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From: | Richard Hadsell |
Subject: | [Openexr-devel] Technical Introduction update ? |
Date: | Mon, 28 Mar 2016 16:56:37 -0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
There has been discussion on the [nuke-prerelease] e-mail list about
DWAA and DWAB compression with OpenExr 2.2. I checked the OpenExr
Technical Introduction, but was disappointed to see that it has not
been updated since November 2013. Is there any chance that someone
is working on an update? It is not difficult to use DWAA and DWAB compressions, which are available in the compression header. That is not the problem. The questions that I would like to see answered pertain more to lossy vs. lossless compression. The [nuke-prerelease] discussion included interesting information like this: On Thu, Mar 17, 2016 at 1:03 PM, Jonathan Egstad <address@hidden> wrote: ... > 3. Does the lossyness cause issues with data aov's, motion vectors, uv, position, normals, etc...? Yup - it will destroy data AOVs like normals, positions, etc.
I believe the codec recognizes typical color-channel names like
'r/R/red/RED', etc and only lossy compresses those. Channels it
doesn't recognize will get lossless compressed with I believe ZIP
- alpha for example is lossless compressed.
One gotcha is I think it traps 'Y/y, u/U, v/V' as valid color
channels and lossy-compresses those, which is a problem for xyz
and uv channels...
This is how our internal codec works so you might want to check
that the one in the official OpenEXR2.2+ release has these
behaviors.
...(end quote) It would be great to see a list of those special channel names. Are they the only channels that are compressed with DWAA/DWAB? What compression would be applied to the other channels? Does this behavior apply to all lossy compressions? I hope to see answers to these questions in an updated Technical Intro (eventually). -- Dick Hadsell 203-992-6320 Fax: 203-992-6001 Reply-to: address@hidden Blue Sky Studios http://www.blueskystudios.com 1 American Lane, Greenwich, CT 06831-2560 |
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