Patent ID: 7330191

Claim:
A method for securely rendering information on a display, the method comprising: rendering a periodic sequence of frames with a frame period, each frame in the sequence of frames is given a frame sequence number; both a foreground region and a background region of each frame uses a selected grayscale level, and each frame comprising a plurality of pixels; selecting a first orbit, consisting of multiple elements of a sequence of displacement vectors which is divisible by the frame period, for the foreground region and a second orbit, consisting of multiple elements of a sequence of displacement vectors which is divisible by the frame period for the background region; and determining the value of a particular pixel comprising the steps of: choosing the particular pixel at a given location in a particular frame with a particular frame sequence number; accessing a particular element of a dither matrix corresponding to the given location of the particular pixel displaced by an element of the sequence of displacement vectors of either, the first orbit if the particular pixel is in the background region, or the second orbit if the particular pixel is in the foreground region, wherein the element of the sequence of displacement vectors is given by the remainder of the particular frame sequence number divided by the frame period; and comparing the particular element with the selected grayscale level to compute the output value for the particular pixel.