Method and apparatus for producing grey levels on a raster scan video display device

Claim 1

Apparatus for driving a one-bit-pixel raster scan video display device, having a display which comprises a plurality of rows each consisting of a plurality of pixels, to display a plurality of grey levels, which apparatus comprises means for generating an input signal for the display device to illuminate selected pixels thereby to indicate the desired grey level, the said means including: means for generating a plurality of repetitive grey level signals, each having a respective repeat period equal to n number of bits wherein n is not the same number for each grey level, each grey level signal being indicative of a selected proportion of pixels to be illuminated to display the corresponding grey level; selector means for selectively applying a said grey level signal as the input signal to the display device in dependence upon the desired grey level of the region of the display addressed; and signal adjustment means, adapted to introduce a row phase shift in each grey level signal, in response to an indication that a new row is to be addressed by the input signal, to cause illumination in successive rows of each frame of a different corresponding plurality of pixels for the same desired grey level, and adapted to introduce a variable frame phase shift of f bits into each grey level signal, in response to an indication that a new frame is to be addressed, to cause illumination in successive frames of a different corresponding plurality of pixels for the same desired grey level, wherein, when the repeat period equal to n for the respective grey level is odd, the frame phase shift f is co-prime and is as close as possible to n/2, and when the repeat period equal to n for the respective grey level is even, the frame phase shift f alternates between (n+2)/2 and n/2, or between n/2 and (n-2)/2).

Claim 6

A method of driving a one-bit-per-pixel raster scan video display device, having a display comprising a plurality of rows each consisting of a plurality of pixels to display a plurality of grey levels, which method comprises: generating an input signal for the display device to illuminate selected pixels thereby to indicate the desired grey level; generating a plurality of repetitive grey level signals, each grey level signal being indicative of a selected proportion of pixels to be illuminated to display the corresponding grey level, and each said signal having a respective repeat period equal to n number of bits in length, the said n number of bits corresponding to n number of pixels of the said display device, wherein n is not the same number for each grey level; selectively applying a said grey level signal as the input signal to the display device in dependence upon the desired grey level of the region of the display addressed, introducing a row phase shift in each grey level signal, in response to an indication that a new row is to be addressed by the input signal, to cause illumination in successive rows of each frame of a different corresponding plurality of pixels for the same desired grey level; and introducing a variable frame phase, shift of f bits into each grey level signal, in response to an indication that a new frame is to be addressed, to cause illumination in successive frames of a different corresponding plurality of pixels for the same desired grey level, wherein the frame phase shift f for each respective grey level is co-prime with the respective repeat period equal to n for the said respective grey level and f is also as close as possible to n/2, and when the repeat period equal to n for the respective grey level is even, the frame phase shift f alternates between first and second pre-determined amounts, wherein either the first and second pre-determined amounts are n/2 and (n+2)/2 or the first and second pre-determined amounts are n/2 and (n-2)/2.

Claim 7

A method of driving a one-bit-per-pixel raster scan video display device, having a display comprising a plurality of rows each consisting of a plurality of pixels to display a plurality of grey levels, which method comprises: generating an input signal for the display device to illuminate selected pixels thereby to indicate the desired grey level; generating a plurality of repetitive grey level signals, each grey level signal being indicative of a selected proportion of pixels to be illuminated to display the corresponding grey level, and each said signal having a respective repeat period equal to n number of bits in length, the said n number of bits corresponding to n number of pixels of the said display device, wherein n is not the same number for each grey level; selectively applying a said grey level signal as the input signal to the display device in dependence upon the desired grey level of the region of the display addressed, introducing a row phase shift in each grey level signal, in response to an indication that a new row is to be addressed by the input signal, to cause illumination in successive rows of each frame of a different corresponding plurality of pixels for the same desired grey level; and introducing a variable frame phase, shift of f bits into each grey level signal, in response to an indication that a new frame is to be addressed, to cause illumination in successive frames of a different corresponding plurality of pixels for the same desired grey level, wherein the frame phase shift f for each respective grey level is co-prime with the respective repeat period equal to n for the said respective grey level and f is also as close as possible to n/2, and when the repeat period equal to n for the respective grey level is even, the frame phase shift f alternates between first and second pre-determined amounts, wherein either the first and second pre-determined amounts are n/2 and (n+2)/2 or the first and second pre-determined amounts are n/2 and (n-2)/2.