pdunlave at cs.williams.edu
Thu Apr 8 12:12:44 EDT 1993
>>>>>> IMPORTED MESSAGE <<<<<<<<<<<<<<<<
Is there any direct or indirect way to convert PICT and/or TIFF files to
raster files for grass4.0?
Not being a GRASS-user myself, I don't know the answer to this question,
but I have dealt with PICT and TIFF a bit. Neither is a "simple" raster
format, rather they can contain multiple image elements. In the case of
PICT, these elements can be bit maps, pix maps, or geometric primitives
(objects). TIFF files consist of one or more images, each one associated
with a number of "tags" that describe various parameters of the image.
There are required tags for things like the image dimensions, bit-depth,
etc., optional tags that are part of the official TIFF specification
(things like image name, gamma correction, etc.), and user-defined tags
(that could be used to, for example, map image coordinates to world
coordinates). TIFF sub-images can be compressed, they can be tiled,
different resolution versions of the same image can be contained in the
same file (e.g. thumbnail version). I've written programs that generate
TIFF files that can be read by other programs - this is pretty easy.
What's not so easy is writing something that can deal with all the possible
variations that can come at you, though if you're fairly certain as to
what you'll be getting most of the time (e.g. always 256 level gray-scale,
uncompress, not tiled), writing a TIFF reader should not be too hard.
This goes for PICT reading also. The Mac Toolbox provides calls to
interpret most standard PICT primitives. You can find out more than
you ever wanted to about PICT in Inside Macintosh. Aldus is the author
and guardian of the TIFF specification. They'll sell you the TIFF
developers toolkit for about $50 (call the Aldus Developers Desk (206)
628-6593) which includes a lot of useful C code as well as the official
specification. Hewlett Packard supposedly has a TIFF compression/
decompression library that is free for the asking.
Pat Dunlavey pdunlave at cs.williams.edu
59 Saulnier Drive (413) 458-9836
Williamstown, MA 01267
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