Leptonica Library

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You can get new versions of leptlib from www.leptonica.org.

You can also send me bug reports and feature requests directly.

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, bmp, pnm, gif, ps, pdf, webp)
• Utilities to handle arrays of image-related data types (e.g., pixa, boxa, pta)
• Utilities for stacks, generic arrays, queues, heaps, lists; 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)
• Skew determination of text images
• Adaptive normalization and binarization
• Segmentation of page images with mixed text and images
• 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: thorough regression tests provided for most basic functions; valgrind tested
• Ansi C: automatically generated prototype header file
• Portable: endian-independent; builds in linux, osx, mingw, cygwin, windows
• Nearly thread-safe: ref counting on some structs
• Documentation: large number of in-line comments; web pages for further background
• Examples: many programs provided to test and show usage of approx. 2200 functions in the library

Open Source Projects that use Leptonica

• php (scripting language for dynamic web pages)
• tesseract (optical character recognition)
• jbig2enc (encodes multipage binary image documents with jbig2 compression)