date:Mar 14, 2011
 -  Copyright (C) 2001 Leptonica.  All rights reserved.
 -  This software is distributed in the hope that it will be
 -  useful, but with NO WARRANTY OF ANY KIND.
 -  No author or distributor accepts responsibility to anyone for the
 -  consequences of using this software, or for whether it serves any
 -  particular purpose or works at all, unless he or she says so in
 -  writing.  Everyone is granted permission to copy, modify and
 -  redistribute this source code, for commercial or non-commercial
 -  purposes, with the following restrictions: (1) the origin of this
 -  source code must not be misrepresented; (2) modified versions must
 -  be plainly marked as such; and (3) this notice may not be removed
 -  or altered from any source or modified source distribution.
gunzip leptonica-1.68.tar.gz
tar -xvf leptonica-1.68.tar

Building Leptonica


This tar includes:

  • src: library source and function prototypes for building liblept

  • 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-1.68. 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.

Building on Linux/Unix/MacOS

There are two ways to build the library:

  1. By customization: Use the existing src/makefile and customize by setting flags in src/environ.h. See src/environ.h and src/makefile for details.


    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:

    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


      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:

      • Including Leptonica I/O functions that depend on external libraries [use flags in src/environ.h]

      • Adding functions for redirecting formatted image stream I/O to memory [use flag in src/environ.h]

      • 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):

      • 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 conversion programs converttops, convertfilestops, convertsegfilestops, printimage and printsplitimage.

    This page summarizes the types and categories of files in the prog directory, and also gives a short description for each file.

  1. 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-1.68/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.

  2. Cross-compiling for windows

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

Building on Windows

  1. 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++ 2008/2010:

    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).

  2. Building with a static makefile via MinGW (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 above. It will also allow building with the static makefile as above if this option is added to the make command:


    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 must be downloaded separately, built, and installed before building the library. Pre-built libraries are available from the GnuWin project.

  3. 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 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 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 <package>

where <package> = {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 sourceforge

  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.

See Image I/O for more details on supported image I/O formats.

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.


For virtually any program you write, you only need:

#include “allheaders.h

to include all the function prototypes and struct definitions for the leptonica library!

It is this simple to write a program using Leptonica:

#include "allheaders.h"
int main(int argc, char **argv) {
    PIX *pixs, *pixd;
    pixs = pixRead("example.png");
    pixd = pixScale(pixs, 0.35, 0.35);  /* downscale by 0.35 */
    pixWrite("downscaled-example.png", pixd, IFF_PNG);
    return 0;


The prototype header file leptprotos.h (supplied) can be automatically generated using xtractprotos. To generate leptprotos.h, first make xtractprotos (all in src):

make  (to make liblept)
make xtractprotos

Then run it:

make allprotos   (generates leptprotos.h)

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

  • xtractprotos is part of Leptonica. You can make it in either src or prog (see the makefile).

  • You can output the prototypes for any C file by running:

    xtractprotos <cfile>     or
    xtractprotos -prestring=[string] <cfile>
  • 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:

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 below for more details on image I/O formats.

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


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:

  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

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 liblebt 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.

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.

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.

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 and Byte Addressing for Efficiency and Portability.

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 in pixalloc.c.

What’s in Leptonica?

There is a sortable and searchable categorized list of all the functions available in Leptonica at Leptonica API (Warning: this page may take a long time to load). There are also summaries of the files in the src and prog directories with short descriptions of each file.


This is a source for a clean, fast implementation of Rasterop (a.k.a. Bitblt). Besides reading that page you should also look 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.

Binary morphology

This is a source for efficient implementations of Binary Morphology and Grayscale Morphology. Besides reading those pages you should also look directly at the source code.

Binary morphology is implemented two ways:

  1. Successive full image rasterops for arbitrary structuring elements (Sels)

  2. 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 (2) is considerably faster than (1), 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.

Grayscale morphology and rank order filters

We give an efficient implementation of grayscale morphology for brick Sels. See Grayscale Morphology 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.

Image scaling

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

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:

  1. Grayscale rotation using area mapping

  2. 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.

  3. 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).

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 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.

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.

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.

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 WEBP formats. 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 only 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.


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.

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().

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, display, gthumb, gqview, xli, 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*().

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, and digit recognition.

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.

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 above for other document image applications.

JBig2 encoder

Leptonica supports an open source jbig2 encoder (yes, there is one!), which can be downloaded from:

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 <imagefile1 ...>  >  <jbig2_file>

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 <imagefile1 ...>

and then generate the pdf:

python output  >  <pdf_file>

See the usage documentation for the jbig2 compressor at:

You can uncompress the jbig2 files using jbig2dec, which can be downloaded and built from:


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. Version numbers are also available programatically via the functions getLeptonicaVersion() (in utils.c) and getImagelibVersions() (in libversions.c). All even versions from 1.42 to 1.60 are archived at, as well as all versions after 1.60.

A brief version chronology is maintained in Version Notes for Leptonica. 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.

Reporting Bugs

Any bugs you find in Leptonica should be reported at

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