720p vs 1080i HDTV
Is 720p vs 1080i worth being concerned about? Yes and no. If
you're a consumer looking for a new TV, you can happily ignore
the 720p vs 1080i debate because every TV which is described as
HDTV or HDTV Ready is required to support both formats.
NOTE: You should be aware though that lots of TVs which support
1080i have fewer than 1080 lines and so scale the 1080 signal
down. That's not a huge issue as even scaled down 1080i is far
ahead of a regular NTSC signal. It is worth bearing in mind that
more expensive HDTVs tend to have better scalers than cheaper
ones, and this may be an issue.
However, for broadcasters it's a live issue. Should they
broadcast 1080 lines of interlaced video or 720 lines of
progressive scan? They could just broadcast two signals, one in
each format, but that would use up a huge chunk of bandwidth and
be hugely expensive for very little gain.
To answer the question, it's important to understand the
difference between 720p vs 1080i. A 720p signal is made up of
720 horizontal lines. Each frame is displayed in its entirety
on-screen for 1/30th of a second. This is know as progressive
scan (hence the 'p')The quality is like watching 30 photographic
images a second on TV. A 1080i signal comprises 1080 horizontal
lines but all the lines are not displayed on-screen
simultaneously. Instead, they are interlaced (hence the 'i'), ie
every other lines is displayed for 1/60th of a second and then
the alternate lines are displayed for 1/60th of a second. So,
the frame rate is still 30 frames per second, but each frame is
split into two fields, which your brain then puts together
subconsciously.
Most of the time interlacing works fine, but for fast moving
images, such as sports like baseball and hockey it can cause
problems which manifest themselves as a 'stepping' effect
on-screen. Progressive scan signals don't have this problem and
so are better suited to sports.
ESPN puts it like this: 'Progressive scan technology produces
better images for the fast moving orientation of sports
television. Simply put, with 104 mph fastballs in baseball and
120 mph shots on goal in hockey, the line-by-line basis of
progressive scan technology better captures the inherent fast
action of sports. For ESPN, progressive scan technology makes
perfect sense.'
Bottom line? For us, as consumers 720p vs 1080i is not a debate
worth worrying about, so you can relax and focus on all the
other criteria on your list when you buy your next HDTV.