Playback, Presentation of Stereo Images
Any method which is able to exclusively show the left field to the left eye and the right field to the right eye is suitable for stereoscopic presentation. If you separate the different viewing methods according to the presentation medium, you get the following rough classification:
A. Methods for 2D Media (eg Prints)
B. Methods Showing the Image on a Monitor
C. Methods Using a Projector and a Screen
A1. Free Viewing
Side by side arranged stereo images can directly be look to without any additional aids up to an image size of about 6 cm. The DGS uses this method within its stereo journal and also on this website. Hereby the eyes look in parallel orientation to infinity, but must focus to vicinity. A small guide to learn this method can be found here.
Figure 1: With free parallel viewing your left eye looks only to the left image and the right eye only to the right image.
A2. Stereo Viewer using Lenses (Lorgnette)
If additionally glasses with collecting lenses are used, the eyes no longer have to focus to the near area, but can relax and look into the distance. The focusing to the close is now taken over by the stereo glasses. This also fits much better to the parallel orientation of the eyes and therefore allows a relaxed vision to stereos. As a further development, for the Holmes Stereoscope prism lenses are used to increase the maximum image size to about 70 to 75 mm.
Figure 2: Using converging lenses in the glasses, we no longer have to focus to the near and can enjoy side-by-side printed stereo images without any effort.
A3. Crossed Eye Viewing
Since for human beings a divergent eye position is extremely uncomfortable (if at all possible), free stereo viewing doesn't allow greater images than about the eye distance. But if you interchange the left and right stereo field, much larger images can be viewed with some inward squint.
Figure 3: Who masters the cross-eyed viewing method, may look to large stereo images without glasses.
The inventors of the KMQ method (named after the inventors Christoph Koschnitzke, Reiner Mehnert and Peter Quick) have stacked the left and right field not stacked side by side but one above the other. Using prisms in the KMQ glasses direct the viewing beam path so that the two fields can be merged again to form a spatial image.
Figure 4: With using prism glasses, the stereo fields can be arranged one above the other.
If (for example) coloring the left field into red and the right field into cyan and printing both fields superimposed, they can be separated afterwards again when viewing, if you wear glasses with corresponding color filters (anaglyph glasses). Since the colors are required now for field separation, the image itself can no longer be colored.
Figure 5: The red side of the spectacles lets only pass the light from the red (left) image field and the blue-green side lets only pass the blue-green light of the right image field.
B1. Polarized Monitor
3D monitors and 3D TVs with passive 3D technology work with circularly polarized light. This methode polarizes (eg) all even row numbers clockwise and all odd row numbers anti-clockwise. With appropriate polarized glasses then the left eye only see the even lines and the right eye only the odd. The correct preparation of the composed image (with interlaced lines) is either made by the player software or by the 3D TV itself.
Figure 6: Passive polarized glasses with sleek modern design.
B2. Shutter Monitor
With shuttering, the left and right fields are alternately displayed. Since then the 3D glasses must be synchronized to the image changes; this technique is also called active.
Figure 7: Active shutter glasses from Nvidia®, the shutter eletronic is integrated into the temples.
B3. Mirror Box (Cobox)
Similar to the Camera Mirror Rig (see Technology - Shooting), a semi-transparent mirror and two normal computer monitors can be used to arranged a 3D viewing device. In appreciation to the Dutch 3D pioneer Co van Ekeren, this vision device is also called Cobox. For image separating the already existing polarization of the monitors is used, so that except the polarization glasses no further optical elements are necessary.
Figure 8: The beam path inside the Cobox. Many commercially available monitors already own from factory the correct polarization.
C1. Projection with polarized light
This method is applicable for analogue slides as well as for digital content in the same manner. The image of two projectors will be projected superimposed onto the screen. For separating of the image information, linearly or circularly polarized light can be used. To avoid depolarization (and intermixing of the two image information with each other), a metallized surface of the projection screen is required ("silver screen").
Figure 9: Arrangement with two beamers for stereo projection. For light separation, linearly polarized light is used here. This method ia also used for the DGS events.
C2. Shutter Projection
Both fields come from only one projector, alternatively for the left and right eye. The separation of the fields could be done again with shutter glasses (see above), which also alternately release the left and right viewing beam. Often the light is additionally polarized, and then for viewing inexpensive polarization glasses can be used.
C3. Infitec Projection
The German company Infitec® is the inventor of an image separation technology using interference filters. As things stand, the middle ranges of the 3 primary color spectrums are used for the right image field and the edges for the left one. Although colors are used for separation similar to anaglyph images, nevertheless differences in colors are virtually no longer detectable in the left and right image. The interference filter technology does not require a silver screen and can score with good light blockings and low transmission losses of the interference filter glasses. Interference technolgy has found worldwide distribution by the company Dolby3D®.
Image 10: Color separation with interference filter method according to Infitec®. In both fields all 3 basic colors are present.
|Parallel Viewing with Glasses||
|Crossed Eye Viewing||
Information: The SIG Projection is focused on all technical aspects of polarization projection with 2 projectors.
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Photo credits: ©Gerhard P. Herbig