Re: [Openexr-devel] Unit scale for Z values

On Thu, Jan 14, 2016 at 4:19 PM, Larry Gritz <address@hidden> wrote:

OIIO 1.6.9 has the -mulc command, but it doesn't work properly with deep images -- that was fixed/added (um, now that you mention it, likely at your request) to the master at the time when I was trying to freeze 1.6 for a release. It seems to be working and safe, so I'll backport it to 1.6, in case it's helpful.

Seems to me that making the IlmImf library itself try to be too smart about unit conversion and scale things under the covers might create as many problems as it solves, but I think it's a really good suggestion for apps (like Houdini or Maya) to apply a scale when writing depth channels -- after all, they know what units they are computing in.

Another thing that may be good practice is to recommend a particular metadata name that reveals what units the depths are in ("DepthUnit" -> "meter" or whatever) and then presumably a really smart Nuke deep merge node might apply appropriate scales to make sure the operand images are in the same space, if they both have documented units but don't match.

-- lg

On Jan 14, 2016, at 4:02 PM, Jason Iversen <address@hidden> wrote:

Hi Larry,

Thanks, and yes - I was one of the people who at least chorused with the request to be able to apply a z-scale within oiiotool. We just installed 1.6.9 here; does that have the -mulc feature?

My question is definitely aimed at the idea of support for automatic conformance to try to aid interchange without incurring pipelining - ie, tracking of originating scale and destination scale, and generating intermediates.

Thanks,

Jason

PS. I have the same question poised for Alembic :)

On Thu, Jan 14, 2016 at 11:13 AM, Larry Gritz <address@hidden> wrote:

I'm not sure if this addresses your question directly (which seemed to be more about automatic conformance to a unit scale upon read/write?), but as far as converting the values of a deep file that already exists:

If you know that the z's are in decimeters and you want to convert to meters, and you know the channels of the file (let's say that you know that there are two channels, "A" and "Z"), you can do

oiiotool decimeters.exr -mulc 1.0,10.0 -o meters.exr

Basically just multiplying every alpha value by 1.0 (keeping it the same) and multiplying every Z value by 10.0 (converting decimeters to meters).

Sorry, I just checked and the deep support for "-mulc" is a recent addition, at this moment is in the "master" branch only. But I can backport it to a stable release branch if people need it.

> On Jan 13, 2016, at 12:27 PM, Jason Iversen <address@hidden> wrote:
>
> Hi all,
>
> Is there any mechanism in place, or planned, or rejected(!), for adjusting (deep) Z values to match a unit scale? In environments where you interchange deep EXR2's between packages which are working in different unit scales (eg. Maya in decimeters and Houdini in meters) you would want to convert to the unit scale to the hosted application upon read. I'd imagine you'd do this be comparing it to a unit-scale stored in metadata.
>
> Regards,
> Jason
>
>
> --
> Jason Iversen
> Production Technology Supervisor
> Digital Domain
>

--
Larry Gritz
address@hidden

--

Jason Iversen

Production Technology Supervisor

Digital Domain

--
Larry Gritz
address@hidden

Jason Iversen

Production Technology Supervisor

Digital Domain

From:	Nicholas Yue
Subject:	Re: [Openexr-devel] Unit scale for Z values
Date:	Fri, 15 Jan 2016 17:06:12 +1100
User-agent:	Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.5.1