The proliferation of hand-held devices containing processors and wireless data connectivity suggests the need to explore how to place a large display into a compact package, both so that the user can share visual information with others in the room who might not have similar devices, and to get around the screen size and resolution limits imposed by the form factors of the devices. Particular requirements for this application include ruggedness, low cost, and low power consumption. We propose the use of linear arrays of vertical cavity surface-emitting lasers operating at visible wavelengths as the basis for 'personal projectors,' and explore the engineering and perceptual issues associated with a prototype design.
We have developed a mechanical, optical and digital system based only on commercially available equipment to allow a seamlessly tiled projection display system to be set up and aligned very rapidly. Using a digital camera and motorized projectors, our prototype system can be unpacked, aligned, and put into use within a half-hour. To minimize the number of projectors for a given pixel count, we do not overlap the projected fields and we do not move the images by digital displacement within the projected field. We use motorized lens mounts to displace the images to proper positions for tiling, a method that does not induce keystone distortion. The movement is under control of a digital camera using an image-processing system, making it unnecessary for an operator to control the movement of the lenses.
We have developed a 5-in. poly-crystal phosphor screens for projection CRTs using poly-crystal materials as the phosphor screen substrate. The poly-crystal materials has the same excellent physicochemical characteristics as the YAG has such as high thermal conductivity and high intensity as well as high optical transparency, but also the bigger diameter of the poly-crystal faceplate can be easily obtained and the cost of the poly-crystal faceplate is only a tenth of that of the same diameter of YAG. Furthermore, poly-crystal substrate is obtained by stamping technological process. The poly-crystal phosphor screens may be satisfied to the needs of large-scale production. An experimental 48-in. rear-projection TV incorporating the projection tubes achieved more than 1600 TV lines of horizontal resolution and 1800 lumens of brightness.
Projection systems for large screens have made tremendous progress during the last years, both in terms of performance and size reduction. Improved UHP lamp systems made a major contribution to enable the new generation of projectors. The arc gap is reduced to 1 mm only and allows a high collection efficiency in the projector. At the same time the lamp wattage was increased. In this way, today's projectors can create high-quality XGA pictures with more than 3000 screen lumens using one single 200 W UHP-lamp. Such a projector reaches an efficiency of more than 10 screen lumens per watt electrical input power. The volume of lamp and driver has been reduced by one order of magnitude during the last six years. This was possible by recent progress that has been achieved on the ignition of the lamp. By using a UV-enhancer cavity in the lamp seal and an additional antenna the ignition voltage could be reduced from 20 kV to below 5 kV. This allows more compact drivers and is ideal for miniaturizing projectors. A new optical concept allows for extremely compact reflector systems: A dichroic coating applied to one half of the UHP burner focuses all light into one hemisphere. Additionally 20-30% more light can be collected in systems with high optical demands.
Making use of both the reduced ignition voltage and the new optical concept a reduction of the volume of lamp and driver by a factor of 10 has been realized.
Micro display devices such as LCOS and DLP(tm) have capitalized on advancement of microelectronics fabrication technologies. Device miniaturization has created a need for high brightness light sources having low numerical apertures. Light sources based on the traditional non-imaging principles such as an ellipsoidal reflector require lamps emitting nearly a point-like source, which prompted reduction of arc sizes and increase in fill pressure in arc lamps. These requirements shorten the life and increase the cost of the lamp. In this paper, we present a novel illumination system that is based on a one-to-one imaging principle. The approach incorporates a so-called Dual Paraboloid Reflector (DPR) system in which two halves of paraboloid reflectors and a hemispherical retro-reflector are used to collect almost all the light emitted from an arc lamp. When combined with a tapered light pipe (TLP), a DPR based illumination system produces a light output having a required area, shape, numerical aperture, and a high and uniform flux density. Contrary to methods based on non-imaging principles DPR illuminators do not require those short lived short arc lamps to satisfy the needs of the projection industry. ASAP simulations of the system and experimental results are presented. The advantages of this system when applied to polarization recovery, polarization recycling, and color recycling will be discussed.
It is being increasingly recognized that temporal measures are an extremely important addition to conventional measures such as brightness, color, and contrast. In addition to flicker, color breakup, and visible flashes, inaccuracies in the portrayal of motion can greatly affect user acceptance of a system. The project team has previously reported on the use of image capture systems that can capture many images of the display for analysis to determine image characteristics and to reconstruct the temporal behavior of the display. This paper will describe how this technique can be extended to produce useful observation of multi-frame sequences. Issues for proper use of this technique include: 1) frame identification by cues in the frame image or other means, 2) externally generated image timestamps for both intra-frame and inter-frame timing, 3) tying image capture to the display's pixel transition timing to avoid erroneous measure taken during pixel transitions, 4) formatting test material to ensure repeatable display performance, and 5) proper sequence reconstruction and analysis to ensure that the reconstructed sequence is accurately representative of system behavior. Finally, the paper will discuss ways in which measurements taken using these techniques can be calibrated by comparison using human subjects and conventional measures.
The need for color consistency throughout an imaging system has made color management an important field. A key to successful color management is to find adequate models for colorimetric characterization of devices, giving accurate mappings between the color spaces of individual devices and a device-independent color space. Due to the considerable spatial non-uniformity typically found with projection displays, a conventional model for colorimetric characterization is only valid at the position the characterization data was measured. In this study a colorimetric camera is introduced and evaluated as a supplement to the traditional and evaluated as a supplement to the traditional spectroradiometer. Inspired by the fact that we are now able to conveniently collect colorimetric data with high spatial resolution, we propose a new global characterization model which enables consistent color reproduction over the entire display. The performance of the global characterization was evaluated based on two criteria, the absolute characterization accuracy of a color displayed at the center and the relative accuracy across the display. The absolute accuracy was tested by displaying 20 random color patches at the center and gave an average color difference ΔEab= 3.66 between measured and predicted color. The relative accuracy across the display was tested by using uniform tristimulus values as input, and measuring non-uniformities in the displayed images. The average color difference across the display for a set of 12 test images was ΔE = 2.59. Applications for the proposed global characterization include high quality image display for commerce, design and simulation applications, and particularly stitching of multiple projector images.
We developed a measurement method for the characteristics of microdisplays specifically aimed at vertically aligned nematic reflective cells. It allows determination of contrast ratio and cell gap, and gives good estimates for the pretilt angle and the elastic surface-coupling constant. The set-up consists of a laser source, high quality polarisers, a beamsplitter mirror, a quarter-wave plate and a sensitive photodiode. A model for the polarization changes in the light caused by each component allows the extraction of the initial phase retardation induced by the cell and gives a first estimate of the thickness. Simulation of the director configuration in liquid crystals is then used to enhance the accuracy by taking into account the properties of a real LC cell. Matching of the simulation and the measurements yields the required values together with a calibrated simulation model.
Tiled displays systems built by combining the images from arrays of projectors can provide huge numbers of pixel elements to applications needing to visually represent lots of information. Such applications are already coming into wide usage and include large scientific visualizations, collaborative virtual environments, and rich multimedia spaces. It is, however, difficult to create the illusion of a unified seamless display for a variety of reasons including optical distortion of the individual projector images due to imperfections in the lenses and basic alignment of the projectors. In this paper we describe an efficient and optimized measurement process using inexpensive components that is tolerant of a wide range of imperfections in components and measurement setup (lighting conditions, camera optics, etc.). Our method nonetheless is capable of accurate and detailed measurement of the layout of all projector images, including the generation of a detailed model of the distortions in each projector optical system. It performs these measurements on the entire array of projectors at once. Once the detailed mapping between projector pixels and mural pixels is measured, the resulting relations can be used in any of a number of ways to improve the appearance of images projected on the display.
One of the most important performance characteristics of a projection system is viewing angle. Screen characteristics alone such as reflectance, transmission, gain and half-gain angle do not predict real system performance. System viewing angle depends on the screen, but also on other factors, including the projector and the viewing environment. This paper describes a model that combines these effects. We use this model to calculate the viewing angles of projection systems.
The characteristics of BlackScreenTM for RP-TV will be described and compared with typical lenticular black-stripe screens. Careful management of light by the BlackScreen structure combines to produce an image that is optimized for human vision. It is high contrast, high-resolution, and visible over a wide viewing angle. Tuning this technology for RP-TV involves refining the screen structure to balance the performance characteristics of contrast and viewing angle. The BlackScreen product offering includes symmetric and asymmetric screens.
A new 3M Polarizing Beamsplitter (PBS) enables high performance optical engines for Liquid Crystal on Silicon (LCOS) projectors. It overcomes the limitations of previous LCOS optical engines that have insufficient light efficiency, contrast, and dark state uniformity. These limitations are the direct result of the performance of existing MacNeille PBS's: poor transmission of p-polarized light (Tp) and reduced contrast at modest beam angles and wavelength sensitivity. 3M has addressed these problems by creating a plastic polarizing film made of alternating layers of different plastics with the refractive indices tailored so that they match in one direction but not in the other. In the unmatched direction, a quarter-wave stack is formed that is highly reflective, while the matched direction appears as a transparent slab of plastic. This film is laminated between glass prisms to form a PBS with none of the problems associated with MacNeille PBS’s. For an F/2 beam, Tp exceeds 92% across the visible and photopic contrast exceeds 2000:1. High contrast is achievable in an optical engine without the use of a post-polarizer, avoiding this 15% loss that is necessary with a MacNeille PBS. Finally, the input light need not be highly polarized, allowing the engineer additional design freedom.
Recently, digital projection systems have evolved quickly in accordance with their important role in multimedia displays and the market demand for higher performance. The general trend has been, higher performance requires more bulky and expensive systems. There are several approaches for the projection and illumination optics to overcome this trend. Among these is the use of aspheric lenses. Normally a plastic aspheric lens fabricated by diamond turning is regarded only for use in prototypes. However, this can be adopted into high-end products by careful consideration of several critical issues. A dffractive/refractive hybrid lens is another possible choice due to recent technical breakthroughs overcoming the superfluous diffracted light that has confined this hybrid lens to several special applications despite many advantages to use this promising element. A possible design example for a projection lens with the hybrid elements is suggested. LED illumination is a novel approach for a projection monitor that can be successfully commercialized in the near future. Because of their superb properties of long lifetime, good color saturation and high efficiency LEDs are useful in this application. An optical system that can maximize LED illumination efficiency is suggested.
The wide acceptance of digital cinema depends on the ability of the projector to at the very least match film in color gamut, contrast, brightness, and resolution consistently. In most cases, digital projection is expected to even outperform film as a requirement for switching from film to digital because of digital projection cost. This paper examines DLP based digital projection and the optics required to produce an acceptable digital image that exceeds theatrical release film. Optical path efficiencies, tolerances, coating properties and the DMD are important parameters for color, brightness, contrast, and uniformity of the image. The efficiency and tolerancing of the optical system are key drivers for obtaining consistent high brightness and uniformity, while coatings and the DMD mainly affect consistency in color and contrast. DLP Cinema projection, based on the optics discussed, is shown to deliver a stable color gamut slightly smaller than film having consistent uniformity <300 K across a native white image with consistent brightness of 12 ft-L on screens up to 15 m. The contrast and resolution are native to the DMD but contrast can be influenced using apertures in the lenses and illumination system. Contrasts up to 3000:1 on/off are possible by the use of asymmetric apertures. These results are compared to the color gamut, contrast, brightness, and resolution of typical theatrical release film.
Two methods to measure the MTF (modulation transfer function) of an optical engine of CRT rear projection HDTV (high definition television) are introduced. A rotating image analyzer on the fluorescent surface with a 2D CCD and a relay lens is used to test in the full-field angle. We developed a software program to automatically locate and measure the position of the maximum value of the MTF at any spatial frequency.
A new synthetic evaluation method for the color display is studied. A testing system to measure the luminance, chromaticity, contrast ratio, uniformity, viewing angle as well as the PMTF (polychromatic modulation transfer function) is presented. The PMTF is calculated from the values of the monochromatic MTFs weighted by the CIE photopic luminous efficiency function of the human visual system. A high-precision XYZ translation stage to move the testing system and a two-axis goniometer to tip and turn the display under test to the desired viewing angle are used.
This paper displays the first prototype for a very low power consuming and portable micro projector. The described prototype may be integrated in a vast set of applications such as a screen alternative device in a portable computer or a cellular phone. The low power consumption is critical factor for such application in order to allow operation from the portable battery of the above-mentioned devices. The paper presents and discussed the vast set of possible applications as well as the prototype’s measured technical set of performance.