Digital cinema projector

Details Digital cinema projector Digital cinema projector

2001-03-20

2003-07-01

Mahoney, Christopher (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C353S020000, C353S034000, C353S037000, C353S038000, C359S489040, C359S668000

Reexamination Certificate

active

06585378

ABSTRACT:

FIELD OF THE INVENTION
This invention relates in general to a digital cinema and in particular relates to a digital projector using spatial light modulators to form an image on a display screen.
BACKGROUND OF THE INVENTION
Conventional motion picture film projectors have proven successful in projecting quality images that satisfy a viewing audience. In recent decades, the overall cinematic experience has benefited by minor improvements in the quality of presentation. However, the most widely adopted technological improvement is cinema digital sound, rather than any change that improves the quality of the projected image. While the successful commercial development of some select large screen film formats, for example, the IMAX 70 mm format, and the supporting projection equipment has improved image quality, theatres equipped with this equipment are special venues, rather than outlets for traditional Hollywood films. Basically, since the introduction of the 1950's of robust color films and xenon arc lamps, motion picture film projection technology has undergone minor improvements, with few technological breakthroughs.
Although the traditional 35 mm motion picture film system has deficiencies scratches such as dirt, and unsteadiness, which degrade the image quality, overall the system has set high standards for image quality. While the effective screen resolution for 35 mm film projection varies with print quality, 2000 line resolution is generally considered to be sufficient for electronic equivalent systems. Cinematic projection systems also provide a wide color gamut and a large frame sequential contrast ratio (>1,000:1). A large contrast range allows the system to properly render abrupt changes of lightness to darkness, such as may occur at dramatic scene changes. Furthermore, to meet the Society of Motion Picture and Television Engineers (SMPTE) projection standards of 16 ft. L (foot Lamberts) of center screen luminance, a typical cinema projector must provide 8,000 to 15,000 screen lumens, depending on the film format and screen size. Thus, the cinema experience demands very high levels of performance, particularly in comparison to the modern electronic business projector, which need only provide 1500 lumens and 250:1 contrast. Electronic or digital cinema projection systems must satisfy these basic cinematic system requirements, as well as meeting other requirements related to modulator and electronic artifacts, data compression, data security, and system robustness.
The earliest electronic projection system which could project “cinema quality” images without the use of motion picture film was the Eidophor system, which was developed by E. F. Fischer (U.S. Pat. Nos. 2,391,451 and 2,605,352) in the 1940's. The Eidophor used an electron beam to write images onto a reflective oil film. The oil film in turn was illuminated, and then imaged to the screen, through a Schlieren type optical system. An alternate system, called the “Talaria,” which was developed in the 1950's by W. Glenn (U.S. Pat. Nos. 2,813,146 and 3,084,590) of General Electric, was similar to the Eidophor, except that it used transmissive, rather than reflective, oil films. Although both of these systems were successful in their own right, and were used successfully in cinematic projection demonstrations, neither had significant impact on the motion picture film projection industry.
Commercially available electronic projection systems are constrained by limited performance, particularly with respect to resolution, light efficiency, and contrast ratio. Typical systems, include those available from manufacturers such as JVC; Barco, headquartered in Ghent, Belgium; Christie Digital Systems, Inc., Kitchener, Ontario, Canada; and In Focus Corporation, Wilsonville, Oreg., among others. In general, these systems output between 500 and 3000 lumens and provide screen contrast ratios ranging from 100:1 to 400:1. These limitations constrain the use of such projection systems to home projection, business, concert, control room, and image simulation functions.
Recently there have been many proposals and technology demonstrations of alternate approaches to cinema. These approaches have ranged from proposed new film formats, to 3-D imaging or immersion systems, and to electronic display system. Most notably, Texas Instruments Inc. of Dallas, Tex., and Victor Company of Japan, Ltd. (JVC), or Yokohama, Japan, have publicly exhibited prototype electronic projection systems as candidates to replace 35 mm film in providing commercial quality cinema projection. While these prototype systems showed substantial merit, they have not yet matched or exceeded all the on-screen image quality and system flexibility standards set by the conventional film-based projection system. In particular, there are opportunities for improvement with respect to image resolution, pixelization, image contrast, color reproduction, and brightness needed to obtain the expected “look and feel” of film.
The most promising solutions for digital cinema projection employ, as image forming devices, one of two types of spatial light modulators, either a digital micro-mirror device (DMD) or a liquid-crystal device (LCD). Texas Instruments has demonstrated prototype projectors using one or more DMDs. DMD devices are described in a number of patents, for example, U.S. Pat. Nos. 4,441,791; 5,535,047; 5,600,383 (all to Hornbeck); and U.S. Pat. No. 5,719,695 (Heimbuch). Optical designs for projection apparatus employing DMDs are disclosed in U.S. Pat. Nos. 5,914,818 (Tejada et al.); 5,930,050 (Dewald); 6,008,951 (Anderson); and 6,089,717 (Iwai). While DMD-based projectors demonstrate some capability to provide the necessary light throughput, contrast ratio, and color gamut, inherent resolution limitations (current devices providing only 1024×768 pixels), high component and system costs have restricted DMD acceptability for high-quality digital cinema projection.
Alternatively, LCD devices appear to have advantages as spatial light modulators for high-quality digital cinema projection systems. Recently, JVC publicly demonstrated a LCD-based projector capable of high-resolution (providing 2,000×1280 pixels), high frame sequential contrast in excess of 1000:1, and high light throughput (nominally, up to 12,000 lumens). This system utilized three vertically aligned LCDs (one per color) driven or addressed by cathode ray tubes (CRTs). While this system demonstrated the potential for an LCD based digital cinema projector, the system complexity, reliability, and cost are not well suited for commercial production. More recently, JVC has developed a new family of vertically aligned LCDs, which are addressed via a silicon backplane rather than by CRTs, although these new devices have not yet been used in digital cinema presentation. The JVC LCD devices are described, in part, in U.S. Pat. No. 5,570,213 (Ruiz et al.) and U.S. Pat. No. 5,620,755 (Smith, Jr. et al.). In contrast to early twisted nematic or cholesteric LCDs, vertically aligned LCDs potentially provide much higher modulation contrast ratios, in excess of 2,000:1. It is instructive to note that, in order to obtain on screen frame sequential contrast of 1,000:1 or better, the entire system must produce >1000:1 contrast, and both the LCDs and the polarization optics must each separately provide ~2,000:1 contrast.
Obviously, the optical performance provided by LCD based electronic projection system is in large part defined by the qualities of the polarization optics and the LCDs. However, numerous other components, including the lamp source, light integration optics, the polarization converter, color filters and prisms, and waveplates also significantly impact performance. For example, as electronic projection systems modulate each red, green, and blue (R, G, B) color component separately, these systems also require color splitting and color recombination optics, including dichroic filters and color prisms, such as the familiar X-prism, commonly used for recombination. Thus, the relative s

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