6.5 Enhancement of Video Performance

When conventional LCD desktop monitors and notebook panels are used to display video from a DVD, for example, the image quality is inferior to that on a CRT. Although the contrast ratio for static images on such displays can exceed 500:1, for moving images degradation in the dynamic contrast ratio is seen and the edges of moving objects blur. This makes the viewing experience less than acceptable. Faster LC fluids have been developed with a lower rotational viscosity and the cell gap can be reduced to about 4 ?m to improve response time (see Eqs. 5.11 and 5.12 in Chapter 5). These measures can lower the transition time from full ON to full OFF and vice versa to 8 msec for TN and MVA modes.

However, this by itself does not reduce smearing of moving video images sufficiently for application of LCDs in televisions. In video imagery the majority of transitions are between intermediate gray levels, which have longer response times, according to Eq. 5.11. The response time between different gray levels can exceed 50 80 msec in a conventional TN cell.

Another factor influencing motion portrayal is the hold-type character of an LCD (i.e., the luminance is continuous during each frame time). A data voltage is applied to each pixel once per frame time and maintained during the entire frame until the next refresh. This sample-and-hold mode of operation cannot eliminate an afterimage on the retina and causes blurring of fast-moving objects on the...