The library supports many operations that are useful on
Document images
Natural images
Fundamental image processing and image analysis operations
Rasterop (aka bitblt)
Affine transforms (scaling, translation, rotation, shear) on images of arbitrary pixel depth
Projective and bilinear transforms
Binary and grayscale morphology, rank order filters, and convolution
Seedfill and connected components
Image transformations with changes in pixel depth, both at the same scale and with scale change
Pixelwise masking, blending, enhancement, arithmetic ops, etc.
Ancillary utilities
I/O for standard image formats (jpg, png, tiff, webp, jp2, bmp, pnm, gif, ps, pdf)
Utilities to handle arrays of image-related data types (e.g., pixa, boxa, pta)
Utilities for stacks, generic arrays, queues, heaps, lists, sets, ordered maps, hashmaps; number and string arrays; etc.
Examples of some applications enabled and implemented
Octcube-based color quantization (w/ and w/out dithering)
Modified median cut color quantization (w/ and w/out dithering)
Determination of skew and orientation of text images
Adaptive background normalization and binarization
Segmentation of page images with mixed text and images
Color segmentation by clustering and seed-filling
Location of baselines and local skew determination
jbig2 unsupervised classifier
Border representations of 1 bpp images and raster conversion for SVG
Postscript generation (levels 1, 2 and 3) of images for device-independent output
PDF generation (G4, DCT, FLATE) of images for device-independent output
Connectivity-preserving thinning and thickening of 1 bpp images
Image warping (captcha, stereoscopic)
Image dewarping based on content (textlines)
Watershed transform
Greedy splitting of components into rectangles
Location of largest fg or bg rectangles in 1 bpp images
Search for least-cost paths on binary and grayscale images
Barcode reader for 1D barcodes (very early version as of 1.55)
Implementation characteristics
Efficient: image data is packed binary (into 32-bit words); operations on 32-bit data whenever possible
Simple: small number of data structures; simplest implementations provided that are efficient
Consistent: data allocated on the heap with simple ownership rules; function names usually begin with primary data structure (e.g., pix); simple code patterns throughout
Robust: all ptr args checked; extensive use of accessors; exit not permitted
Tested: over 140 regression tests provided for basic functions and applications; valgrind tested
jbig2enc (encodes multipage binary image documents with jbig2 compression)
Major contributors to Leptonica
Tom Powers: Tom supported the port of Leptonica to Windows for many years. He made many contributions to code quality and documentation, including the beautiful "unofficial documentation" on the web site.
David Bryan: David has worked for years to support Leptonica on multiple platforms. He designed many nice features in Leptonica, such as the severity-based error messaging system, and has identified and fixed countless bugs. And he has built and tested each distribution many times on cross-compilers.
James Le Cuirot: James has written and supported the autotools scripts on Leptonica distributions for many years, and has helped test every distribution since 1.67.
Jeff Breidenbach: Jeff has built every Debian distribution for Leptonica. He has also made many improvements to formatted image I/O, including tiff, png and pdf. He is a continuous advocate for simplification.
Egor Pugin: Egor is co-maintainer of Leptonica on GitHub. He ported everything, including all the old distributions, from Google Code when it shut down. He set Leptonica up for appveyor and travis testing, and has implemented the sw project, which simplifies building executables on Windows.
Jürgen Buchmüller: Jürgen wrote text converters to modify Leptonica source code so that it generates documentation using doxygen. He also wrote tiff wrappers for memory I/O.
Stefan Weil: Stefan has worked from the beginning to clean up the Leptonica GitHub distribution, including removing errors in the source code. He also: suggested and implemented the use of Coverity Scan; implemented atomic ops for ref counting; helped removing internal struct data from the public interface.
Zdenko Podobny: Zdenko has worked, mostly behind the scenes as a primary maintainer of tesseract, to help with leptonica builds on all platforms, and coordinate with its use in tesseract.
Adam Korczynski: Adam is an expert in testing libraries for safety. He has built most of the open source fuzzers for leptonica in the oss-fuzz project, with significant code coverage.
Installing leptonica (vcpkg)
You can build and install leptonica using vcpkg dependency manager:
git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh # "./bootstrap-vcpkg.bat" for powershell
./vcpkg integrate install
./vcpkg install leptonica
The leptonica port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.
