interlace

[PsyDonia]

What is the diffrent between Interlace and Progressive
In encodeing

[daamon]

Hi PsyDonia,

Look up both terms in the "Glossary" (link is in the top left of the page).

Standard TV's display an interlaced image, while PC monitors display a progressive image.

What are you doing to prompt the question? In encoding, the option usually relates to the source material.

[Abond]

In encoding: Frames are flagged as interlaced even if they are progressive natively, progressive=fields match (top field=bottom field). Scan method of encoder should be alternate (zigzag for progressive). True interlaced require higher bitrate to look as good as progressive.

[gadgetguy]

... progressive=fields match (top field=bottom field). ...

That's not right. In interlaced progressive frames, the top field and bottom field are from the same timeslice, but they are not the same. In true interlaced frames the top field is from a different timeslice from the bottom field. Field order (TFF, BFF) determines which timeslice comes first.

[Abond]

but they are not the same.

Can you tell me how they differ?

[guns1inger]

In true progressive, each frame is captured in it's entirety in a single pass. In true interlace, two fields are taken in the same period that a progressive frame would be taken, each containing an image made up of every second line. They are offset from each other by a single scanline, and the two form a frame.

Taking PAL as an example, a progressive camera would take 25frames per second, each frame containing a whole image. A standard camera would take 2 fields in the same period. On playback, the two fields would appear to be one frame, however closer examination would show they are in fact 1/50th of a second apart.

[Abond]

My question was how the both fields differ in true progressive "each frame captured in its entirety in a single pass" case.

[guns1inger]

If you are shooting 25p then there are no fields, only frames. On playback on an interlaced device you would get repeated frames instead of fields.

[Abond]

If you are shooting 25p then there are no fields, only frames.

This is wrong IMO. There are fields but they are "identical". The question was not for shooting , but encoding. Let say I have this progressive footage and encode it with interlaced settings. It will remain progressive, isn't it?

[lordsmurf]

There are no fields.
Even interlaced MPEG-2 for DVD is encoded as frames, not fields.

[gadgetguy]

Abond,
My comment was based on how progressive frames get telecined. I know the question wasn't addressing the telecine process(yet), but bear with me. If you split a progressive frame into two fields, the first field is from the even scanlines and the second is from the odd scanlines (or visa-versa). Both of these fields are from the same timeslice, but they don't contain the same data. If the subject in the frame is a fabric of scanline height, black and white horizontal stripes, the first field will be white and the second field will be black (or visa-versa). This is what I meant by my comment, and why I considered yours wrong.

Edit: Back to the original post. I assume your question is "should I check the interlaced box of my encoder or not?". The answer depends on your source. If your source is progressive then you don't want to encode interlaced (even though it probably won't make a difference when viewed.) If the source is interlaced, then you want to keep it interlaced when encoding to maintain the correct field order. You want to match the field order of the source.

[manono]

Hi-

If your source is progressive then you don't want to encode interlaced (even though it probably won't make a difference when viewed.)

But Abond's a PAL guy, and knows that the vast majority of PAL DVDs are encoded as interlaced, even if the source is progressive. It could be that's the reason he said earlier, "In encoding: Frames are flagged as interlaced even if they are progressive natively... ". Because here in NTSC land, if it's a movie, it's ordinarily encoded as progressive 23.976fps, with pulldown and the progressive frame flag set. Unless you're encoding already telecined 29.97fps, in which case you encode as interlaced.

lordsmurf said:

There are no fields.
Even interlaced MPEG-2 for DVD is encoded as frames, not fields.

While that's usually true, it doesn't have to be true. It's perfectly "legal" to encode fields and store fields on the DVD, rather than frames.

[gadgetguy]

I can't tell where Abond, you ( manono), or the original poster are from, since you don't have your locations listed. I can't argue about how PAL DVDs are encoded since I've never seen one, but the principle is the same whether it's NTSC or PAL. Encode progressive material as progressive and let the player/display device interlace as required for display. Encode interlaced material as interlaced to keep the field order correct.

[manono]

Sure, I agree with you, gadgetguy. The only reason I know that Abond's from a PAL country is because he showed such knowledge of the telecine process once that I assumed he was from NTSC land, until he set me straight.

[edDV]

I can't tell where Abond, you ( manono), or the original poster are from, since you don't have your locations listed. I can't argue about how PAL DVDs are encoded since I've never seen one, but the principle is the same whether it's NTSC or PAL. Encode progressive material as progressive and let the player/display device interlace as required for display. Encode interlaced material as interlaced to keep the field order correct.

After reading all of this, I think the confusion ("crosstalk") is happening because at least 3 issues are in play not one.

1. progressive vs interlace acquisition (source format)
2. methods for arranging progressive frames or progressive split fields on a DVD.
3. the 23.976 to 29.97 telecine process (NTSC only) needed for encoding progressive film.

PAL discussion is limited to the first two issues. Since in PAL lands, interlace and progressive are both played at 25 fps, progressive can be arranged on the DVD in two ways.

In either case, the fields represent odd or even lines of the image and thus are different even though they originate from the same time sample.

Interlace fields also represent odd or even lines of the frame but are also offset in time by 1/50 sec.

[PsyDonia]

thanks for all answear I think I understand it most.
the reason is that nothinh.
I just want to know the diffrent.
I have test both and could not see anny diffrent in the movie I have encoded.
but now I know the diff.