to exploit dynamic linking on platforms
-  that support it.  In this case, a frontend is linked against a
-  shared library that implements any SANE backend.  Since each
-  dynamically linked backend exports the same set of global symbols
-  (all starting with the prefix \code{sane\_}), the dynamic library
-  that gets loaded at runtime does not necessarily have to be the same
-  one as one the frontend got linked against.  In other words, it is
-  possible to switch the backend by installing the appropriate backend
-  dynamic library.
-
-  More importantly, dynamic linking makes it easy to implement a meta
-  backend that loads other backends {\em on demand}.  This is a
-  powerful mechanism since it allows adding new backends merely by
-  installing a shared library and updating a configuration file.
-
-\item {\bf Network connection:} Arguably the ultimate way to attach to
-  a scanner is by using the network to connect to a backend on a
-  remote machine.  This makes it possible to scan images from any host
-  in the universe, as long as there is a network connection to that
-  host and provided the user is permitted to access that scanner.
-
-\end{itemize}
-
-\begin{figure}[htbp]
-  \begin{center}
-    \leavevmode
-    \includegraphics[width=\textwidth]{figs/hierarchy}
-    \caption{Example SANE Hiearchy}
-    \label{fig:hierarchy}
-  \end{center}
-\end{figure}
-
-The above discussion lists just a few ways for frontends to attach to
-a backend.  It is of course possible to combine these solutions to
-provide an entire hierarchy of SANE backends.  Such a hierarchy is
-depicted in Figure~\ref{fig:hierarchy}.  The figure shows that machine
-A uses a dynamic-linking based meta backend called \code{dll} to
-access the backends called \code{pnm}, \code{mustek}, and \code{net}.
-The first two are real backends, whereas the last one is a meta
-backend that provides network transparent access to remote scanners.
-In the figure, machine B provides non-local access to its scanners
-through the SANE frontend called \code{saned}.  The \code{saned} in
-turn has access to the \code{hp} and \code{autolum} backends through
-another instance of the \code{dll} backend.  The \code{autolum} meta
-backend is used to automatically adjust the luminance (brightness) of
-the image data acquired by the camera backend called \code{qcam}.
-
-Note that a meta backend really is both a frontend and a backend at
-the same time.  It is a frontend from the viewpoint of the backends
-that it manages and a backend from the viewpoint of the frontends that
-access it.  The name ``meta backend'' was chosen primarily because the
-SANE standard describes the interface from the viewpoint of a (real)
-frontend.
-
-
-\section{Image Data Format}\label{sec:imageformat}\index{image data format}
-
-Arguably the most important aspect of an image acquisition system is
-how images are represented.  The SANE approach is to define a simple
-yet powerful representation that is sufficient for vast majority of
-applications and devices.  While the representation is simple, the
-interface has been defined carefully to allow extending it in the
-future without breaking backwards compatibility.  Thus, it will be
-possible to accommodate future applications or devices that were not
-anticipated at the time this standard was created.
-
-A SANE image is a rectangular area.  The rectangular area is
-subdivided into a number of rows and columns.  At the intersection of
-each row and column is a quadratic pixel.  A pixel consists of one or
-more sample values.  Each sample value represents one channel (e.g.,
-the red channel).  Each sample value has a certain bit depth.  The bit
-depth is fixed for the entire image and can be as small as one bit.
-Valid bit depths are 1, 8, or 16 bits per sample.  If a device's
-natural bit depth is something else, it is up to the driver to scale
-the sample values appropriately (e.g., a 4 bit sample could be scaled
-by a factor of four to represent a sample value of depth 8).
-
-\subsection{Image Transmission}
-
-The SANE API transmits an image as a sequence of frames.  Each frame
-covers the same rectangular area as the entire image, but may contain
-only a subset of the channels in the final image.  For example, a
-red/green/blue image could either be transmitted as a single frame
-that contains the sample values for all three channels or it could be
-transmitted as a sequence of three frames: the first frame containing
-the red channel, the second the green channel, and the third the blue
-channel.
-
-Conceptually, each frame is transmitted a byte at a time.  Each byte
-may contain 8 sample values (for an image bit depth of 1), one full
-sample value (for an image bit depth of 8), or a partial sample value
-(for an image bit depth of 16 or bigger).  In the latter case, the
-bytes of each sample value are transmitted in the machine's native
-byte order. For depth 1, the leftmost pixel is stored in the most
-significant bit, and the rightmost pixel in the least significant bit.
-\begin{quote}
-  \begin{center}
-    {\bf Backend Implementation Note}
-  \end{center}
-  A network-based meta backend will have to ensure that the byte order
-  in image data is adjusted appropriately if necessary.  For example,
-  when the meta backend attaches to the server proxy, the proxy may
-  inform the backend of the server's byte order.  The backend can then
-  apply the adjustment if necessary.  In essence, this implements a
-  ``receiver-makes-right'' approach.
-\end{quote}
-
-\begin{figure}[htbp]
-  \begin{center}
-    \leavevmode
-    \includegraphics[width=0.5\textwidth]{figs/xfer}
-    \caption{Transfer order of image data bytes}
-    \label{fig:xfer}
-  \end{center}
-\end{figure}
-
-The order in which the sample values in a frame are transmitted is
-illustrated in Figure~\ref{fig:xfer}.  As can be seen, the values are
-transmitted row by row and each row is transmitted from left-most to
-right-most column.  The left-to-right, top-to-bottom transmission
-order applies when the image is viewed in its normal orientation (as
-it would be displayed on a screen, for example).
-
-If a frame contains multiple channels, then the channels are
-transmitted in an interleaved fashion.  Figure~\ref{fig:pixels}
-illustrates this for the case where a frame contains a complete
-red/green/blue image with a bit-depth of 8.  For a bit depth of 1,
-each byte contains 8 sample values of a {\em single\/} channel.  In
-other words, a bit depth 1 frame is transmitted in a byte interleaved
-fashion.
-
-\begin{figure}[htbp]
-  \begin{center}
-    \leavevmode
-    \includegraphics[width=0.8\textwidth]{figs/image-data}
-    \caption{Bit and byte order or image data}
-    \label{fig:pixels}
-  \end{center}
-\end{figure}
-
-When transmitting an image frame by frame, the frontend needs to know
-what part of the image a frame represents (and how many frames it
-should expect).  For that purpose, the SANE API tags every frame with
-a type.  This version of the SANE standard supports the following
-frame types:
-\begin{quote}
-\begin{description}
-
-\item[\code{\defn{SANE\_FRAME\_GRAY}}:] The frame contains a single
-  channel of data that represents sample values from a spectral band
-  that covers the human visual range.  The image consists of this
-  frame only.
-
-\item[\code{\defn{SANE\_FRAME\_RGB}}:] The frame contains three
-  channels of data that represent sample values from the red, green,
-  and blue spectral bands.  The sample values are interleaved in the
-  order red, green, and blue.  The image consists of this frame only.
-
-\item[\code{\defn{SANE\_FRAME\_RED}}:] The frame contains one channel
-  of data that represents sample values from the red spectral band.
-  The complete image consists of three frames:
-  \code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
-  \code{SANE\_FRAME\_BLUE}.  The order in which the frames are
-  transmitted chosen by the backend.
-
-\item[\code{\defn{SANE\_FRAME\_GREEN}}:] The frame contains one
-  channel of data that represents sample values from the green
-  spectral band.  The complete image consists of three frames:
-  \code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
-  \code{SANE\_FRAME\_BLUE}.  The order in which the frames are
-  transmitted chosen by the backend.
-
-\item[\code{\defn{SANE\_FRAME\_BLUE}}:] The frame contains one channel
-  of data that represents sample values from the blue spectral band.
-  The complete image consists of three frames:
-  \code{SANE\_\-FRA\-ME\_RED}, \code{SANE\_FRAME\_GREEN}, and
-  \code{SANE\_FRAME\_BLUE}.  The order in which the frames are
-  transmitted chosen by the backend.
-
-\end{description}
-\end{quote}
-
-In frames of type \code{SANE\_FRAME\_GRAY}, when the bit depth is 1 there are
-only two sample values possible, 1 represents minimum intensity
-(black) and 0 represents maximum intensity (white).  For all other bit
-depth and frame type combinations, a sample value of 0 represents
-minimum intensity and larger values represent increasing intensity.
-
-The combination of bit depth 1 and \code{SANE\_FRAME\_RGB} (or
-\code{SANE\_FRAME\_RED}, \code{SANE\_FRAME\_GREEN}, \code{SANE\_FRAME\_BLUE})
-is rarely used and may not be supported by every frontend.
-
-\chapter{The SANE Application Programmer Interface (API)}\label{chap:api}
-
-This Section defines version 1 of the SANE application
-programmer interface (API).  Any SANE frontend must depend on the
-interface defined in this section only.  Converseley, any SANE backend
-must implement its functionality in accordance with this
-specification.  The interface as documented here is declared as a C
-callable interface in a file called \filename{sane/sane.h}.  This file should
-normally be included via a C pre-processor directive of the form:
-\begin{verbatim}
-  #include <sane/sane.h>
-\end{verbatim}
-
-
-\section{Version Control}
-
-The SANE standard is expected to evolve over time.  Whenever a change
-to the SANE standard is made that may render an existing frontend or
-backend incompatible with the new standard, the major version number
-must be increased.  Thus, any frontend/backend pair is compatible
-provided the major version number of the SANE standard they implement
-is the same.  A frontend may implement backwards compatiblity by
-allowing major numbers that are smaller than the expected major number
-(provided the frontend really can cope with the older version).  In
-contrast, a backend always provides support for one and only one
-version of the standard.  If a specific application does require that
-two different versions of the same backend are accessible at the same
-time, it is possible to do so by installing the two versions under
-different names.
-
-SANE version control also includes a minor version number and a build
-revision.  While control of these numbers remains with the implementor
-of a backend, the recommended use is as follows.  The minor version is
-incremented with each official release of a backend.  The build
-revision is increased with each build of a backend.
-
-The SANE API provides the following five macros to manage version
-numbers.
-\begin{quote}
-  \begin{description}
-  \item[\code{\defn{SANE\_CURRENT\_MAJOR}}:] The value of this macro is the
-    number of the SANE standard that the interface implements.
-
-  \item[\code{\defn{SANE\_VERSION\_CODE}(\var{maj},\var{min},\var{bld})}:]
-    \label{sec:saneversioncode}
-    This macro can be used to build a monotonically increasing version
-    code.  A SANE version code consists of the SANE standard major
-    version number (\var{maj}), the minor version number \var{min},
-    and the build revision of a backend (\var{bld}).  The major and
-    minor version numbers must be in the range 0\ldots255 and the
-    build revision must be in the range 0\ldots65535.
-
-    Version codes are monotonic in the sense that it is possible to
-    apply relational operators (e.g., equality or less-than test)
-    directly on the version code rather than individually on the three
-    components of the version code.
-
-    Note that the major version number alone determines whether a
-    frontend/backend pair is compatible.  The minor version and the
-    build revision are used for informational and bug-fixing purposes
-    only.
-
-  \item[\code{\defn{SANE\_VERSION\_MAJOR}(\var{vc})}:] This macro returns the
-    major version number component of the version code passed in
-    argument \var{vc}.
-  \item[\code{SANE\_VERSION\_MINOR(\var{vc})}:] This macro returns the
-    minor version number component of the version code passed in
-    argument \var{vc}.
-  \item[\code{SANE\_VERSION\_BUILD(\var{vc})}:] This macro returns the
-    build revision component of the version code passed in argument
-    \var{vc}.
-  \end{description}
-\end{quote}
-
-
-\section{Data Types}
-
-\subsection{Base Types}
-
-The SANE standard is based on just two SANE-specific base types: the
-SANE byte and word.
-\begin{quote}
-  \code{typedef \var{some-scalar-type\/} \defn{SANE\_Byte};} \\
-  \code{typedef \var{some-scalar-type\/} \defn{SANE\_Word};}
-\end{quote}
-\verb|SANE_Byte| must correspond to some scalar C type that is capable
-of holding values in the range 0 to 255.  \verb|SANE_Word| must be
-capable of holding any of the following:
-\begin{itemize}
-  \item the truth values \verb|SANE_FALSE| and \verb|SANE_TRUE|
-  \item signed integers in the range $-2^{31}\ldots2^{31}-1$
-  \item fixed point values in the range $-32768\ldots32767.9999$ with
-    a resolution of $1/65536$
-  \item 32 bits (for bit sets)
-\end{itemize}
-Note that the SANE standard does not define what C type
-\verb|SANE_Byte| and \verb|SANE_Word| map to.  For example, on some
-platforms, the latter may map to \verb|long int| whereas on others it
-may map to \verb|int|.  A portable SANE frontend or backend must
-therefore not depend on a particular mapping.
-
-\subsection{Boolean Type}
-
-\code{\defn{SANE\_Bool}} is used for variables that can take one of
-the two truth values \code{\defn{SANE\_FALSE}} and
-\code{\defn{SANE\_TRUE}}.  The former value is defined to be 0,
-whereas the latter is 1.\footnote{This is different from ANSI C where
-  any non-zero integer value represents logical TRUE.} The C
-declarations for this type are given below.
-\begin{quote}
-\begin{verbatim}
-#define SANE_FALSE      0
-#define SANE_TRUE       1
-typedef SANE_Word SANE_Bool;
-\end{verbatim}
-\end{quote}
-Note that \verb|SANE_Bool| is simply an alias of \verb|SANE_Word|.  It
-is therefore always legal to use the latter type in place of the
-former.  However, for clarity, it is recommended to use
-\verb|SANE_Bool| whenever a given variable or formal argument has a
-fixed interpretation as a boolean object.
-
-\subsection{Integer Type}
-
-\code{\defn{SANE\_Int}} is used for variables that can take integer
-values in the range $-2^{32}$ to $2^{31}-1$.  Its C declaration is
-given below.
-\begin{quote}
-\begin{verbatim}
-typedef SANE_Word SANE_Int;
-\end{verbatim}
-\end{quote}
-Note that \verb|SANE_Int| is simply an alias of \verb|SANE_Word|.  It
-is therefore always legal to use the latter type in place of the
-former.  However, for clarity, it is recommended to use
-\verb|SANE_Int| whenever a given variable or formal argument has a
-fixed interpretation as an integer object.
-
-
-\subsection{Fixed-point Type}
-
-\code{\defn{SANE\_Fixed}} is used for variables that can take fixed
-point values in the range $-32768$ to $32767.9999$ with a resolution
-of $1/65535$.  The C declarations relating to this type are given
-below.
-\begin{quote}
-\begin{verbatim}
-#define SANE_FIXED_SCALE_SHIFT  16
-typedef SANE_Word SANE_Fixed;
-\end{verbatim}
-\end{quote}
-The macro \code{\defn{SANE\_FIXED\_SCALE\_SHIFT}} gives the location
-of the fixed binary point.  This standard defines that value to be 16,
-which yields a resolution of $1/65536$.
-
-Note that \verb|SANE_Fixed| is simply an alias of \verb|SANE_Word|.
-It is therefore always legal to use the latter type in place of the
-former.  However, for clarity, it is recommended to use
-\verb|SANE_Fixed| whenever a given variable or formal argument has a
-fixed interpretation as a fixed-point object.
-
-For convenience, SANE also defines two macros that convert fixed-point
-values to and from C double floating point values.
-\begin{quote}
-  \begin{description}
-
-  \item[\code{\defn{SANE\_FIX}(\var{d})}:] Returns the largest SANE
-    fixed-point value that is smaller than the double value \var{d}.
-    No range checking is performed.  If the value of \var{d} is out of
-    range, the result is undefined.
-
-  \item[\code{\defn{SANE\_UNFIX}(\var{w})}:] Returns the nearest
-    double machine number that corresponds to fixed-point value
-    \var{w}.
-
-  \end{description}
-\end{quote}
-SANE does {\em not\/} require that the following two expressions hold
-true (even if the values of \var{w} and \var{d} are in range):
-\begin{quote}
-\begin{verbatim}
-SANE_UNFIX(SANE_FIX(d)) == d
-SANE_FIX(SANE_UNFIX(w)) == w
-\end{verbatim}
-\end{quote}
-In other words, conversion between fixed and double values may be
-lossy.  It is therefore recommended to avoid repeated conversions
-between the two representations.
-
-
-\subsection{Text}
-
-\subsubsection{Character Type}
-
-Type \code{\defn{SANE\_Char}} represents a single text character or
-symbol.  At present, this type maps directly to the underlying C
-\verb|char| type (typically one byte).  The encoding for such
-characters is currently fixed as ISO LATIN-1.  Future versions of this
-standard may map this type to a wider type and allow multi-byte
-encodings to support internationalization.  As a result of this, care
-should be taken to avoid the assumption that
-\verb|sizeof(SANE_Char)==sizeof(char)|.
-\begin{quote}
-\begin{verbatim}
-typedef char SANE_Char;
-\end{verbatim}
-\end{quote}
-
-\subsubsection{String Type}
-
-Type \code{\defn{SANE\_String}} represents a text string as a sequence
-of C \verb|char| values.  The end of the sequence is indicated by a
-\verb|'\0'| (\defn{NUL}) character.
-\begin{quote}
-\begin{verbatim}
-typedef SANE_Char *SANE_String;
-typedef const SANE_Char *SANE_String_Const;
-\end{verbatim}
-\end{quote}
-The type \code{\defn{SANE\_String\_Const}} is provided by SANE to
-enable declaring strings whose contents is unchangable.  Note that in
-ANSI C, the declaration
-\begin{quote}
-\begin{verbatim}
-const SANE_String str;
-\end{verbatim}
-\end{quote}
-declares a string pointer that is constant (not a string pointer that
-points to a constant value).
-
-
-\subsection{Scanner Handle Type}
-
-Access to a scanner is provided through an opaque type called
-\code{\defn{SANE\_Handle}}.  The C declaration of this type is given
-below.
-\begin{quote}
-\begin{verbatim}
-typedef void *SANE_Handle;
-\end{verbatim}
-\end{quote}
-While this type is declared to be a void pointer, an application must
-not attempt to interpret the value of a \verb|SANE_Handle|.  In
-particular, SANE does not require that a value of this type is a legal
-pointer value.
-
-
-\subsection{Status Type}
-
-Most SANE operations return a value of type \code{\defn{SANE\_Status}}
-to indicate whether the completion status of the operation.  If an
-operation completes successfully, \verb|SANE_STATUS_GOOD| is returned.
-In case of an error, a value is returned that indicates the nature of
-the problem.  The complete list of available status codes is listed in
-Table \ref{tab:status}.  It is recommended to use function
-\code{sane\_strstatus()} to convert status codes into a legible
-string.
-
-\begin{table}[htbp]
-  \begin{center}
-    \begin{tabular}{|l|r|l|}
-      \hline
-      \multicolumn{1}{|c|}{\bf Symbol} & \multicolumn{1}{c|}{\bf Code} &
-      \multicolumn{1}{c|}{\bf Description} \\
-      \hline\hline
-\code{\defn{SANE\_STATUS\_GOOD}}
-        &  0 & Operation completed succesfully. \\
-\code{\defn{SANE\_STATUS\_UNSUPPORTED}}
-        &  1 & Operation is not supported. \\
-\code{\defn{SANE\_STATUS\_CANCELLED}}
-        &  2 & Operation was cancelled. \\
-\code{\defn{SANE\_STATUS\_DEVICE\_BUSY}}
-        &  3 & Device is busy---retry later. \\
-\code{\defn{SANE\_STATUS\_INVAL}}
-        &  4 & Data or argument is invalid. \\
-\code{\defn{SANE\_STATUS\_EOF}}
-        &  5 & No more data available (end-of-file). \\
-\code{\defn{SANE\_STATUS\_JAMMED}}
-        &  6 & Document feeder jammed. \\
-\code{\defn{SANE\_STATUS\_NO\_DOCS}}
-        &  7 & Document feeder out of documents. \\
-\code{\defn{SANE\_STATUS\_COVER\_OPEN}}
-        &  8 & Scanner cover is open. \\
-\code{\defn{SANE\_STATUS\_IO\_ERROR}}
-        &  9 & Error during device I/O. \\
-\code{\defn{SANE\_STATUS\_NO\_MEM}}
-        & 10 & Out of memory. \\
-\code{\defn{SANE\_STATUS\_ACCESS\_DENIED}}
-        & 11 & Access to resource has been denied. \\
-      \hline
-    \end{tabular}
-    \caption{Status Codes}\label{tab:status}
-  \end{center}
-\end{table}
-
-
-\subsection{Device Descriptor Type}
-
-Each SANE device is represented by a structure of type
-\code{\defn{SANE\_Device}}.  The C declaration of this type is given
-below.
-\begin{quote}
-\begin{verbatim}
-typedef struct
-  {
-    SANE_String_Const name;
-    SANE_String_Const vendor;
-    SANE_String_Const model;
-    SANE_String_Const type;
-  }
-SANE_Device;
-\end{verbatim}
-\end{quote}
-\index{device-name}
-The structure provides the unique name of the scanner in member
-\code{name}.  It is this unique name that should be passed in a call
-to \code{sane\_open()}.  The format of this name is completely up to
-the backend.  The only constraints are that the name is unique among
-all devices supported by the backend and that the name is a legal SANE
-text string.  To simplify presentation of unique names, their length
-should not be excessive.  It is {\em recommended\/} that backends keep
-unique names below 32 characters in length.  However, applications
-{\em must\/} be able to cope with arbitrary length unique names.
-
-The remaining members in the device structure provide additional
-information on the device corresponding to the unique name.
-Specifically, members \code{vendor}, \code{model}, and \code{type} are
-single-line strings that give information on the vendor
-(manufacturer), model, and the type of the device.  For consistency's
-sake, the following strings should be used when appropriate (the lists
-will be expanded as need arises):
-
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \hspace{\fill}
-    \begin{tabular}[t]{|ll|}
-      \hline
-      \multicolumn{2}{|c|}{\bf \defn{Vendor Strings}} \\
-      \hline\hline
-      \code{AGFA}            & \code{Microtek} \\
-      \code{Abaton}          & \code{Minolta} \\
-      \code{Acer}            & \code{Mitsubishi} \\
-      \code{Apple}           & \code{Mustek} \\
-      \code{Artec}           & \code{NEC} \\
-      \code{Avision}         & \code{Nikon} \\
-      \code{CANON}           & \code{Plustek} \\
-      \code{Connectix}       & \code{Polaroid} \\
-      \code{Epson}           & \code{Relisys} \\
-      \code{Fujitsu}         & \code{Ricoh} \\
-      \code{Hewlett-Packard} & \code{Sharp} \\
-      \code{IBM}             & \code{Siemens} \\
-      \code{Kodak}           & \code{Tamarack} \\
-      \code{Lexmark}	     & \code{UMAX} \\
-      \code{Logitech}        & \code{Noname} \\
-      \hline
-    \end{tabular}
-    \hspace{\fill}
-    \begin{tabular}[t]{|l|}
-      \hline
-      \multicolumn{1}{|c|}{\bf \defn{Type Strings}} \\
-      \hline\hline
-      \code{film scanner} \\
-      \code{flatbed scanner} \\
-      \code{frame grabber} \\
-      \code{handheld scanner} \\
-      \code{multi-function peripheral} \\
-      \code{sheetfed scanner} \\
-      \code{still camera} \\
-      \code{video camera} \\
-      \code{virtual device} \\
-      \hline
-    \end{tabular}
-    \hspace{\fill}
-    \caption{Predefined Device Information Strings}
-    \label{tab:devinfo}
-  \end{center}
-\end{table}
-Note that vendor string \code{Noname} can be used for virtual devices
-that have no physical vendor associated.  Also, there are no
-predefined model name strings since those are vendor specific and
-therefore completely under control of the respective backends.
-
-
-\subsection{Option Descriptor Type}\label{sec:odesc}
-
-Option descriptors are at the same time the most intricate and
-powerful type in the SANE standard.  Options are used to control
-virtually all aspects of device operation.  Much of the power of the
-SANE API stems from the fact that most device controls are completely
-described by their respective option descriptor.  Thus, a frontend can
-control a scanner abstractly, without requiring knowledge as to what
-the purpose of any given option is.  Conversely, a scanner can
-describe its controls without requiring knowledge of how the frontend
-operates.  The C declaration of the
-\code{\defn{SANE\_Option\_Descriptor}} type is given below.
-\begin{quote}
-\begin{verbatim}
-typedef struct
-  {
-    SANE_String_Const name;
-    SANE_String_Const title;
-    SANE_String_Const desc;
-    SANE_Value_Type type;
-    SANE_Unit unit;
-    SANE_Int size;
-    SANE_Int cap;
-    SANE_Constraint_Type constraint_type;
-    union
-      {
-        const SANE_String_Const *string_list;
-        const SANE_Word *word_list;
-        const SANE_Range *range;
-      }
-    constraint;
-  }
-SANE_Option_Descriptor;
-\end{verbatim}
-\end{quote}
-
-\subsubsection{Option Name}
-
-Member \code{name} is a string that uniquely identifies the option.
-The name must be unique for a given device (i.e., the option names
-across different backends or devices need not be unique).  The option
-name must consist of lower-case ASCII letters (\code{a}--\code{z}),
-digits (\code{0}--\code{9}), or the dash character (\code{-}) only.
-The first character must be a lower-case ASCII character (i.e., not a
-digit or a dash).
-
-\subsubsection{Option Title}
-
-Member \code{title} is a single-line string that can be used by the
-frontend as a title string.  This should typically be a short (one or
-two-word) string that is chosen based on the function of the option.
-
-\subsubsection{Option Description}
-
-Member \code{desc} is a (potentially very) long string that can be
-used as a help text to describe the option.  It is the responsibility
-of the frontend to break the string into managable-length lines.
-Newline characters in this string should be interpreted as paragraph
-breaks.
-
-\subsubsection{Option Value Type}
-
-Member \code{type} specifies the type of the option value.  The
-possible values for type \code{\defn{SANE\_Value\_Type}} are described
-in Table \ref{tab:valuetype}.
-
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|l|p{0.6\textwidth}|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{c|}{\bf Code} &
-\multicolumn{1}{c|}{\bf Description} \\
-\hline\hline
-
-\code{\defn{SANE\_TYPE\_BOOL}} & 0 & Option value is of type
-  \verb|SANE_Bool|. \\
-
-\code{\defn{SANE\_TYPE\_INT}} & 1 & Option value is of type
-  \verb|SANE_Int|. \\
-
-\code{\defn{SANE\_TYPE\_FIXED}}&2 & Option value is of type
-  \verb|SANE_Fixed|. \\
-
-\code{\defn{SANE\_TYPE\_STRING}}&3 & Option value is of type
-  \verb|SANE_String|. \\
-
-\code{\defn{SANE\_TYPE\_BUTTON}} & 4 & An option of this type has no value.
-Instead, setting an option of this type has an option-specific
-side-effect.  For example, a button-typed option could be used by a
-backend to provide a means to select default values or to the tell an
-automatic document feeder to advance to the next sheet of paper. \\
-
-\code{\defn{SANE\_TYPE\_GROUP}} & 5 & An option of this type has no value.
-This type is used to group logically related options.  A group option
-is in effect up to the point where another group option is encountered
-(or up to the end of the option list, if there are no other group
-options).  For group options, only members \code{title} and
-\code{type} are valid in the option descriptor. \\
-
-  \hline
-    \end{tabular}
-    \caption{Option Value Types (\code{SANE\_Value\_Type})}
-    \label{tab:valuetype}
-  \end{center}
-\end{table}
-
-\subsubsection{Option Value Unit}
-
-Member \code{unit} specifies what the physical unit of the option
-value is.  The possible values for type \code{\defn{SANE\_U\-nit}} are
-described in Table \ref{tab:units}.  Note that the specified unit is
-what the SANE backend expects.  It is entirely up to a frontend as to
-how these units a presented to the user.  For example, SANE expresses
-all lengths in millimeters.  A frontend is generally expected to
-provide appropriate conversion routines so that a user can express
-quantities in a customary unit (e.g., inches or centimeters).
-
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|l|l|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{|c|}{\bf Code} &
-\multicolumn{1}{|c|}{\bf Description} \\
-
-\hline\hline
-
-\code{\defn{SANE\_UNIT\_NONE}}   & 0 & Value is unit-less (e.g., page count).\\
-\code{\defn{SANE\_UNIT\_PIXEL}}  & 1 & Value is in number of pixels. \\
-\code{\defn{SANE\_UNIT\_BIT}}    & 2 & Value is in number of bits. \\
-\code{\defn{SANE\_UNIT\_MM}}     & 3 & Value is in millimeters. \\
-\code{\defn{SANE\_UNIT\_DPI}}    & 4 & Value is a resolution in dots/inch. \\
-\code{\defn{SANE\_UNIT\_PERCENT}}& 5 & Value is a percentage. \\
-\code{\defn{SANE\_UNIT\_MICROSECOND}}& 6 & Value is time in $\mu$-seconds. \\
-
-\hline
-    \end{tabular}
-    \caption{Physical Units (\code{SANE\_Unit})}
-    \label{tab:units}
-  \end{center}
-\end{table}
-
-\subsubsection{Option Value Size}\label{sec:valuesize}
-
-Member \code{size} specifies the size of the option value (in bytes).
-This member has a slightly different interpretation depending on the
-type of the option value:
-\begin{quote}
-  \begin{description}
-  \item[\code{SANE\_TYPE\_STRING}:] The size is the maximum size of
-    the string.  For the purpose of string size calcuations, the
-    terminating \code{NUL} character is considered to be part of the
-    string.  Note that the terminating \code{NUL} character must
-    always be present in string option values.
-  \item[\code{SANE\_TYPE\_INT}, \code{SANE\_TYPE\_FIXED}:] The size
-    must be a positive integer multiple of the size of a
-    \verb|SANE_Word|.  The option value is a vector of length
-    \[ \code{size}/\code{sizeof(SANE\_Word)}. \]
-  \item[\code{SANE\_TYPE\_BOOL}:] The size must be set to
-    \code{sizeof(SANE\_Word)}.
-  \item[\code{SANE\_TYPE\_BUTTON}, \code{SANE\_TYPE\_GROUP}:] The
-    option size is ignored.
-  \end{description}
-\end{quote}
-
-\subsubsection{Option Capabilities}
-
-Member \code{cap} describes what capabilities the option posseses.
-This is a bitset that is formed as the inclusive logical OR of the
-capabilities described in Table \ref{tab:capabilities}.  The SANE API
-provides the following to macros to test certain features of a given
-capability bitset:
-\begin{quote}
-  \begin{description}
-
-  \item[\code{\defn{SANE\_OPTION\_IS\_ACTIVE}(\var{cap})}:] This macro
-    returns \code{SANE\_TRUE} if and only if the option with the
-    capability set \var{cap} is currently active.
-
-  \item[\code{\defn{SANE\_OPTION\_IS\_SETTABLE}(\var{cap})}:] This
-    macro returns \code{SANE\_TRUE} if and only if the option with the
-    capability set \var{cap} is software settable.
-  \end{description}
-\end{quote}
-
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|r|p{0.59\textwidth}|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{c|}{\bf Code} &
-\multicolumn{1}{c|}{\bf Description} \\
-\hline\hline
-
-\code{\defn{SANE\_CAP\_SOFT\_SELECT}} & 1 & The option
-  value can be set by a call to \code{sane\_con\-trol\_opt\-ion()}.\\
-
-\code{\defn{SANE\_CAP\_HARD\_SELECT}} & 2 & The option value can be set by
-  user-intervention (e.g., by flipping a switch).  The user-interface
-  should prompt the user to execute the appropriate action to set such
-  an option.  This capability is mutually exclusive with
-  SANE\_CAP\_SOFT\_SELECT (either one of them can be set, but not both
-  simultaneously).  \\
-
-\code{\defn{SANE\_CAP\_SOFT\_DETECT}} & 4 & The option
-  value can be detected by software.  If
-  \code{SANE\_\-CAP\_\-SO\-FT\_SEL\-ECT} is set, this capability {\em must\/}
-  be set.  If \code{SANE\_CAP\_HARD\_SELECT} is set, this capability
-  may or may not be set.  If this capability is set but neither
-  \code{SANE\_CAP\_SO\-FT\_SEL\-ECT} nor \code{SANE\_CAP\_HA\-RD\_SEL\-ECT}
-  are, then there is no way to control the option.  That is, the
-  option provides read-out of the current value only.  \\
-
-\code{\defn{SANE\_CAP\_EMULATED}} & 8 & If set, this capability indicates
-  that an option is not directly supported by the device and is
-  instead emulated in the backend.  A sophisticated frontend may
-  elect to use its own (presumably better) emulation in lieu of an emulated
-  option. \\
-
-\code{\defn{SANE\_CAP\_AUTOMATIC}} & 16 & If set, this capability indicates
-  that the backend (or the device) is capable to picking a reasonable
-  option value automatically.  For such options, it is possible to
-  select automatic operation by calling \code{sane\_control\_option()}
-  with an action value of \code{SANE\_ACTION\_SET\_AUTO}.  \\
-
-\code{\defn{SANE\_CAP\_INACTIVE}} & 32 & If set, this capability indicates
-  that the option is not currently active (e.g., because it's
-  meaningful only if another option is set to some other value). \\
-
-\code{\defn{SANE\_CAP\_ADVANCED}} & 64 &
-  If set, this capability indicates that the option should be
-  considered an ``advanced user option.''  A frontend typically
-  displays such options in a less conspicuous way than regular options
-  (e.g., a command line interface may list such options last or a
-  graphical interface may make them available in a seperate ``advanced
-  settings'' dialog).
-  \\
-
-\hline
-    \end{tabular}
-    \caption{Option Capabilities}
-    \label{tab:capabilities}
-  \end{center}
-\end{table}
-
-\subsubsection{Option Value Constraints}
-
-It is often useful to constrain the values that an option can take.
-For example, constraints can be used by a frontend to determine how to
-represent a given option.  Member \code{constraint\_type} indicates
-what constraint is in effect for the option.  The constrained values
-that are allowed for the option are described by one of the union
-members of member \code{constraint}.  The possible values of type
-\code{\defn{SANE\_Constraint\_Type}} and the interpretation of the
-\code{constraint} union is described in Table~\ref{tab:constraints}.
-
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|r|p{0.5\textwidth}|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{|c|}{\bf Code} &
-\multicolumn{1}{|c|}{\bf Description} \\
-
-\hline\hline
-
-\code{\defn{SANE\_CONSTRAINT\_NONE}} & 0 & The value is unconstrained.
-  The option can take any of the values possible for the option's
-  type. \\
-
-  \code{\defn{SANE\_CONSTRAINT\_RANGE}} & 1 & This constraint is
-  applicable to integer and fixed-point valued options only.  It
-  constrains the option value to a possibly quantized range of
-  numbers.  Option descriptor member \code{constraint.range} points to
-  a range of the type \code{\defn{SANE\_Range}}.  This type is illustrated
-  below:
-  \begin{quote}
-\begin{verbatim}
-typedef struct
-  {
-    SANE_Word min;
-    SANE_Word max;
-    SANE_Word quant;
-  }
-SANE_Range;
-\end{verbatim}
-  \end{quote}
-  All three members in this structure are interpreted according to the
-  option value type (\verb|SANE_TYPE_INT| or \verb|SANE_TYPE_FIXED|).
-  Members \code{min} and \code{max} specify the minimum and maximum
-  values, respectively.  If member \code{quant} is non-zero, it
-  specifies the quantization value.  If $l$ is the minimum value, $u$
-  the maximum value and $q$ the (non-zero) quantization of a range,
-  then the legal values are $v=k\cdot q+l$ for all non-negative
-  integer values of $k$ such that $v<=u$.  \\
-
-\code{\defn{SANE\_CONSTRAINT\_WORD\_LIST}} & 2 & This constraint is applicable
-  to integer and fixed-point valued options only.  It constrains the
-  option value to a list of numeric values.  Option descriptor member
-  \code{constraint.word\_list} points to a list of words that
-  enumerates the legal values.  The first element in that list is an
-  integer (\verb|SANE_Int|) that specifies the length of the list (not
-  counting the length itself).  The remaining elements in the list are
-  interpreted according to the type of the option value
-  (\verb|SANE_TYPE_INT| or \verb|SANE_TYPE_FIXED|). \\
-
-\code{\defn{SANE\_CONSTRAINT\_STRING\_LIST}} & 3 & This constraint is
-  applicable to string-valued options only.  It constrains the option
-  value to a list of strings.  The option descriptor member
-  \code{con\-strai\-nt.str\-ing\_list} points to a \code{NULL} terminated
-  list of strings that enumerate the legal values for the option
-  value.
-\\\hline
-    \end{tabular}
-    \caption{Option Value Constraints}
-    \label{tab:constraints}
-  \end{center}
-\end{table}
-
-
-\section{Operations}
-
-\subsection{\code{sane\_init}}
-
-This function must be called before any other SANE function can be called.
-The behavior of a SANE backend is undefined if this function is not called
-first or if the status code returned by \code{sane\_init} is different from
-\code{\defn{SANE\_STATUS\_GOOD}}.  The version code of the backend is returned
-in the value pointed to by \code{version\_code}.  If that pointer is
-\code{NULL}, no version code is returned.  Argument \code{authorize} is either
-a pointer to a function that is invoked when the backend requires
-authentication for a specific resource or \code{NULL} if the frontend does not
-support authentication.
-\begin{quote}\index{sane\_init}
-\begin{verbatim}
-SANE_Status sane_init (SANE_Int * version_code,
-                       SANE_Authorization_Callback authorize);
-\end{verbatim}
-\end{quote}
-
-The authorization function may be called by a backend in response to
-any of the following calls:
-\begin{quote}
-  \code{sane\_open}, \code{sane\_control\_option}, \code{sane\_start}
-\end{quote}
-If a backend was initialized without authorization function, then
-authorization requests that cannot be handled by the backend itself
-will fail automatically and the user may be prevented from accessing
-protected resources.  Backends are encouraged to implement means of
-authentication that do not require user assistance.  E.g., on a
-multi-user system that authenticates users through a login process a
-backend could automatically lookup the apporpriate password based on
-resource- and user-name.
-
-The authentication function type has the following declaration:
-\begin{quote}\index{SANE\_Authorization\_Callback}
-  \index{domain}\index{username}\index{password}
-\begin{verbatim}
-#define SANE_MAX_USERNAME_LEN   128
-#define SANE_MAX_PASSWORD_LEN   128
-
-typedef void (*SANE_Authorization_Callback)
-    (SANE_String_Const resource,
-     SANE_Char username[SANE_MAX_USERNAME_LEN],
-     SANE_Char password[SANE_MAX_PASSWORD_LEN]);
-\end{verbatim}
-\end{quote}
-Three arguments are passed to the authorization function:
-\code{resource} is a string specifying the name of the resource that
-requires authorization.  A frontend should use this string to build a
-user-prompt requesting a username and a password.  The \code{username}
-and \code{password} arguments are (pointers to) an array of
-\code{SANE\_MAX\_USERNAME\_LEN} and \code{SANE\_MAX\_PASSWORD\_LEN}
-characters, respectively.  The authorization call should place the
-entered username and password in these arrays.  The returned strings
-{\em must\/} be ASCII-NUL terminated.
-
-\subsection{\code{sane\_exit}}
-
-This function must be called to terminate use of a backend.  The
-function will first close all device handles that still might be open
-(it is recommended to close device handles explicitly through a call
-to \code{sane\_clo\-se()}, but backends are required to release all
-resources upon a call to this function).  After this function returns,
-no function other than \code{sane\_init()} may be called (regardless
-of the status value returned by \code{sane\_exit()}.  Neglecting to
-call this function may result in some resources not being released
-properly.
-\begin{quote}\index{sane\_exit}
-\begin{verbatim}
-void sane_exit (void);
-\end{verbatim}
-\end{quote}
-
-
-\subsection{\code{sane\_get\_devices}}
-
-This function can be used to query the list of devices that are
-available.  If the function executes successfully, it stores a pointer
-to a \code{NULL} terminated array of pointers to \verb|SANE_Device|
-structures in \code{*device\_list}.  The returned list is guaranteed
-to remain unchanged and valid until (a) another call to this function
-is performed or (b) a call to \code{sane\_exit()} is performed.  This
-function can be called repeatedly to detect when new devices become
-available.  If argument \code{local\_only} is true, only local devices
-are returned (devices directly attached to the machine that SANE is
-running on).  If it is false, the device list includes all remote
-devices that are accessible to the SANE library.
-\begin{quote}\index{sane\_get\_devices}
-\begin{verbatim}
-SANE_Status sane_get_devices (const SANE_Device *** device_list,
-                              SANE_Bool local_only);
-\end{verbatim}
-\end{quote}
-
-This function may fail with \code{SANE\_STATUS\_NO\_MEM} if an
-insufficient amount of memory is available.
-
-\begin{quote}
-  \begin{center}
-    {\bf Backend Implementation Note}
-  \end{center}
-  SANE does not require that this function is called before a
-  \code{sane\_open()} call is performed.  A device name may be
-  specified explicitly by a user which would make it unnecessary and
-  undesirable to call this function first.
-\end{quote}
-
-
-\subsection{\code{sane\_open}}
-
-This function is used to establish a connection to a particular
-device.  The name of the device to be opened is passed in argument
-\code{name}.  If the call completes successfully, a handle for the
-device is returned in \code{*h}.  As a special case, specifying a
-zero-length string as the device requests opening the first available
-device (if there is such a device).
-\begin{quote}\index{sane\_open}
-\begin{verbatim}
-SANE_Status sane_open (SANE_String_Const name, SANE_Handle * h);
-\end{verbatim}
-\end{quote}
-
-This function may fail with one of the following status codes.
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_DEVICE\_BUSY}:] The device is currently
-  busy (in use by somebody else).
-\item[\code{SANE\_STATUS\_INVAL}:] The device name is not valid.
-\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occured while
-  communicating with the device.
-\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
-  is available.
-\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the device has
-  been denied due to insufficient or invalid authentication.
-\end{description}
-\end{quote}
-
-
-\subsection{\code{sane\_close}}
-
-This function terminates the association between the device handle
-passed in argument \code{h} and the device it represents.  If the
-device is presently active, a call to \code{sane\_cancel()} is
-performed first.  After this function returns, handle \code{h} must
-not be used anymore.
-
-\begin{quote}\index{sane\_close}
-\begin{verbatim}
-void sane_close (SANE_Handle h);
-\end{verbatim}
-\end{quote}
-
-\subsection{\code{sane\_get\_option\_descriptor}}
-
-This function is used to access option descriptors.  The function
-returns the option descriptor for option number \code{n} of the device
-represented by handle \code{h}.  Option number 0 is guaranteed to be a
-valid option.  Its value is an integer that specifies the number of
-options that are available for device handle \code{h} (the count
-includes option 0).  If $n$ is not a valid option index, the function
-returns \code{NULL}.  The returned option descriptor is guaranteed to
-remain valid (and at the returned address) until the device is closed.
-
-\begin{quote}\index{sane\_get\_option\_descriptor}
-\begin{verbatim}
-const SANE_Option_Descriptor *
-    sane_get_option_descriptor (SANE_Handle h, SANE_Int n);
-\end{verbatim}
-\end{quote}
-
-\subsection{\code{sane\_control\_option}}\label{sec:control}
-
-This function is used to set or inquire the current value of option
-number \code{n} of the device represented by handle \code{h}.  The
-manner in which the option is controlled is specified by parameter
-\code{a}.  The possible values of this parameter are described in more
-detail below.  The value of the option is passed through argument
-\code{v}.  It is a pointer to the memory that holds the option value.
-The memory area pointed to by \code{v} must be big enough to hold the
-entire option value (determined by member \code{size} in the
-corresponding option descriptor).  The only exception to this rule is
-that when setting the value of a string option, the string pointed to
-by argument \code{v} may be shorter since the backend will stop
-reading the option value upon encountering the first \code{NUL}
-terminator in the string.  If argument \code{i} is not \code{NULL},
-the value of \code{*i} will be set to provide details on how well the
-request has been met.  The meaning of this argument is described in
-more detail below.
-\begin{quote}\index{sane\_control\_option}
-\begin{verbatim}
-SANE_Status sane_control_option (SANE_Handle h, SANE_Int n,
-                                 SANE_Action a, void *v,
-                                 SANE_Int * i);
-\end{verbatim}
-\end{quote}
-
-The way the option is affected by a call to this function is
-controlled by parameter \code{a} which is a value of type
-\code{\defn{SANE\_Action}}.  The possible values and their meaning is
-described in Table~\ref{tab:actions}.
-
-\begin{table}[h]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|r|p{0.5\textwidth}|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{|c|}{\bf Code} &
-\multicolumn{1}{|c|}{\bf Description} \\
-
-\hline\hline
-
-\code{\defn{SANE\_ACTION\_GET\_VALUE}} & 0 & Get current option value. \\
-
-\code{\defn{SANE\_ACTION\_SET\_VALUE}} & 1 & Set option value.  The
-  option value passed through argument \code{v} may be modified by the
-  backend if the value cannot be set exactly.  \\
-
-\code{\defn{SANE\_ACTION\_SET\_AUTO}} & 2 & Turn on automatic mode.  Backend
-  or device will automatically select an appropriate value.  This mode
-  remains effective until overridden by an explicit set value request.
-  The value of parameter \code{v} is completely ignored in this case and
-  may be \code{NULL}.  \\
-
-\hline
-    \end{tabular}
-    \caption{Action Values (\code{SANE\_Action})}
-    \label{tab:actions}
-  \end{center}
-\end{table}
-
-After setting a value via an action value of
-\verb|SANE_ACTION_SET_VALUE|, additional information on how well the
-request has been met is returned in \code{*i} (if \code{i} is
-non-\code{NULL}).  The returned value is a bitset that may contain any
-combination of the values described in Table~\ref{tab:info}.
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|r|p{0.5\textwidth}|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{|c|}{\bf Code} &
-\multicolumn{1}{|c|}{\bf Description} \\
-
-\hline\hline
-
-\code{\defn{SANE\_INFO\_INEXACT}} & 1 & This value is returned when
-  setting an option value resulted in a value being selected that does
-  not exactly match the requested value.  For example, if a scanner
-  can adjust the resolution in increments of 30dpi only, setting the
-  resolution to 307dpi may result in an actual setting of 300dpi.
-  When this happens, the bitset returned in \code{*i} has this member
-  set.  In addition, the option value is modified to reflect the
-  actual (rounded) value that was used by the backend.  Note that
-  inexact values are admissible for strings as well.  A backend may
-  choose to ``round'' a string to the closest matching legal string
-  for a constrained string value. \\
-
-  \code{\defn{SANE\_INFO\_RELOAD\_OPTIONS}} & 2 & The setting of an
-  option may affect the value or availability of one or more {\em
-    other\/} options.  When this happens, the SANE backend sets this
-  member in \code{*i} to indicate that the application should reload
-  all options.  This member may be set if and only if at least one
-  option changed. \\
-
-\code{\defn{SANE\_INFO\_RELOAD\_PARAMS}} & 4 & The setting of an option may
-  affect the parameter values (see \code{sane\_get\_parameters()}).
-  If setting an option affects the parameter values, this member will
-  be set in \code{*i}.  Note that this member may be set even if the
-  parameters did not actually change.  However, it is guaranteed that
-  the parameters never change without this member being set. \\
-
-\hline
-    \end{tabular}
-    \caption{Additional Information Returned When Setting an Option}
-    \label{tab:info}
-  \end{center}
-\end{table}
-
-This function may fail with one of the following status codes.
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The operation is not
-  supported for the specified handle and option number.
-\item[\code{SANE\_STATUS\_INVAL}:] The option value is not valid.
-\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occured while
-  communicating with the device.
-\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
-  is available.
-\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the option has
-  been denied due to insufficient or invalid authentication.
-\end{description}
-\end{quote}
-
-
-
-\subsection{\code{sane\_get\_parameters}}
-
-This function is used to obtain the current scan parameters.  The
-returned parameters are guaranteed to be accurate between the time a
-scan has been started (\code{sane\_start()} has been called) and the
-completion of that request.  Outside of that window, the returned
-values are best-effort estimates of what the parameters will be when
-\code{sane\_start()} gets invoked.  Calling this function before a
-scan has actually started allows, for example, to get an estimate of
-how big the scanned image will be.  The parameters passed to this
-function are the handle \code{h} of the device for which the
-parameters should be obtained and a pointer \code{p} to a parameter
-structure.  The parameter structure is described in more detail below.
-
-\begin{quote}\index{sane\_get\_parameters}
-\begin{verbatim}
-SANE_Status sane_get_parameters (SANE_Handle h,
-                                 SANE_Parameters * p);
-\end{verbatim}
-\end{quote}
-
-The scan parameters are returned in a structure of type
-\code{\defn{SANE\_Parameters}}.  The C declaration of this structure
-is given below.
-\begin{quote}
-\begin{verbatim}
-typedef struct
-  {
-    SANE_Frame format;
-    SANE_Bool last_frame;
-    SANE_Int bytes_per_line;
-    SANE_Int pixels_per_line;
-    SANE_Int lines;
-    SANE_Int depth;
-  }
-SANE_Parameters;
-\end{verbatim}
-\end{quote}
-
-Member \code{format} specifies the format of the next frame to be
-returned.  The possible values for type \code{\defn{SANE\_Frame}} are
-described in Table~\ref{tab:frameformat}.  The meaning of these
-values is described in more detail in Section~\ref{sec:imageformat}.
-\begin{table}[htbp]
-  \begin{center}
-    \leavevmode
-    \begin{tabular}{|l|r|l|}
-\hline
-\multicolumn{1}{|c|}{\bf Symbol} &
-\multicolumn{1}{|c|}{\bf Code} &
-\multicolumn{1}{|c|}{\bf Description} \\
-
-\hline\hline
-
-\code{\defn{SANE\_FRAME\_GRAY}} & 0 & Band covering human visual range. \\
-\code{\defn{SANE\_FRAME\_RGB}} & 1 & Pixel-interleaved red/green/blue bands. \\
-\code{\defn{SANE\_FRAME\_RED}} & 2 & Red band of a red/green/blue image. \\
-\code{\defn{SANE\_FRAME\_GREEN}} & 3 & Green band of a red/green/blue image. \\
-\code{\defn{SANE\_FRAME\_BLUE}} & 4 & Blue band of a red/green/blue image. \\
-
-\hline
-    \end{tabular}
-    \caption{Frame Format (\code{SANE\_Frame})}
-    \label{tab:frameformat}
-  \end{center}
-\end{table}
-
-Member \code{last\_frame} is set to \code{SANE\_TRUE} if and only if
-the frame that is currently being acquired (or the frame that will be
-acquired next if there is no current frame) is the last frame of a
-multi frame image (e.g., the current frame is the blue component of a
-red, green, blue image).
-
-Member \code{lines} specifies how many scan lines the frame is
-comprised of.  If this value is -1, the number of lines is not known a
-priori and the frontend should call \code{sane\_read()} until it
-returns a status of \code{SANE\_STATUS\_EOF}.
-
-Member \code{bytes\_per\_line} specifies the number of bytes that
-comprise one scan line.
-
-Member \code{depth} specifies the number of bits per sample.
-
-Member \code{pixels\_per\_line} specifies the number of pixels that
-comprise one scan line.
-
-Assume $B$ is the number of channels in the frame, then the bit depth
-$d$ (as given by member \code{depth}) and the number of pixels per
-line $n$ (as given by this member \code{pixels\_per\_line}) are
-related to $c$, the number of bytes per line (as given by member
-\code{bytes\_per\_line}) as follows:
-\[
-  c >= \left\{
-  \begin{array}{ll}
-    B\cdot \lfloor (n + 7) / 8\rfloor & \mbox{if $d=1$}\\
-    B\cdot n \cdot d / 8 & \mbox{if $d>1$}
-  \end{array}
-  \right.
-\]
-Note that the number of bytes per line can be larger than the minimum
-value imposed by the right side of this equation.  A frontend must be
-able to properly cope with such ``padded'' image formats.
-
-
-\subsection{\code{sane\_start}}
-
-This function initiates aquisition of an image from the device
-represented by handle \code{h}.
-\begin{quote}\index{sane\_start}
-\begin{verbatim}
-SANE_Status sane_start (SANE_Handle h);
-\end{verbatim}
-\end{quote}
-This function may fail with one of the following status codes.
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_CANCELLED}:] The operation was cancelled through
-  a call to \code{sane\_cancel}.
-\item[\code{SANE\_STATUS\_DEVICE\_BUSY}:] The device is busy. The
-  operation should be retried later.
-\item[\code{SANE\_STATUS\_JAMMED}:] The document feeder is jammed.
-\item[\code{SANE\_STATUS\_NO\_DOCS}:] The document feeder is out of
-  documents.
-\item[\code{SANE\_STATUS\_COVER\_OPEN}:] The scanner cover is open.
-\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occurred while communicating
-  with the device.
-\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
-  is available.
-\item[\code{SANE\_STATUS\_INVAL}:] The scan cannot be started with the current
-  set of options. The frontend should reload the option descriptors, as if
-  \code{\defn{SANE\_INFO\_RELOAD\_OPTIONS}} had been returned from a call to
-  \code{sane\_control\_option()}, since the device's capabilities may have
-  changed.
-\end{description}
-\end{quote}
-
-
-\subsection{\code{sane\_read}}
-
-This function is used to read image data from the device represented
-by handle \code{h}.  Argument \code{buf} is a pointer to a memory area
-that is at least \code{maxlen} bytes long.  The number of bytes
-returned is stored in \code{*len}.  A backend must set this to zero
-when a status other than \code{SANE\_STA\-TUS\_GOOD} is returned.
-When the call succeeds, the number of bytes returned can be anywhere in
-the range from 0 to \code{maxlen} bytes.
-\begin{quote}\index{sane\_read}
-\begin{verbatim}
-SANE_Status sane_read (SANE_Handle h, SANE_Byte * buf,
-                       SANE_Int maxlen, SANE_Int * len);
-\end{verbatim}
-\end{quote}
-If this function is called when no data is available, one of two
-things may happen, depending on the I/O mode that is in effect for
-handle \code{h}.
-\begin{enumerate}
-\item If the device is in blocking I/O mode (the default mode), the
-  call blocks until at least one data byte is available (or until some
-  error occurs).
-
-\item If the device is in non-blocking I/O mode, the call returns
-  immediately with status \code{SANE\_STA\-TUS\_GOOD} and with
-  \code{*len} set to zero.
-\end{enumerate}
-The I/O mode of handle \code{h} can be set via a call to
-\code{sane\_set\_io\_mode()}.
-
-This function may fail with one of the following status codes.
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_CANCELLED}:] The operation was cancelled through
-  a call to \code{sane\_cancel}.
-\item[\code{SANE\_STATUS\_EOF}:] No more data is available for the
-  current frame.
-\item[\code{SANE\_STATUS\_JAMMED}:] The document feeder is jammed.
-\item[\code{SANE\_STATUS\_NO\_DOCS}:] The document feeder is out of
-  documents.
-\item[\code{SANE\_STATUS\_COVER\_OPEN}:] The scanner cover is open.
-\item[\code{SANE\_STATUS\_IO\_ERROR}:] An error occurred while communicating
-  with the device.
-\item[\code{SANE\_STATUS\_NO\_MEM}:] An insufficent amount of memory
-  is available.
-\item[\code{SANE\_STATUS\_ACCESS\_DENIED}:] Access to the device has
-  been denied due to insufficient or invalid authentication.
-\end{description}
-\end{quote}
-
-
-\subsection{\code{sane\_cancel}}
-
-This function is used to immediately or as quickly as possible cancel
-the currently pending operation of the device represented by handle
-\code{h}.
-\begin{quote}\index{sane\_cancel}
-\begin{verbatim}
-void sane_cancel (SANE_Handle h);
-\end{verbatim}
-\end{quote}
-This function can be called at any time (as long as handle \code{h} is
-a valid handle) but usually affects long-running operations only (such
-as image is acquisition).  It is safe to call this function
-asynchronously (e.g., from within a signal handler).  It is important
-to note that completion of this operaton does {\em not\/} imply that
-the currently pending operation has been cancelled.  It only
-guarantees that cancellation has been {\em initiated}.  Cancellation
-completes only when the cancelled call returns (typically with a
-status value of \code{SANE\_STATUS\_CANCELLED}).  Since the SANE API
-does not require any other operations to be re-entrant, this implies
-that a frontend must {\em not\/} call any other operation until the
-cancelled operation has returned.
-
-
-\subsection{\code{sane\_set\_io\_mode}}
-
-This function is used to set the I/O mode of handle \code{h}.  The I/O mode
-can be either blocking or non-blocking.  If argument \code{m} is
-\code{SANE\_TRUE}, the mode is set to non-blocking mode, otherwise it's set to
-blocking mode.  This function can be called only after a call to
-\code{sane\_start()} has been performed.
-\begin{quote}\index{sane\_set\_io\_mode}
-\begin{verbatim}
-SANE_Status sane_set_io_mode (SANE_Handle h, SANE_Bool m);
-\end{verbatim}
-\end{quote}
-By default, newly opened handles operate in blocking mode.  A backend
-may elect not to support non-blocking I/O mode.  In such a case the
-status value \code{SANE\_STATUS\_UNSUPPORTED} is returned.  Blocking
-I/O must be supported by all backends, so calling this function with
-argument \code{m} set to \code{SANE\_FALSE} is guaranteed to complete
-successfully.
-
-This function may fail with one of the following status codes:
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_INVAL}:] No image acquisition is pending.
-\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The backend does not support
-  the requested I/O mode.
-\end{description}
-\end{quote}
-
-
-\subsection{\code{sane\_get\_select\_fd}}
-
-This function is used to obtain a (platform-specific) file-descriptor
-for handle \code{h} that is readable if and only if image data is
-available (i.e., when a call to \code{sane\_read()} will return at
-least one byte of data).  If the call completes successfully, the
-select file-descriptor is returned in \code{*fd}.
-\begin{quote}\index{sane\_get\_select\_fd}
-\begin{verbatim}
-SANE_Status sane_get_select_fd (SANE_Handle h, SANE_Int *fd);
-\end{verbatim}
-\end{quote}
-This function can be called only after a call to \code{sane\_start()}
-has been performed and the returned file-descriptor is guaranteed to
-remain valid for the duration of the current image acquisition (i.e.,
-until \code{sane\_cancel()} or \code{sane\_start()} get called again
-or until \code{sane\_read()} returns with status
-\code{SANE\_STA\-TUS\_EOF}).  Indeed, a backend must guarantee to
-close the returned select file descriptor at the point when the next
-\code{sane\_read()} call would return \code{SANE\_STA\-TUS\_EOF}.
-This is necessary to ensure the application can detect when this
-condition occurs without actually having to call \code{sane\_read()}.
-
-A backend may elect not to support this operation.  In such a case,
-the function returns with status code
-\code{SANE\_STATUS\_UNSUPPORTED}.
-
-Note that the only operation supported by the returned file-descriptor
-is a host operating-system dependent test whether the file-descriptor
-is readable (e.g., this test can be implemented using \code{select()}
-or \code{poll()} under UNIX).  If any other operation is performed on
-the file descriptor, the behavior of the backend becomes
-unpredictable.  Once the file-descriptor signals ``readable'' status,
-it will remain in that state until a call to \code{sane\_read()} is
-performed.  Since many input devices are very slow, support for this
-operation is strongly encouraged as it permits an application to do
-other work while image acquisition is in progress.
-
-This function may fail with one of the following status codes:
-\begin{quote}
-\begin{description}
-\item[\code{SANE\_STATUS\_INVAL}:] No image acquisition is pending.
-\item[\code{SANE\_STATUS\_UNSUPPORTED}:] The backend does not support
-  this operation.
-\end{description}
-\end{quote}
-
-
-\subsection{\code{sane\_strstatus}}
-
-This function can be used to translate a SANE status code into a
-printable string.  The returned string is a single line of text that
-forms a complete sentence, but without the trailing period
-(full-stop).  The function is guaranteed to never return \code{NULL}.
-The returned pointer is valid at least until the next call to this
-function is performed.
-\begin{quote}\index{sane\_strstatus}
-\begin{verbatim}
-const SANE_String_Const sane_strstatus (SANE_Status status);
-\end{verbatim}
-\end{quote}
-
-\section{Code Flow}\index{code flow}
-
-The code flow for the SANE API is illustrated in
-Figure~\ref{fig:flow}.  Functions \code{sane\_init()} and
-\code{sane\_exit()} initialize and exit the backend, respectively.
-All other calls must be performed after initialization and before
-exiting the backend.
-
-\begin{figure}[htb]
-  \begin{center}
-    \leavevmode
-    \includegraphics[height=0.5\textheight]{figs/flow}
-    \caption{Code flow}
-    \label{fig:flow}
-  \end{center}
-\end{figure}
-
-Function \code{sane\_get\_devices()} can be called any time after
-\code{sane\_init()} has been called.  It returns the list of the
-devices that are known at the time of the call.  This list may change
-over time since some devices may be turned on or off or a remote host
-may boot or shutdown between different calls.  It should be noted that
-this operation may be relatively slow since it requires contacting all
-configured devices (some of which may be on remote hosts).  A frontend
-may therefore want to provide the ability for a user to directly
-select a desired device without requiring a call to this function.
-
-Once a device has been chosen, it is opened using a call to
-\code{sane\_open()}.  Multiple devices can be open at any given time.
-A SANE backend must not impose artificial constraints on how many
-devices can be open at any given time.
-
-An opened device can be setup through the corresponding device handle
-using functions \code{sane\_get\_opt\-ion\_desc\-riptor()} and
-\code{sane\_control\_option()}.  While setting up a device, obtaining
-option descriptors and setting and reading of option values can be
-mixed freely.  It is typical for a frontend to read out all available
-options at the beginning and then build a dialog (either graphical or
-a command-line oriented option list) that allows to control the
-available options.  It should be noted that the number of options is
-fixed for a given handle.  However, as options are set, other options
-may become active or inactive.  Thus, after setting an option, it
-maybe necessary to re-read some or all option descriptors.  While
-setting up the device, it is also admissible to call
-\code{sane\_get\_parameters()} to get an estimate of what the image
-parameters will look like once image acquisition begins.
-
-The device handle can be put in blocking or non-blocking mode by a
-call to \code{sane\_set\_io\_mode()}.  Devices are required to support
-blocking mode (which is the default mode), but support for
-non-blocking I/O is strongly encouraged for operating systems such as
-UNIX.
-
-After the device is setup properly, image acquisition can be started
-by a call to \code{sane\_start()}.  The backend calculates the exact
-image parameters at this point.  So future calls to
-\code{sane\_get\_parameters()} will return the exact values, rather
-than estimates.  Whether the physical image acquisition starts at this
-point or during the first call to \code{sane\_read()} is unspecified
-by the SANE API.  If non-blocking I/O and/or a select-style interface
-is desired, the frontend may attempt to call
-\code{sane\_set\_io\_mode()} and/or \code{sane\_get\_select\_fd()} at
-this point.  Either of these functions may fail if the backend does
-not support the requested operation.
-
-Image data is collected by repeatedly calling \code{sane\_read()}.
-Eventually, this function will return an end-of-file status
-(\code{SANE\_STATUS\_EOF}).  This indicates the end of the current
-frame.  If the frontend expects additional frames (e.g., the
-individual channels in of a red/green/blue image or multiple images),
-it can call \code{sane\_start()} again.  Once all desired frames have
-been acquired, function \code{sane\_cancel()} must be called.  This
-operation can also be called at any other time to cancel a pending
-operation.  Note that \code{sane\_cancel()} must be called even if the
-last read operation returned \code{SANE\_STATUS\_EOF}.
-
-When done using the device, the handle should be closed by a call to
-\code{sane\_close()}.  Finally, before exiting the application,
-function \code{sane\_exit()} must be called.  It is important not to
-forget to call this function since otherwise some resources (e.g.,
-temporary files or locks) may remain unclaimed.
-
-
-\section{Well-Known Options}\index{well-known options}
-
-While most backend options are completely self-describing, there are a
-cases where a user interface might want to special-case the handling
-of certain options.  For example, the scan area is typically defined
-by four options that specify the top-left and bottom-right corners of
-the area.  With a graphical user interface, it would be tedious to
-force the user to type in these four numbers.  Instead, most such
-interfaces will want to present to the user a preview (low-resolution
-scan) of the scanner surface and let the user pick the scan area by
-dragging a rectangle into the desired position.  For this reason, the
-SANE API specifies a small number of option names that have
-well-defined meanings.
-
-\subsection{Option Number Count}\index{option count}
-
-Option number 0 has an empty string as its name.  The value of this
-option is of type \code{SANE\_TYPE\_INT} and it specifies the total
-number of options available for a given device (the count includes
-option number 0).  This means that there are two ways of counting the
-number of options available: a frontend can either cycle through all
-option numbers starting at one until
-\code{sane\_get\_option\_descriptor()} returns \code{NULL}, or a
-frontend can directly read out the value of option number 0.
-
-\subsection{Scan Resolution Option}\index{scan resolution}\index{resolution option}
-
-Option \code{resolution} is used to select the resolution at which an
-image should be acquired.  The type of this option is either
-\code{SANE\_TYPE\_INT} or \code{SANE\_TYPE\_FIXED}.  The unit is
-\code{SANE\_UNIT\_DPI} (dots/inch).
-
-This option is not mandatory, but if a backend does support it, it
-must implement it in a manner consistent with the above definition.
-
-\subsection{Preview Mode Option}\index{preview mode}
-
-The boolean option \code{preview} is used by a frontend to inform the
-backend when image acquisition should be optimized for speed, rather
-than quality (``preview mode'').  When set to \code{SANE\_TRUE},
-preview mode is in effect, when set to \code{SANE\_FALSE} image
-acquisition should proceed in normal quality mode.  The setting of
-this option \emph{must not\/} affect any other option.  That is, as
-far as the other options are concerned, the preview mode is completely
-side effect free.  A backend can assume that the frontend will take
-care of appropriately setting the scan resolution for preview mode
-(through option \code{resolution}).  A backend is free to override the
-\code{resolution} value with its own choice for preview mode, but it
-is advised to leave this choice to the frontend wherever possible.
-
-This option is not mandatory, but if a backend does support it, it
-must implement it in a manner consistent with the above definition.
-
-\subsection{Scan Area Options}\index{scan area options}
-
-The four most important well-known options are the ones that define
-the scan area.  The scan area is defined by two points (x/y coordinate
-pairs) that specify the top-left and the bottom-right corners.  This
-is illustrated in Figure~\ref{fig:area}.  Note that the origin of the
-coordinate system is at the top-left corner of the scan surface as
-seen by the sensor (which typically is a mirror image of the scan
-surface seen by the user).  For this reason, the top-left corner is
-the corner for which the abscissa and ordinate values are
-simultaneously the {\em smallest} and the bottom-right corner is the
-corner for which the abscissa and ordinate values are simulatenously
-the {\em largest}.  If this coordinate system is not natural for a
-given device, it is the job of the backend to perform the necessary
-conversions.
-\begin{figure}[tbp]
-  \begin{center}
-    \leavevmode
-    \includegraphics[height=0.3\textheight]{figs/area}
-    \caption{Scan area options}
-    \label{fig:area}
-  \end{center}
-\end{figure}
-
-The names of the four options that define the scan area are given in
-the table below:
-\begin{center}
-\begin{tabular}{ll}
-{\bf Name} & {\bf Description} \\
-\code{\defn{tl-x}} & Top-left $x$ coordinate value \\
-\code{\defn{tl-y}} & Top-left $y$ coordinate value \\
-\code{\defn{br-x}} & Bottom-right $x$ coordinate value \\
-\code{\defn{br-y}} & Bottom-right $y$ coordinate value \\
-\end{tabular}
-\end{center}
-There are several rules that should be followed by front and backends
-regarding these options:
-\begin{itemize}
-
-\item Backends must attach a unit of either pixels
-  (\code{SANE\_UNIT\_PIXEL}) or millimeters (\code{SANE\_UNIT\_MM}) to
-  these options.  The unit of all four options must be identical.
-
-\item Whenever meaningful, a backend should attach a range or a
-  word-list constraint to these options.
-
-\item A frontend can determine the size of the scan surface by first
-  checking that the options have range constraints associated.  If a
-  range or word-list constraints exist, the frontend can take the
-  minimum and maximum values of one of the x and y option
-  range-constraints to determine the scan surface size.
-
-\item A frontend must work properly with any or all of these options
-  missing.
-
-\end{itemize}
-
-\input{net.tex}
-
-\chapter{Contact Information}\label{chap:contact}
-
-The SANE standard is discussed and evolved via a mailing list.
-Anybody with email access to the Internet can automatically join and
-leave the discussion group by sending mail to the following address.
-\begin{quote}\index{mailing list}
-\url{sane-devel-request@alioth-lists.debian.net}
-\end{quote}
-To subscribe, send a mail with the body ``\verb|subscribe sane-devel|'' to the
-above address.
-
-A complete list of commands supported can be obtained by sending a
-mail with a subject of ``\code{help}'' to the above address.  The
-mailing list is archived and available through the SANE home page at
-URL:
-\begin{quote}
-\url{http://www.sane-project.org/}
-\end{quote}
-
-\newpage
-\input{sane.ind}
-
-\end{document}
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