|Publication number||US20050225732 A1|
|Application number||US 11/156,881|
|Publication date||13 Oct 2005|
|Filing date||20 Jun 2005|
|Priority date||23 Dec 2003|
|Also published as||CN1898969A, EP1698181A1, US7182463, US7300157, US20050134805, US20070091274, WO2005067307A1|
|Publication number||11156881, 156881, US 2005/0225732 A1, US 2005/225732 A1, US 20050225732 A1, US 20050225732A1, US 2005225732 A1, US 2005225732A1, US-A1-20050225732, US-A1-2005225732, US2005/0225732A1, US2005/225732A1, US20050225732 A1, US20050225732A1, US2005225732 A1, US2005225732A1|
|Inventors||Arlie Conner, Gary Kingsley|
|Original Assignee||3M Innovative Properties Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (19), Referenced by (28), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation of U.S. Ser. No. 10/744,997, filed Dec. 23, 2003, currently pending, the disclosure of which is herein incorporated in its entirety by reference.
The present invention relates to projection lens assemblies for projection display systems and, in particular, to a projection lens assembly that includes a pixel-shifting element to provide optical interlacing of pixels for increased addressability.
In many types of display systems images are formed by pixelated optical modulators such as conventional liquid crystal displays, digital micromirror devices, liquid crystal-on-silicon modulators, etc. Although there are many advantages of these pixelated displays, they can also bring with them the disadvantage of fixed and relatively coarse addressability. Resolution relates to the number of pixels in a pixelated display panel, and addressability relates to the number of pixel locations in a display image (i.e., the display panel resolution times the number of distinct positions that each pixel can occupy in a display image).
Another problem is that each picture element in some pixelated displays includes a central imaging area or aperture that transmits or reflects image information and is bounded by an opaque border. The opaque borders can encompass significant portions of the picture elements relative to the optical apertures. In projection display systems, the projected images of these picture elements can have discernible image artifacts relating to the picture element borders. The image artifacts can include rough image edges and visible dark disruptions in image consistency.
Attempts have been made to improve the image appearance by physically shifting light from pixelated display devices in order to shift pixel images and thereby increase addressability. In one instance, a pixelated front projector shifted display pixels using a pixel-shifting device preceding or following a projection lens assembly. In one implementation, a pixel-shifting assembly included silicone material pressed between two glass plates. The assembly was positioned after a projection lens assembly and three solenoids operated together to tilt the glass plates relative to each other to effect fill-in pixel scanning. In another implementation, a cantilevered glass plate was positioned in front of a projection lens assembly and driven by a pair of modulators also to effect fill-in pixel scanning.
While providing in-fill pixel scanning both of the implementations can suffer from disadvantages relating to maintaining optimal image clarity. The pixel-shifting assembly positioned after a projection lens operates in a diverging optical space where light from the projection lens is diverging as it propagates toward a display screen. Shifting pixel locations in such a diverging optical space can introduce defects relating to differences in the propagation angles of light being projected toward different portions of the display screen. The pixel-shifting assembly positioned before a projection lens operates in a telecentric optical space in which the tilted plate causes astigmatism and reduces the lens performance.
These disadvantages could be even more greatly exaggerated if the addressability improvement methods for front projectors were employed in rear projectors. A front projector is positioned in front of a reflective display screen, together with the viewers of any displayed image. In contrast, a rear projector is positioned behind a transmissive display screen, opposite the viewers of the displayed images. Rear projectors typically have relatively short focal lengths relative to the size of the display screen, so projection lens assemblies in these projectors have much steeper projection angles of up to about 45 degrees compared to projection angles of about 25-30 degrees for projection lens assemblies in front projectors. As a consequence, addressability improvements for front projectors are likely to be substantially less successful for rear projectors.
Accordingly, the present invention includes a projection lens assembly for a projection display system. The projection lens assembly includes multiple projection lens elements that are configured to receive light imparted with display information by a pixelated display device. The projection lens elements project the light toward a display screen. A pixel-shifting element is included within the projection lens assembly to cyclically shift between at least two positions within the projection lens assembly to form, at a display screen, at least two interlaced arrays of pixels. An electromechanical transducer is coupled to the pixel-shifting element to impart on it the cyclic shifting between positions. The invention also includes a projection display system incorporating such a lens assembly.
The projection lens assembly with a pixel-shifting element included among the lens elements can often provide resolutions that are at least twice the actual resolution of the pixelated display device. In addition, the optical space within the projection lens is typically significantly less susceptible to introducing image artifacts that are pixel-scanners positioned before or after a projection lens. Furthermore, shifting pixels within the projection lens assembly can allow the pixel-shifting element to be formed of a smaller size, which can reduce any difficulty of manipulating a pixel-shifting element at the required speeds.
Additional description and implementations of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.
Illumination system 12 directs illumination light at pixelated display device 14, which imparts display information on the illumination light in any conventional or similar manner. Pixelated display device 14 may include a liquid crystal display, a digital micromirror device, or any other type of pixelated display device. Illumination light may be transmitted through pixelated display device 14 as illustrated or may alternatively be reflected from it. Projection lens assembly 16 projects onto a display surface 20 the display information received from pixelated display device 14, thereby to form a display image. Display surface 20 may be primarily reflective so that the display image is reflected toward one or more viewers, as in a front projector, or may be primarily transmissive so that the display image is transmitted through toward one or more viewers, as in a rear projection display. Examples of suitable projection display systems with reflective display surfaces 20 are described in U.S. Pat. No. 6,486,997.
Pixel-shifting element 18 is included within projection lens assembly 16 and cyclically shifts between at least two positions to shift optical paths of light as it passes through projection lens assembly 16, thereby cyclically shifting where the optical paths meet display screen 20. Image information imparted by picture elements of pixelated display 14 is carried along the optical paths to meet display screen 20 as image pixels. The cyclic shifting of pixel-shifting element 18 results in pixels being shifted in position at display screen 20.
Within this context pixel shifting element 18 functions to cyclically shift pixels on display screen 20 along at least one axis 34 that is transverse (e.g., perpendicular) to rows 31. As a result, pixels 30 are positioned in rows 31 during one time period, and shifted-pixels 35 (not in bold lines) are positioned in rows 36 during a second time period. This forms two interlaced arrays of pixels 30 and 35. Pixels 30 in rows 31 and shifted-pixels 35 in rows 36 are alternately rendered on display screen 20. Rows 31 and 36 are offset from each other by about one-half their shared pitch 37, so that shifted-pixels 35 have light apertures 38 that overlap opaque borders 33 of pixels 30 in rows 31. It will be understood that the pixels in this embodiment and the other embodiments described herein could be shifted additionally or alternatively to form offset columns. For example, the pixels could be shifted in the appropriate direction to form offset columns in a manner similar to the formation of offset rows 31 and 36.
The cyclic shifting between rows 32 and 36 represents a one-dimensional shifting that doubles the effective number of pixels 30 and 35 on display screen 20 relative to the number of picture elements in pixelated display device 14. This doubling has the benefit of providing twice the apparent number of imagining positions, which results in improved image quality.
It will be appreciated that pixels 30 in rows 31 are shifted relative to shifted-pixels 35 in rows 36 to the same extent that shifted-pixels 35 in rows 36 are shifted relative to pixels 30 in rows 31. The terminology “pixels 30” and “shifted-pixels 35” is used merely for purposes of illustration and does not indicate a functional distinction between the pixels 30 and 35.
Within this context pixel shifting element 18 functions to cyclically shift pixels 40 on display screen 20 along at least one axis 43 that is transverse (e.g., perpendicular) to rows 41. As a result, pixels 40 are positioned in rows 41 during one time period, and shifted-pixels 44 (not in bold lines) are interposed between pixels 40 in adjacent rows 41 during a second time period. This doubles the number of pixels 40 in each row 41. Pixels 40 and shifted-pixels 44 are alternately rendered on display screen 20.
Within this context pixel shifting element 18 functions to cyclically shift pixels 46 on display screen 20 along at least one axis 48 that is transverse (e.g., perpendicular) to interdigitated rows 47. As a result, pixels 46 are positioned in rows 47 during one time period, and shifted-pixels 49 (not in bold lines) are positioned in adjacent rows 47 during a second time period. Shifted-pixels 49 are shifted by about one-half the pitch of rows 47 and provide increased pixel addressability. Pixels 40 and shifted-pixels 49 are alternately rendered on display screen 20.
The cyclic shifting along axes 58 and 59 represents two-dimensional shifting that provides on display screen 20 four-times the number of picture elements in pixelated display device 14. As with the one-dimensional shifting, this two dimensional shifting provides the benefit of improved image quality.
Wedge-shaped pixel-shifting element 64 is positioned at about a pupil or stop location 65 within projection lens assembly 60. At least one of plates 61 of pixel-shifting element 64 is physically rocked across deformable material 63 by an actuator 68 to alternately provide the upward tilt and the downward tilt. Actuator 68 is coupled to a control circuit 70, which provides pixel-shifting control signals that are coordinated with the activation of picture elements of pixelated display device 14.
Actuator 68 may be implemented with a piezoelectric or piezoceramic transducer configured to impart the back and forth rocking motion. As is known in electromechanical systems design, actuator 68 may alternatively be implemented with or include a voice-coil, a solenoid, or any other electromagnetic effect that can achieve the desired motion. In some implementations, pixel-shifting element 64 is moved into distinct positions in an approximation of a square-wave type motion. In other implementations, pixel-shifting element 64 can be moved into the positions with a sinusoidal, resonant motion. Generally, pixel-shifting element 64 shifts between positions during times when the display image is dark (e.g., blanked) or inactive, such as during a retrace period.
To provide two-dimensional pixel shifting as illustrated in
In this implementation, pixel shifts 80 between first and second pixel positions 84 and 86 are coordinated with the blue color-component sub-frames 82B, which represents a time period of about 3 milliseconds. The timing coordination implementation illustrated in
The human visual system is much less sensitive to blue wavelengths, and in many color display the blue color-component makes up only about 8% of the luminance. By comparison, the green color-component is commonly about 69% of luminance and the red color component is about 23% of luminance at a balanced white point. As a result, shifting during the blue color component can be nearly invisible, which is advantages during color television moving pictures and in case of any overshooting and other complex motions of pixel-shifting actuator 68.
Pixel-shifting fold mirror element 104 is positioned in a center region of projection lens assembly 100 in the vicinity of a pupil or stop location 108. Pixel-shifting element 104 is physically tilted by an actuator 110, which may be implemented with a piezoceramic transducer, or an alternative actuator, to impart the tilting motion at an edge of element 104. Pixel-shifting fold mirror element 104 is supported at its edges by a stiff, light-weight frame (not shown) that is supported at a hinge or pivot aligned with rotational axis 106. Actuator 110 is coupled to the frame and is controlled by a control circuit 112, which provides pixel-shifting control signals that are coordinated with the activation of picture elements of pixelated display device 14.
In an implementation with one-dimensional pixel shifting, pixel-shifting element 104 may tilted over a range of about 0.02 degrees between a pair of positions to provide pixel-shifting of about one-half the pixel pitch. This implementation could include pixelated display device 14 with a diagonal dimension of 0.6 inch (15.25 mm) and a 13.8 μm pixel pitch, and display screen 20 with a diagonal dimension of 50 inches (127 cm). Such tilting can be achieved with actuator 110 imparting a translation of edges of pixel-shifting element 104 of about 10 μm during the cyclic tilting. Such translational distances are within the scope of commercially-available piezoelectric devices.
Pixel-shifting element 124 is physically tilted by a pair of actuators 130X and 130Y, which may be implemented with piezoceramic transducers, or an alternative actuators, configured to impart the tilting motion at edges of element 124. Pixel-shifting fold mirror element 124 is supported at its edges by a stiff, light-weight frame (not shown) that is supported at a gimbaled pair of hinges or pivots aligned with rotational axes 126X and 126Y. Actuators 130X and 130Y are coupled to the frame and provide tilting about respective axes 126X and 126Y. A control circuit 132 provides to actuators 130X and 130Y pixel-shifting control signals that are coordinated with the activation of picture elements of pixelated display device 14.
To provide one-dimensional pixel shifting as illustrated in
Projection lens assembly 140 is distinguished from projection lens assembly 60 in that the former does not include a separate element (e.g., pixel-shifting wedge element 64) that functions solely to provide pixel shifting. Instead, pixel shifting lens element 144 has at least one curved major surface that cooperates with lens elements 144 to provide the optical characteristics of projection lens assembly 140. The choice of which lens element or elements to operate as pixel shifting element 144 can be made depending on optical sensitivity. A lens element with more optical power (i.e., a shorter focal length) will have a faster displacement effect. Powerful negative (e.g., concave) lens elements can also be moved to effect pixel shifting.
Pixel-shifting element 144 is physically moved in lateral directions 146 by an actuator 148, which may be implemented with a piezoceramic transducer, or an alternative actuator, configured to impart the lateral motion. Actuator 148 is coupled to a control circuit 150, which provides pixel-shifting control signals that are coordinated with the activation of picture elements of pixelated display device 14. In implementations with either one- or two-dimensional pixel shifting, translational shifting of pixel-shifting element 144 by a distance of, for example, 20 um along either translational axis produces a half-pixel shift at the projected image.
During its illumination by illumination system 168A, pixelated display device 170 is imaged upon wedge 166A, which directs pixels 174A (only one shown) to a first offset location. During its illumination by illumination system 168B, pixelated display device 170 is imaged upon wedge 166B, which directs pixels 174B (only one shown) to a second offset location that is different from the first location. Illumination systems 168A and 168B may be may be alternately activated or shuttered to provide the alternating illumination.
Pixel-shifting fold mirror element 186 is physically moved in oppose directions 190 by an actuator 192, which may be implemented with a piezoceramic transducer, or an alternative actuator. Translational shifting or mirror 186 in directions 190 that are perpendicular to the plane of mirror 186 cause a displacement of the optical center of projection lens assembly 188, and thereby the desired one-half pixel shift. Actuator 192 is coupled to a control circuit 194, which provides pixel-shifting control signals that are coordinated with the activation of picture elements of pixelated display device 182. In an alternative implementation, Fresnel lens 184 may also be shifted with mirror 186.
In view of the many possible embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. Rather, we claim as our invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.
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|U.S. Classification||353/31, 348/E09.027|
|Cooperative Classification||H04N9/3188, H04N9/3197|
|European Classification||H04N9/31S5, H04N9/31V|