exr/screenWindowWidth is calculated by the display driver the same way I described, so yes, it should give the same result.
However, I was not sure whether exr/screenWindowWidth is standard for all versions of the prman exr display driver. On Thu, Apr 28, 2011 at 2:22 PM, [email protected] < [email protected]> wrote: > I think I remember also doing it like this with the default prman metadata. > > H_aperture=node.metadata('exr/screenWindowWidth', frame_numb) > V_aperture=H_aperture/Aspect > > > On Thu, Apr 28, 2011 at 1:29 PM, Ivan Busquets <[email protected]>wrote: > >> The projection matrix from prman only stores a FOV, or the relationship >> between focal-length and horizontal aperture. >> If you want the "real" focal length values, you will need to know the size >> of your filmback. >> >> If you don't care about the "real" focal length value, you can still get >> the right projection values by setting the focal length to 1, and getting >> the filmback size like this (proj_matrix is a Matrix4 object filled from the >> exr/worldToNDC metadata key): >> >> lx = (-1 - proj_matrix[12] - proj_matrix[8]) / proj_matrix[0] >> by = (-1 - proj_matrix[13] - proj_matrix[9]) / proj_matrix[5] >> rx = (1 - proj_matrix[12] - proj_matrix[8]) / proj_matrix[0] >> ty = (1 - proj_matrix[13] - proj_matrix[9]) / proj_matrix[5] >> >> swW = max( lx , rx ) - min( lx , rx ) # Screen Window Width >> swH = max( by , ty ) - min( by , ty ) # Screen Window Height >> >> If you have access to the real filmback size (either from custom metadata >> or because you can assume you'll always be dealing with cameras that have >> the same filmback size), you could then get a "real" focal length value from >> filmBack.width / swW. >> >> Hope that helps. >> >> Cheers, >> Ivan >> >> >> 2011/4/28 Lucien Fostier <[email protected]> >> >>> Hi fellow tds >>> >>> I m trying to create a camera from exr metadata coming from prman. >>> >>> So i use the projection matrix world to camera which give me position and >>> orientation in space. >>> >>> Id like to extract the focal lenght from this data but i cant find how to >>> do it. >>> >>> May someone help me about this or give me some pointer? >>> >>> Thanks >>> >>> Lucien >>> >>> Envoyé de mon iPhone_______________________________________________ >>> Nuke-python mailing list >>> [email protected] >>> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-python >>> >> >> >> _______________________________________________ >> Nuke-python mailing list >> [email protected] >> http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-python >> >> > > _______________________________________________ > Nuke-python mailing list > [email protected] > http://support.thefoundry.co.uk/cgi-bin/mailman/listinfo/nuke-python > >
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