i or p?

[Giannis Pass]

Hello,
I don't have a clear vision for the difference between i and p.
is it possible to help me?

I am Pal user from Athens, Greece and i have ex1r.

Thanks

[David Heath]

p means progressive - so each frame is a discrete single image, as a still photo. All lines of the image are from the same point in time.

i means interlace - each frame is divided into two so lines 1,3,5 etc are best considered one image (at one point in time), lines 2,4,6 etc another (at a later point in time). So one frame is split into two fields.

You really need to think of them in conjunction with the other features of the system - the no of lines and the frame rate, and modern nomenclature writes systems as "(no lines)(scanning system)/(frame rate)". Hence the relevant ones for the EX are 720p/50, 1080p/25 and 1080i/25.

[In old terminology, it was normal to refer to the latter as 1080/50i, and you still see that used often. It used to be the case that p systems used the frame rate, i systems the field rate, but the recommendation is now to always specify the frame rate - hence 1080i/25.]

In terms of what you see, 720p/50 and 1080i/25 both give "smooth motion" (so are especially suitable for sports etc), whilst 1080p/25 gives a jerkiness to movement akin to film, and is often preferred for such as drama. It does give the greatest sharpness of the systems.

[Blake Cavett]

i = Interlaced
p = Progressive

When recording interlaced, your camera actually records the 1st horizontal line of video, then the 3rd, then the 5th, etc. All the way to all 1,079 lines. All those odd numbered lines are a 'field.'

<----------> Line 1

<----------> Line 3

<----------> Line 5

Then a split second later it records the 2nd horizontal line, then the 4th, 6th, and so on. All the way down to 1,080. That's the second 'field.'

<-----------> Line 2

<-----------> Line 4

<-----------> Line 6

If you put those two fields together, you 'interlace' them to make one full frame of video.

<----------> Line 1
<----------> Line 2
<----------> Line 3
<----------> Line 4
<----------> Line 5
<----------> Line 6

Your camera does this 29.97 times a second.

For progressive, the recording is the same (I think) but on playback you see each line of video PROGRESSIVELY. Meaning you see each line displayed right after one another... 1, 2, 3, 4... all the way up to 1,080.

Interlaced video is actually TWO pictures spliced together to make ONE frame of video.
Progressive is one full, actual frame.

*Edit to add: And what David said!

[Craig Seeman]

interlace alternating odd and even fields.
Progressive entire field is shown.

Example 1080i50
50 images (fields) a second (which is 25 frames a second).
Each field is 1920x540
two fields is one frame of 1920x1080

Example 720p50
50 images (frames) a second.
Each frame is 1280x720

So in 1/50 of a second
1080i50 is 1920x540
720p50 is 1280x720
so the latter actually has higher vertical resolution.

They have the same temporal resolution (50 units/pictures a second) though.

Progressive scan - Wikipedia, the free encyclopedia

Interlace - Wikipedia, the free encyclopedia

[David Heath]

Originally Posted by Craig Seeman

1080i50 is 1920x540
720p50 is 1280x720
so the latter actually has higher vertical resolution.

No, that's not true, remember that consecutive fields don't relate to the same point in space, they are offset a line. That's the difference between a 1080i/25 system and a hypothetical 540p/50 system.

So it may then seem that a resolution of 1080 is possible with 1080i/25. Theoretically, it is. Practically, you'd get an unacceptable 25Hz flicker on fine detail when detail was present on one field but not another. Hence chips are scanned for interlace in a way which reduces the flicker, but results in lower resolution. Practically, it turns out to be anout 750 lines, so a 1080i system has not much more resolution vertically than one of 720p - though it's far superior horizontally.

To get the highest resolution, you have to use 1080p, which currently effectively means 25fps motion - not 50.

[Craig Seeman]

I over simplified the answer for sure. I'm trying to think of simple ways to explain the difference of i vs p inherently as well as how the eye/mind perceives them at a given frame rate as well. I think the charts in the linked wiki pages do show in more detail. Look at interline twitter.
http://en.wikipedia.org/wiki/Interla...erline_twitter

[Nick Wilson]

Originally Posted by David Heath

No, that's not true, remember that consecutive fields don't relate to the same point in space, they are offset a line. That's the difference between a 1080i/25 system and a hypothetical 540p/50 system.

So it may then seem that a resolution of 1080 is possible with 1080i/25. Theoretically, it is. Practically, you'd get an unacceptable 25Hz flicker on fine detail when detail was present on one field but not another. Hence chips are scanned for interlace in a way which reduces the flicker, but results in lower resolution. Practically, it turns out to be anout 750 lines, so a 1080i system has not much more resolution vertically than one of 720p - though it's far superior horizontally.

I think I remember reading that the EX cameras use line averaging to produce the two interlaced fields, so the vertical resolution is effectively halved. I have yet to work out what the difference is between 1080/50i and 1920x540/50p. Most displays de-interlace by line doubling.

As I understand it, the EX camera imagers output 1080/50p and the recorder chucks away half the data, either by binning every other frame (1080/25p), every other line (1080/50i), 55.5% of the pixels (720/50p) or 55.5% of the pixels and every other frame (720/25p).

[Paul Kellett]

Gordon Bennett, 50p looks better for sd-dvd.

Paul.

[David Heath]

Originally Posted by Nick Wilson

I think I remember reading that the EX cameras use line averaging to produce the two interlaced fields, so the vertical resolution is effectively halved.

First half of that is true, the second half isn't.

The reason is because the line averaging differs between odd and even fields. For an odd field, the averaging might be such that line 1 is formed from chip lines 1&2, for line 3 from 3&4, line 5 from 5&6 etc. For an even field, it's such that line 2 is formed from chip lines 2&3, line 4 from 4&5, line 6 from 6&7 etc. Hence the lines of the odd fields differ from those of the even fields.

In practice, this means that whilst the averaging means that vertical resolution must be less 1080, the way it's done also means it must be more than 540. A figure of 750-800 is realistic, which correlates well with practice and "a bit better than 720" in a progressive system.

[Craig Seeman]

Adam Wilt ran tests on this a long while back

ProVideo Coalition.com: Camera Log by Adam Wilt | Founder | Pro Cameras, HDV Camera, HD Camera, Sony, Panasonic, JVC, RED, Video Camera Reviews

____
In 1080p, that 1000 lines is visible in both H & V directions. In interlace, vertical detail drops to “only” 800 lines, since dual-row summation is used to avoid frame-rate twitter (a distracting flicker of thin lines that appear in only one field). In 720p modes, resolution drops to roughly 700 TVl/ph in both H & V, as it should. Sony’s downsampling to 720p effectively squashes any aliasing at the smaller frame size.
____
So Adam measures the resolution at about 800 lines at 1080i and 700 lines at 720p. This is what David is describing as well.

[Idar Lettrem]

will windows media player accept any framerate ?

Say - if my footage is 720p/50 and played off in wmp - will it be "1/2 speed - slow mo"

[Richard Hunter]

Originally Posted by Paul Kellett

Gordon Bennett, 50p looks better for sd-dvd.

Paul.

Hi Paul. Does an SD DVD player accept 50p discs? I didn't think this was a supported DVD format.

Richard