Re: [Openexr-devel] 3dsMax OpenEXR support

[Florian Kainz]

An xViewAngle attribute may not be necessary; the OpenEXR file header 
already has a few required attributes that are meant to describe the 
view pyramid.

- pixelAspectRatio (type float) defines the aspect ratio (width over
  height) of a single pixel.  Together with the display window,
  pixelAspectRatio defines the image's aspect ratio.
  
- We assume that the image is produced by a pin hole camera with the
  pin hole at the coordinate origin.  The camera points into positive
  z direction, and projects the image onto the z == -1 plane (the
  "projection plane".

  The (display window of) the image stored in the file corresponds to
  a rectangular region in the projection plane, the "screen window".
  The screen window's center and width are defined by the header's
  screenWindowCenter (type V2f) and screenWindowWidth (type float)
  attributes.  The screen window's height is equal to screenWindowWidth 
  divided by the image's aspect ratio.
  
This definition of the view pyramid is more complicated than the
xViewAngle, but it allows oblique view pyramids where the projection
center does not coincide with the center of the image (for example,
in photographs taken with wide-angle shift lenses).  If necessary, 
the definition can also be expanded for orthographic views.


Drew Hess wrote:
> 
> Cool.
> 
> Greg Ward posted something to the (old Sourceforge-based?) list awhile ago
> proposing some standard names and datatypes for some of these attributes.
> I think he's already using them in his Photosphere application.  I've
> cut-and-pasted them below for reference.
> 
> As we get more of these plugins, I think it would be in everyone's
> interest if use a standard set of attributes.  Let's start with Greg's
> list.  If you have things to add or would like to modify something, post
> it to the list so we can get feedback from others who are developing
> plugins.  (I realize as I'm writing this that our own Renderman display
> driver doesn't use any of these yet.)
> 
> thanks!
> -dwh-
> 
> -----
> 
> I don't know if this is the right forum, but I wanted to suggest
>  standardizing the following header attributes in OpenEXR:
> 
>  "capDate"              a StringAttribute that records the date the image
>                         was created/captured in standard Exif format,
>                         i.e., "YYYY:MM:DD HH:MM:SS"
> 
>  "sampToNits"           a FloatAttribute that gives the absolute scale to
>                         get from sample values to Nits (cd/m^2) for the
>                         purposes of photometric calibration
> 
>  "xDensity"             a FloatAttribute for the standard horizontal
>                         output density, in pixels per inch.
>                         We could also specify yDensity, but this is
>                         redundant (and therefore  dangerous)
>                         with respect to the existing "pixelAspect" and
>                         image size information
> 
>  "xViewAngle"           a FloatAttribute for the horizontal view angle of
>                         a perspective image in degrees.
>                         Again, we could have yViewAngle, but this would be
>                         redundant as well
> 
>  "focus"                a FloatAttribute for the world focus distance, in
>                         meters
> 
>  "owner"                a StringAttribute giving the content owner's name
> 
>  "comments"             a StringAttribute with additional image information
> 
>  Of these, the first two are the most critical as far as I'm concerned.
>  Any thoughts on others?
> 
>  -Greg
> 
> 
> On Tue, 15 Apr 2003, Steve Blackmon wrote:
> 
> > Greetings All,
> >
> > I just wanted to drop a note to the list to mention that we are
> > finishing up an OpenEXR 3dsMax Bitmap I/O plugin.  The binary will be
> > freely available via our website in the coming few days, with builds
> > supporting 3dsMax R3,R4, and R5.  Once the plugin is released and any
> > outstanding issues are resolved, we plan to spend some extra time
> > polishing up the code, after which we would like to submit the plugin
> > source for inclusion in the OpenEXR distribution.
> >
> > The plugin includes full support for writing all the standard 'g-buffer'
> > channel data from 3dsMax, including z-buffer, object id, material id,
> > velocity data, etc., with user specifiable attribute identifiers to
> > allow for maximum compatability with various compositing applications
> > and other software that supports OpenEXR.  The plugin will also provide
> > the option to embed some scene specific information in the file
> > including camera transform data and projection information such as FoV
> > and Aperture.
> >
> > It's been a bit of a bumpy ride getting this working, but we're very
> > happy with the results (thanks to the great work by the folks at ILM.)
> > Great job guys, this format rocks :)
> >
> > -Steve Blackmon
> >
> > -------------------------------------------------------------
> > 'I know a song, would you like to hear it.  Daisy...daisy...'
> > address@hidden
> >
> > Brazil r/s
> > SplutterFish LLC
> > www.splutterfish.com
> >
> >
> >
> > _______________________________________________
> > Openexr-devel mailing list
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> > http://mail.nongnu.org/mailman/listinfo/openexr-devel
> >
> 
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