Re: [Openexr-user] Per-pixel Object Identifiers?

[Florian Kainz]

Storing plain integer IDs without any auxiliary data is already possible;
no additional work is required for that.  What I am proposing would be a
way to associate those integer IDs with additional information; I don't
think it would interfere with storing IDs that aren't mapped to lists of
strings.  The two types of data would simply be stored in separate channels.

Florian

Scott Squires wrote:
> I'm thinking of cases where the numeric values are processed and manipulated 
> where necessary.
> This makes it useful for other things than user ID of 3D objects such as 
> segments or or other aux data.
>
> Scott
>
>
>
> On Apr 14, 2011, at 5:04 PM, Florian Kainz wrote:
>
> > Hi Scott,
> >
> > Our use case for the object IDs would be kind of like this: "the skin on that
> > CG creature doesn't move right.  What is the creature's name, and which version
> > was used when this picture was rendered?"
> >
> > Storing object IDs directly in the pixels, without a lookup, seems to imply
> > that your production process identifies assets using 32-bit integers instead
> > of names.  10-digit numbers aren't very user-friendly.  Do artists really
> > refer to "asset number 3780456321" instead of "Davy Jones, version 3.4?"
> >
> > Florian
> >
> >
> > Scott Squires wrote:
> > > Yes, this would be useful.
> > > I'm assuming it might also be useful to have a simple version of this where a 
> > > ObjectID is simply saved as a UINT for each pixel without being
> > > forced to go through the lookup/remap process.
> > > That's doable now but if you're standardizing on ObjectID formats for EXR it 
> > > would it should probably be covered as well.
> > > Scott
> > > On Apr 14, 2011, at 3:13 PM, Florian Kainz wrote:
> > > > Hi,
> > > >
> > > > At ILM we want to implement a workflow where a computer graphics artist
> > > > can bring up an OpenEXR image of, say, a scene from Rango on his or her
> > > > screen, point to a pixel, and be find out that the object seen at that
> > > > pixel is called "Beans/dress/button3."
> > > >
> > > > This will require storing per-pixel object identifiers in an OpenEXR file.
> > > > In order to avoid re-inventing the wheel, I would like to find out if any
> > > > OpenEXR user have done something like this already. If you have done it,
> > > > would you be willing to share how you did it?
> > > >
> > > > Also, is there any interest in per-pixel object identifiers outside ILM?
> > > >
> > > > Florian
> > > >
> > > >
> > > > Unless somebody has a better idea, we'll probably do something like this:
> > > >
> > > >   Add a channel called objectID, of type UINT, to the image.
> > > >   If the image has multiple views, then add an objectID channel
> > > >   to every view.
> > > >
> > > >   Add an attribute called objectID to the header.  The type of the
> > > >   attribute is a map from unsigned integers to lists of strings.
> > > >   If the image has multiple views, then add multiple attributes
> > > >   with names of the form <view name>.objectID.
> > > >
> > > >   For each unsigned integer value that occurs in one or more pixels
> > > >   in the objectID channel, a corresponding map entry in the objectID
> > > >   attribute contains a list of all objects that are visible in those
> > > >   pixels.  More than one object may be visible in a given pixel because
> > > >   of transparency, motion blur, reflections, or anti-aliasing.
> > > >
> > > >   To find out which object or objects cover a given pixel, application
> > > >   software first looks up the value stored in the objectID channel for
> > > >   that pixel, then it looks up the corresponding list of object names
> > > >   in the objectID attribute.
> > > >
> > > >   In images with lots of transparency or motion blur any given object
> > > >   name may occur multiple times in the map from unsigned integers to
> > > >   string lists.  In order to save disk space the objectID attribute
> > > >   could be compressed by using a two-stage lookup, where the attribute
> > > >   contains two maps, one from pixel values lists of integer object
> > > >   identifiers, and one from object identifiers to object names.
> > > >
> > > >   With 32-bit UINT pixel values this scheme could run out of object
> > > >   identifiers for images with more than four Gigapixels, but in VFX
> > > >   production images that large are rare.
> > > >
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