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    README  (12 Jan 2012)
    --------------------

    gunzip leptonica-1.69.tar.gz
    tar -xvf leptonica-1.69.tar

Building leptonica
I/O libraries leptonica is dependent on
Developing with leptonica
What's in leptonica?

## Building leptonica

    1. Top view

      This tar includes:
        (1) src: library source and function prototypes for building liblept
        (2) prog: source for regression test, usage example programs, and
            sample images
      for building on these platforms:
         -  Linux on x86 (i386) and AMD 64 (x64)
         -  OSX (both powerPC and x86).
         -  Cygwin and mingw on x86
      It should compile properly with any version of gcc from 2.95.3 onward.
      There is an additional zip file for building with MS Visual Studio.

      Libraries, executables and prototypes are easily made, as described below.

      When you extract from the archive, all files are put in a
      subdirectory 'leptonica-1.69'.  In that directory you will
      find a src directory containing the source files for the library,
      and a prog directory containing source files for various
      testing and example programs.

    2. Building on Linux/Unix/MacOS

      There are two ways to build the library:

        (1) By customization:  Use the existing static makefile,
            src/makefile.static and customize the build by setting flags
            in src/environ.h.  See src/environ.h and src/makefile for details.
            Note: if you are going to develop with leptonica, I encourage
            you to use the static makefiles.

        (2) Using autoconf.  Run ./configure in this directory to
            build Makefiles here and in src.  Autoconf handles the
            following automatically:
                * architecture endianness
                * enabling Leptonica I/O image read/write functions that
                  depend on external libraries (if the libraries exist)
                * enabling functions for redirecting formatted image stream
                  I/O to memory (on linux only)
            After running ./configure: make; make install.

      In more detail:

        (1) Customization using the static makefiles:

           * FIRST THING: Run make-for-local.  This simply renames
                   src/makefile.static  -->  src/makefile
                   prog/makefile.static -->  prog/makefile
             [Note: the autoconf build will not work if you have any files
              named "makefile" in src or prog.  If you've already run
              make-for-local and renamed the static makefiles, and you then
              want to build with autoconf, run make-for-auto to rename them
              back to makefile.static.]

           * You can customize for:
             (a) Including Leptonica I/O functions that depend on external
                 libraries [use flags in src/environ.h]
             (b) Adding functions for redirecting formatted image stream
                 I/O to memory [use flag in src/environ.h]
             (c) Specifying the location of the object code.  By default it
                 goes into a tree whose root is also the parent of the src
                 and prog directories.  This can be changed using the
                 ROOT_DIR variable in makefile.

           * Build the library:
             - To make an optimized version of the library (in src):
                   make
             - To make a debug version of the library (in src):
                   make DEBUG=yes debug
             - To make a shared library version (in src):
                   make SHARED=yes shared
             - To make the prototype extraction program (in src):
                   make   (to make the library first)
                   make xtractprotos

           * To use shared libraries, you need to include the location of
             the shared libraries in your LD_LIBRARY_PATH.

           * To make the programs in the prog directory, first make liblept
             in src, and then do 'make' in the prog directory.

           VERY IMPORTANT: the 190+ programs in the prog directory are
           an integral part of this package.  These can be divided into
           three types:
             (1) Programs that are complete regression tests.  The most
                 important of these are named *_reg.  We are in the process
                 of standardizing the regression tests, and making it easy
                 to write them.  See regutils.h for details.
             (2) Programs that were used to test library functions or
                 auto-gen library code.  These are useful for testing
                 the behavior of small sets of functions, and for
                 providing example code.
             (3) Programs that are useful applications in their own right.
                 Examples of these are the PostScript and pdf conversion
                 programs converttops, convertfilestops, convertsegfilestops,
                 printimage, printsplitimage, convertfilestopdf and
                 convertsegfilestopdf.

        (2) Building using autoconf  (Thanks to James Le Cuirot)

           Use the standard incantation, in the root directory (the
           directory with configure):
              ./configure    [build the Makefile]
              make   [builds the library and shared library versions of
                      all the progs]
              make install  [as root; this puts liblept.a into /usr/local/lib/
                             and all the progs into /usr/local/bin/ ]

           Configure also supports building in a separate directory from the
           source.  Run "/(path-to)/leptonica-1.69/configure" and then "make"
           from the desired build directory.

           Configure has a number of useful options; run "configure --help" for
           details.  If you're not planning to modify the library, adding the
           "--disable-dependency-tracking" option will speed up the build.  By
           default, both static and shared versions of the library are built.  Add
           the "--disable-shared" or "--disable-static" option if one or the other
           isn't needed.

           By default, the library is built with debugging symbols.  If you do not
           want these, use "CFLAGS=-O2 ./configure" to eliminate symbols for
           subsequent compilations, or "make CFLAGS=-O2" to override for this
           compilation only.

           For the debian distribution, we only build a small subset of
           the programs in the prog directory..

        (3) Cross-compiling for windows

           You can use src/makefile.mingw for cross-compiling in linux.

    3. Building on Windows

       (a) Building with Visual Studio

           Tom Powers has provided a set of developer notes and project files
           for building the library and applications under windows with VC++ 2008:

http:///www.leptonica.org/vs2008doc/index.html
http:///www.leptonica.org/download.html#VS2008

           He has also supplied a zip file that contains the entire 'lib'
           and 'include' directories needed to build Windows-based programs
           using static or dynamic versions of the leptonica library
           (including static library versions of zlib, libpng, libjpeg,
           libtiff, and giflib).

leptonica-1.66-win32-lib-include-dirs.zip

           You can download Tom's vs2008 package either from the download
           page or from code.google.com/p/leptonica.

       (b) Building for mingw with MSYS
           (Thanks to David Bryan)

           MSYS is a Unix-compatible build environment for the mingw compiler.
           Installing the "MinGW Compiler Suite C Compiler" and the "MSYS Basic
           System" will allow building the library with autoconf as in (2) above.
           It will also allow building with the static makefile as in (1) above if
           this option is added to the make command:

             CC="gcc -D_BSD_SOURCE -DANSI"

           Only the static library may be built this way; the autoconf method must
           be used if a shared (DLL) library is desired.

           External image libraries (see below) must be downloaded separately,
           built, and installed before building the library.  Pre-built libraries
           are available from the GnuWin project.

       (c) Building for Cygwin
           (Thanks to David Bryan)

           Cygwin is a Unix-compatible build and runtime environment.  Installing
           the "Base", "Devel", and "Graphics" packages will allow building the
           library with autoconf as in (2) above.  If the graphics libraries are
           not present in the /lib, /usr/lib, or /usr/local/lib directories, you
           must run make with the "LDFLAGS=-L/(path-to-image)/lib" option.  It
           will also allow building with the static makefile as in (1) above if
           this option is added to the make command:

             CC="gcc -ansi -D_BSD_SOURCE -DANSI"

           Only the static library may be built this way; the autoconf method must
           be used if a shared (DLL) library is desired.

## I/O libraries leptonica is dependent on

       Leptonica is configured to handle image I/O using these external
       libraries: libjpeg, libtiff, libpng, libz, libgif, libwebp

       These libraries are easy to obtain.  For example, using the
       debian package manager:
           sudo apt-get install
       where  = {libpng12-dev, libjpeg62-dev, libtiff4-dev}.

       Leptonica also allows image I/O with bmp and pnm formats, for which
       we provide the serializers (encoders and decoders).  It also
       gives output drivers for wrapping images in PostScript, which
       in turn use tiffg4, jpeg and png encoding.

       There is also a programmatic interface to gnuplot.  To use it, you
       need only the gnuplot executable (suggest version 3.7.2 or later);
       the gnuplot library is not required.

       If you build with automake, libraries on your system will be
       automatically found and used.

       The rest of this section is for building with the static makefiles.
       The entries in environ.h specify which of these libraries to use.
       The default is to link to these four libraries:
          libjpeg.a  (standard jfif jpeg library, version 6b or 7 or 8))
          libtiff.a  (standard Leffler tiff library, version 3.7.4 or later;
          libpng.a   (standard png library, suggest version 1.4.0 or later)
          libz.a     (standard gzip library, suggest version 1.2.3)
                      current non-beta version is 3.8.2)

       These libraries (and their shared versions) should be in /usr/lib.
       (If they're not, you can change the LDFLAGS variable in the makefile.)
       Additionally, for compilation, the following header files are
       assumed to be in /usr/include:
          jpeg:  jconfig.h
          png:   png.h, pngconf.h
          tiff:  tiff.h, tiffio.h

       If for some reason you do not want to link to specific libraries,
       even if you have them, stub files are included for the eight
       different output formats (bmp, jpeg, png, pnm, ps, tiff, gif and webp).
       For example, if you don't want to include the tiff library,
       in environ.h set:
           #define  HAVE_LIBTIFF   0
       and the stubs will be linked in.

       If additionally, you wish to read and write gif files:
          (1) Download version giflib-4.1.6 from souceforge
          (2) #define  HAVE_LIBGIF   1  (in environ.h)
          (3) If the library is installed into /usr/local/lib, you may need
              to add that directory to LDFLAGS; or, equivalently, add
              that path to the LD_LIBRARY_PATH environment variable.
          (4) Note: do not use giflib-4.1.4: binary comp and decomp
              don't pack the pixel data and are ridiculously slow.

       To link these libraries, see prog/makefile for instructions on selecting
       or altering the ALL_LIBS variable.  It would be nice to have this
       done automatically.

## Developing with leptonica

    You are encouraged to use the static makefiles if you are developing
    applications using leptonica.  The following instructions assume
    that you are using the static makefiles and customizing environ.h.

    1. Automatic generation of prototypes

       The prototypes are automatically generated by the program xtractprotos.
       They can either be put in-line into allheaders.h, or they can be
       written to a file leptprotos.h, which is #included in allheaders.h.
       Note: (1) We supply the former version of allheaders.h.
             (2) all .c files simply include allheaders.h.

       First, make xtractprotos:
           make xtractprotos

       Then to generate the prototypes and make allheaders.h, do one of
       these two things:
           make allheaders  [puts everything into allheaders.h]
           make allprotos   [generates a file leptprotos.h and includes it
                             in allheaders.h]

       Things to note about xtractprotos, assuming that you are developing
       in Leptonica and need to regenerate the prototypes in allheaders.h:

         (1) xtractprotos is part of Leptonica.  You can 'make' it in either
             src or prog (see the makefile).
         (2) You can output the prototypes for any C file to stdout by running:
                 xtractprotos      or
                 xtractprotos -prestring=[string]
         (3) The source for xtractprotos has been packaged up into a tar
             containing just the Leptonica files necessary for building it
             in linux.  The tar file is available at:
                 www.leptonica.com/source/xtractlib-1.5.tar.gz

    2. GNU runtime functions for stream redirection to memory

       There are two non-standard gnu functions, fmemopen() and open_memstream(),
       that only work on linux and conveniently allow memory I/O with a file
       stream interface.  This is convenient for compressing and decompressing
       image data to memory rather than to file.  Stubs are provided
       for all these I/O functions.  Default is not to enable them, in
       deference to the OSX developers, who don't have these functions
       available.  To enable, #define HAVE_FMEMOPEN  1  (in environ.h).
       See 19 for more details on image I/O formats.

       If you're building with the autoconf programs, these two functions are
       automatically enabled if available.

    3. Typedefs

       A deficiency of C is that no standard has been universally
       adopted for typedefs of the built-in types.  As a result,
       typedef conflicts are common, and cause no end of havoc when
       you try to link different libraries.  If you're lucky, you
       can find an order in which the libraries can be linked
       to avoid these conflicts, but the state of affairs is aggravating.

       The most common typedefs use lower case variables: uint8, int8, ...
       The png library avoids typedef conflicts by altruistically
       appending "png_" to the type names.  Following that approach,
       Leptonica appends "l_" to the type name.  This should avoid
       just about all conflicts.  In the highly unlikely event that it doesn't,
       here's a simple way to change the type declarations throughout
       the Leptonica code:
        (1) customize a file "converttypes.sed" with the following lines:
            /l_uint8/s//YOUR_UINT8_NAME/g
            /l_int8/s//YOUR_INT8_NAME/g
            /l_uint16/s//YOUR_UINT16_NAME/g
            /l_int16/s//YOUR_INT16_NAME/g
            /l_uint32/s//YOUR_UINT32_NAME/g
            /l_int32/s//YOUR_INT32_NAME/g
            /l_float32/s//YOUR_FLOAT32_NAME/g
            /l_float64/s//YOUR_FLOAT64_NAME/g
        (2) in the src and prog directories:
           - if you have a version of sed that does in-place conversion:
                sed -i -f converttypes.sed *
           - else, do something like (in csh)
               foreach file (*)
               sed -f converttypes.sed $file > tempdir/$file
               end

       If you are using Leptonica with a large code base that typedefs the
       built-in types differently from Leptonica, just edit the typedefs
       in environ.h.  This should have no side-effects with other libraries,
       and no issues should arise with the location in which liblept is
       included.

       For compatibility with 64 bit hardware and compilers, where
       necessary we use the typedefs in stdint.h to specify the pointer
       size (either 4 or 8 byte).  This may not work properly if you use
       an ancient gcc compilers before 2.95.3.

    4. Compile-time control over stderr output

       Leptonica provides some compile-time control over messages
       and debug output.  Messages are of three types: error,
       warning and informational.  They are all macros, and
       are suppressed when NO_CONSOLE_IO is defined on the compile line.
       Likewise, all debug output is conditionally compiled, within
       a #ifndef NO_CONSOLE_IO clause, so these sections are
       omitted when NO_CONSOLE_IO is defined.   For production code
       where no output is to go to stderr, compile with -DNO_CONSOLE_IO.

    5. In-memory raster format (Pix)

       Unlike many other open source packages, Leptonica uses packed
       data for images with all bit/pixel (bpp) depths, allowing us
       to process pixels in parallel.  For example, rasterops works
       on all depths with 32-bit parallel operations throughout.
       Leptonica is also explicitly configured to work on both little-endian
       and big-endian hardware.  RGB image pixels are always stored
       in 32-bit words, and a few special functions are provided for
       scaling and rotation of RGB images that have been optimized by
       making explicit assumptions about the location of the R, G and B
       components in the 32-bit pixel.  In such cases, the restriction
       is documented in the function header.  The in-memory data structure
       used throughout Leptonica to hold the packed data is a Pix,
       which is defined and documented in pix.h.

    6. Conversion between Pix and other in-memory raster formats

     . If you use Leptonica with other imaging libraries, you will need
       functions to convert between the Pix and other image data
       structures.  To make a Pix from other image data structures, you
       will need to understand pixel packing, pixel padding, component
       ordering and byte ordering on raster lines.  See the file pix.h
       for the specification of image data in the pix.

    7. Custom memory management

       Leptonica allows you to use custom memory management (allocator,
       deallocator).  For Pix, which tend to be large, the alloc/dealloc
       functions can be set programmatically.  For all other structs and arrays,
       the allocators are specified in environ.h.  Default functions
       are malloc and free.  We have also provided a sample custom
       allocator/deallocator for Pix, in pixalloc.c.

## What's in leptonica?

    1. Rasterops

       This is a source for a clean, fast implementation of rasterops.
       You can find details starting at the Leptonica home page,
       and also by looking directly at the source code.
       The low-level code is in roplow.c and ropiplow.c, and an
       interface is given in rop.c to the simple Pix image data structure.

    2. Binary morphology

       This is a source for efficient implementations of binary morphology
       Details are found starting at the Leptonica home page, and by reading
       the source code.

       Binary morphology is implemented two ways:

         (a) Successive full image rasterops for arbitrary
             structuring elements (Sels)

         (b) Destination word accumulation (dwa) for specific Sels.
             This code is automatically generated.  See, for example,
             the code in fmorphgen.1.c and fmorphgenlow.1.c.
             These files were generated by running the program
             prog/fmorphautogen.c. Results can be checked by comparing dwa
             and full image rasterops; e.g., prog/fmorphauto_reg.c.

       Method (b) is considerably faster than (a), which is the
       reason we've gone to the effort of supporting the use
       of this method for all Sels.  We also support two different
       boundary conditions for erosion.

       Similarly, dwa code for the general hit-miss transform can
       be auto-generated from an array of hit-miss Sels.
       When prog/fhmtautogen.c is compiled and run, it generates
       the dwa C code in fhmtgen.1.c and fhmtgenlow.1.c.  These
       files can then be compiled into the libraries or into other programs.
       Results can be checked by comparing dwa and rasterop results;
       e.g., prog/fhmtauto_reg.c

       Several functions with simple parsers are provided to execute a
       sequence of morphological operations (plus binary rank reduction
       and replicative expansion).  See morphseq.c.

       The structuring element is represented by a simple Sel data structure
       defined in morph.h.  We provide (at least) seven ways to generate
       Sels in sel1.c, and several simple methods to generate hit-miss
       Sels for pattern finding in selgen.c.

       In use, the most common morphological Sels are separable bricks,
       of dimension n x m (where either n or m, but not both, is commonly 1).
       Accordingly, we provide separable morphological operations on brick
       Sels, using for binary both rasterops and dwa.  Parsers are provided
       for a sequence of separable binary (rasterop and dwa) and grayscale
       brick morphological operations, in morphseq.c.  The main
       advantage in using the parsers is that you don't have to create
       and destroy Sels, or do any of the intermediate image bookkeeping.

       We also give composable separable brick functions for binary images,
       for both rasterop and dwa.  These decompose each of the linear
       operations into a sequence of two operations at different scales,
       reducing the operation count to a sum of decomposition factors,
       rather than the (un-decomposed) product of factors.
       As always, parsers are provided for a sequence of such operations.

    3. Grayscale morphology and rank order filters

       We give an efficient implementation of grayscale morphology for brick
       Sels.  See the Leptonica home page and the source code.

       Brick Sels are separable into linear horizontal and vertical elements.
       We use the van Herk/Gil-Werman algorithm, that performs the calculations
       in a time that is independent of the size of the Sels.  Implementations
       of tophat and hdome are also given.  The low-level code is in graymorphlow.c.

       We also provide grayscale rank order filters for brick filters.
       The rank order filter is a generalization of grayscale morphology,
       that selects the rank-valued pixel (rather than the min or max).
       A color rank order filter applies the grayscale rank operation
       independently to each of the (r,g,b) components.

    4. Image scaling

       Leptonica provides many simple and relatively efficient
       implementations of image scaling.  Some of them are listed here;
       for the full set see the web page and the source code.

       Grayscale and color images are scaled using:
          - sampling
          - lowpass filtering followed by sampling,
          - area mapping
          -  linear interpolation

       Scaling operations with antialiased sampling, area mapping,
       and linear interpolation are limited to 2, 4 and 8 bpp gray,
       24 bpp full RGB color, and 2, 4 and 8 bpp colormapped
       (bpp == bits/pixel).  Scaling operations with simple sampling
       can be done at 1, 2, 4, 8, 16 and 32 bpp.  Linear interpolation
       is slower but gives better results, especially for upsampling.
       For moderate downsampling, best results are obtained with area
       mapping scaling.  With very high downsampling, either area mapping
       or antialias sampling (lowpass filter followed by sampling) give
       good results.  Fast area map with power-of-2 reduction are also
       provided.  Optional sharpening after resampling is provided to
       improve appearance by reducing the visual effect of averaging
       across sharp boundaries.

       For fast analysis of grayscale and color images, it is useful to
       have integer subsampling combined with pixel depth reduction.
       RGB color images can thus be converted to low-resolution
       grayscale and binary images.

       For binary scaling, the dest pixel can be selected from the
       closest corresponding source pixel.  For the special case of
       power-of-2 binary reduction, low-pass rank-order filtering can be
       done in advance.  Isotropic integer expansion is done by pixel replication.

       We also provide 2x, 3x, 4x, 6x, 8x, and 16x scale-to-gray reduction
       on binary images, to produce high quality reduced grayscale images.
       These are integrated into a scale-to-gray function with arbitrary
       reduction.

       Conversely, we have special 2x and 4x scale-to-binary expansion
       on grayscale images, using linear interpolation on grayscale
       raster line buffers followed by either thresholding or dithering.

       There are also image depth converters that don't have scaling,
       such as unpacking operations from 1 bpp to grayscale, and
       thresholding and dithering operations from grayscale to 1, 2 and 4 bpp.

    5. Image shear and rotation (and affine, projective, ...)

       Image shear is implemented with both rasterops and linear interpolation.
       The rasterop implementation is faster and has no constraints on image
       depth.  We provide horizontal and vertical shearing about an
       arbitrary point (really, a line), both in-place and from source to dest.
       The interpolated shear is used on 8 bpp and 32 bpp images, and
       gives a smoother result.  Shear is used for the fastest implementations
       of rotation.

       There are three different types of general image rotators:

         a.  Grayscale rotation using area mapping
             - pixRotateAM() for 8 bit gray and 24 bit color, about center
             - pixRotateAMCorner() for 8 bit gray, about image UL corner
             - pixRotateAMColorFast() for faster 24 bit color, about center

         b.  Rotation of an image of arbitrary bit depth, using
             either 2 or 3 shears.  These rotations can be done
             about an arbitrary point, and they can be either
             from source to dest or in-place; e.g.
             - pixRotateShear()
             - pixRotateShearIP()

         c.  Rotation by sampling.  This can be used on images of arbitrary
             depth, and done about an arbitrary point.  Colormaps are retained.

       The area mapping rotations are slower and more accurate,
       because each new pixel is composed using an average of four
       neighboring pixels in the original image; this is sometimes
       also called "antialiasing".  Very fast color area mapping
       rotation is provided.  The low-level code is in rotateamlow.c.

       The shear rotations are much faster, and work on images
       of arbitrary pixel depth, but they just move pixels
       around without doing any averaging.  The pixRotateShearIP()
       operates on the image in-place.

       We also provide orthogonal rotators (90, 180, 270 degree; left-right
       flip and top-bottom flip) for arbitrary image depth.
       And we provide implementations of affine, projective and bilinear
       transforms, with both sampling (for speed) and interpolation
       (for antialiasing).

    6. Sequential algorithms

       We provide a number of fast sequential algorithms, including
       binary and grayscale seedfill, and the distance function for
       a binary image.  The most efficient binary seedfill is
       pixSeedfill(), which uses Luc Vincent's algorithm to iterate
       raster- and antiraster-ordered propagation, and can be used
       for either 4- or 8-connected fills.  Similar raster/antiraster
       sequential algorithms are used to generate a distance map from
       a binary image, and for grayscale seedfill.  We also use Heckbert's
       stack-based filling algorithm for identifying 4- and 8-connected
       components in a binary image.  A fast implementation of the
       watershed transform, using a priority queue, is included.

    7. Image enhancement

       A few simple image enhancement routines for grayscale and
       color images have been provided.  These include intensity mapping
       with gamma correction and contrast enhancement, as well as edge
       sharpening, smoothing, and hue and saturation modification.

    8. Convolution and cousins

       A number of standard image processing operations are also
       included, such as block convolution, binary block rank filtering,
       grayscale and rgb rank order filtering, and edge and local
       minimum/maximum extraction.   Generic convolution is included,
       for both separable and non-separable kernels, using float arrays
       in the Pix.

    9. Image I/O

       Some facilities have been provided for image input and output.
       This is of course required to build executables that handle images,
       and many examples of such programs, most of which are for
       testing, can be built in the prog directory.  Functions have been
       provided to allow reading and writing of files in JPEG, PNG,
       TIFF, BMP, PNM ,GIF and WEBPformats.  These formats were chosen
       for the following reasons:

        - JFIF JPEG is the standard method for lossy compression
          of grayscale and color images.  It is supported natively
          in all browsers, and uses a good open source compression
          library.  Decompression is supported by the rasterizers
          in PS and PDF, for level 2 and above.  It has a progressive
          mode that compresses about 10% better than standard, but
          is considerably slower to decompress.  See jpegio.c.

        - PNG is the standard method for lossless compression
          of binary, grayscale and color images.  It is supported
          natively in all browsers, and uses a good open source
          compression library (zlib).  It is superior in almost every
          respect to GIF (which, until recently, contained proprietary
          LZW compression).  See pngio.c.

        - TIFF is a common interchange format, which supports different
          depths, colormaps, etc., and also has a relatively good and
          widely used binary compression format (CCITT Group 4).
          Decompression of G4 is supported by rasterizers in PS and PDF,
          level 2 and above.  G4 compresses better than PNG for most
          text and line art images, but it does quite poorly for halftones.
          It has good and stable support by Leffler's open source library,
          which is clean and small.  Tiff also supports multipage
          images through a directory structure.  See tiffio.c

        - BMP has (until recently) had no compression.  It is a simple
          format with colormaps that requires no external libraries.
          It is commonly used because it is a Microsoft standard,
          but has little besides simplicity to recommend it.  See bmpio.c.

        - PNM is a very simple, old format that still has surprisingly
          wide use in the image processing community.  It does not
          support compression or colormaps, but it does support binary,
          grayscale and rgb images.  Like BMP, the implementation
          is simple and requires no external libraries.  See pnmio.c.

        - GIF is still widely used in the world.  With the expiration
          of the LZW patent, it is practical to add support for GIF files.
          The open source gif library is relatively incomplete and
          unsupported (because of the Sperry-Rand-Burroughs-Univac
          patent history).   See gifio.c.

        - WEBP is a new wavelent encoding method derived from libvpx,
          a video compression library.  Leptonica provides an interface
          through webp into the underlying codec.  You need to download
          libvpx, libwebp and yasm,

       Here's a summary of compression support and limitations:
          - All formats except JPEG support 1 bpp binary.
          - All formats support 8 bpp grayscale (GIF must have a colormap).
          - All formats except GIF support 24 bpp rgb color.
          - All formats except PNM support 8 bpp colormap.
          - PNG and PNM support 2 and 4 bpp images.
          - PNG supports 2 and 4 bpp colormap, and 16 bpp without colormap.
          - PNG, JPEG, TIFF and GIF support image compression; PNM and BMP do not.
          - WEBP supports 24 bpp rgb color.
       Use prog/ioformats_reg for a regression test on all but GIF and WEBP.
       Use prog/gifio_reg for testing GIF.

       We provide wrappers for PS output, from all types of input images.
       The output can be either uncompressed or compressed with level 2
       (ccittg4 or dct) or level 3 (flate) encoding.  You have flexibility
       for scaling and placing of images, and for printing at different
       resolutions.  You can also compose mixed raster (text, image) PS.
       See psio1.c for examples of how to output PS for different applications.
       As examples of usage, see:
         * prog/converttops.c for a general image --> PS conversion
               for printing.  You can specify compression level (1, 2, or 3).
         * prog/convertfilestops.c to generate a multipage level 3 compressed
               PS file that can then be converted to pdf with ps2pdf.
         * prog/convertsegfilestops.c to generate a multipage, mixed raster,
               level 2 compressed PS file.

       We provide wrappers for PDF output, again from all types of input images.
       You can do the following for PDF:
         * Put any number of images onto a page, with specified input
           resolution, location and compression.
         * Write a mixed raster PDF, given an input image and a segmentation
           mask.  Non-image regions are written in G4 (fax) encoding.
         * Concatenate single-page PDF wrapped images into a single PDF file.
         * Build a PDF file of all images in a directory or array of file names.

       Note: any or all of these I/O library calls can be stubbed out at
             compile time, using the environment variables in environ.h.

       For all formatted reads and writes, we support read from memory
       and write to memory.  (We cheat with gif, using a file intermediary.)
       For all formats except for TIFF, these memory I/O functions
       are supported through open_memstream() and fmemopen(),
       which only is available with the gnu C runtime library (glibc).
       Therefore, except for TIFF, you will not be able to do memory
       supported read/writes on these platforms:
           OSX, Windows, Solaris
       By default, these non-POSIX functions are disabled.  To enable memory
       I/O for image formatted read/writes, see environ.h.

    10. Colormap removal and color quantization

       Leptonica provides functions that remove colormaps, for conversion
       to either 8 bpp gray or 24 bpp RGB.  It also provides the inverse
       function to colormap removal; namely, color quantization
       from 24 bpp full color to 8 bpp colormap with some number
       of colormap colors.  Several versions are provided, some that
       use a fast octree vector quantizer and others that use
       a variation of the median cut quantizer.  For high-level interfaces,
       see for example: pixConvertRGBToColormap(), pixOctreeColorQuant(),
       pixOctreeQuantByPopulation(), pixFixedOctcubeQuant256(),
       and pixMedianCutQuant().

    11. Programmatic image display

       For debugging, several pixDisplay* functions in writefile.c are given.
       Two (pixDisplay and pixDisplayWithTitle) can be called to display
       an image using one of several display programs (xv, xli, xzgv, l_view).
       If necessary to fit on the screen, the image is reduced in size,
       with 1 bpp images being converted to grayscale for readability.
       (This is much better than letting xv do the reduction).
       Another function, pixDisplayWrite(), writes images to disk under
       control of a reduction/disable flag, which then allows
       either viewing with pixDisplayMultiple(), or the generation
       of a composite image using, for example, pixaDisplayTiledAndScaled().
       These files can also be gathered up into a compressed PostScript file,
       using prog/convertfilestops, and viewed with evince, or converted
       to pdf.  Common image display programs are: xv, xli, xzgv, display,
       gthumb, gqview, evince, gv, xpdf and acroread.  The Leptonica program
       xvdisp generates nice quality images for display with xv.
       Finally, a set of images can be saved into a pixa (array of pix),
       specifying the eventual layout into a single pix, using pixSaveTiled*().

    12. Document image analysis

       Some functions have been included specifically to help with
       document image analysis.  These include skew and text orientation
       detection; page segmentation; baseline finding for text;
       unsupervised classification of connected components, characters
       and words; dewarping camera images, adaptive binarization,
       and digit recognition.

    13. Data structures

       Simple data structures are provided for safe and efficient handling
       of arrays of numbers, strings, pointers, and bytes.  The generic
       pointer array is implemented in four ways: as a stack, a queue,
       a heap (used to implement a priority queue), and an array with
       insertion and deletion, from which the stack operations form a subset.
       Byte arrays are implemented both as a wrapper around the actual
       array and as a queue.  The string arrays are particularly useful
       for both parsing and composing text.  Generic lists with
       doubly-linked cons cells are also provided.

    14. Examples of programs that are easily built using the library:

        - for plotting x-y data, we give a programmatic interface
          to the gnuplot program, with output to X11, png, ps or eps.
          We also allow serialization of the plot data, in a form
          such that the data can be read, the commands generated,
          and (finally) the plot constructed by running gnuplot.

        - a simple jbig2-type classifier, using various distance
          metrics between image components (correlation, rank
          hausdorff); see prog/jbcorrelation.c, prog/jbrankhaus.c.

        - a simple color segmenter, giving a smoothed image
          with a small number of the most significant colors.

        - a program for converting all tiff images in a directory
          to a PostScript file, and a program for printing an image
          in any (supported) format to a PostScript printer.

        - converters between binary images and SVG format.

        - a bitmap font facility that allows painting text onto
          images.  We currently support one font in several sizes.
          The font images and postscript programs for generating
          them are stored in prog/fonts/.

        - a binary maze game lets you generate mazes and find shortest
          paths between two arbitrary points, if such a path exists.
          You can also compute the "shortest" (i.e., least cost) path
          between points on a grayscale image.

        - a 1D barcode reader.  This is in an early stage of development,
          with little testing, and it only decodes 6 formats.

        - a utility that will dewarp images of text that were captured
          with a camera at close range.

        - a sudoku solver, including a pretty good test for uniqueness

        - see (13, above) for other document image applications.

    15. JBig2 encoder

       Leptonica supports an open source jbig2 encoder (yes, there is one!),
       which can be downloaded from:
           http://www.imperialviolet.org/jbig2.html.
       To build the encoder, use the most recent version.  This bundles
       Leptonica 1.63.  Once you've built the encoder, use it to compress
       a set of input image files:  (e.g.)
           ./jbig2 -v -s   >
       You can also generate a pdf wrapping for the output jbig2.  To do that,
       call jbig2 with the -p arg, which generates a symbol file (output.sym)
       plus a set of location files for each input image (output.0000, ...):
            ./jbig2 -v -s -p
       and then generate the pdf:
           python pdf.py output  >
       See the usage documentation for the jbig2 compressor at:
           http://www.imperialviolet.org/binary/jbig2enc.html
       You can uncompress the jbig2 files using jbig2dec, which can be
       downloaded and built from:
           http://jbig2dec.sourceforge.net/

    16. Versions

       New versions of the Leptonica library are released approximately
       6 times a year, and version numbers are provided for each release in
       the makefile and in allheaders.h.  All even versions from 1.42 to 1.60
       are archived at http://code.google.com/p/leptonica, as well as all
       versions after 1.60.

       A brief version chronology is maintained in version-notes.html.
       Starting with gcc 4.3.3, error warnings (-Werror) are given for
       minor infractions like not checking return values of built-in C
       functions.  I have attempted to eliminate these warnings.
       In any event, you can expect some warnings with the -Wall flag.