4 Replies Latest reply on May 10, 2011 7:43 AM by Todd_Kopriva

    Scanning System

    Not_Relevant Level 1

      Dear friends,

       

      I have read some information about scanning systems on the website below and I have a couple questions to get everything straight.

       

      http://www.lurkertech.com/lg/video-systems/

       

      Now, interlaced or progressive scan is the feature of video file itself or the feature of device you are recording with/watching on that video? Maybe it's even a feature of transmitting TV signals?

       

      The document explains the differences between interlaced and progressive scanning, but it does not say why interlaced scanning system is more popular than progressive, even though it comes along with such drawbacks as "tearing".

       


      Thank you for your answers.

        • 1. Re: Scanning System
          Todd_Kopriva Level 8

          > Now, interlaced or progressive scan is the feature of video file itself or the feature of device you are recording with/watching on that video? Maybe it's even a feature of transmitting TV signals?

           

           

          All of the above. See this page.

           

          Interlacing is used as a way of getting twice as much temporal (time-based) resolution out of the same number of bits. E.g., if you have 60 fields per second, you can see some motion that you can't see at 30 progressive frames per second. But the image has half the spatial resolution---i.e., it looks worse.

           

          Interlacing is being used less and less (thank goodness). It's irrelevant for video intended for computers, mobile devices, and digital cinema. As far as delivery formats, it's only relevant for some television.

           

          Don't overthink this or fret about it. After Effects takes care of almost all of this for you. Instead of asking general conceptual questions, I recommend coming back with specific questions when you encounter interlacing issues in real work. Chances are that you won't.

          • 2. Re: Scanning System
            Not_Relevant Level 1

            Thanks for your answer.

             

            OK, here are some more specific questions.

             

            Let's say I create a title sequence in After Effects. And I want it to be shown on TV.

             

            1) Do I have to Render Fields? Why?

            2) If so, which Field Order to choose? On what it depends?

            3) What happens if I watch a progressive scan video on a TV?

            4) If I watch a captured video and see a "tearing" effect on my computer screen would it be visible on a TV screen?

            • 3. Re: Scanning System
              Mylenium Most Valuable Participant

              You're drifting too much into generics again. There is no answer that is right under all circumstances. What settings to use very much depends on what the TV station wants. Now this sounds like a causal loop, but that's the way it is. While there are theoretical specs for everything, practical implementation is another. It's not that uncommon that fields get swapped either for genuine technical reasons or just because some program in the whole chain is playing quirky... anyway, let me at least try to answer the theoretical stuff a bit.

              2) If so, which Field Order to choose? On what it depends?

               

              On the TV standard and region of the world. NTSC = lower/even field first, PAL broadcast full = upper/ odd field first, PAL DV = lower/ even field first, all interlaced HD formats = upper/odd field first.

               

              3) What happens if I watch a progressive scan video on a TV?

               

              It might look jerky, but many TVs these days being LCDs and using framerate doubling/tripling/quadrupling and adaptive scaling, it may not. Again, you are expecting a simple answer where there is none.

               

              4) If I watch a captured video and see a "tearing" effect on my computer screen would it be visible on a TV screen?

               

              Could be, could be not. Same as before. If the TV expects interlaced, it will display alternating fields in accordance with its display frequency, if it expects progressive and has no built-in deinterlacer, it will display both fields at once and show the tearing. But then again, it could be scaling or doing otehr fancies and minimize those artifacts.

               

              Mylenium

              • 4. Re: Scanning System
                Todd_Kopriva Level 8

                Here's a video that I made that explains the basics of fields and interlacing and shows how to work with them.

                 

                It's linked to from the page that I pointed you to before, but I wanted to make sure that you saw this simple video specifically. It would also be good if you worked your way through the rest of the information on that page and what it points to.