Optical: systems and elements – Optical modulator
Reexamination Certificate
2000-05-11
2002-04-02
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
C359S223100, C359S224200, C348S203000, C073S504020
Reexamination Certificate
active
06366387
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention generally relates to a system and method of eliminating the appearance of pixels on an image, and more particularly to a mechanical method of removing such pixel images.
Currently, spatial light modulators (SLM's) are used to create digital image displays. The most common type of a SLM is the liquid crystal display (LCD) used in laptop computers and projectors. The LCD consists of an array of pixels (i.e., picture elements) that individually modulate a quantity of light impinging thereon. The individual pixels modulate the light from off to on or some level therebetween. The LCD may utilize polarization rotation to modulate the light level at each pixel. Alternatively, another class of spatial light modulators use a Schlieren system whereby incident light is deflected on or off an aperture to thereby modulate the light level. The SLM may be used in a projector to generate large images on a screen. In this respect, light is directed through the SLM to form the image on the screen.
The sharpness of an image is determined by the contrast ratio produced between two adjoining pixels. The contrast ratio is not dependent upon the resolution of the image, or whether discrete pixels or the grain in film creates the image. Generally, the contrast ratio for video is 200:1, while the contrast ratio for cinema is greater than 600:1. In order to maintain the contrast ratio for a SLM, any optics downstream of the SLM must have a transfer function two times greater than the limiting resolution of the modulator (i.e., Nyquist limit).
In a spatial light modulator, the array of pixels are generally arranged in rows and columns. Accordingly, each pixel is spatially isolated from an adjoining pixel by a black border. The active area of the pixel, as compared to the area of the pixel pitch, is known as the aperture ratio. The aperture ratio typically ranges from 92% to 45%. As will be recognized, the area around the pixel has no picture information in it and is optically opaque. Accordingly, the borders around the pixels create an array of black lines and columns superimposed around the pixels. This effect is commonly referred to as the screen door effect, as the image is similar to looking through a screen door.
Another deficiency with the current SLM's is the visual effect known as aliasing. Because the pixels are generally square and arranged in columns and rows, a line drawn on the display will appear as a stair-step if drawn at any angle other than horizontal or vertical. The worst case occurs when the pixels are square and the line is drawn at 45°. The line will appear as isolated squares joined at their corners. Accordingly, aliasing is the effect of a non-horizontal or non-vertical line appearing as a stair-step when produced by the spatial light modulator.
In rear projection video displays it is common practice for the screen to comprise an array of lenticular lenses separated by black strips. The black strips absorb light transmitted from the observers side of the screen and make the screen look blacker than it would otherwise be. By making the screen look blacker, the effective contrast ratio of the produced image is increased. However, if the spatial light modulator and the screen array are close in spatial frequency, a Moiré pattern will occur at a very low frequency. The Moiré pattern is a series of interference fringes which degrade the image on the screen.
The present invention addresses the above-mentioned deficiencies in prior art display systems by providing a system which removes undesired artifacts. Accordingly, the present invention reduces or illuminates the occurrence of the screen door effect through mechanical means. Additionally, the present invention eliminates Moiré patterns by shifting the temporal frequency of the projected image above the threshold that the human eye detects. Further, the present invention reduces the effects of aliasing by mechanically overlapping the corners of the adjacent pixels. As such, the present invention provides a projection system whereby the created image appears smoother without reducing the contrast ratio thereof.
BRIEF SUMMARY OF THE INVENTION
A depixelizer for enhancing an image generated by a spatial light modulator having an array of pixels. The depixelizer comprises a translatable stage having the spatial light modulator attached thereto. The stage is moveable in a first axis of motion and a second axis of motion. The movement of the stage in at least one axis oscillates the spatial light modulator and enhances the image generated thereby.
In the preferred embodiment, the first axis is generally perpendicular to the second axis and the stage is configured to be moveable in both the first and second axes of motion simultaneously. In order to translate the stage in both the first and second axes, the stage of the depixelizer comprises an outer stage moveable in the first axis of motion and an inner stage moveable in the second axis of motion.
In accordance with the present invention, the depixelizer further includes a first actuator attached to the outer stage and operative to translate the outer stage in the first axis of motion. Similarly, the depixelizer includes a second actuator attached to the inner stage and operative to translate the inner stage in the second axis of motion. As will be recognized, the inner stage is disposed within the outer stage by a set of inner stage mounting fingers attached to the inner stage and the outer stage. Accordingly, the second actuator is attached to the inner stage and the outer stage. Similarly, the depixelizer includes a frame that the outer stage is disposed within. The first actuator is attached to the outer stage and the frame by a set of outer stage mounting fingers.
Further, the depixelizer of the present invention includes an inner stage actuator mount spring attached to the outer stage and the second actuator and an outer stage actuator mount spring attached to the frame and the first actuator. The inner and outer stage actuator mount springs dampen vibration between the frame and the inner and outer stages. Typically, the inner stage mounting fingers, the outer stage mounting fingers, the inner stage, the outer stage, and the frame are integrally formed from a single sheet of metallic material.
In accordance with the present invention, there is provided a method of depixelizing an image generated by a spatial light modulator having a plurality of pixels with a prescribed pitch. The method comprises the step of oscillating the spatial light modulator in the direction of a first axis by a distance less than ½ the pitch of the pixels. Further, the method comprises oscillating the spatial light modulator in the direction of a second axis by a distance less than ½ the pitch of the pixels. Typically, the second axis will be generally perpendicular to the first axis. In the preferred embodiment, the spatial light modulator will be oscillated by the depixelizer in the direction of the first axis and the second axis to produce an elliptical motion of the spatial light modulator. The spatial light modulator will be oscillated in the frequency range of from about 30 Hz to 180 Hz in order to reduce the contrast ratio of the spatial light modular from 300:1 to about 2:1.
REFERENCES:
patent: 5864326 (1999-01-01), Rallison
patent: 5864417 (1999-01-01), Ho
patent: 5897980 (1999-04-01), Phillips et al.
patent: 5905328 (1999-05-01), Wilkinson
patent: 5926319 (1999-07-01), Phillips et al.
patent: 5945967 (1999-08-01), Rallison et al.
patent: 6118569 (2000-09-01), Plesko
Epps Georgia
Stetina Brunda Garred & Brucker
Thompson Tim
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