3D visualization and stereographic techniques for medical research and education.Stud Health Technol Inform. 2001; 81:434-9.SH
While computers have been able to work with true 3D models for a long time, the same does not apply to the users in common. Over the years, a number of 3D visualization techniques have been developed to enable a scientist or a student, to see not only a flat representation of an object, but also an approximation of its Z-axis. In addition to the traditional flat image representation of a 3D object, at least four established methodologies exist: Stereo pairs. Using image analysis tools or 3D software, a set of images can be made, each representing the left and the right eye view of an object. Placed next to each other and viewed through a separator, the three dimensionality of an object can be perceived. While this is usually done on still images, tests at Mednet have shown this to work with interactively animated models as well. However, this technique requires some training and experience. Pseudo3D, such as VRML or QuickTime VR, where the interactive manipulation of a 3D model lets the user achieve a sense of the model's true proportions. While this technique works reasonably well, it is not a "true" stereographic visualization technique. Red/Green separation, i.e. "the traditional 3D image" where a red and a green representation of a model is superimposed at an angle corresponding to the viewing angle of the eyes and by using a similar set of eyeglasses, a person can create a mental 3D image. The end result does produce a sense of 3D but the effect is difficult to maintain. Alternating left/right eye systems. These systems (typified by the StereoGraphics CrystalEyes system) let the computer display a "left eye" image followed by a "right eye" image while simultaneously triggering the eyepiece to alternatively make one eye "blind". When run at 60 Hz or higher, the brain will fuse the left/right images together and the user will effectively see a 3D object. Depending on configurations, the alternating systems run at between 50 and 60 Hz, thereby creating a flickering effect, which is strenuous for prolonged use. However, all of the above have one or more drawbacks such as high costs, poor quality and localized use. A fifth system, recently released by Barco Systems, modifies the CrystalEyes system by projecting two superimposed images, using polarized light, with the wave plane of the left image at right angle to that of the right image. By using polarized glasses, each eye will see the appropriate image and true stereographic vision is achieved. While the system requires very expensive hardware, it solves some of the more important problems mentioned above, such as the capacity to use higher frame rates and the ability to display images to a large audience. Mednet has instigated a research project which uses reconstructed models from the central nervous system (human brain and basal ganglia, cortex, dendrites and dendritic spines) and peripheral nervous system (nodes of Ranvier and axoplasmic areas). The aim is to modify the models to fit the different visualization techniques mentioned above and compare a group of users perceived degree of 3D for each technique.