Six degrees of freedom in an “virtual reality head mounted display” (VR HMD) means that the visual sensations you perceive are the same as in the real world. That is, perceiving parallax and stereography at the same time.
So far these images, used in VR games, have been produced using “computer generated images” (CGI). A 3D stage is built in equirectangular format and then 6 different renderings are made to obtain the six degrees of freedom.
The six degrees of freedom are obtained thanks to parallax. Parallax is simply a capture or render with two points of view. When we alternate both points of view, the effect called “DISOCCLUSION” is produced, which allows us to see what is behind a column or a railing. Thanks to disocclusion we obtain the visual information that an algorithm cannot be invented.
In a “3D Facebook photo” made from a monoscopic image, the depth map will give us the sensation of parallax, but we will perceive blurred areas (marked in yellow) at the side photo. Using a stereoscopic image, when using the depth map, these blurred areas disappear. By moving the image to the right or left, we will see what we saw at the moment of capture on each of the cameras. So a stereoscopic image has parallax on the lateral axis
If we want to be able to move our head to the right and left we will need two side views. If we want to stand on tiptoe or bend our knees to see what is behind a railing, we need two vertical views. And if we want to move our nose forward or backward, we need two more longitudinal views. So a 6Dof image needs six different panoramas.
So as a summary, to obtain six degrees of freedom, we need parallax on the three axes, and the graphic representation of the 6dof frame is composed of three stereo-pairs.
Click on image to download it at 8K x 6.
WALKING INSIDE A PHOTO
ODSP photography should be understood as a frame of a “Virtual Tour” in which we can move in different directions. We can simply create a corridor, and follow the IKEA path. We will be able to create interceptions, and thus be able to walk through a museum. Or we can scan an entire room. The possibilities are endless. From creating a “Scape Room” to a “Museo del Prado” virtual tour.
THE PHOTOGRAPHIC CAPTURE
Let us consider as a point of non-paralax of our nonal head, the point where the three Cartesian axes cross.
The six cameras represent the nodal misalignment with which the six panoramas will be captured.
This capture is possible by using a nodal head and a tripod. It is hard work that requires precision. The process is long, because if we want a perfect quality, each panorama will be composed of 8 photos, so in total there will be 48 shots.
Post-production is also complex, and long, because you need a large computer capacity to render 48 APSC images.
There is another way to obtain a 6Dof panorama, it is a much simpler technique that only requires 18 shots. All you have to do is misalign the entrance pupil with respect to the point of no parallax in the nodal head. This misalignment must be done in the longitudinal axis and in the positive direction.
The capture is very easy, much more than we can imagine. Just imagine a Rhombicuboctahedron and take a picture on each square side.
First row: The first photo will be taken looking at the zenith. Second row: Descend 45º with the vertical arm, and take a 90º shot, 4 photos. Third row: Descend another 45º and take a 45º shot, 8 photos. Fourth row: Descend another 45º and take another 90º shot. Your 6Dof shot is ready.