Methods for driving electro-optic displays
An electro-optic display, having at least one pixel capable of achieving any one of at least four different gray levels including two extreme optical states, is driven by displaying a first image on the display, and rewriting the display to display a second image thereon, wherein, during the rewriting of the display, any pixel which has undergone a number of transitions exceeding a predetermined value without touching an extreme optical state, is driven to at least one extreme optical state before driving that pixel to its final optical state in the second image.
1. A method for rewriting an electrophoretic display from a first image to a second image, the display having a plurality of pixels divided into a plurality of rows, the method comprising:
(a) writing a first image on the display;
(b) after the first image has been written on the display, selecting each of the rows of pixels in succession and applying to each of the pixels in the selected row either a drive voltage or a non-drive voltage, the scanning of all the rows of pixels being completed in a first frame period; and
(c) repeating the scanning of the rows of pixels during a second frame period, thereby forming a second image on the display;
wherein the scanning of the rows of pixels is interrupted during a pause period between the first and second frame periods, this pause period being not longer than the first or second frame period.
2. A method according to claim 1 wherein the first and second frame periods are equal in length.
3. A method according to claim 2 wherein the length of the pause period is a sub-multiple of the length of one of the first and second frame periods.
4. A method according to claim 1 wherein the method comprises scanning the rows of pixels during at least first, second and third frame periods, and interrupting the scanning of the rows of pixels during at least first and second pause periods between successive frame periods.
5. A method according to claim 4 wherein the first, second and third frame periods are substantially equal in length, and the total length of the pause periods is equal to one frame period or one frame period minus one pause period.
6. A method according to claim 1 wherein the scanning of the display is effected such that, for any series of transitions undergone by a pixel, the integral of the applied voltage with time is bounded.
7. A method according to claim 1 wherein the electrophoretic display comprises an encapsulated electrophoretic medium.
8. A method according to claim 1 wherein the electrophoretic display comprises a microcell electrophoretic medium.