PNG and MNG tools EXIF and PNG

Converting TIFF-EP or EXIF files to PNG format (Draft 0.0, July 30, 2000)

Notices:

Copyright 2000, Glenn Randers-Pehrson, randeg@alum.rpi.edu, all rights reserved.

You may link to this file or (preferably) to the directory in which it resides, but please do not copy this file to your web site. If and when this document emerges from draft status, it will be released on more generous terms, identical to those of the PNG extensions document [PNGEXT].

Status of this document

This is a draft of a proposal to the PNG Development Group for registration of a new text keyword (EXIF) or a new special-purpose chunk (eXIf or eXIF). It has not been approved by any approving body.

This document and the latest version of this document can be found at <http://pmt.sourceforge.net/exif>. If at some date the files move to another site, I intend to leave a link to the new location here, if possible.

Scope:

This document proposes a new PNG [PNG] registered keyword, "EXIF", and may propose a new PNG special-purpose chunk, "eXIf" or "eXIF" or both. It shows how to preserve the EXIF information [EXIFFORMAT] that is present in a TIFF-EP [TIFF-EP] file, when converting the file to PNG or JNG [JNG] format (JNG is a sub-format of the MNG (Multiple-image Network Graphics) [MNG] format.

Mapping of TIFF-EP data to PNG chunks:

Tags that provide details about the TIFF compression itself are no longer useful and are dropped. Other tags can be converted to existing PNG chunks, or to a tEXt/zTXt/iTXt chunk using the "EXIF" keyword, as shown in this table.

Usage of the proposed EXIF text keyword

All of the EXIF information should be written in a single text EXIF chunk (multiple chunks can be used, provided that no particular tag appears in more than one of them), with a newline terminating the data for each item. In TIFF-EP tags whose data is a string ending with a null, the terminating null is replaced with a newline character, and embedded newlines are permitted. Any CRLF sequences in such strings are replaced with the newline character. If any character outside the Latin-1 character set is present (which would violate the TIFF-EP Standard but might happen anyway), the strings must be converted to UTF-8 format and the iTXt chunk must be used. The data field of the text chunk must begin with the EXIF keyword plus a caution not to edit the data manually:

EXIF\0Caution: Do not manually edit the data in this chunk.\n

Software

Software applications for converting to and from the PNG format are beyond the scope of this document. It is clearly evident that Thierry Bousch's exifdump [EXIFDUMP] software could be easily modified to do the job.

Issues to be resolved:

• Use of text chunks versus defining a new "eXIf" or "eXIF" chunk.

• Items marked with "?" in the table.

• Get a copy of the actual EXIF spec.

• Converting "EXIF/JPEG" files to JNG.

• Integrate this proposal with the DCF (Digital Camera Format) standard.

• Extending this proposal to address saving the EXIF thumbnail image. That can be done with MNG (the "very low complexity" version, MNG-VLC [MNG-VLC]) but not with PNG or JNG, which are single-image formats.

• Approval of this proposal by the PNG Development Group according to the PNG specification.

References:

[EXIFDUMP] Bousch, Thierry, exifdump.py, v 1.13 (Python source code for exifdump), 1999/08/21, available at
http://topo.math.u-psud.fr/~bousch/exifdump.py

[EXIFFORMAT] Tachibanaya, TsuruZoh, "Description of Exif File Format", Revision 1.2, July 19, 2000, available at
http://www.butaman.ne.jp/~tsuruzoh/Computer/Digicams/exif.html (Japanese) http://www.butaman.ne.jp/~tsuruzoh/Computer/Digicams/exif-e.html (English)

[EXIFSPEC] I have not seen the formal specification of the EXIF format. It is not available on-line.

[JNG] Randers-Pehrson, Glenn, et. al., "JNG (JPEG Network Graphics) Specification, version 0.97, February, 2000, available at
ftp://swrinde.nde.swri.edu/pub/mng/documents.

[MNG] Randers-Pehrson, Glenn, et. al., "MNG (Multiple-image Network Graphics) Format, version 0.97", February, 2000, available at
ftp://swrinde.nde.swri.edu/pub/mng/documents.

[MNG-VLC] Randers-Pehrson, Glenn, et. al., "MNG-VLC (Multiple-image Network Graphics--Very Low Complexity) Format, version 0.97", February, 2000, available at
ftp://swrinde.nde.swri.edu/pub/mng/documents.

[PNG] Randers-Pehrson, Glenn, et. al., "PNG (Portable Network Graphics) Specification, version 1.2", July, 1999, available at
ftp://swrinde.nde.swri.edu/pub/png/documents.

[PNGEXT] Randers-Pehrson, Glenn, et. al., "Extensions to the PNG 1.2 Specification, version 1.2.0", July, 1999, available at
ftp://swrinde.nde.swri.edu/pub/png/documents.

[TIFF-EP] ISO/DIS 12234-2, "Photography---Electronic still picture imaging--- Removable memory---Part 2: Image data format---TIFF-EP", November 24, 1998, available at
http://www.pima.net/standards/iso/standards/documents/N4378.pdf

[HOME] | [UP]