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DLP, LCD and Image Persistence

If you are into large screen video gaming, you'll not want to miss the next review. Bill is currently testing five 1280x800 format projectors to see how they stack up as video gaming machines. We should have the results of this work posted next week.

We are also continuing to work on an updated article comparing the relative merits of LCD and DLP. One of the areas we've been examining is the susceptibility of LCD technology to image persistence. At the Infocomm show in June, Texas Instruments demonstrated the tendency of LCD projectors to retain a faint ghost of a static image that had been displayed for an extended period of time. The point of the demo was to highlight the fact that DLP projectors are not susceptible to this particular phenomenon.

In trying to reproduce the demo that was featured in TI's booth, we discovered that not all LCD products behave the same with regard to image persistence. In particular, we tested a total of ten LCD projectors, five of which had inorganic LCD panels, and the other five had organic panels. The unexpected surprise in our testing was that the inorganic units showed very little susceptibility to image persistence. On four of the five, we simply could not get them to retain a ghost image no matter how long we displayed a static image. On one inorganic model, we found an extremely faint residual image which was easily reversed with a few minutes of white screen display.

On the other hand, the five organic units did indeed retain a ghost after at least an hour of displaying a high contrast black and white static image. (We used the ANSI contrast checkerboard test pattern for this evaluation.) In general, the ghost image could be reversed by displaying a full white screen for about half the length of time the original checkerboard image had been displayed. On four out of five of the organic models, the image persistence was fully eliminated using this technique. On the fifth unit, we found that an extremely faint residual ghost could be detected on a 50 IRE gray screen no matter how long we displayed the white screen. The image faded substantially, but never was completely eliminated.

This has been an interesting set of results. We will discuss it more in the upcoming article on the differences between LCD and DLP technologies.

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