Furthermore, even with the price differential, manufacturers are able to sell every active matrix color notebook they can produce. In other words, a positive and then an equal but opposite negative charge is applied to the LC material every other frame. By applying dual polarity addressing, the LC material changes twist direction every other cycle and the net charge is zero. Furthermore, since the liquid crystal material is changing twist directions every other cycle, screen savers or screen inverters are not required and in reality do absolutely nothing. When the two pieces of glass are assembled into a display, the intersection of a row and column form a pixel element.
Problems arise as the number of rows and columns increase.
With higher pixel density, the electrode size must be reduced and the amount of voltage necessary to drive the display rapidly increases. Even though only one row and column are selected, the liquid crystal material near the row and column being charged are affected by the pulse. The partially active pixels reduce the display contrast and degrade image quality. Most STN materials are between 150 and 250 milliseconds and can not switch from black to a white image that quickly. As discussed in part I section 1.24, the STN curve does not possess an intrinsic gray scale capability like the TN curve, therefore driving methods have been developed to create the illusion of true gray scale.