Interlaced / Progressive - am I right?

[videoapelsin]

Hi

I’ve just been reading ”Video basics” at http://www.doom9.org/video-basics.htm, and now I’ve some questions about interlaced / progressive.

Both PAL and NTSC can be interlaced, but NTSC can only be interlaced? Right or wrong?

Let’s pretend i’m recording from an interlaced PAL-source with my DVB-T-card, and then author a dvd with the recorded material, do I need to deinterlace this recording, or can I just leave it like it is? And then if I play an interlaced video on my computer, I’ll see “lines” in the picture, if I don’t use a deinterlace filter?

Please help me out on this, I’m a little confused here ;P

[gadgetguy]

As I understand it, both PAL and NTSC are interlaced, analog, broadcast standards. I have not seen new definitions that include the capabilities of digital transmissions, (although I assume they exist somewhere, I haven't seen them and don't know what they are)
IMHO, if you are capturing interlaced material that is destined for DVD, then you want to keep it interlaced. If you use decent player software, (for example PowerDVD), then you won't notice interlace artifacts when viewing on your computer.

[junkmalle]

Standard definition television is broadcast as a series of fields. SD televisions display one field at a time as they are received. By the time a field is being drawn the previous field has faded away. You never seen an entire frame.

When such a signal is digitized, pairs of fields are woven together to make entire frames. If the two fields are from different points in time, or different pictures, the file is interlaced. If the two fields are from the same picture the video is progressive.

The PAL field rate is 50 fields per second. Digitized pairs of fields therefore represent 25 frames per second. Since film is shot at 24 frames a second it is close enough to the PAL frame rate to just speed the film up a bit. So film movies broadcast on PAL systems usually ends up as progressive digital files.

The NTSC rate of 59.94 fields per second, 29.97 frames per second digitized, is too fast to simply speed up the film. So the 3:2 pulldown method was developed. Film frames are broadcast alternately for three and two fields. If you capture this you will see a distinctive pattern of 3 progressive frames followed by 2 interlaced frames, repeating over and over.

Video cameras output fields, usually with each field from a unique point in time. So live sporting events, news, etc end up as interlaced digital video files.

Some DV camcorders have progressive modes where they digitize and save entire frames. These still have to be sent to the TV one field at a time. The progressive video can be 29.97 frames per second or 23.976 frames per second. In the former case the two fields are separated and sent to the TV once each. In the latter case a 3:2 pulldown is performed.

Any time you play a digital video file on a standard definition television, the playback device separates the fields and sends them one at a time to the television. With an interlaced file you must send the fields in the proper temporal order. Unfortunately there is no universal agreement on whether fields should be captured top first or bottom first. That is, since the original broadcast signal is simply an alternating sequence of top and bottom fields, they can be paired together starting with a top field then adding the next bottom field, or starting with a bottom field and adding the next top.

NTSC DVDs usually encode film as 23.976 progressive frames per second and instruct the DVD player to perform the 3:2 pulldown as it plays the DVD. But some DVDs contain 29.97 interlaced frames per second. These are simply split into fields and sent to the TV one field at a time.

To answer your question, if you capture a PAL video where each field comes from a separate point in time, the result will be an interlaced digital file. When output to a TV it must separated into fields and the fields must be displayed in the right order. When you view the video on a progressive computer monitor you will see both fields at the same time. You will see interlace comb lines any time something is moving -- unless you are using a player that deinterlaces on-the-fly.