LibTiff Mailing List

TIFF and LibTiff Mailing List Archive
November 1998

Previous Thread
Next Thread

Previous by Thread
Next by Thread

Previous by Date
Next by Date

The TIFF Mailing List Homepage
This list is run by Frank Warmerdam
Archive maintained by AWare Systems

1998.11.11 16:06 "Re: Four-gig limit?", by Ed Grissom

d_smith -

I asked a similar question on this list a couple of months ago (in a message
entitled "Large images (>2gb & >4gb)" )

I got very little response.

The scanners that we manufacture will also get close to the 4GB limit right
now, and since we always include reduced resolution "overviews" in our
images, this takes them over the limit.  Currently we disable creation of
files that would go over the limit.

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

There are basically two routes to go, and both require adding to the TIFF
spec to allow 64-bit data types and offsets:

One route is to have the initial IFD offset be 8 bytes instead of the
current 4.  This will break all existing TIFF readers, and will probably
require a version number change (from the current "42") to something else.

The other route is to always include a initial image that is less than 2 GB
that current viewers can understand.  This could either be a reduced
resolution version of the big image, or a warning page with text that says
"This image is >4 GB and cannot be read by this software".  Then, a private
tag in the first image could point to an hidden IFD that uses the 64-bit
offsets to access the big image.  The method could be codified into a Tiff
Technical Note that could be stored at archive sites so that anyone could
create / read these images.

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

The private tag idea comes from Niles Ritter, and the warning page idea was
suggested by Michel Plungjan.

I'd be glad to hear from anyone else that is running into this problem, and
send you my proposal for using the private tag method.  

I have yet to hear anything from Adobe about their plans for TIFF 7.0, but
this problem should surely be addressed in any revision to the TIFF spec.
Adobe's web page actually sounds like they are giving up maintenance of the
spec and point you to this mailing list for active development...


--
ed grissom
egrissom@ingr.com

> -----Original Message-----
> From:	d_smith@ecrm.com [SMTP:d_smith@ecrm.com]
> Sent:	Wednesday, November 11, 1998 8:02 AM
> To:	tiff@sgi.com
> Subject:	Four-gig limit?
> 
> We (and others) use various flavors of TIFF format as the preferred file
> format for representing bitmapped images to be output on our imagesetters.
> 
> One of our present imagesetters is mechanically and optically capable of
> producing images up to 80" long on 25" wide media at 3556 dpi resolution =
> 3.16 gig. As we experiment with, um, pushing out the envelope, we are
> discovering all sorts of fascinating software limitations in various
> things that start creeping in at about 2 gig. In particular, the TIFF spec
> presently seems to be limited to 4 gig maximum. Sort of like Y2K, this
> isn't a big issue for us now, but we see it becoming a real issue within a
> few years.
> 
> Are there any plans to support TIFF images >4 gig? Anyone doing this now?
> Official or unofficial extensions? Any real-world experience with giant
> TIFF files that would be worth sharing?