Photocopying – Projection printing and copying cameras – Multicolor picture
Reexamination Certificate
2001-09-05
2003-10-21
Fuller, Rodney (Department: 2851)
Photocopying
Projection printing and copying cameras
Multicolor picture
C355S067000, C355S070000
Reexamination Certificate
active
06636292
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to digital film writing apparatus for writing onto photosensitive media and more particularly relates to an apparatus for writing images from digital data onto motion picture film.
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 could 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 could then serve as an intermediate for print film production, following the conventional sequence used for film production using optical equipment. However, it can be well 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 do not allow imaging directly to print film economically. Using conventional equipment, an intermediate film is required, with an accompanying loss of some measure of image quality in transfer between the intermediate negative film and the final print film.
It is recognized to those knowledgeable in the film production arts that slow print speeds keep digital film production at a disadvantage. 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.
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. Exemplary 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.
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 would be 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 where light sources must be shuttered. However, single LEDs do not generally provide sufficient brightness for high-speed imaging. Moreover, LEDs exhibit some amount of color “crosstalk” causing unwanted “punch-through” whereby a portion of light energy intended for imaging in one color impacts a second color. Narrowband filters could be used to prevent such crosstalk, but this would result in a significant loss of light. These disadvantages limit the acceptance 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.
Color motion picture printing uses sequenced exposures at discrete red, green, and blue (RGB) wavelengths. This can complicate printing apparatus, requiring that a separate optical path be provided for each color and that the light then be recombined, such as using an X-cube, or requiring that the same optical path be time-shared or multiplexed between multiple colors. In conventional color printing systems using spatial light modulators, both separate-path and shared-path types of optical arrangements are used. U.S. Pat. No. 6,215,547 (Ramanujan et al.) discloses a shared-path optical arrangement for a printer using a single spatial light modulator, in which the different colors used for exposure are multiplexed through the same optical path. As with any type of optical apparatus, it is recognized that there are advantages to design of systems requiring a minimal number of components.
It is worthwhile to note that color film, and color photosensitive media in general, can exhibit dramatically different levels of response to light at different wavelengths. It is well established, for example, that silver-halide (AgX) emulsions are generally much more sensitive to light radiation within the blue spectrum than within the red spectrum. These differences in film response by wavelength can be plotted as is shown in the example of
FIG. 4
that shows, for a typical motion picture intermediate film, the relation of the log of film sensitivity to wavelength.
Given photosensitive media characteristics as shown in the example of
FIG. 4
, a conventional approach followed in intermediate film imaging design has been to consider and design to accommodate the worst-case sensitometric response. Thus, for example, if a single light source were used with filters, such a light
Roddy James E.
Zolla Robert J.
Eastman Kodak Company
Fuller Rodney
Nelson Adrian Blish
LandOfFree
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