91 lines
4.5 KiB
Plaintext
91 lines
4.5 KiB
Plaintext
Date: Fri, 01 Aug 1997 20:14:52 MDT
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To: Sam Leffler <sam@cthulhu.engr.sgi.com>
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From: "Conrad J. Poelman (WSAT)" <poelmanc@plk.af.mil>
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Subject: Potential TIFF library additions
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Delivery-Date: Fri, 01 Aug 1997 19:21:06 -0700
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Sam,
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You probably don't remember me, but I sent in a couple of bug fixes
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regarding the TIFF library about a 16 months ago or so...
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I just wanted to send you two other additions that I have made to our
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local version of the TIFF library in hopes that you will want to
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incorporate them into your next major release of the TIFF library.
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(These additions are based on TIFF version 3.4beta31, but they sit on
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top of the library so they shouldn't be much trouble to incorporate them
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into any more recent version.) They are internally documented to a
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reasonable extent and we've been successfully using them in our code
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here for over a year. If you think they would make good additions to the
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TIFF library, I'd be happy to clean them up more, document them more,
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and/or integrate them with the latest version of the TIFF library, but I
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figured I'd see if you were interested in using them before I went to
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all that trouble.
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TIFF Image Iterator
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-------------------
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Your ReadRGBA() routine works well for reading many different formats
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(TILED, STIP, compressed or not, etc.) of the most basic types of data
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(RGB, 8-bit greyscale, 8-bit colormapped) into an SGI-style data array,
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and serves as a good template for users with other needs. I used it as
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an example of how to make an iterator which, rather than fill a data
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array, calls an arbitrary user-supplied callback function for each
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"chunk" of data - that "chunk" might be a strip or a tile, and might
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have one sample-per-pixel or two, and might be 8-bit data or 16-bit or
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24-bit. The callback function can do whatever it wants with the data -
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store it in a big array, convert it to RGBA, or draw it directly to the
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screen. I was able to use this iterator to read 16-bit greyscale and 32-
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and 64-bit floating point data, which wasn't possible with ReadRGBA().
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I have tested this routine with 8- and 16-bit greyscale data as well as
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with 32- and 64-bit floating point data. I believe nearly all of our
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data is organized in strips, so actually I'd appreciate it if you had
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some tiled images that I could test it with.
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It should certainly be possible and would be cleanest to reimplement
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ReadRGBA() in terms of the image iterator, but I haven't done that.
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Private Sub-Directory Read/Write
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--------------------------------
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TIFF-PL is a Phillips Laboratory extension to the TIFF tags that allows
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us to store satellite imaging-specific information in a TIFF format,
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such as the satellite's trajectory, the imaging time, etc. In order to
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give us the flexibility to modify the tag definitions without getting
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approval from the TIFF committee every time, we were given only three
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TIFF tags - a PL signature, a PL version number, and PL directory
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offset, which lists the position in the file at which to find a private
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sub-directory of tags-value pairs. So I wrote two routines:
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TIFFWritePrivateDataSubDirectory(), which takes a list of tags and a
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"get" function and writes the tag values into the TIFF file, returning
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the offset within the file at which it wrote the directory; and
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TIFFReadPrivateDataSubDirectory(), which takes an offset, a list of
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tags, and a "set" function and reads all the data from the private
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directory. The functions themselves are pretty simple. (The files are
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huge because I had to basically copy all of the tif_dirread.c and
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tif_dirwrite.c files in order to access the various fetching routines
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which were all declared static and therefore inaccessible in the TIFF
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library.)
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I'm including the four source files (tif_imgiter.h, tif_imgiter.c,
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tif_pdsdirread.c, tif_pdsdirwrite.c) in case you want to take a look at
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them. I can also send you some sample code that uses them if you like.
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If you're interested in having them incorporated into the standard TIFF
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library, I'd be happy to do that integration and clean up and document
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the routines. (For example, I've already realized that instead of
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limiting the SEP callback function to three bands (R,G,B) it should take
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an array to enable the handling of n-banded multi-spectral data...) If
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not, I'll just leave them as they are, since they work fine for us now.
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Holler if you have any questions.
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-- Conrad
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__________________________________________________________________
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Capt Conrad J. Poelman PL/WSAT (Phillips Laboratory)
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505-846-4347 3550 Aberdeen Ave SE
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(FAX) 505-846-4374 Kirtland AFB, NM 87117-5776
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