ViewSonic Overdrive LCDs: A New Era of Very Fast Panels?

Disadvantages Of Overdrive

When a technology like this one appeals to the general public with its qualities, it's easy to let enthusiasm mask its disadvantages. The "overshoot" measured at the pixels is significant in its amplitude and duration in relation to the refresh rate. That means that there is a certain risk of video noise being visible on color masses.

Why? When the image is fixed, there is no problem - the pixels don't change regardless of their values. That's the advantage of LCD. But imagine a subtle color shading. When a tracking shot in a movie moves through those subtle colors, the pixels have to change from one value to another, but the colors are really very close. Unfortunately, Overdrive temporarily causes a much greater variation in the value of the pixel and since all the pixels don't react in the same way - certain ones being faster than others -the result is that the viewer sees video noise.

We were able to demonstrate that in certain scenes from The Bourne Supremacy. During a scene emerging from a tunnel, the walls are shaded from white to black and during the tracking shot, the VP191b showed "sparkle."

Another problem is that this technique may be incompatible with dithering. Dithering is a technique for recreating color on panels that are capable of displaying a limited number of colors. It operates by rapidly alternating pixels and using the human eye's ability to see the "average" color.

Dithering is normally invisible to the naked eye if the viewer is far enough away, but Overdrive could amplify the visual nuisance stemming from the strong brightness escaping from the panel during the Overdrive period. That may well be what motivated the choice of a 16.7-million-color MVA panel for the implementation of Overdrive.

But you should know that certain compressed video formats use dithering extensively in their encoding and decoding procedures. And the VP191b could amplify the phenomenon.