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

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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>>>> [email protected]
>>>> http://lists.nongnu.org/mailman/listinfo/openexr-user
> 
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