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:
     

   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.

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.

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.