Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2002-05-20
2003-11-18
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S094000
Reexamination Certificate
active
06648475
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to imaging apparatus for display of images from digital data and more particularly relates to an apparatus and method for improving the color gamut of projected high-resolution motion picture images.
BACKGROUND OF THE INVENTION
A number of different color spaces have been used to describe the human visual system. In one attempt to define a workable color space, Commission Internationale de l'Eclairage (International Commission on Illumination) developed the CIE Chromaticity Diagram, published in 1931. The CIE color model employed the tristimulus values X, Y, Z based on a standard human observer. The diagram in x and y was later modified to a u′ and v′ diagram in which equal distances on the diagram represent equal perceived color shifts. Useful background discussion of color perception and color models can be found in Billmeyer and Saltzmann's
Principles of Color Technology
, Third Edition, Wiley and Sons, and in Dr. R. W. G. Hunt's
The Reproduction of Color
, Fifth Edition, Fountain Press, England.
FIG. 1
shows a familiar color gamut representation using CIE 1976 L*u*v* conventions, with the perceived eye-brain color gamut in u′-v′ coordinate space represented as a visible gamut
100
. Pure, saturated spectral colors are mapped to the “horseshoe” shaped periphery of visible gamut curve
100
. The interior of the “horseshoe” contains all mappings of mixtures of colors, such as spectral red with added blue, which becomes magenta, for example. The interior of the horseshoe can also contain mixtures of pure colors with white, such as spectral red with added white, which becomes pink, for example. The overall color area defined by the “horseshoe” curve of visible gamut
100
is the full range of color perceptible to the human visual system. It is desirable to represent as much as possible of this area in a color display to come as close as possible to representing the original scene as we would perceive it if we were actually viewing it.
Conventional motion picture display, whether for large-scale commercial color projection from film or for color television cathode ray tubes (CRTs), operates within a fairly well-established color gamut. Referring again to the mapping of
FIG. 1
, observe that visible gamut
100
shows the full extent of human-perceivable color that, in theory, could be represented for motion picture display. A motion picture film gamut
102
is mapped out within visible gamut
100
, showing the reduced extent of color representation achievable with conventional film media. An NTSC TV gamut
104
shows the further restriction placed on achievable colors using conventional color CRT phosphors. It is instructive to note that, because the colors of the CRT phosphors for NTSC TV gamut
104
are not typically saturated, the points defining the color of each phosphor do not lie on the periphery of visible gamut
100
. Hence, for example, colors such as turquoise and neon orange can be perceived by the eye in the actual scene but are beyond the color capability of a CRT phosphor system. As is clear from
FIG. 1
, the range of colors that can be represented using conventional film or TV media falls far short of the full perceivable range of visible gamut
100
.
The component colors used for conventional motion picture film employ red, green, and blue dyes (or their complementary counterparts cyan, magenta, and yellow). Component colors for conventional color television CRTs employ red, green, and blue phosphors. Although initially limited in the colors that they could represent, apparatus using these dyes and phosphors have been steadily improved. However, as is clear from the gamut mapping represented in
FIG. 1
, there is still room for improvement in approximating visible gamut
100
in both motion picture and TV environments.
With the advent of digital technology and the demonstration of all-digital projection systems, there is renewed interest in increasing the range or gamut of colors that can be displayed in order to provide a more realistic, more vivid image than is possible with the gamut limitations of film dyes or phosphors. The most promising solutions for digital cinema projection employ, as image forming devices, one of two types of spatial light modulators (SLMs). 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 transmitted or reflected light from a light source. There are two salient types of spatial light modulators that are conventionally employed for forming images in digital projection and printing apparatus: digital micromirror devices (DMDs) and liquid crystal devices (LCDs).
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; and 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. No. 5,914,818 (Tejada et al.); U.S. Pat. No. 5,930,050 (Dewald); U.S. Pat. No. 6,008,951(Anderson); and U.S. Pat. No. 6,089,717 (Iwai). 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.).
While there has been some success with respect to color representation using spatial light modulators, there is a long-felt need for a further broadening of the projection color gamut that will enhance special effects and heighten the viewing experience.
Faced with a similar problem of insufficient color gamut, the printing industry has used a number of strategies for broadening the relatively narrow gamut of pigments used in process color printing. Because conventional color printing uses light reflected from essentially white paper, the color representation methods for print employ a subtractive color system. Conventionally, the process colors cyan (blue+green), magenta (red+blue), and yellow (red+green) are used for representing a broad range of colors. However, due to the lack of spectral purity of the pigment, combinations of cyan, magenta, and yellow are unable to yield black, but instead provide a dark brown hue. To improve the appearance of shadow areas, black is added as a fourth pigment. As is well known in the printing arts, further refined techniques, such as undercolor removal could then be used to take advantage of less expensive black pigments in full-color synthesis. Hence, today's conventional color printing uses the four color CMYK (cyan, magenta, yellow, and black) method described above.
However, even with the addition of black, the range of colors that can be represented by printing pigments is limited. There remain specialized colors such as metallic gold or silver, or specific colors such as those used for corporate identity in logos and packaging, for example, that cannot be adequately reproduced using the CMYK “process color” system. To meet this need, a fifth pigment can be added to a selected print run in order to provide “spot color” over specific areas of an image. Using this technique, for example, many companies use special color inks linked to a product or corporate identity and use these colors in packaging, advertising, logos, and the like, so that the consumer recognizes a specific product, in part, by this special color. This type of solution, while not increasing the overall color gamut of a printing process, at least allows the reproduction of one or more out-of-gamut colors.
Colors in addition to the conventional CMYK process color set have been employed to extend the overall color gamut in printing applications. For example, EP 0 586 139 (Litvak) discloses a method for expanding the conventional color gamut using the four-color CMYK space to a color space using five or more colors.
Referring back to
FIG. 1
, it is instructive to note that the color gamu
Markis William R.
Roddy James E.
Zolla Robert J.
Blish Nelson Adrian
Dowling William
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