[Openexr-devel] Tiled OpenEXR format changes

[Florian Kainz]

When we announced OpenEXR 1.1.0 as a "development release",
we mentioned that it was possible that the tiled file format
would have to change before the official 1.2 release.

In the next release, OpenEXR 1.1.1, the format of tiled image
files will change in a way that is not compatible with version
1.1.0.  Scan-line based files will not be affected by this change.

While adding a new lossy compressor to the code, we discovered
a serious bug in how pixel data from different channels are
interleaved before they are sent to the compressor.  With the
existing lossless compressors, the bug affects only the tiled
file's compression factor, but lossy compressors scramble the
image.

Fixing this bug changes the tiled file format.  Since 1.1.0 is
a development release, and the fix affects many lines of code
in the IlmImf library, we will not attempt to maintain backward
compatibility with 1.1.0 in the library.  However, we will provide
a way to rescue any valuable tiled files you might have.

Florian