Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2002-10-16
2004-10-12
Mathews, Alan A. (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S122000
Reexamination Certificate
active
06802613
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to display systems that form a two-dimensional image and more particularly relates to a color display apparatus and method for generating images having a broadened color gamut using electromechanical grating devices.
BACKGROUND OF THE INVENTION
With the advent of digital technology and the demonstration of all-digital projection systems, there is considerable 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 familiar tristimulus CIE color model developed by Commission International de l'Eclairage (International Commission on Illumination) shows the color space perceived by a standard human observer.
FIG. 1
a
shows the CIE color model, which represents a visible gamut
200
as a familiar “horseshoe” curve. Within visible gamut
200
, the gamut of a conventional display device can be represented by a three-sided device gamut
202
, such as standard SMPTE (Society of Motion Picture and Television Engineers) phosphors, for example. As is well known in the color projection arts, it is desirable for a display device to provide as much of visible gamut
200
as possible in order to faithfully represent the actual color of an image.
Referring to
FIG. 1
a
, pure, saturated spectral colors are mapped to the “horseshoe” shaped periphery of visible gamut
200
. The component colors of a display, typically Red, Green, and Blue (RGB) define the vertices of the polygon for a color gamut, thereby defining the shape and limits of device gamut
202
. Ideally, these component colors are as close to the periphery of visible gamut
200
as possible. The interior of the “horseshoe” then contains all mappings of mixtures of colors, including mixtures of pure colors with white, such as spectral red with added white, which becomes pink, for example.
One simple strategy to increase the size of device gamut
202
is to use light sources that are spectrally pure, or have at least a good degree of spectral purity. Lasers, due to their inherent spectral purity, are particularly advantaged for maximizing device gamut
202
. A second strategy for expanding color gamut is to move from the conventional triangular area of device gamut
202
, as shown in
FIG. 1
a
, to a polygonal area, shown as an expanded device gamut
204
in
FIG. 1
b
. In order to do this, one or more additional component colors must be added.
There have been projection apparatus solutions proposed that may employ more than 3 component colors from various color light sources. For the most part, however, the solutions proposed have not targeted color gamut expansion; in some cases, added colors are not selected for spectral purity, but are selected for some other characteristic. Disclosures of projectors using more than three component color sources include the following: U.S. Pat. No. 6,256,073, Jul. 3, 2001 (Pettitt) discloses a projection apparatus using a filter wheel arrangement that provides four colors in order to maintain brightness and white point purity. However, the fourth color added in this configuration is not spectrally pure, but is white in order to add brightness to the display and to minimize any objectionable color tint. It must be noted that white is an “intragamut” color addition; in terms of color theory, adding white can actually reduce the color gamut. Similarly, U.S. Pat. No. 6,220,710 by Raj et al. issued Apr. 24, 2001 discloses the addition of a white light channel to standard R, G, B light channels in a projection apparatus. As was just noted, the addition of white light may provide added luminosity, but constricts the color gamut. U.S. Pat. No. 6,191,826 Feb. 20, 2001 (Murakami et al.) discloses a projector apparatus that uses four colors derived from a single white light source, where the addition of a fourth color, orange, compensates for unwanted effects of spectral distribution that affect the primary green color path. In the apparatus of U.S. Pat. No. 6,191,826, the specific white light source used happens to contain a distinctive orange spectral component. To compensate for this, filtering is used to attenuate undesirable orange spectral content from the green light component in order to obtain a green light having improved spectral purity. Then, with the motive of compensating for the resulting loss of brightness, a separate orange light is added as a fourth color. The disclosure indicates that some expansion of color range is experienced as a side effect. However, with respect to color gamut, it is significant to observe that the solution disclosed in U.S. Pat. No. 6,191,826 does not appreciably expand the color gamut of a projection apparatus. In terms of the color gamut polygon described above with reference to
FIGS. 1
a
and
1
b
, addition of an orange light may add a fourth vertex; however, any added orange vertex would be very close to the line already formed between red and green vertices. Thus, the newly formed gamut polygon will, at best, exhibit only a very slight increase in area over the triangle formed using three component colors. Moreover, unless a substantially pure wavelength orange is provided, there could even be a small decrease in color gamut using the methods disclosed in U.S. Pat. No. 6,191,826.
It is worthwhile to note that none of the solutions listed above has targeted the expansion of the color gamut as a goal or disclosed methods for obtaining an expanded color gamut. In fact, for each of the solutions listed above, there can even be some loss of color gamut with the addition of a fourth color.
In contrast to the above patent disclosures, Patent Application WO 01/95544 A2 (Ben-David et al.) discloses a display device and method for color gamut expansion as shown in
FIG. 1
b
using spatial light modulators with four or more substantially saturated colors. In one embodiment, Application WO 01/95544 teaches the use of a color wheel for providing each of the four or more component colors to a single spatial light modulator. In an alternate embodiment, this Application teaches splitting light from a single light source into four or more component colors and the deployment of a dedicated spatial light modulator for each component color. However, while the teaching of Application WO 01/95544 may show devices that provide improved color gamut, there are several drawbacks to the conventional design solutions disclosed therein. When multiplexing a single spatial light modulator to handle more than three colors, a significant concern relates to the timing of display data. The spatial light modulator employed must provide very high-speed refresh performance, with high-speed support components in the data processing path. Parallel processing of image data would very likely be required in order to load pixel data to the spatial light modulator at the rates required for maintaining flicker-free motion picture display. It must also be noted that the settling time for conventional LCD modulators, typically in the range of 10-20 msec for each color, further shortens the available projection time and thus constrains brightness. Loss of brightness, already an acknowledged disadvantage of tricolor color wheel solutions, becomes a successively larger problem with each additional color added, since a smaller proportionate amount of light is then available for any one color. Moreover, the use of a filter wheel for providing the successive component colors at a sufficiently high rate of speed has further disadvantages. Such a filter wheel must be rotated at very high speeds, requiring a precision control feedback loop in order to maintain precision synchronization with data loading and device modulation timing. The additional “dead time” during filter color transitions, already substantial in devices using three-color filter wheels, would further reduce brightness and complicate timing synchronization. Coupling the filter wheel with a neutral density filter, also rotating in the light
Agostinelli John A.
Horvath Louis S.
Kowarz Marek W.
Eastman Kodak Company
Mathews Alan A.
Sever Andrew
Shaw Stephen H.
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