2005.08.04 15:33 "Re: [Tiff] tiff unknown field of tag", by Steven Woody

i got back some scaned tiff's from a photo lab. openning with xv or gimp

just got a warning message: unkown field of tag 34665(0x8769). i want to know

>> what's wrong with thoese files and how do a work around.

The warning does not mean there is something "wrong" with the file, it just means that there is a tag in the file that libtiff does not support. Usually this is benign.

for the tiffinfo output, i still has two questions desiring kind help from you.

1. what means "ICC Profile: <present>"? and what is ICC?

ICC is the International Color Consortium (http://www.color.org/) and an ICC profile is a type of reference "lookup table" which ensures accurate color as long as the using software also properly support ICC profiles. It allows you to do things like print your photo to a printer (which also has an ICC profile) and obtain accurate color.

what will happen if the ICC embeded in my pic differ with the ICC in the printer?

and, i also heard photographers talk about color spaces such as sRGB, which are also some kind of lookup tables. is there any relation between ICC and color space?

2. i noticed this file is uncompressed. so what's the benefit the lab save

>> result in tiff rather than a bmp?

While the latest BMP version supports attaching ICC profiles, many software packages will simply fail to load the BMP entirely. TIFF is seen as a format used by "professionals" and is well supported by desktop publishing software. As far as the actual image goes, a 24-bit BMP is just as good as a 24-bit TIFF.

i noticed that tiff support loseless compression, in this case, i beleive that tiff will be as good as bmp up to the image quality. but if or not tiff supports loss compression? in this case, i think image quality will going down. right?

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/

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steven woody (id: narke)