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Upconverting 720p to 1080i


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#1 Jonathan Bryant

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Posted 21 October 2005 - 10:30 PM

How good does 720p hold up after you convert it to 1080i? Is it noticeable softer?
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#2 David Cox

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Posted 22 October 2005 - 08:14 PM

How good does 720p hold up after you convert it to 1080i? Is it noticeable softer?


I'm guessing the question is "how does 'upres ed' 720 compare to native 1080 shots when cut together", because converting 720 to 1080 itself won't make much difference to it.

It depends what you are looking at the result on. For most normal to large TV screens, there's not a *huge* difference. If we are talking about final delivery to cinema, then there will be a difference that is most noticeable on detailed wide shots. So your wide of the New York skyline with all those little windows will show the differences more than the soft focus, big close up of your female lead.

You are probably aware that the Panasonic Varicam records at 720 internally, and I have seen plenty of excellent footage shot with this that would be very hard to distinguish from 1080.

Notice that I took of the "p" and the "i" from the HD standards. If you shoot 720P, then after conversion your output will have the appearance of 1080p not "i", since the P and I relate to the number of different pictures per second you are shooting. For example, 720P at 30 FPS or 1080i at 60 (ish) fields per seconds. After conversion, the 1080i recording would have pairs of fields from the same frame sample, so would have the look of a progressive image rather than a field based one.

Hope that helps :-)

David Cox
Baraka Post Production
www.baraka.co.uk
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#3 John Sprung

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Posted 02 November 2005 - 02:39 PM

How good does 720p hold up after you convert it to 1080i? Is it noticeable softer?

720p to 1080i is a down, not up, conversion. 1080i is acutally 540 lines, not 1080. It's just that every other set of 540 lines is offset to land between the lines of the adjacent set. Theoretically, this gets you a little extra resolution at the expense of some flicker artifacts. So, 1080i is pretty much equivalent to about 700 progressive lines.

The conversion can look near perfect if it's done by the best broadcast quality equipment, or it can look a bit soft if it's just the cheap conversion built into a consumer CRT HD set.



-- J.S.
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