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---+ <nop>BigTIFF Design

This is a working place for preparing a 64-bit (larger than 4GB) TIFF format specification.	The design is based on a proposal by Steve Carlsen of Adobe, with input from various other parties. 


---++ Briefly

	* Version = 43
	* 8-byte offset to first IFD
	* Value/Offset fields are 8 bytes
	* 8-byte offset to the next IFD
	* add TIFFType of LONG8, an 8 byte (unsigned) int
	* <nop>StripOffsets and <nop>TileOffsets and <nop>ByteCounts can be LONG8
<br>

---++ More Detail

	* The Version ID, in header bytes 2-3, formerly decimal 42, now changes to 43

	* Header bytes 4-5 contain the decimal number 8.
		* If there is some other number here, a reader should give up.
		* This is to provide a nice way to move to 16-byte pointers some day.

	* Header bytes 6-7 are reserved and must be zero.
		* If they're not, a reader should give up.

	* Header bytes 8-15 contain the 8-byte offset to the first IFD.

	* Value/Offset fields are 8 bytes long, and take up bytes 8-15 in an IFD entry.
		* If the value is <= 8 bytes, it must be stored in the field.
		* All values must begin at an 8-byte-aligned address.

	* 8-byte offset to the Next_IFD, at the end of an IFD.

	* To keep IFD entries 8-byte-aligned, we begin with an 8-byte (instead of 2-byte) count of the number of directory entries.

	* Add TIFFTypes of LONG8 (= 16), an 8 byte (unsigned) int, and SLONG8 (= 17).

	* Add TIFFType IFD8 (=18) an 8byte IFD offset. 

	* <nop>StripOffsets and <nop>TileOffsets and <nop>ByteCounts may be LONG8 or the traditionally allowed LONG or SHORT. 

	* The proposed extension is ".tf8", and call it "8-Byte TIFF".

Otherwise, it's just like "original TIFF." ("TIFF Classic?")
<br>

--------------------
---++ Open Issues
	* What to call the new format
		* Main.ChrisCox -- I don't think end users will understand what "8-byte TIFF" means
		* Main.AndreyKiselev - 23 Sep 2004 -- What about TIFF64? "64" is a widely used buzzword and should be directly associated with the 64-bit offsets and 64-bit architectures.
	* What 3 character file extension to use (gotta be DOS compatible)
	* What 4 character file type to use (for Macintosh)
	* What MIME type to use

--------------------
---++ Samples

	* Example files from Steve Carlsen, see attachments below.

--------------------

---+++ Changes

	* TIFFType 13 is ttIFD, 14 is assigned to ttUnicode, and 15 is assigned to ttComplex.	So, I changed the types for ttLong8 and ttSLong8 to 16 and 17, respectively.
		* Main.AndreyKiselev - 23 Sep 2004 -- Where are these fields defined? Is there any new Technical Note or something? And what is encoding behind the word "Unicode"?
		* Main.ChrisCox - 27 Sep 2004 -- They are in the Adobe TIFF definitions.  I am still working on releasing updated TIFF documentation.

	* Added list of open issues
-- Main.ChrisCox - 15 June 2004

	* settle on version 43
	* cleanup
-- Main.ChrisCox - 14 Sept 2004

	* TIFFType 18 (8 byte IFD) added. 
	* Clarified that fields which may be LONG8 can also be one of the old supported types. 
-- FrankWarmerdam - 21 Sept 2004
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