Difference between Field and Parity

[EEBA]

Hi,

There were so many discussions about Field (TFF or BFF) and Parity in interlaced video. What is the actual difference between them? Can some one explain the terms?

Thanks

EEBA

[jggimi]

I'm not sure what is meant by "parity" in this instance, but a field is merely one half of a frame, either the odd lines or the even lines.

NTSC video has 59.94 fields per second, PAL has 50. BFF = Bottom Field First, TFF = Top Field First. From www.doom9.org/ivtc-tut.htm:INTERLACING is the use of two half-frames (fields) instead of one whole frame. The two fields are shown at a slight time difference and in a way so line 1,3,5... is from the first field and line 2,4,6... is from the second. Most TV’s will show the picture this way, first field 1 then field 2. Computer monitors on the other hand will show both fields at once, so some form of deinterlacing must be used on interlaced material.

[EEBA]

Thanks for your reply. I don't have problem in understanding the term "field" (TFF or BFF).

But if you look at this discussion here (http://forum.doom9.org/showthread.php?s=&threadid=35387&highlight=pal+to+ntsc), they are also taking about parity (or ComplementParity()). It is this thread, which confused me. I still don’t fully understand what a "parity" is in interlaced source.

[trevlac]

I did not read the thread you mentioned ...

but maybe this will help:

http://forum.doom9.org/showthread.php?s=&threadid=69164&highlight=parity

Anyway ...

Imagine 2 lines A & B. If you paint these you have 4 options.

A A A
B B B

A A A
B B B

B B B
A A A

B B B
A A A

I believe parity means which one is painted 1st. Like case 1 vs case 2. If you do a swapfields you go from 1 to 3 (change the 'weave' order). As you can see both 1 and 3 are TFF. To go from 1 to 2, move the lines up by 1.

If fields are 'swapped', you can tell on a still picture. If the parity is off, you need some movement to tell.


PS ... I think I got this right. Read the thread I posted. Here is another link mentioned by Simon.

http://www.lurkertech.com/lg/dominance.html

[EEBA]

Thanks trevlac. I have read lots of your posting in this forum and dvdrhelp.com. Very impressive. Here is a follow-up question for you.

I have an 720x480 interlaced AVI file (no compression - 75GB for 1 hour) captured with AverTV Stereo card. To determine the field order, I used the following script:

AVISource("MyFile_avi")
AssumeTFF().SeparateFields()

I ran the file through windows media player and found smooth movement. To confirm myself, I ran the "AssumeBFF().SeparateFields()" script, the movements were jerky . So, it is 100% sure the AVI file is TFF.

Here is my question. How do I check the parity of the file?

Thanks in advance.

EEBA

[trevlac]

Originally posted by EEBA
Thanks trevlac. I have read lots of your posting in this forum and dvdrhelp.com. Very impressive. Here is a follow-up question for you.

:o :o :o Well, you better watch out. I generally only know about 1/2 of what I am talking about. But heck, that's how I learn. Always find another source or two. (And make sure they don't all link to each other.) :D




Here is my question. How do I check the parity of the file?


Find a scene with movement (like someone walking past the camera) and step thru it. If it is off, they will move forward then back then forward. If it is ok, they will just move forward.

When I was getting a handle on this stuff ... I found a clip and made a copy with all 4 options. Stepped thru it on the PC and watched a Test DVD (with the 4 clips) on a TV. Thing most people miss is that there is a spacial order and a temporal order.

[EEBA]

Thanks for the clarification. I will try to step through my AVI file in VDub this weekend.

EEBA