Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2002-02-06
2003-09-23
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S487030, C359S490020
Reexamination Certificate
active
06624949
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to apparatus for writing digitally encoded color images onto photosensitive media and more particularly relates to an apparatus for writing color images onto motion picture film from digital data using a single spatial light modulator with a plurality of light sources.
BACKGROUND OF THE INVENTION
In conventional motion picture film preparation, a master negative film is developed and prepared as an intermediate from which copies can be mass-produced as print films. One example of a motion picture printer using conventional optical methods for producing print films is the Model 6131 Series Printer manufactured by BHP Incorporated, Chicago, Ill. Using such conventional methods and optical equipment, projection-quality print films for distribution can be produced economically, at high speed.
With the advent of digital motion picture imaging, conventional optical methods can still be used for print film preparation. That is, a master negative film can be prepared using digital imaging equipment. This same master negative film then serves as an intermediate for print film production, following the conventional sequence used for film production using optical equipment. However, it can be appreciated that there are benefits to film production methods that offer increased speed, lowered cost, and increased versatility over earlier methods. As one example, conventional methods don't allow imaging directly to print film economically. Using conventional equipment, an intermediate film is still required, with an accompanying loss of some measure of image quality in transfer between the intermediate negative film and the final print film.
Those knowledgeable in the film production arts will realize that relatively slow writing speeds are a disadvantage for digital film production. Conventional digitally-based motion picture film imaging systems, using CRT writers or using lasers in conjunction with a spinning polygon, yield writing output speeds measured in multiple seconds per frame. However, high-speed film duplication using older optical exposure methods achieves speeds measured in multiple frames per second. Thus, in order to provide a competitive alternative to optical film production methods, digital film production methods must improve upon current printing times.
Light Modulators for Printing
For motion picture film and other photosensitive media in general, spatial light modulators show considerable promise as image forming components. Originally developed for digital projection equipment, spatial light modulators are being more widely used for imaging onto film and other photosensitive media. Spatial light modulators used for this purpose include liquid crystal devices (LCDs) from Victor Company of Japan (JVC), Yokohama, Kanagawa, Japan, and digital micromirror devices (DMDs) from Texas Instruments, Dallas, Tex. A spatial light modulator can be considered essentially as a two-dimensional array of light-valve elements, each element corresponding to an image pixel. Each array element is separately addressable and digitally controlled to modulate light. An LCD, for example, modulates light intensity for a pixel by modulating the polarization state of light from the array location corresponding to that pixel. For operation, the LCD must be provided with plane polarized light.
Both LCD and DMD arrays have advantages over other types of image-forming devices. Because LCD and DMD arrays can image a complete frame at a time, there is minimal mechanical complexity and thus, lower cost. Thus, LCDs and DMDs enjoy complexity and cost advantages, particularly in contrast to writing systems using lasers with spinning polygons.
Though not as widely used, other types of spatial light modulators used for photosensitive media include gated light valves such as lead lanthanum zirconate titanate (PLZT) light valves. The gated light valve is essentially an array of light-transmitting elements arranged in linear fashion to provide a 1×m pixel array, where the width of the array, m, is typically in the range of a few thousand pixels. One example of a gated light valve is a Micro Light Valve Array (MLVA) used in the Noritsu model QSS-2711 Digital Lab System, manufactured by Noritsu Koki Co., located in Wakayama, Japan. The same basic imaging principle used with spatial light modulators applies, whereby individual elements in the array vary in the intensity of light emitted. However, using a linear array provides only one line of the two-dimensional image at a time, and therefore requires movement of the photosensitive media relative to the printhead in order to expose a complete frame.
Alternative Light Sources
There are a number of alternative light sources for use with a spatial light modulator in an apparatus that images onto a photosensitive medium, including the following:
(a) tungsten or halogen lamp. These sources, although used in many types of film development and processing systems, are not advantageous for high-speed film printing using spatial light modulators. Substantial filtering and polarization optics are typically required to adapt lamp sources to spatial light modulators, with concomitant loss of brightness. Shuttering components would be necessary for color printing using multiple sources. Heat management would also be necessary for tungsten or halogen sources.
(b) LED. These light sources are low cost and have favorable response speeds when compared against other light sources that must be shuttered. However, single LEDs do not generally provide sufficient brightness for high-speed imaging. Arrays comprising multiple LEDs are one possible solution; however, conventional solutions using LED arrays face aperture size and cone angle constraints, which force tradeoffs between cost, complexity, and brightness. These disadvantages have, therefore, limited the use of LEDs as light sources for high-speed production of motion picture films.
(c) laser. The laser has advantages including high brightness and narrow bandwidth. As a further advantage, laser output is inherently polarized, not requiring polarization conditioning by lossy components in the optical path. However, lasers are higher in cost, particularly in some wavelengths.
Overall, LEDs and lasers are more durable than lamps and provide a favorable solution for imaging systems needing light at specific wavelengths and having high brightness levels.
Illumination Optics Path Considerations for Color Printing
Color motion picture printing uses sequenced exposures at discrete red, green, and blue (RGB) wavelengths. As a general rule for throughput efficiency, printing speed is primarily a factor of the achievable brightness of the light source. The preferred approach for illumination optics, as disclosed in U.S. Pat. No. 6,215,547 (Ramanujan et al.) teaches the use of a single illumination optics path to one spatial light modulator for successive modulation of red, green, and blue light. Using a time-sequenced illumination scheme, the red, green, and blue light sources are sequentially modulated by the spatial light modulator and focused onto a photosensitive medium.
U.S. Pat. No. 6,215,547 discloses a number of possible alternative light sources, including a lamp provided with a rotating filter wheel or multiple LEDs arrayed in different parts of a circular aperture. A notable advantage of the arrangement disclosed in U.S. Pat. No. 6,215,547 is that the same illumination and imaging optics path is used for light of each color. This eliminates the need for registration of separate color path components and allows a minimum of components to be employed for full-color imaging onto the photosensitive medium. However, the arrangement disclosed in U.S. Pat. No. 6,215,547 presents some obstacles. Aperture size and optical cone angle constraints can limit the number of LED or other light sources provided, thus limiting the brightness achieved. Compromises that can be made include deploying, within the limited space available, a different number of LEDs or other light sources f
Federico Richard J.
Roddy James E.
Zolla Robert J.
Blish Nelson Adrian
Dang Hung Xuan
Eastman Kodak Company
Hindi Omar
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