PNG (Portable Network Graphics) Specification, Version 0.91

Copyright 1995, Thomas Boutell. Permission is granted to reproduce this specification in complete and unaltered form. Excerpts may be printed with the following notice: "excerpted from the PNG (Portable Network Graphics) specification, version 0.91." No notice is required in software that follows this specification; notice is only required when reproducing or excerpting from the specification itself.

Contents

• 0. Status
• 1. Introduction
• 2. Data Representation
  • Integers and byte order
  • Color values
  • Image layout
  • Alpha channel
  • Filtering
  • Interlaced data order
  • Gamma correction
  • Text strings
• 3. File Structure
  • PNG file signature
  • Chunk layout
  • Chunk naming conventions
  • CRC algorithm
• 4. Chunk Specifications
  • Critical Chunks
  • Ancillary Chunks
  • Summary of Standard Chunks
  • Additional Chunk Types
• 5. Deflate/Inflate Compression
• 6. Filter Algorithms
  • Filter type 0: None
  • Filter type 1: Sub
  • Filter type 2: Up
  • Filter type 3: Average
  • Filter type 4: Paeth
• 7. Chunk Ordering Rules
• 8. Miscellaneous Topics
  • File name extension
  • Macintosh file layout
  • Multiple-image extension
  • Security considerations
• 9. Recommendations for Encoders
  • Bit depth scaling
  • Encoder gamma handling
  • Alpha channel creation
  • Suggested palettes
  • Filter selection
  • Text chunk processing
  • Use of private chunks
• 10. Recommendations for Decoders
  • Chunk error checking
  • Pixel dimensions
  • Truecolor image handling
  • Bit depth rescaling
  • Decoder gamma handling
  • Background color
  • Alpha channel processing
  • Progressive display
  • Palette histogram usage
  • Text chunk processing
• 11. Glossary
• 12. Appendix: Rationale
  • Why a new file format?
  • Why these features?
  • Why not these features?
  • Why not use format XYZ?
  • Byte order
  • Interlacing
  • Why gamma?
  • Non-premultiplied alpha
  • Filtering
  • Text strings
  • PNG file signature
  • Chunk layout
  • Chunk naming conventions
  • Palette histograms
• 13. Appendix: Gamma Tutorial
• 14. Appendix: Sample CRC Code
• 15. Credits