What happens when I send a 1080i video source to my HDTV when my HDTV only has a 1366x768 resolution?

Question

My Sharp LCD HDTV has a 1366x768 native resolution, with progressive scanning capabilities like many other HDTV sets.

Naturally, it's suppose to display every line of 720p material.

I know that many HDTV's such as mine, will upscale any incoming source, whether its 480i or 480p, to the natural resolution of my screen.... but what happens when you send a signal with greater resolution than the display capabilities of the set?

In my case, I've found that when setting my upconverting DVD player or my cable box to 1080i output to my HDTV, that the picture is sharper. I lose the progressive scan benefits, but I prefer the sharper picture.

So in this case, what is my tv doing when it's accepting a 1080i signal? Or even a 1080p signal?

Any ideas? Websites that have articles on this?

Thanks everyone.

If 1080i is down-scaled to my native resolution, does it display in progressive scan or interlaced mode?

Answer 1

1080i signal means that your TV gets two fields, 540 lines each, every 60-th of a second.

Depending on the deinterlacer of your TV, the TV can do two things:
a) Cheap deinterlacer (most old TVs); Throw away one filed and scale the other one to 736 pixels
b) Good deinterlacer; The TV will combine information from both fields and create a new frame with 736 lines.

For 1080p signals. Assuming the TV supports 1080p input, it will scale it down to 736 lines.

Answer 2

This is a question often completely overlooked when poeple are purchasing TV's ... and indeed when people are attempting to sell TV's.

Think about it, if you have 768 vertical pixels then, a 720p signal has not got enough lines to fill your screen. So even on a 720p signal, your tv will be scaling the image.

I garuntee that ANY signal source that is sent to your TV (with the possible exception of a pc input running at 1366x768) will be interpreted, scaled, mangled, mashed and all sorts before it's displayed.

BUT FEAR NOT! This doesn't mean that the image is going to be bad, far from it. The scalers implemented in TV's these day are very impressive pieces of kit!

Think about it this way, a 720p image is not quite enough for your TV to display, so it upscales it. A 1080i signal is almost twice the amount of information that your TV needs to display, so it downscales it. It would make sense that it's easier for it to scale an image when it has too much information than when it has not enough.

Ultimatley, use what you think looks best, I have a 768 line plasma, and run my xbox 360 at 1080i because I think it looks better. Simple.

Answer 3

Its down converting back to native resolution. And your tv does not upscale.