Hi Lars, I only ever created stereo slide pairs using vwright, in which case, simply moving the slides closer together a small amount alleviated any discomfort. It amounts to the same as -vs (modulo the image borders).
I wrote vwright before introducing the notion of viewing distance (the length of the -vd vector). I could add an option to vwright for the screen distance that would take the view distance and turn on the kind of automatic adjustment you propose. I don't have any way to test it, unfortunately. Do you think the adjustment of -vh is really necessary? Regardless of what you do with it, the borders will not match for all objects, anyway. Cheers, -Greg > From: "Lars O. Grobe" <gr...@gmx.net> > Date: April 9, 2012 1:45:04 PM PDT > > Hi all, > > I just found that vwright, which looked like the perfect tool to support > stereoscopic image pair generation, generates a new view by simply > moving the view-point -vp. This does not consider the fact that our eyes > (hopefully) are able to focus on an object, not looking parallel into > infinity. So my resulting frames do not really match (I tried it and it > looked ugly...). Paul Bourke provides a great page explaining the > background of such stereo pairs on his website: > > http://paulbourke.net/miscellaneous/stereographics/stereorender/ > > To correct this, I would propose to manipulate the -vs and -vh > parameters in the view file generated by vwright. I am not that great in > doing reprojections, but from what I understand, this should work. I > have made a simple sketch to visually explain what I attempted to do > (and probably what I did wrong): > > web-browsers with svg-support > http://static.larsgrobe.de/stereoscopic_vwright.svg > > pdf of the same sketch > http://static.larsgrobe.de/stereoscopic_vwright.pdf > > Here is my approach: > > e [scene units]: eye seperation > is given as input to vwright, known > > f [scene units]: distance from either eye point to the image plane > can simply be calculated from view direction vector vd_x, vd_y, vd_z: > f = sqrt(vd_x^2+vd_y^2+vd_z^2) > > alpha [degrees]: half horizontal view angle > can simply be calculated from view's vh: alpha = vh/2 > > a [scene units]: alpha projected on the image plane > a = f * tan(alpha) > > 1) Calculate horizontal shift value vs for views: > > vs [] : shift fraction (eye separation e / projected image width 2*a) > can be calculated from above as vs = e / 2*a > > For the left view, I modify vs as above, for the right view I use its > negative value. > > 2) Correct the horizontal field of view vh for views: > > The stereoscopic image can be displayed only the overlapping image area > for both views. Thus we need to cut the left border from the left and > the right border from the right view. > > beta [degrees]: the angle corresponding to this border (having the same > width as the eye separation, but being located in the image plane) > calculated as beta = alpha - atan ( (a-e)/f ) > > This allows calculating the corrected horizontal view angle vh_corr, > which will replace the vh in my view files: > > vh_corr [degrees]: corrected horizontal field of view > as vh_corr = vh - beta > > 3) The full procedure: > > - take a view, derive left and right views from it by running vwright > (+/-) e/2 > > - calculate vs and vh_corr and replace the corresponding values in both > views > > - render, take on your glasses, and enjoy stereoscopic 3d images.... > > I hope this is correct, for me it gave results looking much better then > those by simply using vwright's view parameters. I think that having > this in vwright as an option (either active by default, or, to preserve > backwards compatibility, switched by e.g. -s as stereographic) would > make rendering of stereo pairs with Radiance much more fun. > > Any comments? Cheers, Lars. > _______________________________________________ Radiance-dev mailing list Radiance-dev@radiance-online.org http://www.radiance-online.org/mailman/listinfo/radiance-dev
