[Openexr-devel] congratulations and thanks, but...

[Dana Batali]

Congratulations and thanks to ILM and NVidia for the promotion of HDR 
images and the contribution of OpenEXR!  We're considering adding 
support for it to Pixar's RenderMan but, in a brief scan through the 
description on the web site, I've identified a few important 
(critical?) limitations:

1. the format doesn't appear to support image tiles.
Can this be true?  If so, I suggest that this is an important flaw that 
should be corrected at the earliest possible moment.  Specifically, the 
format appears to be exclusively scan line oriented.  For many 
applications it is more convenient and efficient to store data in 
regular rectangular "tiles".  For example, both TIFF and Maya's IFF 
formats support tiles.

2. the format doesn't appear to support multiple images.
The idea here it may be useful to store a related collection of images 
within a single file. Each image has it's own resolution and 
independent channel specs. We need to store image pyramids in a single 
file.  There are numerous other situations where this feature is 
required.

3. the format doesn't appear to support different compressors for 
different channels.
Kudos for allowing arbitrary numbers and combination of channels per 
image! Given this potential mix of data types (and even image contents 
(imagery versus alpha, for example)) you'll be able to get smaller 
files by supporting per-channel compression types.

These are the off-the-top-of-my-head reservations about this new file 
format. The new 16bit floats and the associated compression 
methodologies are superior to anything publicly available that I'm 
aware of.  The arbitrary channel count is also very desirable.   But 
the limitations outlined above aren't present in TIFF and Maya's IFF 
and might impede the widespread adoption of this format.

I hope someone can tell me I'm missing something?

Thanks,
Dana Batali
RenderMan Products
Pixar Animation Studios