PNG Tags

Tags extracted from PNG images. See http://www.libpng.org/pub/png/spec/1.2/ for the official PNG 1.2 specification.

According to the specification, a PNG file should end at the IEND chunk, however ExifTool will preserve any data found after this when writing unless it is specifically deleted with -Trailer:All=. When reading, a minor warning is issued if this trailer exists, and ExifTool will attempt to parse this data as additional PNG chunks.

Tag ID Tag Name Writable Values / Notes 'IHDR' ImageHeader - --> PNG ImageHeader Tags 'PLTE' Palette N   'bKGD' BackgroundColor N   'cHRM' PrimaryChromaticities - --> PNG PrimaryChromaticities Tags 'dSIG' DigitalSignature N   'fRAc' FractalParameters N   'gAMA' Gamma N (ExifTool reports the gamma for decoding the image, which is consistent with the EXIF convention, but is the inverse of the stored encoding gamma) 'gIFg' GIFGraphicControlExtension N   'gIFt' GIFPlainTextExtension N   'gIFx' GIFApplicationExtension N   'hIST' PaletteHistogram N   'iCCP' ICC_Profile - --> ICC_Profile Tags (this is where ExifTool will write a new ICC_Profile) 'iCCP-name' ProfileName N (not a real tag ID, this tag represents the iCCP profile name) 'iTXt' InternationalText - --> PNG TextualData Tags 'oFFs' ImageOffset N   'pCAL' PixelCalibration N   'pHYs' PhysicalPixel - --> PNG PhysicalPixel Tags 'sBIT' SignificantBits N   'sCAL' SubjectScale - --> PNG SubjectScale Tags 'sPLT' SuggestedPalette N   'sRGB' SRGBRendering N 0 = Perceptual 1 = Relative Colorimetric 2 = Saturation 3 = Absolute Colorimetric 'sTER' StereoImage - --> PNG StereoImage Tags 'tEXt' TextualData - --> PNG TextualData Tags 'tIME' ModifyDate Y   'tRNS' Transparency N   'tXMP' XMP - --> XMP Tags (obsolete location specified by a September 2001 XMP draft) 'vpAg' VirtualPage - --> PNG VirtualPage Tags 'zTXt' CompressedText - --> PNG TextualData Tags

PNG ImageHeader Tags

Index1 Tag Name Writable Values / Notes 0 ImageWidth N   4 ImageHeight N   8 BitDepth N   9 ColorType N 0 = Grayscale 2 = RGB 3 = Palette 4 = Grayscale with Alpha 6 = RGB with Alpha 10 Compression N 0 = Deflate/Inflate 11 Filter N 0 = Adaptive 12 Interlace N 0 = Noninterlaced 1 = Adam7 Interlace

PNG PrimaryChromaticities Tags

Index4 Tag Name Writable Values / Notes 0 WhitePointX N   1 WhitePointY N   2 RedX N   3 RedY N   4 GreenX N   5 GreenY N   6 BlueX N   7 BlueY N

PNG TextualData Tags

The PNG TextualData format allows arbitrary tag names to be used. The tags listed below are the only ones that can be written (unless new user-defined tags are added via the configuration file), however ExifTool will extract any other TextualData tags that are found. All TextualData tags (including tags not listed below) are removed when deleting all PNG tags.

These tags may be stored as tEXt, zTXt or iTXt chunks in the PNG image. By default ExifTool writes new string-value tags as as uncompressed tEXt, or compressed zTXt if the Compress (-z) option is used and Compress::Zlib is available. Alternate language tags and values containing special characters (unless the Latin character set is used) are written as iTXt, and compressed if the Compress option is used and Compress::Zlib is available. Raw profile information is always created as compressed zTXt if Compress::Zlib is available, or tEXt otherwise. Standard XMP is written as uncompressed iTXt.

Alternate languages are accessed by suffixing the tag name with a '-', followed by an RFC 3066 language code (eg. "PNG:Comment-fr", or "Title-en-US"). See http://www.ietf.org/rfc/rfc3066.txt for the RFC 3066 specification.

Some of the tags below are not registered as part of the PNG specification, but are included here because they are generated by other software such as ImageMagick.

Tag ID Tag Name Writable Values / Notes 'Artist' Artist string (unregistered) 'Author' Author string   'Comment' Comment string   'Copyright' Copyright string   'Creation Time' CreationTime string   'Description' Description string   'Disclaimer' Disclaimer string   'Document' Document string (unregistered) 'Label' Label string (unregistered) 'Make' Make string (unregistered) 'Model' Model string (unregistered) 'Raw profile type 8bim' Photoshop_Profile - --> Photoshop Tags (unregistered) 'Raw profile type APP1' APP1_Profile - --> EXIF Tags --> XMP Tags (unregistered. This is where ExifTool will create new EXIF) 'Raw profile type exif' EXIF_Profile - --> EXIF Tags (unregistered) 'Raw profile type icc' ICC_Profile - --> ICC_Profile Tags (unregistered) 'Raw profile type icm' ICC_Profile - --> ICC_Profile Tags (unregistered) 'Raw profile type iptc' IPTC_Profile - --> Photoshop Tags (unregistered. May be either IPTC IIM or Photoshop IRB format. This is where ExifTool will add new IPTC, inside a Photoshop IRB container) 'Raw profile type xmp' XMP_Profile - --> XMP Tags (unregistered) 'Software' Software string   'Source' Source string   'TimeStamp' TimeStamp string (unregistered) 'Title' Title string   'URL' URL string (unregistered) 'Warning' PNGWarning string   'XML:com.adobe.xmp' XMP - --> XMP Tags (unregistered, but this is the location according to the June 2002 or later XMP specification, and is where ExifTool will add a new XMP chunk if the image didn't already contain XMP) 'create-date' CreateDate string (unregistered) 'modify-date' ModDate string (unregistered)

PNG PhysicalPixel Tags

These tags are found in the PNG pHYs chunk and belong to the PNG-pHYs family 1 group. They are all created together with default values if necessary when any of these tags is written, and may only be deleted as a group.

Index1 Tag Name Writable Values / Notes 0 PixelsPerUnitX int32u   4 PixelsPerUnitY int32u   8 PixelUnits int8u 0 = Unknown 1 = meters

PNG SubjectScale Tags

Index1 Tag Name Writable Values / Notes 0 SubjectUnits N 1 = meters 2 = radians 1 SubjectPixelWidth N   2 SubjectPixelHeight N

PNG StereoImage Tags

Index1 Tag Name Writable Values / Notes 0 StereoMode N 0 = Cross-fuse Layout 1 = Diverging-fuse Layout

PNG VirtualPage Tags

Index4 Tag Name Writable Values / Notes 0 VirtualImageWidth N   1 VirtualImageHeight N   2 VirtualPageUnits N

<-- ExifTool Tag Names