Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-12-18
2001-09-04
Hjerpe, Richard (Department: 2775)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S096000, C348S742000
Reexamination Certificate
active
06285346
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to display systems for displaying continuously updated image information signals arranged in successive frames, employing electro-optic light modulators, and more particularly relates to a scrolling color projection display system in which color bars are repetitively scrolled across a single electro-optic light modulator panel to produce a color display.
Such single panel scrolling color display systems are known. See, for example, commonly assigned U.S. Pat. No. 5,532,763, incorporated herein by reference.
These display systems are particularly suitable for displaying color information in the form of continuously updated image information signals arranged in successive frames representing full color frames, each frame comprised of component color subframes, such as color video information. These systems employ an electro-optic light modulator comprised of a row-and-column matrix array of pixels, for modulating light in accordance with the image information signals during successive frame periods. The signal information is applied to the pixel rows of the array a line at a time during each frame period for each component color.
Such display systems employing a single reflective high-density active-matrix liquid crystal display (AMLCD) on silicon as the electro-optic light modulator are being considered for high resolution color projection systems, due to the fact that the matrix structure of row and column electrodes, switches and storage capacitors can all be integrated on the silicon substrate below the reflective pixel electrodes, thus enabling the high pixel density required for such high resolution displays.
Unfortunately, the location of the reflective pixel electrodes in the LC cell structure leads to an asymmetric electrical behavior during driving, in the form of a DC off-set in the drive voltage, even in the case of AC driving. This DC off-set is perceived as flicker by the viewer of a continuously updated display image, such as a video image
One way to suppress this flicker (George: is this publicly known?) is to adjust the drive voltage to compensate for the DC off-set. However, such a compensation scheme is difficult to implement, since the off-set voltage tends to be non-uniform over the pixel array, and also tends to vary with time.
Another way to suppress this flicker would be to operate the system at a frame rate well above the limit where flicker can be perceived. However, such an operation would reduce the brightness of the display. The reason for this is that guard bars (
30
,
34
and
38
in
FIGS. 2 and 3A
) separate the color bars (
32
,
36
and
40
), in order to accommodate the finite switching time of the LC material, and thus preserve color purity.
Operating the system at a higher frame rate) would reduce the size of the color bars (
46
,
50
,
54
,
58
,
62
,
66
in
FIG. 3B
) in the scrolling direction, since the time period for addressing the pixel array with each new frame of color information would be reduced. However, the size of the guard bars (
44
,
48
,
52
,
56
,
60
,
64
) would remain the same, because the switching time of the LC material remains the same. Thus, the proportion of dead time in which the pixel array is not being addressed with color information would be reduced.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a display system for displaying continuously updated image information signals arranged in successive frames, and employing a reflective electro-optic light modulator, in which flicker of the display is reduced without substantially reducing the brightness of the display.
It is another object of the invention to provide such a projection system employing scrolling color bars, in which flicker of the display is reduced without substantially reducing the brightness of the display.
It is yet another object of the invention to provide such a scrolling color bar projection system employing a reflective AMLCD light modulator, in which flicker due to electrical asymmetry in the AMLCD is reduced without substantially reducing the brightness of the display.
It is a still further object of the invention to provide a method for addressing a display system employing a reflective electro-optic light modulator in which flicker of the display is reduced without reducing the brightness of the display.
In accordance with the invention, a display system is provided for displaying continuously updated image information signals arranged in successive frames representing color frames, the system employing a reflective electro-optic light modulator comprised of a row-and-column matrix array of pixels, for modulating light in accordance with the image information signals during successive frame periods, wherein each row of the array is addressed at least twice during each frame period with the image information.
In accordance with a preferred embodiment of the invention, the matrix array is illuminated with scrolling color bars corresponding to the color signal information being addressed.
In accordance with another embodiment of the invention, each frame comprises two or more component color sub-frames, and each row of the array is addressed at least twice during each frame period with the image information signals for at least one of the component color sub-frames, and preferably for all of the component color sub-frames.
Preferably, the reflective electro-optic light modulator is an active matrix liquid crystal display (AMLCD) device.
REFERENCES:
patent: 5337068 (1994-08-01), Stewart et al.
patent: 5448314 (1995-09-01), Heimbuch et al.
patent: 5969700 (1999-10-01), Fitgibbons et al.
patent: 6002452 (1999-12-01), Morgan
patent: 0875881A2 (1998-11-01), None
Janssen Peter
Melnik George
Eisen Alexander
Hjerpe Richard
Philips Electronics North America Corporation
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