.TIFF File Format
Description with Compix Private Tags
The Tag Image File Format (TIFF) was developed jointly by Aldus Corporation and Microsoft Corporation in conjunction with other interested parties. Specifically, the data is stored as "Class-P Palette color images" with accompanying palette data containing information about how this data was displayed at the time it was stored. For a complete description of TIFF data structures see pages 1 - 22 of the "Tag Image File Format Specification, Revision 5.0" dated 8/8/88. The TIFF file begins as follows:
The image file header
The image file directory
The tags begin immediately following the above header. The tags and their likely values listed below are not necessarily in the order that they will be encountered in the file.
4 bytes next_ifd = 0 signals end of tags
The main purpose of the data in private tag #1 is to enable COM6 (and any other software) to correctly interpret the real physical meaning of the data. Another purpose is to enable COM6 to redisplay the data as it was saved. Yet another requirement is to be able to restore the status of the Compix 6000 Thermal Imaging System when a previously uploaded file is downloaded back to the 6000. Hence, some items are unimportant to interpreting the data in any environment outside the 6000.
In the following descriptions of the data items contained in private tag #1 hexadecimal values are denoted with a suffix h.
The 193*244 = 47,092 byte image array is pointed to by TIFF tag# 273 and corresponds to the last 47,092 bytes of the old in-house format. In either case, the following description applies.
These bytes are stored beginning with the upper left corner, followed by the rest of the top row, and then proceeding down through the image row by row.
The temperature represented by each byte is calculated as follows:
0.1 * ( RefTemp + 10*( (ArrayByte - RefVal) * ---------- ) )