[Openexr-devel] Multipart backward compatibility?

[Dalai Felinto]

Hi there,

I'm working in supporting a multiview pipeline in Blender, and part of
this involves supporting OpenEXR multiview format. I'm currently
wondering what is the best option to save the images with the most
backward compatibility.

At first I considered dumping the data in a single-part file:

R
G
B
A
right.R
right.G
right.B
right.A

This works fine (open in an old exrdisplay for example) and is what I
get out of the multiview files generated with the exrmultiview
(exrmultiview left imgL.exr right imgR.exr imgLR.exr). I then went
back to re-read the documentation and it seems multipart was
implemented specially to take care of multiview.

""Multi-part files support multiple independent parts. This allows
storing multiple views in the same file for stereo images (...)"""

I then tried to convert the multiview exr with the exrmultipart
utility (exrmultipart -convert -i imgLR.exr -o imgLR_multipart.exr).

The result is this file:
http://dalaifelinto.com/ftp/multiview/sample-multipart.exr

The result loads in current Blender (showing only the left view of
course), but it actually fails to load in an old version of exrdisplay
(1.0.1-6) with the following error:

"""Cannot read image file
"/home/guest/Downloads/sample-multipart.exr". The file format version
number's flag field contains unrecognized flags."""

Is exrdisplay being picky or multipart is indeed not supposed to be
fully backward compatible?

My current implementation is exporting multipart files and that would
be likely fast for our loading pipeline too. Thus I wouldn't mind
sticking to it if they are known to be backward compatible. Otherwise
I will stick to single part.

Example of multiview-multipart exported from Blender:
http://dalaifelinto.com/ftp/multiview/blender-multiview-multipart.exr

Thanks for your time,
Dalai
--
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dalaifelinto.com