In most 3D graphical content the true 3D proportions are not conserved. This is true both for stereoscopic and lenticular pictures. Special 3D pictures which preserve the true object proportions are called "Ortho-3D".
Making an Ortho-3D picture requires special photography. The rules for stereo ortho-3D photography ("Ortho-Stereoscopy") were discussed by me previously, and for lenticular photography in my recent book.
In stereoscopic pictures, Ortho-3D view is possible only from a single point in space. Multiview pictures, like 3D lenticular, offer Ortho-3D view from a relatively large viewing zone, thus creating a compelling virtual presence sensation, especially for imaged human objects.
The objects displayed in a 3D picture are usually scaled to fit the picture frame. In an Ortho-3D image all three spatial dimensions are scaled by the same factor. Therefore, the displayed depth is modified with respect to the unscaled object. For instance, if the scaling factor is 0.5, the displayed depth will be 50% of the original object depth. Pictures which display the object without scaling (or with a scale factor of 1) are called "Pure Ortho-3D".