Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Patent
1996-10-24
2000-05-02
Saras, Steven J.
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
345 84, 345 98, G09G 334
Patent
active
060578165
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to display devices and more particularly to circuits and methods for driving display devices. The invention particularly relates to display devices including a matrix array of switchable elements, each switchable element being switchable between at least two states, the form of the image displayed by the display device being dependent on which state each switchable element of the array is in.
BACKGROUND OF THE INVENTION
Such switchable elements may take the form of spatial light modulators which spatially modulate light from a light source, the spatially modulated light being projected onto a display screen to produce a displayed image. Examples of spatial light modulators include deflectable mirror devices as, for example, described in "Deformable Mirror Spatial Light Modulators" by Hornbeck, published in the Proceedings of SPIE, Vol. 1150, August 1989. Such deflectable or "deformable" mirror devices (DMDs) include an array of switchable mirror devices, each mirror device being mounted on a torsion element over a control electrode. Applying an electric field between each mirror device and the electrode causes the mirror device to pivot, thus changing the direction of light reflected from the mirror device.
Another example of a spatial light modulator is a liquid crystal device.
Alternatively, the matrix array of switchable elements may take the form of an array of light sources which themselves can be switched either "on" or "off", as for example in an array of light emitting diodes.
Generally such display devices are digital devices, that is each switchable element of the display device is effective to switch the light passing from the element to the displayed image either "on" or "off" so as to produce either "white" or "black" pixels on the displayed image. It is, however, possible to display grey scale images by controlling the time for which each switchable element of the display device is in a state such that light from the element arrives at the displayed image, and using the integrating response of the eye of an observer who will perceive a grey scale image from the element.
An example of such an arrangement is described in GB 2014822 which discloses a display device incorporating an X-Y array of energizable light emitting devices. The display device described in GB 2014822 takes data in binary digital forms, for example via an 8 bit signal, the device being driven a line at a time in a number of periods during which the modulators may be "on" or "off". The "ton"/"off" state of each pixel during each time period is determined by the state of the corresponding bit of the digital input data.
Display devices incorporating spatial light modulators, for example in the form of deflectable mirror devices, operate in an analogous manner. In deflectable mirror devices, however, the entire pixel array is driven simultaneously in sympathy with the video source vertical scan rate.
For an 8-bit input video signal, the eight time periods within each display frame period are of different lengths corresponding to bits D0 to D7 of the input video signal. The length of the time period corresponding to the least significant bit (LSB) or D0 in the input signal for any particular frame is set at a predetermined value, the duration of the time period corresponding to the next to the least significant bit (D1) being twice as long as that corresponding to the LSB, and so on. Thus, the length of the time period corresponding to the most significant bit (MSB) or D7 in the input signal is 128 times that corresponding to the LSB. Provided that all the time periods are included within a display frame period of less than around 20 msecs duration, the eye of the observer will integrate the periods and respond as if to a single period having a level of brightness corresponding to the binary signal value. All the bits of the same significance are entered into the element of the array effectively simultaneously. At the end of each sub-frame period corresponding to a single bit of t
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Digital Projection Limited
Nelson Alecia D.
Russell, Esq. Dean W.
Saras Steven J.
Turton, Esq. Michael J.
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