Television – Video display – Projection device
Reexamination Certificate
1999-04-19
2002-09-24
Miller, John (Department: 3614)
Television
Video display
Projection device
C348S746000, C348S747000, C348S806000, C345S501000
Reexamination Certificate
active
06456340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to image processing for a digital display system, and relates more particularly to an apparatus and method for performing image transforms and multi-frame processing of input images to produce high-quality output images.
2. Discussion of Prior Art
Cathode Ray Tubes (CRTs), used in conventional televisions and computer monitors, are analog devices which scan an electron beam across a phosphor screen to produce an image. Digital image-processing products that enhance display graphics and video on CRTs have been increasingly available, because CRTs can operate with many different input and output data formats. Further, CRTs can display moving images with high quality screen brightness and response. However, CRTs have considerable limitations in such applications as portable flat-screen displays where size and power are important. Additionally, as direct-view CRT display size increases, achieving high image quality across the complete display becomes more difficult and expensive.
Many recent portable and desktop systems include digital displays using liquid crystal displays (LCDs), a term which generally describes flat-panel display technologies and in particular, may include active matrix liquid crystal displays (AMLCDs), silicon reflective LCDs (si-RLCDs), ferroelectric displays (FLCs), field emission displays (FEDs), electroluminescent displays (ELDs), plasma displays (PDs), and digital mirror displays (DMDs).
Compared to traditional CRT displays, LCDs have the advantages of being smaller and lighter, consuming less power, and having discrete display elements which can provide consistent images across the entire display. However, manufacturing LCDs requires special processing steps to achieve acceptable visual quality. Further, large screen direct view LCDs are expensive, and LCDs usually require a display memory.
Both CRT and LCD technologies can provide economical projection-system large screen displays. CRT-based projection systems usually require three CRTs and three projection tubes, one for each of the Red (R), Green (G), and Blue (B) color components. Each tube must produce the full resolution display output at an acceptable brightness level, which makes the tubes expensive. Achieving proper tolerances for mechanical components in projection systems, including alignment hardware and lenses, is also expensive. Consequently, manufacturing CRT-based projection systems is costly. Since CRTs are analog devices, applying digital image-processing techniques to CRT-based systems usually requires a frame buffer memory to effectively represent the digital image data.
Projection display systems also may use transmissive or reflective LCD “microdisplay” technologies. Achieving the desired full color gamut in LCD-based parallel color projection systems, as in CRT-based projection systems, uses three separate LCD image modulators, one for each of the R, G, and B color components. A single LCD image modulator which produces R, G, and B, either through spatial color filters or with sequential color fields at a sufficiently high rate, can provide a low cost system.
FIG. 1
shows a prior art projection system
150
that includes a light system
100
, mirrors
102
,
104
,
106
, and
108
, transmissive image modulators
110
,
112
, and
114
, dichroic recombiners
116
and
118
, and a projection lens
120
. Light system
100
includes an illumination source such as a xenon lamp and a reflector system (not shown) for focusing light.
Mirrors
102
,
104
,
106
, and
108
, together with other components (not shown) constitute a separation subsystem that separates the light system
100
output white light beam into color components Red (R), Green (G), and Blue (B). The separation subsystem can also use prisms, including x-cube dichroic prism pairs or polarizing beam splitters.
Each image modulator
110
,
112
, and
114
receives a corresponding separated R, G, or B color component and functions as an active, full resolution, monochrome light valve that, according to the desired output images, modulates light intensities for the respective R, G, or B color component. Each image modulator
110
,
112
, and
114
can include a buffer memory and associated digital processing unit (not shown). A projection system may use only one image modulator which is responsible for all three color components, but the three image modulator system
150
provides better chromaticity and is more efficient.
Dichroic recombiners
116
and
118
combine modulated R, G, and B color components to provide color images to projection lens
120
, which focuses and projects images onto a screen (not shown).
FIG. 1
system
150
can use transmissive light valve technology which passes light on axis
1002
through an LCD shutter matrix (not shown). Alternatively, system
150
can use reflective light valve technology (referred to as reflective displays) which reflects light off of digital display mirror display (DMD) image modulators
110
,
112
, and
114
. Because each image modulator
10
,
112
, and
114
functions as an active, full resolution, monochrome light valve that modulates the corresponding color component, system
150
requires significant buffer memory and digital image processing capability.
Because of inherent differences in the physical responses of CRT and LCD materials, LCD-based projection and direct view display systems each have different flicker characteristics and exhibit different motion artifacts than CRT-based display systems. Additionally, an intense short pulse depends on the properties of CRT phosphors to excite a CRT pixel, whereas a constant external light source is intensity modulated during the frame period of an LCD display. Further, LCDs switch in the finite time it takes to change the state of a pixel. Active matrix thin film transistor (TFT) displays, which have an active transistor controlling each display pixel, still require a switching time related to the LCD material composition and thickness, and to the techniques of switching.
Most LCD-based image modulators (such as
110
,
112
,
114
) are addressed in raster scan fashion and each pixel requires refreshing during each display frame interval. Accordingly, every output pixel is written to the display during every refresh cycle regardless of whether the value of the pixel has changed since the last cycle. In contrast, active matrix display technologies and some plasma display panel technologies may allow random access to the display pixels. Other panels use a simpler row-by-row addressing scheme that is similar to the raster scan of a CRT. Additionally, some displays have internal storage to enable output frames to self-refresh based on residual data from the previous output frame.
Field Emission Displays (FEDs) may include thousands of microtips grouped in several tens of mesh cells for each pixel. The field emission cathodes in FEDs can directly address sets of row or column electrodes in FEDs, and FEDs have rapid response times. FEDs can use external mesh addressing for better resolution images, but this requires increased input/output (I/O) bandwidth outside of the FED.
Opto-mechanical systems can provide uniform brightness and high chromaticity for high quality displays. Additionally, high quality projection lens systems can provide bright and uniform images. However, component and assembly tolerances in opto-mechanical systems can result in system imperfections including imprecise image modulator alignment and geometric lens distortion.
Commercially-available digital image processing systems, usually part of an electronic control subsystem, can process analog or digital input data and format the data into higher resolution output modes. These processing systems typically perform operations such as de-interlacing, format conversion and line doubling or quadrupling for interlaced analog input data. Some systems include a decompression engine for decompressing compressed digital data, and input data scaling to match the resolutio
Miller John
Pixonics LLC
Tran Trang U.
Wells St. John P.S.
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