The Leptonica Image Processing Library

• README
  • Building Leptonica
    • Overview
    • Building on Linux/Unix/MacOS
    • Building on Windows
  • I/O libraries Leptonica is dependent on
  • Developing with Leptonica
    • Simplicity
    • leptprotos.h
    • GNU runtime functions for stream redirection to memory
    • Typedefs
    • Compile-time control over stderr output
    • In-memory raster format (Pix)
    • Conversion between Pix and other in-memory raster formats
    • Custom memory management
  • What’s in Leptonica?
    • Rasterops
    • Binary morphology
    • Grayscale morphology and rank order filters
    • Image scaling
    • Image shear and rotation (and affine, projective, ...)
    • Sequential algorithms
    • Image enhancement
    • Convolution and cousins
    • Image I/O
    • Colormap removal and color quantization
    • Programmatic image display
    • Document image analysis
    • Data structures
    • Examples of programs that are easily built using the library
    • JBig2 encoder
  • Versions
  • Reporting Bugs
• Version Notes for Leptonica
  • 1.68 – 14 Mar 11
  • 1.67 – 9 Nov 10
  • 1.66 – 3 Aug 10
  • 1.65 – 5 Apr 10
  • 1.64 – 3 Jan 10
  • 1.63 – 8 Nov 09
  • 1.62 – 26 Jul 09
  • 1.61 – 26 Apr 09
  • 1.60 – 19 Jan 09
  • 1.59 – 11 Jan 09
  • Earlier Versions
• Source Code and Information
  • Download
  • Related Publications
• Source Downloads
  • Leptonica
  • Microsoft Visual Studio 2008
  • Xtractlib
  • Plotlib
• Overview of the Leptonica Library
  • Introduction
  • Reading and writing images
  • Affine transforms
    • Rasterops
• Supplemental Notes on Using the Library
  • I/O: File read/write
  • The Pix data structure
  • Rasterops
  • Scaling
  • Rotation
  • Shear
  • Affine, projective and bilinear transforms
  • Binary morphology
  • Grayscale morphology
  • Block convolution
  • Connected components
• Leptonica API
  • Function Summary by Category
  • Functions
• /src Directory Contents (API Implementation)
  • File Summary by Category
  • File Descriptions
• /prog Directory Contents (Examples)
  • File Summary by Category
  • File Summary by Type
  • File Descriptions
• Image Processing Operations
  • Rasterop (a.k.a. Bitblt)
    • What is rasterop?
    • What else can you do with rasterop?
    • How is rasterop implemented efficiently?
    • What special cases have been implemented?
    • What is the calling sequence for rasterops?
  • Binary Morphology
    • Introduction
    • References and meta-references
    • What is binary morphology?
      • And there is more to morphology than translationally-invariant, increasing primitives
    • What about boundary conditions?
    • The rasterop implementation of binary morphology
    • The destination word accumulation implementation of binary morphology
      • Auto-generated dwa code interfaces
    • Separable atomic operations with block Sels, Sel decomposition, sequence interpreters and simplicity of use
      • Atomic separable functions
      • Interpreters for sequences of atomic operations
    • Summary of available implementations
      • Full image rasterops
      • Destination word accumulation
      • Sequence interpreters
      • Performance comparisons
    • Binary morphology and cellular automata
  • Grayscale Morphology
    • What is grayscale morphology?
    • Implementation using the van Herk/Gil-Werman algorithm
    • The Tophat and H-dome transforms
    • Generalization: rank order filters
      • Definition
      • How is a brick rank order filter implemented efficiently?
      • Points of interest in the implementation
  • Fast Convolution
    • What is a convolution?
    • Grayscale convolution using an accumulator
    • Binary rank-order and median filter using an accumulator
  • Image Scaling
    • Overview of image scaling
      • What types of image scaling are useful?
    • Grayscale Image Scaling
      • How do you scale a grayscale image?
        • Sampling
        • Area mapping (or area averaging) and lowpass filtering
        • Mip-mapping
        • Min-max
        • Linear interpolation
      • Implementation of linear interpolation scaling
      • Considerations of efficiency for linear interpolation scaling
    • Binary Image Scaling
      • Arbitrary binary rescaling
      • Special case: power-of-2 binary expansion
      • Special case: 2x binary reduction
    • Binary to Gray Downscaling (“scale-to-gray”)
    • Gray to binary upscaling (“scale-to-binary”)
    • Fast scaling with depth change
    • Summary of scaling functions in leptonica
  • Image Rotation
    • How do you rotate an image by an arbitrary angle?
    • Rotation by Shear
    • Rotation by Area Mapping
    • Fast rotation by Area Mapping
    • Special rotations by 90, 180 or 270 degrees
      • 180 degree rotation
      • 90 degree rotation
  • Affine Transformations (and cousins)
    • What is an affine transformation?
    • How are affine transformations implemented?
      • Sequential affine transform
    • Some related transforms
      • Conformal affine transform
      • Projective transform
      • Bilinear transform
    • Shearing an image
  • Seed Filling and Connected Components
    • What is the seed fill operation?
    • Seed filling to identify connected components
    • Seed filling using binary morphology
    • Seed filling using iterative raster-ordered filling
    • Seed filling extended to grayscale images (grayscale reconstruction)
    • Generation of a distance function within connected components
    • Labelling pixels using distance function and grayscale reconstruction
    • Watershed transform on seeded grayscale images
  • Grayscale and Color Image Enhancement
    • What do we mean by grayscale and color image enhancement?
      • What other types of enhancement operations exist?
    • Gamma correction
    • Contrast enhancement
    • Unsharp masking (edge enhancement)
    • Image smoothing
  • Grayscale Mapping and Binarization
    • Locally adapted grayscale mapping
    • Locally adapted binarization
      • Sauvola binarization
      • Local background normalization
      • Local background normalization with Otsu
      • Local background normalization with two thresholds
    • Global binarization
  • Connectivity-preserving Thinning
• Image Processing Applications
  • Removing dark lines from a light pencil drawing
  • Dewarping Text Pages
    • What distortions do you expect with camera images?
    • How do you dewarp a camera image based on text lines?
    • Example showing images and disparity fields
  • Measuring the Skew of Document Images
    • For further reading . . .
  • Color Quantization
    • How did the need for color quantization arise?
    • What are the basic problems in color quantization?
    • Why is error diffusion dithering important?
    • What methods have been proposed for color quantization?
    • Modified median cut implementation
    • Octree implementation
      • What is the octree data structure used in Leptonica?
      • How is the octree formed?
      • What color is associated with each octcube in the color table?
      • How are color indices assigned to the image pixels?
      • How is the error diffusion dithering applied?
      • How fast is the implementation?
    • For further reading on color quantization . . .
  • Color Segmentation
    • What is color segmentation and why do it?
    • How does color segmentation differ from color quantization?
    • How do we generate the color segmented images?
    • How does a color segmented image look?
  • Border Representations of Connected Components
    • Overview of connected component borders
    • Generating chain codes for connected components
    • Serializing the data for a compressed file format
    • Forming a single border for each connected component
    • Rendering the outline as a filled raster
    • Putting it together
  • Document Image Analysis
  • Jbig2 Classifier
    • What is the origin of the Jbig2 application?
    • What is jbig2?
    • What is provided in Leptonica?
    • What is the definition of the hausdorff distance, and how is it implemented efficiently?
    • How are the images aligned for comparison?
    • What’s special about the Leptonica implementation?
    • Open source implementation of jbig2
    • What is Mixed Raster format?
• Byte Addressing for Efficiency and Portability
• What is “Well-Tested” C Code?
• Some Issues in Software Design
  • Software design principles
  • What happens when things go wrong?
  • Extremism in programming languages
  • Some practical issues in programming
  • Some issues with memory management
  • A low-level gotcha: operator precedence in C
  • Anecdotes on managing complexity in programming
    • Fred Hoyle’s N² law of complexity
    • Complexity at the interface
    • Getting managed by complexity
    • Managing the complexity
• Selected Papers on Image Processing and Image Analysis
  • Low-level image processing
  • Basic methods of image segmentation
  • Document Image Decoding
  • Image Compression
  • Simple Document Image Applications
  • Complex Document Applications using Segmentation
  • Papers by Luc Vincent
  • Comprehensive bibliography
• About the Copyright License
• What is the Significance of the Name “leptonica”?
• Glossary