Module png_pong::chunk

Low-level PNG API

A PNG file consists of a sequence of Chunks in a specific order.

PNG Chunk Order

Key

• Required - Count must be exactly one.
• Optional - Count must be exactly one or zero.
• Multiple - Count can be any number, including zero.

Order

The PNG/APNG chunk order must be as follows:

• Required ImageHeader “IHDR”
• In any order:
  • Optional Chromaticities
  • Optional Gamma “gAMA”
  • Optional ColorProfile “iCCP”
  • Optional SignificantBits “sBIT”
  • Optional SRgb “sRGB”
  • Optional Physical “pHYs”
  • Multiple SuggestedPalette “sPLT”
  • Optional Time “tIME” (If didn’t appear earlier)
  • Multiple InternationalText “iTXt”
  • Multiple Text “tEXt”
  • Multiple CompressedText “zTXt”
  • Optional AnimationControl “acTL” (APNG)
  • Optional FrameControl “fcTL” (APNG)
  • Optional ImageOffset “oFFs” (Extension)
  • Optional PixelCalibration “pCAL” (Extension)
  • Optional SubjectPhysical “sCAL” (Extension)
  • Multiple GifGraphicControlExt “gIFg” (Extension)
  • Multiple GifApplicationExt “gIFx” (Extension)
• Optional Palette “PLTE”
• In any order:
  • Optional Background “bKGD”
  • Optional PaletteHistogram “hIST”
  • Optional Transparency “tRNS”
  • Optional Physical “pHYs” (If didn’t appear before PLTE)
  • Multiple SuggestedPalette “sPLT”
  • Optional Time “tIME” (If didn’t appear earlier)
  • Multiple InternationalText “iTXt”
  • Multiple Text “tEXt”
  • Multiple CompressedText “zTXt”
  • Optional AnimationControl “acTL” (APNG, If didn’t appear earlier)
  • Optional FrameControl “fcTL” (APNG, If didn’t appear earlier)
  • Optional ImageOffset “oFFs” (Extension, If didn’t appear earlier)
  • Optional PixelCalibration “pCAL” (Extension, If didn’t appear earlier)
  • Optional SubjectPhysical “sCAL” (Extension, If didn’t appear earlier)
  • Multiple GifGraphicControlExt “gIFg” (Extension)
  • Multiple GifApplicationExt “gIFx” (Extension)
• Multiple ImageData “IDAT”
• In any order:
  • Optional Time “tIME” (If didn’t appear earlier)
  • Multiple InternationalText “iTXt”
  • Multiple Text “tEXt”
  • Multiple CompressedText “zTXt”
  • Multiple FrameControl “fcTL” (APNG)
  • Multiple FrameData “fdAT” (APNG, must be somewhere after “fcTL”)
  • Multiple GifGraphicControlExt “gIFg” (Extension)
  • Multiple GifApplicationExt “gIFx” (Extension)
• Required ImageEnd “IEND”

Structs

• CompressedText
  Compressed Text Chunk Data (zTXt)
• ImageData
  Image Data Chunk Data (IDAT)
• ImageEnd
  Image End Chunk Data (IEND)
• ImageHeader
  Image Header Chunk Data (IHDR)
• InternationalText
  International Text Chunk Data (iTXt)
• Palette
  Palette Chunk Data (PLTE)
• Physical
  Physical dimensions chunk (pHYs)
• Text
  Non-International Text Chunk Data (tEXt and zTXt)
• Time
  Time chunk (tIME)
• Unknown
  An unknown PNG data chunk

Enums

• Background
  Suggested background color chunk (bKGD)
• Chunk
  A chunk within a PNG file.
• ColorType
  Standard PNG color types.
• Transparency
  Alpha Palette Chunk Data (tRNS)