Stereo projection using interference filters is an advanced wavelength multiplexing approach, that specifically takes into account the nature of the human eye, which is characterized by three types of color receptors. Accordingly, the filters used to code image information for the left and for the right eye image have three narrow bands each. In the present paper the current status of the interference filter technique for stereo imaging is outlined.

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Abstract— Stereo projection using interference filters is an advanced wavelength multiplexing approach that specifically takes into account the nature of the human eye, which is characterized by three types of color receptors. Accordingly, the filters used to code image information for the left‐eye and for the right‐eye image have three narrow bands each. Wavelength multiplexing represents a modern approach by overcoming earlier drawbacks in the color reproduction of image‐separation methods such as anaglyph technologies. Unlike polarizing technologies, there is no need of polarization reservation or a restraint to the projection technology.

oal of this work was the optimization of brightness and colors performance of the interference filter system for projection. Special emphasis was on avoiding, or at least reducing, the need for color correction, which was one of reasons for low luminous efficiencies in the past.On the base of datasets for various projectors (DLP, LCoS, LCD) and lamps (UHP and Xenon), the optimization for a high efficiency stereoscopic interference filter system was carried out. Focus of our study was on three by four (3-4) filter system. We also examined filter designs with higher numbers of transmission bands up to seven per filter. The results show that the 3-4 band filters design exhibits the highest efficiency of all inherently color balanced filter systems because of a minimum number of gaps between adjacent transmission bands. Results also revealed that Xenon lamp based systems and UHP lamp based systems have different optimum filters. However, differences are such small that it becomes possible to cover both systems by a unitary type of 3D glasses lenses

We demonstrate a significant improvement of the color and transmission performance of a complementary interference filter system used for stereoscopic imaging. A 3D transmission of 30% for a UHP lamp projection system was achieved. The differences in color and luminance between left and right filter were minimized. IntroductionStereoscopic imaging in projection system has gained plenty of interest since the success of 3D cinema movies in the past. Currently three basic stereoscopic technologies for large venues are at present in the market share their common glasses based approaches [1].1) Polarization technology either utilizes the prepolarized light emission of the projector or uses a polarizer filter system in front of the projector. Although, this system requires a polarization maintaining screen it is still attractive since passive low cost glasses can be used.2) Active systems are blocking time sequentially left or right image by an active LCD shutter as filter of the glasses. This system requires continuous synchronization to displaying system. Usually, those glasses are battery driven.3) Interference filter systems left and right images are multiplexed into two complementary spectral ranges. Spectral filtering is implemented into the projector which can be a dual projector system or a single projector with a rotating filter wheel. Glasses are passive and based on interference filter technology [2].In stereoscopic projection white screen technologies avoid the so called "hot spot" effect and offer homogeneous image quality. Furthermore passive systems are desired because they are robust, easy cleanable and cheap. Interference filter design configurations 2.1. Triple band interference filter systemFull color stereoscopic interference filter imaging requires at least one independent stimulus for each color receptor in the human eye. The nature of the eye having three cones defines the triple band filter system as the minimum concept for full color stereoscopic images. Figure 1. Projector white output spectrum and triple band filter configurationColors of the left and right channel usually differ and therefore require an electronical color correction. Figure 2. Color gamut of triple band A and B filter for a UHP projector (CIE1931 x-y-diagram)Most high end projectors support color correction and compensate differences so that left and right eye perceive the same color gamut and brightness. Although the average transmission of the filter amounts 30-32%, the requirement of equal white points and similar luminance for each color reduces this value to approximately 8% for the B-filter and 12% for the A-filter. The luminance differences of left and right filter may additionally adjusted if desired. A recent study [3] indicates that even luminance level differences of up to 60% do not affect the ability to perceive full stereo depth. SID 11 DIGEST • 317