1997.03.04 07:05 "Re: Questions on proposed replacement TIFF/JPEG Spec.", by Rainer Wiesenfarth
I recently downloaded the README file located in the graphics/tiff section of the ftp site sgi.com and had some questions regarding the proposed replacement for the TIFF 6.0 TIFF/JPEG Specification.
You mention in the 'Overview of the solution' section that the JPEGTables field can be stored only once for a multi-segment TIFF file. First, is this 'field' also called a TIFF Tag? Second, am I correct that when you refer to a multi-segment TIFF file you are referring to a TIFF file with multiple images (i.e. a multipage TIFF file), or is "multi-segment" in reference to the JPEG compression? Third, if a multipage TIFF file is generated will each image that uses this proposed compression scheme require a separate JPEGTables field?
- Yes, it is a TIFF Tag.
- No, a multi-segment TIFF _image_ is an image that consists of more than one strip or tile. As I understand it, JPEGTables is stored for one image and applies to all strips/tiles of this image. These strips/tiles are JPEG compressed individually.
- Yes. JPEG compression is not a matter of a TIFF _file_, but of TIFF _images_. If more than one image form a file, each of these images has it's own JPEGTables. Furthermore, it is even possible (though not common) to have e.g. three images in a file where the first is a JPEG compressed RGB image, the second a uncompressed greyscale and the third a CCITT whatever compressed bilevel image.
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