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Old May 21st, 2009, 10:00 AM   #1
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resolution of 24p v.s. 60i

Sorry if this is an oft asked question. I've been scanning the web but have not been able to find the answer elsewhere so am asking here.

In discussing 24p mention is often made that "Vertical resolution of the resulting video is about 25% lower that theoretically possible..." This would also seem to be saying that this missing resolution would be there in footage shot in 60i. Is this correct? Is resolution of footage shot in 60i in an HDV camera like my Canon ZH A1 visibly better (putting the issue of "film look" and motion artifacts of HDV etc. aside for the moment).

Thanks.

John
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Old May 21st, 2009, 03:47 PM   #2
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Good question, would like to know myself, plus would there be a difference if one shot 60i and converted to 24p?
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Old May 21st, 2009, 06:21 PM   #3
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Originally Posted by John Whiteway View Post
In discussing 24p mention is often made that "Vertical resolution of the resulting video is about 25% lower that theoretically possible..." This would also seem to be saying that this missing resolution would be there in footage shot in 60i. Is this correct?
Other way round, surely?

With progressive footage, each frame stands alone and resolution wise should be no different to a still image. With interlace, the difference between lines on alternate fields in the case of a moving object means that the instant resolution must be less - though since moving objects are frequently blurred by their movement, it may not matter as much as is sometimes made out.

It may be thought that an interlace system will give full vertical resolution for a stationary image. In practice it doesn't work out like that. If we take the case of a sensor and display with 1080 vertical pixels, then a one to one releationship between input and output would give severe vertical twittering at 30Hz on sharp horizontal edges. Hence, video line one is formed by summing sensor lines 1+2, video line 3 by summing 3+4 etc for the first field. For the opposite field, video line 2 is formed by summing 2+3, line 4 by 4+5 and so on.

The above approach eliminates the twitter at the expense of vertical resolution, but does improve the video sensitivity. It's why the VERTICAL resolution of a 1080i system is not much more than that of a 720p system.

Note that it's very wrong to then call 1080i and 720p comparable in resolution terms. The above explanation is only true in the vertical direction, 1080i will be superior to 720p horizontally - 1920 to 1280.

And the above is true for 1080i/25 v 720p/50. If film motion is actively desired, 1080p25 is far sharper than 720p/25 in both directions.
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Old May 22nd, 2009, 11:40 AM   #4
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Quote:
Originally Posted by John Whiteway View Post
Sorry if this is an oft asked question. I've been scanning the web but have not been able to find the answer elsewhere so am asking here.

In discussing 24p mention is often made that "Vertical resolution of the resulting video is about 25% lower that theoretically possible..." This would also seem to be saying that this missing resolution would be there in footage shot in 60i. Is this correct? Is resolution of footage shot in 60i in an HDV camera like my Canon ZH A1 visibly better (putting the issue of "film look" and motion artifacts of HDV etc. aside for the moment).

Thanks.

John
I wiki'd up the reference - it was from a 2002 article mention frame pair summation.

I was going to mention that it doesn't seem to be much of an issue but then the post above - which I should have read before posting - gives a really good explanation.
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