Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-05-27
2003-01-28
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C348S750000
Reexamination Certificate
active
06512502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to lightvalve optical projection displays in which each pixel of the displayed image is formed from red, green, and blue subpixels, and more particularly to projectors using two such lightvalves to avoid the difficulty of fabricating all subpixels together in a single lightvalve, while also avoiding the complex optical systems required when the subpixels are divided between three lightvalves (red, green, and blue).
2. Discussion of the Prior Art
Many low cost data projectors make use of lightvalves in which each pixel in the screen image is formed from adjacent red, green, and blue (R,G,B) subpixels. Each lightvalve R,G,B subpixel is driven with the corresponding color component of the image pixel. A patterned color filter ensures that the illuminating light modulated by each subpixel is of the appropriate color.
An advantage of these systems is that they avoid the complexity of the color separating and recombining optics that are needed in projectors with separate lightvalves for R, G, and B. A disadvantage is that the lightvalve must incorporate at least 3 addressable pixel elements for each individual image element.
Generally there is a direct yield impact from the increased number of pixel elements. Moreover, in a given lightvalve technology there is usually some minimum practical pixel size [for acceptable image brightness, as well as for feasibility of fabrication], and the cost/yield implications of the 3× area increase needed to amalgamate all R,G,B subpixels into one lightvalve is quite significant, even when the subpixels are of minimum size. If the lightvalve image pixel count, denoted P, is near the state of the art, the cost of a single lightvalve with 3P subpixels is often considerably larger than that of 3 lightvalves with P pixels each. The patterned filter approach therefore tends to be adopted only at the low end of the market; for example in VGA (307,200 image pixels) or SVGA (480,000 image pixels) projectors at a time when more expensive 3-panel displays project XGA images (786,432 pixels).
In the case of color sequential lightvalve displays there are known arrangements that project two lightvalves with optical systems whose complexity is only slightly greater than that needed to project a single lightvalve. For example, Texas Instruments markets optical projection engines incorporating two DMD lightvalves, where one lightvalve is operated in a color sequential mode while the second projects red light only. This arrangement compensates the red deficient output of many short arc lamps. Another example is U.S. Pat. No. 5,517,340, to Doany et al., employing two sequentially-addressed lightvalves in order to ease the fast switching speed required when a single lightvalve must sequentially project all three colors.
For projectors employing lightvalves with patterned color filters, what is needed is a way to reduce the number of subpixels on the lightvalves while avoiding the complex optical systems used in projectors incorporating three lightvalves.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a projection display in which the complex optical systems used in projectors incorporating three lightvalves is avoided.
It is yet another object of the present invention to provide a projection display in which the expensive optical systems used in projectors incorporating three lightvalves is avoided.
Accordingly, a lightvalve projection system is provided in which the R,G,B color content of the image is divided between two lightvalves, so that each lightvalve need contain only a 1.5× increased number of subpixels, instead of the 3X increase needed in the conventional one-LV approach. The projection display incorporates an optical system using TIR prisms that can project two lightvalves at little greater cost than a single lightvalve [because no external dichroic filtering is required], making the invention suitable for the low-end market where the patterned filter approach is popular. The incoming data stream can be suitably divided between the two light valves by buffering the input R,G,B data stream in groups of 6 subpixel data values; it is not necessary to buffer entire subframes. The active layer response time required in the Light valves is the same as in conventional 3-LV configurations.
More specifically, disclosed herein is a projection display for displaying a color image formed of a plurality of color pixels. Each color pixel comprises a combination of different color light components. The display comprises a light source for supplying light to an optical path. A projection lens is disposed in the optical path, as are first and second light valves. The first and second light valves each have a plurality of subpixels. Each subpixel has an associated color filter for reflecting a corresponding color light component. The sub-pixels are grouped into groups of three, each group comprising a single sub-pixel from one of the first or second light valves and the remaining two sub-pixels from the other light valve, which together combine to form a color pixel of the color image for each of the color pixels of the color image. Lastly, directing means are provided for directing the light from the light source to the first and second light valves and for directing the respective color light components reflected from the light valves towards the projection lens which projects and magnifies the color pixels onto a screen thereby forming the color image.
Also provided is a method for displaying a color image with the projection display of the present invention. The method comprises a first step of supplying light from the light source. In a second step, the light is directed by means of the directing means towards the first and second light valves. In a third step, the respective color light components reflected from the light valves are directed by means of the directing means towards the projection lens. In a fourth step, each color light component of the single sub-pixel is projected and magnified onto the screen. In a fifth step, the color light components of each of the remaining two sub-pixels are simultaneously projected and magnified onto the screen to combine each single sub-pixel with its corresponding remaining two sub-pixels to form the color pixels of the color image.
REFERENCES:
patent: 5517340 (1996-05-01), Doany et al.
patent: 5555035 (1996-09-01), Mead et al.
patent: 5767924 (1998-06-01), Hiroki et al.
patent: 5808797 (1998-09-01), Bloom
patent: 5875006 (1999-02-01), Nagae et al.
patent: 5892497 (1999-04-01), Robertson
patent: 5900982 (1999-05-01), Dolgoff et al.
Ho Kenneth C.
Rosenbluth Alan Edward
Frenel Vanel
Morris, Esq. Daniel P.
Shalwala Bipin
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