Fields and fun stuff

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Fields and fun stuff

Postby Yogurtron » Tue Aug 27, 2002 3:33 am

I've been wondering about these fields for a long time, and so, I might as well ask about them on the forum.

Firstly, what exactly are these "fields." I know that they are used in video, and that most animation on DVDs and TV broadcasts are sent as "fields" as opposed to full frames. At least, that's what I believe I've heard about them. Nonetheless though, what exactly are they, if I'm incorrect there.

Secondly, being somebody who went to the first attempt at showing the AMV contest at AX2002, I heard about the blunder that was their reversed field orders. Why did reversing the field order mess up the showing of the video, and why would it show the "hand moving down, then jerking back up again," that the announcer spoke of (i thought it would just do the funky interlacing, myself).

Thirdly, when working with video editting, I've set scenes to work in reverse. There is massive interlacing that occurs when I do that, and to fix it, I have to, "reverse field dominance." Why is that? what exactly does reversing the the field dominance do?

Fourthly, when I make a video and reverse the field dominance on that clip, if I were to export it to an MPG or something like that, and send that file to an MPEG, would that clip have a problem with the reversed field order (like AX2002), while the rest would be okay?
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Re: Fields and fun stuff

Postby trythil » Tue Aug 27, 2002 3:59 am

Yogurtron wrote:I've been wondering about these fields for a long time, and so, I might as well ask about them on the forum.

Firstly, what exactly are these "fields." I know that they are used in video, and that most animation on DVDs and TV broadcasts are sent as "fields" as opposed to full frames. At least, that's what I believe I've heard about them. Nonetheless though, what exactly are they, if I'm incorrect there.


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standard answers: guides, google.


Yogurtron wrote:Secondly, being somebody who went to the first attempt at showing the AMV contest at AX2002, I heard about the blunder that was their reversed field orders. Why did reversing the field order mess up the showing of the video, and why would it show the "hand moving down, then jerking back up again," that the announcer spoke of (i thought it would just do the funky interlacing, myself).


As noted in the above link, most consumer electronics (which includes TVs) draw in two passes: one set of fields, then the other. The first set contains one image, the second set another. Some electronics draw odd -> even; others draw even -> odd. If your video depends on a certain field order...well, you figure the rest out.

Yogurtron wrote:Thirdly, when working with video editting, I've set scenes to work in reverse. There is massive interlacing that occurs when I do that, and to fix it, I have to, "reverse field dominance." Why is that? what exactly does reversing the the field dominance do?


Field dominance states which field gets drawn first: the odd or even field. Thus, when you reverse interlaced video, you may need to also reverse the field order.

Yogurtron wrote:Fourthly, when I make a video and reverse the field dominance on that clip, if I were to export it to an MPG or something like that, and send that file to an MPEG, would that clip have a problem with the reversed field order (like AX2002), while the rest would be okay?


Depends on the electronics they use.
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Postby trythil » Tue Aug 27, 2002 4:04 am

I should have added this:

A good source for information on fields (and a lot more) can be found @ Luke's Video Guide, esp.: http://www.lukesvideo.com/interlacing.html

There used to be some very good information on SGI's website, but I can't find it anymore.
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Postby Yogurtron » Tue Aug 27, 2002 1:11 pm

Ah, alright, I understand. Thank you for the answers and the link to that website. The help was much appreciate ^_^.
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