Optical: systems and elements – Projection screen
Reexamination Certificate
2001-05-15
2003-10-28
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
C359S449000, C359S454000, C359S459000, C359S489040, C359S490020
Reexamination Certificate
active
06639719
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates generally to optical imaging systems, and more particularly to a system and method for scanning multiple regions with respective scanning beams. For example, the system may simultaneously scan regions—often called “tiles”—of an image onto a display screen with respective image (on) beams. Scanning an image as multiple tiles often provides the image with a higher resolution for a given scan rate.
BACKGROUND OF THE INVENTION
Imaging-system manufactures strive to develop reasonably priced imaging systems that provide high-quality, high-resolution images. For example, manufacturers strive to develop reasonably priced image-capture or -display systems that can scan high-resolution images.
But increasing the resolution of a scanned image often requires increasing the image scan rate, which often requires increasing the complexity, and thus the cost, of an image-capture or -display system.
Therefore, engineers have developed “tiling” image systems that separately scan respective regions, i.e., tiles, of an image. Thus, for a given scan rate, a tiling system often provides images having a higher resolution than a non-tiling system.
Unfortunately, tiling image systems may capture or display images that are dim, have uneven brightness, or have other artifacts that reduce the quality of the captured or displayed images.
OVERVIEW OF IMAGE-DISPLAY DEVICES AND TECHNIQUES
A variety of image-display/image-projection devices and techniques are available for visually displaying/projecting graphical or video images—often called video frames—to a viewer. Typically, a graphical image is an image that changes slowly or not at all. For example, a flight-instrument graphic is an image of cockpit instruments that overlays a pilot's view. This graphic may be projected onto a viewing area such as the windshield or may be projected directly into the pilot's eyes such that he/she sees the flight instruments regardless of his/her viewing direction. There is typically little change in this graphic other than the movement of the instrument pointers or numbers. Conversely, video frames are a series of images that typically change frequently to show movement of an object. For example, a television set displays video frames.
A cathode-ray-tube (CRT) display, such as used in a television or a computer monitor, is a common image-display/image-projection device that, unfortunately, has several limitations. For example, a CRT is typically bulky and consumes a significant amount of power, thus making it undesirable for many portable or head-mounted applications.
Flat-panel displays, such as liquid-crystal displays (LCDs), organic LEDs, plasma displays, and field-emission displays (FEDs), are typically less bulky and consume significantly less power than a CRT having a comparable viewing area. But, flat panel displays often lack sufficient luminance and adequate color purity and/or resolution for many head-mounted applications.
A common problem with both CRTs and flat-panel displays is that the displayed/projected image may include visible artifacts that are introduced into the image during the capturing, processing, or displaying of the image. Typically, an image-capture device such as a vidicon tube or charge-coupled device (CCD) captures an image of an object by converting light reflected by the object into electrical signals. A display/projection system that includes one of the aforementioned display/projection devices receives these electrical signals and processes them. The display/projection device converts these processed electrical signals into an array of pixels, which a viewer perceives as an image of the object. Unfortunately, visible errors and degradations, often called artifacts, may be introduced into the image during the conversion of the reflected light into electrical signals, during the processing of the electrical signals, or during the converting of the electrical signals into pixels.
Recently, engineers have developed an image amplifier that can display an image or project the image onto a display screen. Typically, an image amplifier is less complex, less expensive, and can be made smaller than a CRT or flat-panel display, and an image-amplifier display system typically uses significantly less power than a CRT or flat-panel display system. Furthermore, because it does not necessarily convert light into electrical signals and back again, an image-amplifier display system typically introduces fewer artifacts into an image.
FIG. 1
is a perspective view of a conventional image-amplifier display system
20
that includes an image amplifier
22
, an illuminator
24
, and an image generator
26
. For example, the image amplifier
22
may be a Light Smith, which was developed by Simac Company of Boise, Id. Although, as discussed above, the system
20
is often less complex, cheaper, and smaller than a CRT or flat-panel display system, it can display/project a relatively bright and high-quality image
28
.
The image amplifier
22
of the system
20
includes transparent front and back electrodes
30
and
32
and a display/projection screen
34
having a display/projection surface
36
and a scan surface
38
. An electric-field generator (not shown) is coupled to the electrodes
30
and
32
and generates an electric field across the screen
34
. This electric field allows the image generator
26
to set the brightness levels—here the reflectivity levels—of the regions of the display/projection surface
36
such that the generator
26
can generate bright and dark pixels of an image. For example, the generator
26
can set the reflectivity of the region
44
on the surface
36
to a relatively high level such that the region
44
reflects a relatively high percentage of the incident light from the illuminator
24
. Therefore, in this example, the pixel of the image
28
corresponding to the region
44
is a relatively bright pixel.
The illuminator
24
typically includes an incoherent light source such as an incandescent bulb (not shown), which illuminates the display/projection surface
36
of the screen
34
. The surface
36
reflects the light from the illuminator
24
according to the reflectivity of each region
44
to display the image
28
—that is, project the image
28
directly into a viewer's (not shown) eye—or to project the image
28
onto a display screen
46
through an optical train
47
, which is represented by a lens.
The image generator
26
generates the image
28
on the display/projection surface
36
of the screen
34
by erasing the surface
36
with an electromagnetic erase burst
40
and then scanning an image beam
42
across the scan surface
38
.
More specifically, erasing the surface
36
of the screen
34
entails simultaneously setting all the regions
44
on the surface
36
to the same or approximately the same predetermined reflectivity level with the erase burst
40
. Typically, this predetermined reflectivity level is a low reflectivity level—which represents black—although it can be any other desired reflectivity level. The erase burst
40
typically is an energy burst having a first wavelength in the visible, ultraviolet, or infrared range of the electromagnetic spectrum and is wide enough to simultaneously strike the entire scan surface
38
. Where the erase level is black, the screen
34
is typically constructed such that exposing the scan surface
38
to this first wavelength reduces the reflectivity levels of the regions
44
. Because these reflectivity levels may be different from one another before the erase cycle, the generator
26
generates the burst
40
long enough to reduce the reflectivity levels of all the regions
44
to the black level regardless of their pre-erase reflectivity levels. Furthermore, because it typically “turns off” the reflectivities of the regions
44
, the burst
40
is sometimes called an “off” burst.
Generating the image
28
on the screen
34
entails scanning the image beam
42
across the scan surface
38
to set the reflectivity levels of the regions
44
Lewis John R.
Tegreene Clarence T.
Urey Hakan
Adams Russell
Cruz Magda
Graybeal Jackson Haley LLP
Microvision Inc.
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