Re: [Openexr-devel] OpenEXR 3D texture format

[Florian Kainz]

Hi Derek,

Right now there is no standard way to store 3D texture maps in OpenEXR
files.  You'll have to come up with your own method.  (In the long run,
OpenEXR should probably have built-in support for 3D pixel grids,
including mipmaps and ripmaps.)

As you mentioned, you could store a 3D pixel block with nx by ny by nz
pixels in a 2D image that is nx pixels wide by ny pixels high and has nz
layers.  Alternatively you could use a single-layer 2D image with a
resolution of nx by ny*nz pixels. (Or nx*nz by ny, or nx*ny by nz, etc.)

This should work well for single-level images, but with mipmaps and
ripmaps some amount of file space is wasted.  With any of the 2D workarounds
mipmap level L in the 2D image contains (nx*ny*nz / pow(2,-2*L)) pixels,
but in a true 3D mipmap, level L should contain (nx*ny*nz / pow(2,-3*L))
pixels.  Overall, a file using a 2D workaround will be about 16% larger
than a true 3D mipmap.

Florian

Derek Gerstmann wrote:
> Hi.  I just wanted to find out if there was a common structure
> that most developers are using to store 3d textures or volumetric
> datasets as OpenEXR image data.
>
> My initial idea would be to use the recent addition of layers
> to the ChannelList class to identify 2D slices of volumetric data,
> where such that "layername.channelname" identifies the volumetric
> slice and type of data allocated per channel, eg "Z0.A" would be
> the "A" channel of slice 0 along the Z axis.
>
> Anyone have any other suggestions or solutions they've adopted
> (other than arbitrary header tags)?
>
> Thanks!
>
> -[dg]
>
> ....
>
> Derek Gerstmann
> Jitter Engineer
> Cycling '74
>
>
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