HDTV and LCD/PLasma displays

[vicmel]

I appreciate that LCD and Plasma displays iperate in the basis of discreet pixels, each of which has to be adresses/energised by the electronics. HDTV seems to require either 720 or 1080 vertical lines of resolution - presumably 720 or 1080 pixels. Whether interlaced of progressively scanned it is easy to understand that this is the 'vertical' pixel count required. However, practically all currently offered LCD or Plasma screens quote 780 or thereabouts. Clearly these screens could not display a future 1080p requirement. But how do they deal with the 1080interlaced signal?

[Mattk]

Isnt 1080i essentially 540p ?

[rojash]

You have to remember that the image is delivered not as a raster scan but as a compressed video image. Just as it's possible to view a movie on your computer at a different size (resolution) than that in which it was originally encoded, so is it possible to do the same on a digital TV. The image is decoded and resized using software interpolation/extrapolation.

And, of course, just as with a movie on your computer, viewing it at a different resolution will cause a deterioration in the quality.

And no, on an LCD or Plasma screen, 1080i is not essentially 540p, 1080i will have twice as many lines of resolution, but only alternate lines will be drawn in each refresh cycle, thus halving the bandwidth.

[Mattk]

Thats what I meant - only 540 lines at any one time.

[rojash]

Yes Mattk, but the question referred specifically to the number of discrete pixels on the display, and if you will need 1080 physical pixels to display 1080i, and only 540 to display 540p. The "i" doesn't affect the resolution - only the refresh rate.

[vicmel]

Thank you Rojash. That helps a lot. So would it be true to say that the proposed 720p HDTV would fit well onto the currently available screens without too much reprocessing but the 1080i would be a reprocessed picture to fit the pixel limitations of the screen. Similarly eventually a screen with at least 1080 'vertical' pixels would be needed to display the next generation - 1080p. So the present 'HD ready' kit is only future proof until 1080p comes along.

[rojash]

Well, vicmel, I would say that sums it up pretty well.