Re: [Openexr-devel] 3dsMax OpenEXR support

[Florian Kainz]

Florian Kainz wrote:
> 
> 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.


As Greg Ward pointed out, screenWindowCenter and screenWindowWidth
were not documented anywhere on our web site.  This has been fixed.
Look for a picture of a coordinate system roughly in the middle of
http://www.openexr.com/details.html.

Florian