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Old February 25th, 2008, 11:05 PM   #1
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Is 60i really 30p?

I tried capturing 60i HDV footage in FCP 5.1 for the first time (I usually use 24f), and whenever I capture it it shows up as 30f (29.97). And yes, I'm using the HDV 60i easy setup, and I even tried the AIC HDV 60i easy setup, and it turns out the same 29.97. I'm assuming is has to do with HDV tape limitations?

Edit -- I see that basically they are similar except 60i is half the resolution, right?
But I still ask, why cant I capture properly to a 60i format in FCP. Is it that it actually did capture at 60i, but only will
show as 30f?
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Old February 26th, 2008, 08:01 AM   #2
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60i and 30p (30F) are the same resolution (well, technically 60i is a bit more resolution than 30F).

Sixty fields equals thirty frames. They are the same amount of bandwidth.
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Old February 26th, 2008, 11:50 AM   #3
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(well, technically 60i is a bit more resolution than 30F).
I haven't heard that one before, would you explain?
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Old February 26th, 2008, 11:57 AM   #4
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There is a slight loss of vertical resolution in Frame mode. It's been heavily discussed in previous threads. It seems to be a stumbling block for armchair measurebators, but a complete non-issue for serious shooters.
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Old February 26th, 2008, 12:23 PM   #5
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There is a slight loss of vertical resolution in Frame mode. It's been heavily discussed in previous threads. It seems to be a stumbling block for armchair measurebators, but a complete non-issue for serious shooters.
Why would you mention it when deinterlacing causes a far greater loss of resolution? Even on an interlaced display it introduces a variety of artifacts for some scenes, such as twittering on one-pixel line detail.

In 1998, one could probably assume that a video would be seen on an interlaced display. But it's 2008! Does anyone really want to cut the resolution heavily by deinterlacing (in post-production or in the viewer's display) for over half the audience? Even if interlacing wasn't evil incarnate, progressive video would still be a safe choice because it looks fine on an interlaced display.

So, I wouldn't say the 30F has slightly less resolution; rather, that 60i has far less resolution except when viewed on an ancient display based on 1930's technology.
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Old February 26th, 2008, 01:04 PM   #6
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Returning to the original question, does anybody have any help as to why I can't capture straight to 60i?
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Old February 26th, 2008, 01:06 PM   #7
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Sixty fields equals thirty frames. They are the same amount of bandwidth.
So it isn't 60 individual interlaced frames, it's 60 fields? Ok, I'm confused??
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Old February 26th, 2008, 01:15 PM   #8
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Interlaced NTSC video runs at 30 frames per second, but each frame is made up of two fields, hence the term 60i. There are not 60 frames, only 60 fields. Each field interlaces to form a single frame.

I've been shooting everything in the 24F mode, editing in FCP's HDV 1080p24 timeline, and when I export the final program, because it's progressive, I no longer have to worry about those pesky interlace artifacts coming in and out of dissolves.
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Old February 26th, 2008, 01:34 PM   #9
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There are not 60 frames, only 60 fields. Each field interlaces to form a single frame.
Bill I think you meant to say each pair of fields interlaces to form a single frame.
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Old February 26th, 2008, 01:37 PM   #10
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Why would you mention it when deinterlacing causes a far greater loss of resolution? Even on an interlaced display it introduces a variety of artifacts for some scenes, such as twittering on one-pixel line detail.
Deinterlacing may reduce spatial resolution (if done badly) but it also reduces temporal resolution. i.e., 30p doesn't necessarily look better than 60i. Noticeable flicker can be an issue - which is why interlacing was developed in the first place. Even 24fps movies are projected at 48fps (to reduce flicker).
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Old February 26th, 2008, 01:38 PM   #11
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Why would you mention it when deinterlacing causes a far greater loss of resolution?
Because if I don't mention it, invariably some measurebator will, trying to give Frame mode a negative spin. It's just a pre-emptive strike to throw that in there, in parenthesis.

Quote:
...except when viewed on an ancient display based on 1930's technology.
And yet it's still most commonly found in living rooms across the U.S. today.
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Old February 26th, 2008, 01:39 PM   #12
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30p doesn't necessarily look better than 60i.
Fully agreed. There are applications in which 60i excels... I can't stand to watch sports or anything fast in progressive.
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Old February 26th, 2008, 01:47 PM   #13
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So it isn't 60 individual interlaced frames, it's 60 fields? Ok, I'm confused??
60i is where one field, which is half a frame, is followed by another field 1/60th of a second later, which is the other half of the frame (odd lines followed by even, followed by odd followed by even, and so on). The odd lines followed by even lines is the "interlace" in 60i. Sixty fields per second. Sixty fields to make up thirty frames per second... two fields per frame.

30p is broken down into interlace fields when it's recorded, *except* there's no longer a 1/60th of a second between fields because those fields were acquired at the same instant in time. Instead, there is 1/30th of a second separation between frames.

When you're editing, you're editing whole frames, not half fields. That's why it shows that you're editing thirty frames per second, because you're not handling individual fields but whole frames each made up of two fields. It's still 60i because that's how you shot it. Hope that helps,
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Old February 26th, 2008, 01:55 PM   #14
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Even 24fps movies are projected at 48fps (to reduce flicker).
Well sort of. As you know, each single frame is actually flashed twice, but the film goes through the projector at a rate of 24 fps. However, this projection technique mirrors the behavior at the acquisition phase of the 180 degree shutter exposing each frame twice at a 1/48 sec interval (when shooting at 24fps).

But back to the topic at hand...

60i is not really 30P regardless of which camera shoots it. 30P is 30 whole frames per second so each motion sample is taken at 1/30 second interval. In contrast, 60i samples half a frame every 1/60 second, by odd numbered lines, then even numbered lines. If watching 60i material on an interlaced television, you never really see a whole frame at once. You see odd, then even, then odd, then even.. repeating every 1/60 of a second. However, due to the persistence of vision, along with the persistence of phosphor (still glows a short time after the electron beam is removed), you appear to see whole frames one after the other, yet with the smoothness of motion that sampling every 1/60 second provides. The NTSC engineers came up with this scheme to achieve smooth motion, given the bandwidth limitations of electronic circuitry in the 1950's.

As we move away from the limitations of the NTSC system and early tv sets, we will be looking at everything in true progressive format, but 30P will be a bit slow for smooth motion on faster subjects. This is why broadcasters prefer the faster frame rate of 720 60P HD, rather than 1080i for sports and other fast motion events. At some point 1080 60P will probably become the norm as it represents fast motion sampling with the added benefit of a whole frame at once resolution.

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Old February 26th, 2008, 02:36 PM   #15
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Hi Eduardo,

Did you try to trash the preferences? You can use 'FCP rescue 5' for that.

Best regards,

Robert
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