1999.12.01 17:39 "Re: ZIP compression [was: libtiff 3.5.3 release.]", by Bryan H. Maret

Libtiff uses a Compression value from the private range for ZIP compression - that's all that Sam could do without Adobe's official blessing. The actual TIFF 7 spec uses a Compression value from the "official" range for Deflate compression. Adobe's ImageReady uses the official value, since its developers had the benefit of the real spec.

regards-
-Bryan Maret (formerly Adobe's TIFF person)
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