| Video Noise June 2004
HD-Capable vs. HD-Compatible
Plasma Displays
I get more questions from people I know about which
plasma display is the best deal for them than I have ever gotten about anything
else having to do with audio or home theater. Typically, these folks will be willing to
spend $3000 on a plasma, thinking it will be the ultimate statement of "We are a
modern-technology family." They’re excited about finding the latest
hot-technology product that will fit their budget, and they’re very enthusiastic
about the capability of displaying high-definition TV that their new plasma must certainly
possess. After all, the hot new product everybody’s talking about must be an
HDTV.
The first thing I tell seekers of $3000 plasmas is usually,
"You know, that won’t be a high-definition TV." They then almost always
say, "Yes it is, it says so right on the front of it." I then have to explain
that that means it will display HDTV images, but it won’t display HDTV images at
high-definition resolution.
As of spring 2004, all $3000 plasma sets are limited to 852
horizontal pixels by 480 vertical pixels. The two hi-def formats are 1280x720p and
1920x1080i. Video displays with lower-than-HD resolution must convert HD images to a much
lower resolution that might not look any better than DVD resolution. HD images on a
lower-than-HD fixed-pixel display might look better than conventional TV, but they
won’t produce the wow factor of HDTV images displayed at full HDTV resolution.
But, you might be thinking, "852x480 doesn’t seem
all that much smaller than 1280x720, the lower of the two HDTV resolutions. The resolution
is reduced by a third or so, but HD images are so good, this won’t make that big a
difference." That sounds reasonable, but it’s wrong. Here’s why.
When you multiply 852x480, you get just over 400,000
pixels. But every image you view is made up of three colors. There will be 400,000 red
pixels, 400,000 green pixels, and 400,000 blue pixels -- a total of 1.2 million pixels for
that low-cost plasma screen. Sounds like a lot, right? Well, it’s not very impressive
when compared to high definition. The 720p HDTV format has almost 2.8 million pixels per
image. (The p in 720p stands for progressive
scan, in which all the lines that comprise the image are displayed in one pass over the
screen, as in your computer monitor.) The $3000 economy plasma screen will have less than
half the resolution of the 720p HD format.
The other HD format is 1080i. (The i stands for interlaced: the odd-numbered lines are displayed first,
then the even-numbered lines; the eye-brain reads the two half-images as a single image.)
The 1080i format has a staggering 6.2 million pixels per image. Images produced on
displays with this many pixels are spectacular in their detail. The economy plasma screen
will miss five million pixels of that detail. The images on the $3000 plasma screen will
be, roughly, only a sixth as sharp as a 1080i HD image.
Even though the economy plasma screen is
"HD-capable," it will never give you HD resolution. And without HD resolution,
HDTV is just digital TV with good, but not-HD images. I get eight HD channels via cable
TV, all but two of them with programming that’s duplicated on non-HD channels, and
there’s nothing worth seeing on any of those channels unless you can see the images
in true HD resolution -- or at least resolution much better than conventional TV. The two
channels that are not duplicated on conventional channels carry old movies transferred to
HD (with varying results, most not very impressive) and borderline-quality travel
programming. There’re also a few sports events you can usually find on some non-HD
channel at the same time. So there’s little advantage in having a
lower-than-HD-resolution TV that displays HD channels at low resolution -- except for a somewhat
higher resolution and the colors.
I threw colors in there because the HD specification allows
for a wider range of colors to be transmitted and displayed than a conventional TV can
display. The color on that $3000 plasma will be a little nicer, and the digital
transmission will usually mean that there are none of the common analog video artifacts,
such as ghosts, static, and moiré patterns. But that’s still not enough to make an
economy plasma screen all that impressive.
To display HD images on lower-than-HD TVs, the TV must have
special electronics that convert the larger number of pixels in the signal to the smaller
number of pixels for the display. This is hard to do well -- there are products on the
market that sell for thousands of dollars that do nothing but this one task. Imagine,
then, the quality of the downconversion circuitry in a plasma screen that sells for $3000
or less. It won’t be topnotch. Once again, watching HD programming on a budget
HD-capable plasma screen will be compromised.
The prices of 42", 852x480 plasma screens range from
$2500 to $4500. The more expensive one might have a more attractive design and be a bit
brighter and have better color, but 852x480 resolution will look the same on both -- minus
any differences in video-processing capabilities.
So before you get too excited about the prospects of a
$3000 plasma screen, you need to understand what you’ll be getting for your money.
You might decide that all the hype and hoopla is just that -- all fluffed up by
tech-driven people who have never actually seen a hi-def image side by side with their
medium-to-lo-def plasma screen. Today’s low-cost plasma screens may not be what you
want or need to enhance your home-theater experience.
...Doug Blackburn
db@hometheatersound.com |
