Per-channel DWA compression scheme / custom clasifiers

[vmsrc]

Currently DWA compressed images use different compression schemes - LOSSY_DCT, RLE.
Compresson scheme upon EXR writing is determined using hard-coded classifiers - sDefaultChannelRules[].
Would it be possible to add ability for per-channel compression scheme selection?
Probably - by using custom channel classifiers?
This would make it possible to use lossless compression for the "Y" channel.
And this would make it possible to store coordinates or vector normals.
For example - storing "Normal.X", "Normal.Y", "Normal.Z", "WorldPosition.X", "WorldPosition.Y", etc.
Using lossy DCT does not work fine for such values, that could be negative values.

[peterhillman]

The ChannelList attribute does have space that future versions of OpenEXR could use to store flags that are per-channel hints to lossy compression algorithms.

An approach that's already possible is to use multipart files: store the RGB channels in one part using DWA compression, and all the XYZ in another part using a lossless compression type. That way you can pick the optimal lossless compressor to use.