People working out of OIIO master, please be aware of some changes from PR 
#1864 that I just merged, that are related to OCIO color transformations:

* ImageBufAlgo::colorconvert() and the various ocio_etc() functions have had 
the default value of their optional parameter 'unpremult' changed from false to 

Also, pertaining to oiiotool:

* oiiotool --colorconvert (and --ocio_etc) take an optional modifier, 
--colorconvert:unpremult=1 which causes the color transformation to be 
bracketed by an unpremult/premult pair internally. The default currently is =0, 
but we anticipate that in a later change we will set the default to 1.

* Explicit --unpremult now more clearly marks its output metadata as 
unpremultiplied, and you will get a warning from oiiotool if you do both 
--unpremult and specific unpremult=1 modifier to the color conversion.

* oiiotool --autocc now properly does an internal unpremult/premult when it 
does any color transformations. Previously, it did not, which I now think was 

I would strongly recommend using --colorconvert:unpremult=1 rather than an 
explicit --unpremult before and --premult after the color conversion (which is 
much more error prone -- it's easy to leave one out, or to accidentally edit 
the command line to have other operations inappropriately between them).

If your pipeline is one where your image filenames always embed OCIO color 
space names (e.g., foo_lnh.0001.exr or foo_vd16.0001.jpg), then I recommend 
using --autocc on your oiiotool command lines to automatically transform to 
linear space upon input and back to the named space upon output, rather than 
have explicit --colorconvert commands that merely do the same input->output 
transformations by hand.

Larry Gritz

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