1080i OTA signals more like 1075i?

[RonH]

I used to only have a 768p sony LCD, and it overscanned a bit, so I lost a few rows of pixels off the ends of the screen (normal).

I have a 1080p Pioneer now as well, and I was playing around with the "dot-by-dot" mode you can use when watching a 1080i channel (or 1080p source) such that there minimal processing and no overscanning.  When I did this during the NFL games last night on NBC, there seemed to be about 5 lines of black pixels on the top of the screen (which normally you can't see because most TVs overscan a few rows of pixels).  There were white dots turning on and off in seemingly random patterns only on the left side of the screen in those 5 rows of black pixels.  When the producers would switch to a different camera, it would go away, it only appeared for the main camera used for the game.  All other views/cameras were fine.

I know I'm not the only one who has experienced this, as I remember many years ago seeing it a friends house on his sharp 1080p LCD.

Is this from the signal?  Is this a screw up on the TVs processing?  Do most people never see this because we don't use dot-by-dot that often and almost all TVs overscan?  Anyone have any background info on this?

[mhz40]

I doubt its a TV problem.  All screens overscan 2-5%.  Just 1% of 1080 is 10.5 lines.

[brewtownska]

I'm sure someone here can give a more technical explanation, but the way I understand it is this:

With the NTSC standard, stations would use those top few lines (which were usually hidden by overscan) to send out closed captioning and other "data" with the picture.  With the new HD standard, there is a different way they can send the data that doesn't necessarily use resolution lines of the picture, though some stations still end up using the lines for the data.  I commonly see it on any show that is being upconverted from SD to HD, or when the local channels go from an HD show to a local commercial that is SD.  Usually shows produced and transmitted in HD don't have that problem.

On some channels, instead of the lines on the top, you might see 1 solid line on one side (I tend to see a thin line on the left side of my screen SOMETIMES during the Thursday night NBC shows ER, Earl, 30 Rock and The Office).

So the bottom line is it's NOT your TV, just the way the local stations send the signal.  I'm not sure if it'll get better once all the stations send out only a digital signal starting the end of Feb, but I hope so.

Mike

[Xizer]

You should probably enable overscan for when this occurs. I have my TV set up so it shows the entire native picture. Your TV should have an overscan function. Mine does.

[RonH]

My tv overscans in most cases and when in "auto" mode.  But I set to dot-by-dot just this one time as I read and assumed that would give the best possible picture.  Nothing as clear I thought as fresh "OTA" mpeg2 1080i coming in directly to the TVs ATSC tuner and being displayed in dot-by-dot mode.

But apparently NBC uses the top 5 lines for something like what was mentioned above on certain camera angles during football games, so I'll go back to overscan modes.