TIFF/EP

Tag Image File Format/Electronic Photography (TIFF/EP) is a digital image file format standardISO 12234-2, titled "Electronic still-picture imaging – Removable memory – Part 2: TIFF/EP image data format". This is different from the Tagged Image File Format, which is a standard administered by Adobe currently called "TIFF, Revision 6.0 Final – June 3, 1992".

TIFF/EP
Filename extension.tiff, .tif
Developed byInternational Organization for Standardization
Initial release2001 (2001)
Latest release
ISO 12234-2:2001
(2001 (2001))
Type of formatImage file formats
Container forMetadata
Extended fromTIFF and Exif
Extended toDigital Negative Specification
StandardISO 12234-2

The TIFF/EP standard is based on a subset of the Adobe TIFF standard, and a subset of the JEITA Exif standard, with some differences and extensions.

One of the uses of TIFF/EP is as a raw image format. A characteristic of most digital cameras (but excluding those using the Foveon X3 sensor or similar, hence especially Sigma cameras) is that they use a color filter array (CFA). Software processing a raw image format for such a camera needs information about the configuration of the color filter array, so that the raw image can identify separate data from the individual sites of the sensor. Ideally this information is held within the raw image file itself, and TIFF/EP uses the tags that begin "CFA", CFARepeatPatternDim and CFAPattern, which are only relevant for raw images.

This standard has not been adopted by most camera manufacturers – Exif/DCF is the current industry standard file organisation system which uses the Exchangeable image file format. However, TIFF/EP provided a basis for the raw image formats of a number of cameras. One example is Nikon's NEF raw file format, which uses the tag TIFF/EPStandardID (with value 1.0.0.0).[1] Adobe's DNG (Digital Negative) raw file format was based on TIFF/EP, and the DNG specification states "DNG... is compatible with the TIFF-EP standard".[2] Several cameras use DNG as their raw file format, so in that limited sense they use TIFF/EP too.[3]

New Tags

The following new tags are defined in the TIFF/EP standard, all to be placed in the first TIFF Image File Directory (IFD)

TIFF/EP Tag#Tag Name
014A16SubIFDs
015B16JPEGTables
828D16CFARepeatPatternDim
828F16BatteryLevel
83BB16IPTC/NAA
877316InterColorProfile
882916Interlace
882A16TimeZoneOffset
882B16SelfTimerMode
920D16Noise
921116ImageNumber
921216SecurityClassification
921316ImageHistory
921616TIFF/EPStandardID

Differences from TIFF and Exif

There are no major departures by the TIFF/EP standard from the TIFF standard, except that many of the TIFF tags are ignored.

The TIFF/EP standard does however have a few notable differences from the Exif standards:

  • All tags used by TIFF/EP which are defined by the Exif standard to reside within the Exif Sub-IFD now reside directly under the first (main) TIFF IFD.
  • The Exif IFD Sub-IFD, Interoperability Sub-IFD and the MakerNote Tag have all been omitted.
  • Unlike the TIFF 6.0 standard, the TIFF/EP standard defines a method of dealing with thumbnail images. This however is different from the method that is used in the Exif standard.
  • Several tags defined by the Exif standard have been re-defined in the TIFF/EP standard – see table below.
TIFF/EP Tag#Exif Tag#Tag Name
920B16A20B16FlashEnergy
920C16A20C16SpatialFrequencyResponse
920E16A20E16FocalPlaneXResolution
920F16A20F16FocalPlaneYResolution
921016A21016FocalPlaneResolutionUnit
921416A21416SubjectLocation
921516A21516ExposureIndex
921716A21716SensingMethod
828E16A30216CFAPattern

Compression

Images in TIFF/EP files may be stored in uncompressed form, or using JPEG baseline DCT-based lossy compression. TIFF/EP also allows usage of other compression methods, but TIFF/EP readers are not required to decompress these images. All TIFF/EP readers shall support the DCT (lossy) baseline version of the TIFF/JPEG compression method described in TIFF 6.0 Technical note #2. The JPEG compression is indicated using a value of 000716 in the Compression tag-field as a binary value.[4]

There may be more than one image (subfile) in a TIFF 6.0 file. Each subfile is defined by Image File Directory (IFD). If an image compression method is used in TIFF/EP, an uncompressed Baseline TIFF-readable "thumbnail" image (with a reduced-resolution) should also be stored in the 0th IFD of TIFF/EP, to allow the images to be viewed and identified using a Baseline TIFF 6.0 reader. (Note: JPEG compression is not required for Baseline TIFF 6.0 readers.)[4]

TIFF/EP files may optionally use lossless JPEG compression and other JPEG compressions, but TIFF/EP readers are not required to decompress these images. If the lossless JPEG compression is used, the recommended form is lossless sequential DPCM using Huffman coding. TIFF/EP files may also optionally support vendor unique compression, but TIFF/EP readers are only required to open the uncompressed "thumbnail" image that may be present in IFD0. Proprietary compression methods can be used by obtaining a private compression tag value from the TIFF administrator (Adobe).[4]

TIFF/EP complies with the TIFF 6.0 specification. The reason is to maintain compatibility with existing TIFF readers, and to make the adoption of TIFF/EP as easy as possible.

The TIFF Tag 259 (010316) stores the information about the Compression method. Its use is mandatory in TIFF/EP. There is no default value in TIFF/EP, but the tag value shall equal "000116" for the thumbnail IFD. The following is a list of defined TIFF/EP compression schemes:[4]

TIFF/EP Compression Tag values
Tag valueCompression schemeDescription
000116UncompressedShall be supported by TIFF/EP readers; shall be used for the thumbnail IFD; may be used for images
000716TIFF/JPEG compression ('new-style' JPEG)TIFF/EP readers are only required to support Baseline DCT JPEG method
Other values > 7FFF16Vendor unique compression methodsTIFF/EP readers are not required to support these compressions

Timeline for development and revision

Dates limited to publicly available sources:

Date Event
1998 A DIS (Draft International Standard) of TIFF/EP was available from ISO.[5][6]
2001 TIFF/EP was ratified and published by ISO as an International Standard.[7]
2006 TIFF/EP began its 5-year revision cycle by ISO Working Group WG18.[8]
2007 (March) An email from WG18 stated "The Adobe DNG format was derived from this standard and the group has Adobe's permission to incorporate modifications and developments made for DNG in the new standard".[9]
2008 (May) There was further confirmation that Adobe had offered the DNG specification to ISO as part of ISO's TIFF/EP standard.[10]
2008 (September) Minutes of ISO/TC 130/WG2 — Prepress Data Exchange, 37th Meeting: "WG 18 is revising the two-part standard (ISO 12234), which addresses digital camera removable memory. The revision of Part 1 will add JPEG2000; the revision of Part 2 will add DNG into TIFF/EP."[11]
2009 (September) Minutes of ISO/TC 130/WG2 — Prepress Data Exchange, 39th Meeting: the revision "is comprehensive to support many different use cases, including backward compatibility with current TIFF readers and support of Adobe DNG. There are two interoperability profiles defined: Profile 1 (proposed extension .tif) will provide an intended output-referred interpretation (reproduction color appearance), supporting any color encoding that can be supported using an ICC profile, including output-referred, scene-referred, and demosaiced camera raw... Profile 2 (proposed extension .dng, if Adobe is in agreement) is intended for camera raw images, including un-demosaiced images... This format will be similar to DNG 1.3, which serves as the starting point for development."[12]

See also

References

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