Data encoding algorithms find a rich application field in the realm of electronic video displays, particularly with respect to flat panel display systems. While in no way limiting the present invention, or associated prior art, to this application, it is instructive to tabulate the features of such example applications to illustrate how prior art has evolved and been applied. This approach is followed in the discussion immediately following.
The first illustrative example for the application of such encoding algorithms is a direct-view flat panel display system that uses sequentially-pulsed bursts of red, green, and blue colored light emanating from the display surface to create a full color image. The human visual system effectively integrates the pulsed light from a light source to form the perception of a level of light intensity. By making an array of pixels (picture elements on the video display) emit, or transmit, light in a properly pulsed manner, one can create a full-color display. A term commonly used to define this technique is called field sequential color (hereafter, FSC), and U.S. Pat. No. 5,319,491 (Selbrede) entitled “Optical Display,” uses this phenomenon as a basis for a flat panel display and is incorporated by reference herein.
The gray scale level generated at each point on the display surface is proportional to the percentage of time the pixel is ON during the primary color subframe time, tcolor. The frame rates at which this occurs are high enough to create the illusion of a continuous stable image, rather than a flickering one. During each primary color's determinate time period, tcolor, one can dictate the shade of that primary color by having its associated pixel open for the appropriate fraction of tcolor. For example, producing 24-bit encoded color requires 256 (0-255) shades defined for each primary color. If one pixel requires a 50% shade of red, then that pixel will be assigned with shade 128 ( 128/256=0.5) and stay on for 50% of tcolor. This form of data encoding assumes a constant magnitude light source to be modulated across the screen. Moreover, it achieves gray scales by evenly subdividing tcolor into fractional temporal components.
To generalize from this specific video-based application to a wider range of suitable applications, it is appropriate to define terms to be used throughout this disclosure. The individual video pixels, which correspond to array elements from the standpoint of the incoming data, serve to modulate (by on/off gating) the light present within the display screen. The light within the screen (the global quantity to be modulated by gating at each array element) is emitted at a determinate intensity for a determinate duration. This physical effect, of known intensity and duration, shall henceforth be termed a transmission pulse. It is the quantity that will be modulated by the encoding data within the array. The light illuminating the video display, then, is a surrogate for a larger class of quantifiable entities which can be mathematically encoded and controlled using the methods disclosed in this disclosure. Said quantifiable entities symbolized by the term “transmission pulse” may not necessarily be intensities of light energy, as the application range of the encoding method is far broader than the field of video displays.
Other technologies use FSC and pulse width modulation (hereafter, PWM) address schemes to create a projection-based system (as opposed to the direct-view system referenced above). Such a projection-based display is found in the Digital Light Processor™ (DLP) from Texas Instruments, a patented projector system which uses an array of micromirrors as disclosed in the patent for the Digital Micromirror Device™ (DMD) (see U.S. Pat. Nos. 5,278,652 and 5,778,155, respectively). In the DMD, the mirrors are tilted one way to reflect light through a lens in a projection display system and tilted the opposite way to prevent light from reflecting through the projection lens. By timing precisely when and for how long the mirrors are oriented to reflect light, the DMD reflects the correct shade, or brightness, of a either a constant primary light source or a white light source that is filtered through use of a continuously rotating color wheel. The encoding strategy implemented in these Texas Instruments devices divides the cycle time into unequal fractions, as opposed to the equal duration time slice strategy disclosed for the direct-view device in Selbrede. The unequal fractional durations are temporally proportioned as ascending powers of two (e.g., the second fraction is twice the length of the first; the third fraction is twice the length of the second, up to the largest fraction contemplated).