Message-Id: <199709251620.JAA24036@dns.ccit.arizona.edu> Date: Thu, 25 Sep 1997 06:56:59 +0000 From: "Louis H. Sharpe II" <mailto:lsharpe@PICTUREL.COM> Subject: Re: TIFF Formats To: mailto:IMAGELIB@LISTSERV.ARIZONA.EDU
At 04:07 PM 9/19/97 +0200, you wrote:>I am looking for a reference that will explain the difference in TIFF
>files, especially TIFF 4 and TIFF 5, compressed and uncompressed. Also,
>software that can convert TIFF 5 and TIFF 5 compressed to TIFF 4 and
>TIFF 4 compressed.
Reading between the lines, I am wondering if you have a piece of software which claims to read TIFF 4 files, which is choking on some later vintage file you are submitting to it.
In that narrow context or in the wider one of your question, there are a few things to say.
1. TIFF files of a single version still come in multiple "flavors," each supporting different compression types, pixel depths, number of colors, etc.
2. The practical difference between files having different TIFF versions may well be much smaller than the difference between TIFF files of the same version which are of different "flavors."
3. The above said, the best approach is to "dump" the structure of the offending ("TIFF 5") files and of an instance of the files of the desired ("TIFF 4") type. This is most easily accomplished using a public domain DOS utility we have compiled and placed on our web site at:
http://www.picturel.com/utils.html
The utility is called TIFFLOAD.EXE. After downloading to an appropriate machine, run the command lines:
tiffload tiff5im.tif > tiff5im.txt tiffload tiff4im.tif > tiff4im.txt
A careful look at the two text files will tell you what the differences are.
4. These differences may be of several sorts:
a. The TIFF 5 file may have compression types not supported in TIFF 4 (likely). In particular, the early TIFF versions used a variant version of CCITT Group 3 compression (sometimes called "TIFF Group 3") for binary images, which has no end of line (EOL) codes. This method is no longer advisable to use. b. The TIFF 5 file may have tags not supported in TIFF 4 (guaranteed, but good TIFF readers are supposed to ignore tags they do not understand, without dying). Utilities exist to remove tags deemed offensive, although important semantics can be lost in this way. One utility called tiffcp is available on a wide variety of machines as part of the libtiff TIFF library package (a good TIFF dumper is also included).
I seem to have mislaid my copies of the TIFF 4 and 5 specifications. If anyone can provide a copy of either, I would be grateful.
Hope this helps!
Lou
Louis H. Sharpe II mailto:lsharpe@picturel.com Picture Elements, Inc. +1 303-444-6767 410 22nd Street, Boulder, CO 80302 USA fax +1 303-415-1392 http://www.picturel.com PGP Key Available: http://www.pgp.com