Here's one from the mailbag:
Avi, We want to buy a 37" LCD TV. Is there a significant difference between 720P and 1080P?
Yes, there is a significant difference between 720p and 1080p –
though it depends on what you’re watching on it, and even then you may not be
able to see the difference. The bottom line is that you can almost always
get away with buying a 720p set and saving the money, but nobody seems to
believe this answer, so here’s a slightly more involved one:
First, two quick definitions:
1. the
“p” in 1080P or 720P = progressive, where the signal has information in every
horizontal line, just like a computer monitor.
2. the
“i” in 1080i = interlaced, where the signal alternates horizontal lines
similar to the way an analog TV works – the information alternates fast enough
that you usually can’t tell the difference.
Now you need to answer two questions:
What are you watching? (You want to be able to display all the
information that your signal contains, but how much information is actually in
that signal?)
·
If you’re watching a DVD, it’s 480p. So even a 720p TV is
overkill – either the TV or the DVD player will do some magic to “fill in” the
extra pixels it has to make up the picture.* A 1080p set has to fill in even
more pixels with guesswork.
·
If you’re watching HDTV, it’s either 720p or 1080i. Some channels
use one resolution (for example, NBC uses 1080i) and some use the other (for
example, Fox uses 720p) – this happens behind the scenes when you change
channels; you don’t have to do anything. 720p and 1080i both have about the
same amount of picture information (720p tends to look better for fast motion
like sports, while 1080i tends to look better for scenes without much motion,
like dramas), both count as real HDTV, and both look spectacular when displayed
properly on an HDTV.
o
When you watch a 720p channel on a 720p TV, you’re seeing
everything that’s there.
o
When you watch a 1080i channel on a 720p TV, first it fills in
the interlacing by guessing what the missing line ought to be, and then drops a
bit of the resolution.
o
When you watch a 720p channel on a 1080p TV, it does some magic
to “fill in” the extra pixels.
o
When you watch a 1080i channel on a 1080p TV, it fills in the
interlacing by guessing what the missing line ought to be.
·
If you’re watching a Blu-ray disc, congratulations, you’re
watching the only consumer format capable of displaying full 1080p.
o
A 720p set throws out some of that resolution; it usually still
looks better than a DVD.
o
A 1080p set displays all the information on there without any
changes.
Now, let’s assume you are going to watch Blu-ray discs 100% of
the time. Question two: can you actually see the difference between 720p and
1080p?
This will depend on several factors:
·
How good is your eyesight? Seriously.
·
How big is the TV, and how far away are you sitting? In smaller screen
sizes it usually doesn’t matter if you’re cramming one or two million pixels
into the set; unless you’re sitting two feet away you won’t be able to see the
difference. Higher resolution allows you to sit closer to the set and does
nothing for you if you’re farther back. For example, if you’re sitting ten to
twelve feet back from a 50” TV you literally cannot see the difference between
720p and 1080p. Some people want to get the higher resolution anyway. I am not
one of those people. My couch is about 12 feet away from my displays, and my
50” plasma is a 720p model. My projector, on the other hand, projects onto an
8’ screen that comes down in front of the plasma; the projector is a 1080p
model because when the images are projected that large, the difference between
720p and 1080p is quite obvious.
Conclusion: unless you plan to sit awfully close to that 37” set
and watch a lot of Blu-ray discs, there’s no reason to spend more on a 1080p
version. If you insist on spending money for something you can’t see, I won’t
stop you. But you’ll be much happier if you put the extra money into a good
surround sound system.
Does the upcoming change in broadcasting frequency have any impact on the reception?
It depends. If you’re getting your TV shows from cable or
satellite, the analog/digital switchover will make no difference whatsoever.
None. You do not need to do anything at all.
If you’re getting your TV shows from an antenna, then you’ll
need either a new HDTV with a digital tuner built in, or a new tuner/converter
box. Your reception will either get much better or much worse, and it will vary
by channel, how far away you are from the station, and (in some cases) your
physical location (i.e., if you’re at the bottom of a hill or sandwiched
between big buildings). Digital channels do not degrade gradually. A rough rule
of thumb is that if you get a reasonably clear channel today, you’ll probably
get an even better looking version of it on digital. On the other hand, if you
have a snowy channel that’s just sort of watchable today, once it goes digital
you probably won’t get it at all.
Hope this helps,
-avi
*720x480 progressive, or about 350,000 pixels of actual
information per frame. This is a gross oversimplification, but it provides a good
basis for comparison. 1280 x 720 = around 900,000 pixels. Incidentally, this is
why watching analog TV channels or VHS video on an HDTV usually looks much,
much worse than it did on your old analog TV; the new TV is trying to take very
little information (VHS is roughly 240i, or 480x240 every other frame, or the
equivalent of about 60,000 pixels) and displaying it on something expecting
more than ten times that information to create the picture. Without much to go
on, the TV fudges, which, instead of looking soft and fuzzy like an analog set,
looks blocky and horrible.
