LCD vertical banding or DLP rainbows?

Evan Powell, May 24, 2005
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If you are planning to spend in the range of $1,000 to, say $5,000 for a home theater projector, you have a basic choice to make: an LCD projector or a DLP projector. Each technology has advantages over the other, and neither is perfect. LCD and DLP both have the potential to produce undesirable artifacts in the picture. LCD can have vertical banding and DLP can produce rainbow artifacts. Here is how you manage these problems . . .

LCD vertical banding

On occasion, LCD projectors can manifest a problem known as vertical banding. Vertical banding consists of subtle (sometimes not so subtle) vertical bands often in the range of about 1-inch thick, evenly spaced across the entire picture. DLP projectors don't have this problem. Most LCD projectors don't either-it is not an automatic byproduct of the technology. It is a flaw that can occur in the manufacturing process of the LCD panels themselves, and some LCD panels will tend to manifest it more noticeably than others. The panels that cause the most visible problems are usually weeded out in the vendor's quality control process. However, those that create just a hint of banding often pass through QC, since it is prohibitively expensive to discard all parts that exhibit flaws which may have no practical impact on picture quality.

So, we end up with a situation in which some LCD projectors, even within a given production run on one model, will have no banding at all,

some may have a hint of it that does not rise to the level of a significant issue, and some may have a more visible problem that really does impair the enjoyment of the viewing experience. In the latter case, sometimes the problem can be mitigated with internal adjustments made by the dealer or vendor service departments, and sometimes the LCD panels or the entire unit need to be replaced.

As an example, we have two Panasonic AE700s in house. The older of the two was one of the first units built, and it is the unit we reviewed last fall. We saw some subtle vertical banding on that unit and reported it in the review. It produced some noticeable texture in gray screen test patterns, and in video on infrequent occasions depending on subject matter, but it was not considered to be a significant flaw. In December, Panasonic engineers came to visit, and on that occasion they called up the service menu and tweaked our AE700. The adjustments they made reduced the visibility of the banding on test patterns by about 50%. So a problem that wasn't a big problem to begin with was reduced, but not eliminated entirely, with internal adjustments.

We acquired a second AE700 about two months ago. This unit shows almost no banding at all on gray screen test patterns although it is still detectable. However it is even less visible than it was on our first unit after tweaking. On the second unit, banding is essentially zero with normal video material playing. When we detect it at all, it is because we are specifically looking for it.

Therefore, those who say they see no banding at all on their AE700 are correct, and those who say they've had a problem with banding on the AE700 are also correct. And this phenomenon can occur with any LCD projector. However, the good news is that since vendors are more in tune with the fact that home theater buyers really don't like vertical banding artifacts, we are seeing less of it these days than we did before.

You can manage your risk on the vertical banding issue by simply buying from a dealer with a consumer oriented return policy. Some dealers allow you ample time to receive and check out your unit, and if there are problems, not only with vertical banding, but with anything in the performance of the projector, you can return it for exchanges or refunds without restocking fees. If the unit you receive has a vertical banding problem, you will see it immediately. So it doesn't take long to check it out.

Always read the fine print on the dealer's Return Policy section of their website so you understand clearly the rules of the transaction. But the better Internet dealers, in particular the dealers who specialize in projectors, will enable you buy without worries of getting stuck with a unit that does not perform to your satisfaction.

Contents: LCD Vertical Banding DLP Rainbows