Interlaced or Progressive???

[xeen]

I have a couple of questions regarding interlaced and progressive encoding. I always thought that all Region 1 NTSC DVDs were required to be interlaced video. But then I analyzed a few DVDs and found out that many of them are in fact progressive. My first question is which is better and why?
My second question is what settings to choose when making a progressive movie from an interlaced source. My source is DV-AVI (which is interlaced and buttom field first). If I decide to convert to progressive when I export it, will it affect the quality or not??
When exporting DV-AVI to progressive MPEG-2, what should I choose for Frame Order: Buttom first, Top First, or should I choose None and select DeInterlace option? Thanks in advance for help.

[SomeJoe]

Otay. There is a difference between how a movie is shot and how it is viewed. You can be interlaced or progressive on either end, independently of each other.

For instance, look at how a movie might be shot: If you shoot on 24 fps film, you are shooting "progressive" footage. Progressive footage means that the entire scene's picture was all captured to film/recording medium at the same instant in time. For film, the entire film frame was exposed at once.

Another way to shoot is interlaced: NTSC DV cameras shoot one "field" of video every 1/60th of a second. A field is only half of the frame, however -- one field is all of the odd scanlines and one field is all of the even scanlines. But remember, that the two fields that make up a frame were shot at different points in time. So you cannot take two fields and put them together, and get a nice picture. You will see the "comb" effects because moving objects are in a different position in the two fields.

Now, there are similarly two ways to view a movie. On a movie screen in the theater or on your computer monitor, you are viewing progressive. Both of these displays will show an entire frame at once.

The other way is to view interlaced: Most TVs are interlaced devices, showing one field at a time.

Now, if you have shot interlaced footage, and view it on an interlaced display, everything will look beautiful and clean. (i.e. shoot DV and playback on a TV). Similarly, if you have shot progressive footage and view it on a progressive display, it also looks great (shoot on film and watch it in the theater).

The problems arise when we have footage in one format and need to view it on a display that it the other format.

Two different processes are used to adapt one type of footage to the other kind of display: One process is called telecine, also known as 3:2 pulldown, it is used when progressive footage needs to be viewed on an interlaced display. The other process is called deinterlacing, and is used when interlaced footage needs to be viewed on a progressive display.

The telecine process takes 24 fps footage (typically shot on film), and turns it into 30 fps footage, which is suitable for viewing on an interlaced display. This is what most Hollywood DVDs do. The original film was shot at 24 fps, placed on the DVD, and flagged such that the DVD player performs the telecine. Now you can view the progressive footage on the interlaced TV.

Deinterlacing does the opposite. DV footage (which is interlaced) can be viewed on a computer, for instance. But a deinterlacing algorithm is used to manufacture the missing lines in each field. So now you have frames to show on the progressive computer monitor instead of fields.

Telecine and deinterlace can be applied to the footage during encoding or during playback. The Hollywood DVDs (the good ones) perform it during playback. The stored frames on the DVD are actually 24fps, and the DVD performs the telecine during playback.

Another example might be a DVD with interlaced footage on it that you're going to watch on your computer. The DVD playback software (like WinDVD) performs the deinterlacing during playback.


Now, to answer some of your original questions: Generally, progressive video (that was originally shot progressive) looks better than interlaced video. This is because film has a much higher resolution than DV video.

However, any source always looks better when viewed natively than when viewed after it has been processed by either telecine or deinterlacing. Since your DV is natively interlaced, it will look best if encoded and viewed interlaced.

The only time you should deinterlace it is if the desired display device is progressive. In other words, if you're planning for people to view your footage on a computer monitor, then deinterlace. Otherwise, leave it interlaced and view it on a TV.

When you export your interlaced DV to MPEG-2, you should choose lower/bottom field first to keep your footage interlaced.

Also, there is a large thread here in this forum regarding the best encoders and encoding options for encoding interlaced video like DV, you should definitely take a look at that.

[xeen]

Thanks for that long explanation. I finally now understand what interaced/progressive is. Your explanantion was so much better than anywhere else I've read. However I still have a few questions:
1)Exactly how much does the quality worsen by changing interlaced to progressive and is it noticable?

2)What exactly is the point of having interlaced stuff when it doesnt capture the entire frame?

3)My files are NTSC DV-Avi, meaning they are interlaced with buttom field first. My planned destination is a dvd that is to be equally viewed BOTH on computer AND TV. SO which do you think is better: progressive or interlaced?

and 4) Suppose I decide to make my interlaced DV-AVIs progressive upon exporting to MPEG-2 files which will later be used for DVD. What option should then be used for Exporting Field Order: Top, Bottom, or NONE (I'm guessing None since progressive = no fields but full frame). And should I choose the deinterlace option?

Thanks a lot!

[SomeJoe]

1. It depends on how the deinterlacing is done. When deinterlacing for display on a computer monitor, the deinterlacing is almost not noticable. The computer monitor refresh rate is high enough that the fluid motion of NTSC video is not lost. Good deinterlacing software/algorithms can look surprisingly good.

2. Unfortunately, when TVs were invented in the late 1940s, technology wasn't good enough to allow 50/60 frames per second with entire frames. But at half that rate (25/30 frames per second), if the frames were still progressive, the result was very annoying flicker on the TV screen. So a compromise was reached where the screen would be updated at a high enough rate to remove the flicker (50/60 times per second), but only every other line would be used on each update, reducing the quantity of information that had to be broadcast over the air. The result was interlaced video. And here we are, 55 years later, still engineering algorithms around fields and frames. :rolleyes:

3. Encode and author your DVDs interlaced. They will look great on the TV screen, and a nice DVD playback application on the computer like WinDVD will deinterlace on playback, and the deinterlacing will look fine.

4. To make them progressive, you would choose the no fields option, and the deinterlace option. The deinterlacer built into Premiere is not particularly good. There are better deinterlacing packages available, but most need to be used with AVISynth and frameserving from Premiere. The resulting footage will look fine on a computer monitor, but will have a kind of jumpy look to in when viewed on TV. In addition, you will lose some resolution and fine detail.