4:3 NTSC vs. 4:3 ATSC
 

When I watch NBC on my HDTV by tuning into Comcast Cable's standard NBC
channel (channel 7 in Boston), I get a 4:3 image that has fairly wide gray
bars on the left and right. I understand the gray bars are inserted by the
TV. When I then watch NBC by tuning into Comcast's HD NBC channel (channel
807), I again see a 4:3 image (if they are retransmitting and up-converting
a 4:3 show), but this time I see bars on the right and left that are this
time much narrower and that are black.

I understand that on the HD NBC channel the black bars plus the image make
up the overall 16:9 picture and that the black bars are inserted by NBC.
What I find fascinating is that the black bars are much narrower than the
gray bars that I see on the standard NBC channel.

I found some information on this PBS web site:

http://www.pbs.org/opb/crashcourse/r...ion/pixel.html

On that site it says, "The old NTSC format uses rectangular pixels that are
slightly taller than they are wide. The new HDTV format is composed of
square pixels, just like most computer monitors. This will remove some of
the image distortion seen on older televisions."

Is this the reason the black bars are so much narrower on the HD channel
than the gray bars on the standard channel?

Neil Donovan
Salem, Massachusetts USA

One channel might be using different amounts of overscan and cropping of
the 4x3 images. The different sizes of the pillarboxe.s does not
necessarily mean the geometry is incorrect. Chances are the NBC HD is using
minimal overscan correction, and just letting more show on the sides, so it
looks sort of like a 14:9 image.

Actually, some HDTV sets have rectangular pixels, not square. The
scanning rate is interpolated to the sets native resolution.

All my local stations that broadcast in a 720p, 420p or 1080i format all day
with 4:3 stuff have slightly different black bar width, ranging from the usual
width to about half as wide...Frenchy

All my local stations that broadcast in a 720p, 420p or 1080i format all day
with 4:3 stuff have slightly different black bar width, ranging from the usual
width to about half as wide...Frenchy