19 Replies Latest reply on Jun 9, 2008 4:54 PM by Jim_Simon

    Interlacing

      Hey all,
      I was just wondering if someone could explain to me when you should de-interlace your footage? I am a little confused - apparently, Premiere, when de-interlacing, throws away half your vertical res. How then, can I put my footage on dvd without de-interlacing with Premiere? Or have I got it all wrong?!?!
      Thanks alot!
      Brad
        • 1. Re: Interlacing
          Jim_Simon Level 8
          Generally, you shouldn't deinterlace. When going to DVD, leave it as it originally was.
          • 2. Re: Interlacing
            Harm Millaard Level 7
            Even Hollywood DVD's are interlaced.
            • 3. Re: Interlacing
              Webshark2000 Level 1
              Interlacing is necessary for most Standard Def Televisions (the big CRT TVs). The reason for interlacing was because the information couldn't be sent fast enough over the air waves to draw an entire frame on the screen at one time. So what would happen is the electron gun in the television would draw all of the odd lines first, then go back to the beginning and draw the even lines. It happens so fast that you brain just sees it as one solid image.

              If you pause a VHS tape (and, like Harm Millaard said, many DVD movies), you'll probably see the interlacing (you'll see separate lines that don't match up perfectly). Most newer televisions can use a progressive signal (480p, 720p, 1080p, the 'p' means progressive), which means they're drawing an entire frame all at once. Personally, I think it makes a big difference in the picture quality, but a lot of people don't see any difference. Standard def is 480 lines of resolution, so you can have 480i (interlaced) or 480p (progressive, with the newer TVs).

              If you're making something for broadcast, or something you think may be played back on older televisions that can't play back a progressive signal, you probably want to stick with interlaced. If you tell Premiere that you're outputting to a standard def DVD, the Mpeg2 file it outputs will be interlaced. You can change this in the settings when you go to output.

              Hope this helps.
              • 4. Re: Interlacing
                Level 1
                Thanks very much everyone! So am I right in saying that if you are uploading to the web, you de-interlace, otherwise you don't?
                • 5. Re: Interlacing
                  Jim_Simon Level 8
                  That's a good rule of thumb.
                  • 6. Re: Interlacing
                    Dan Isaacs Level 2
                    > Even Hollywood DVD's are interlaced

                    Most "Hollywood" movie DVDs are, in fact, progressive frame (at least those sold in the USA). Film is 24 fps. This is slowed slightly to 23.976 fps and put on DVD as progressive frame -- so called "24p".

                    So, Hollywood DVDs are interlaced -- except, of course, those which are not.
                    • 7. Re: Interlacing
                      Harm Millaard Level 7
                      In part you are correct. Film is 24 FPS, but all those are converted to 50i/60i for burning on DVD. The simple reason is that otherwise a whole lot of set top boxes would be incompatible with progressive material, since they do not have P capability.
                      • 8. Re: Interlacing
                        Webshark2000 Level 1
                        > Brad 902 - 1:46pm Jun 4, 08 PST

                        > Thanks very much everyone! So am I right in saying that if you are uploading to the web, you de-interlace, otherwise you don't?

                        Yes, although you may want to de-interlace when going to a DVD as well, just depends on how you're going to use your video. Computer monitors have always used a progressive signal, so you should use progressive in your web videos. Also, since computers have the ability to resize images you can really use any resolution you want if your video is going to the web, but the most standard is 320x240 because some people still have slow connections (this is the size YouTube uses).

                        Premiere Pro has options for web formatting when you go to export your movie. You can choose one of the presets so you don't have to worry about all the little details.
                        • 9. Re: Interlacing
                          Jeff Bellune Adobe Community Professional
                          Harm is correct. *Some* progressive DVD players are able to reconstruct the original full frames from the interlaced fields stored on the DVD.
                          • 10. Re: Interlacing
                            Dan Isaacs Level 2
                            I know Wikipedia is not always an absolute authority, but this quote matches my observation:

                            > DVDs, however, are capable of storing the native 24p frames. Every Hollywood movie is laid to disc as a 24p (actually 23.976p see below) stream. With a progressive-scan DVD player and a progressive display, such as an HDTV, only the progressive frames are displayed and there is no conversion to an interlaced format eliminating the appearance of any interlace or de-interlacing artifacts. When displayed on a standard NTSC TV (which only display 60i) the DVD player will add 3:2 pulldown to the signal.

                            Open a .VOB from a "Film" NTSC DVD in a program such as DGIndex. You will likely see that it is 23.976 fps, progressive frame.
                            • 11. Re: Interlacing
                              Harm Millaard Level 7
                              I know that at least 3 DVD players here in my house are not progressive, just interlaced. They can't play progressively burnt disks, however they all play Hollywood DVD's. QED.
                              • 12. Re: Interlacing
                                Dan Isaacs Level 2
                                > know that at least 3 DVD players here in my house are not progressive, just interlaced. They can't play progressively burnt disks however they all play Hollywood DVD's

                                1.) What are the makes/models of these DVD players?
                                2.) What do you mean by "progressively burnt"? Are these 23.976p, 24p, 25p, 29.97p ? Encoding with what settings in what program?
                                3.) What type of Hollywood DVDs? Are they PAL or NTSC? Have you looked at frames from these (on your PC) to check for combing? Or are they progressive frames encoded as if interlaced? What does DGIndex (or other MPEG2 decoder) report for frame rate and interlaced flag status?

                                I'd be happy to provide my own findings to this end also, but I am many miles from my DVD collection and workstation, so that won't be possible for a few weeks yet.
                                • 13. Re: Interlacing
                                  Harm Millaard Level 7
                                  1. Daewoo (don't know the model, have to check that), Sony DVP-NS905V and Panasonic DVD-A350.
                                  2. As you said in question 3, encoded as if interlaced. All 25p.
                                  3. PAL DVD's. Tried it with Pearl Harbor, Gladiator and other major movies. There is no combing on the PC with PowerDVD but they are encoded as if interlaced. DGIndex does not seem to work (version 1.5). Can you help me on what to do with DGIndex to find that info?
                                  • 14. Re: Interlacing
                                    Jeff Bellune Adobe Community Professional
                                    Use GSpot if DGIndex won't work. The 24 fps progressive frames are stored as 29.97 interlaced with 3:2 pulldown flags.
                                    • 15. Re: Interlacing
                                      Jim_Simon Level 8
                                      In this case, I believe the Wikipedia article is incorrect.

                                      The studio, of course, will have the option to add their own 3:2 pulldown during telecine, thereby storing the standard NTSC 30i signal, or they can encode with the progressive flag, (because the actual signal is interlaced on all DVDs, with or without that flag) and have the player add the 3:2 pulldown during playback.

                                      For myself, I found that adding my own 3:2 pulldown gives me better, smoother results than letting the DVD player do it. I suspect many studios might agree (though I haven't checked any DVDs yet for confirmation.)
                                      • 16. Re: Interlacing
                                        Dan Isaacs Level 2
                                        > Can you help me on what to do with DGIndex to find that info?

                                        RTFM, Harm :)

                                        As I said, I'm not near a suitable workstation right now. I think all you need to do is select "Preview" from the File menu -- a little window will open showing you lots of good info. If the DVD is copyrighted, you may need a decyption program (AnyDVD or the like).

                                        So, it looks like (from what you said) PAL "Film" titles are progressive frame (sped up from 24 to 25 fps), but encoded with the interlaced flag to avoid compatibility issues. That is interesting. I believe, though, that "24p" (23.976 fps) is really part of the NTSC DVD standard and is compatible with any U.S. DVD player. I don't know any of this for certain and I'd love more info about this subject from those in the know.
                                        • 17. Re: Interlacing
                                          Jim_Simon Level 8
                                          >PAL "Film" titles are progressive frame (sped up from 24 to 25 fps), but encoded with the interlaced flag to avoid compatibility issues.

                                          Actually, the video would be stored as Interlaced, with a Progressive flag.

                                          >"24p" (23.976 fps) is really part of the NTSC DVD standard

                                          It is. The player will add the pulldown for display.
                                          • 18. Re: Interlacing
                                            Dan Isaacs Level 2
                                            > Actually, the video would be stored as Interlaced, with a Progressive flag

                                            Maybe I misuderstand you, Jim. What does "stored as Interlaced" mean?

                                            By my reading of your statement, this means that the video would contain interlaced material (combing artifacts, interlaced chroma subsampling, etc.) but the stream would be flagged as progressive. This would cause a progressive scan DVD player to assume these interlaced frames are really progressive and to pass them through unaltered to a progressive scan HDTV, etc. That is not and cannot be correct, can it?
                                            • 19. Re: Interlacing
                                              Jim_Simon Level 8
                                              The first part about storing the material as interlaced frames is right. The progressive flag then tells the DVD player how to restore the original frames (which fields to recombine).