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Thread: Interlacing lines in interlaced project issue??

  1. #1

    Default Interlacing lines in interlaced project issue??

    I wonder if someone can shed some advice on this issue for me....

    I am working in a 1080 50i project in Vegas Pro (upper field first) with 50i footage shot on a Canon C100 mkii. The footage appears ok. But if I crop and zoom in you can clearly see the awful field lines? It just distorts the image. I usually work progressive but this project needed to be interlaced. I've never had this issue with progressive.
    Is this right with interlaced footage? I know it won't look the best on a PC/laptop LCD monitor as progressive but as bad as this?
    If I de-interlace (blend/interpolate) in the project settings it solves it, but what if I want this project interlaced?


    Below are images of the differences

    Original


    Zoomed


    Zoomed further


    Zoomed further still



    As you can see, the further it's cropped and closer it becomes....the finer the lines become?

    I appreciate any help.

    Thanks
    Martin

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    OK
    I'm assuming you understand that in interlaced footage, the camera alternately records odd and even scan lines In other words filming at 1080/50i The image is split into 1080 lines and in the first 50th of a second the camera records 540 "even" lines with the image in position "A", then in the next 50th of a second it will record the "odd" lines of the image in position "B", so if you superinpose the first image onto the second you will get a very fine "comb" effect.

    But, in the normal course of events, we don't superimpose one on top of the other we show them alternately and our eyes are tricked into seeing a nice smooth motion image.

    Now imagine what happens if you zoom in - lets say to double height.
    Each one of your lines now takes up the height that two lines previously took up so your "odd" line is now split across one odd and one even "output" line (for want of a better way of describing it). In other words half of the image from the lines that were in "position A" are now being replaved on the second 1/50th of a second. Depending on how much you zoom in, you can see that the effect of doing this will differ which is exactly the phenomenon we can see above.

    You need to de-interlace any footage if you are going to zoom even if your output will be interlaced.

    (It took me a while to understand this as well as it sounds contrary to what we are trying to do).

    You do this in File | Project Properties - in "Deinterlace Method". Set it to Blend Fields or Interpolate Fields. Experiment to see which works best for your footage.I believe that this is "smart" in that it will only deinterlace footage which requires it (ie footage you zoom into or out of)

    Some will advise going outside of Vegas and deinterlacing first in something else

    Hope this helps.
    Tim

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    Are you sure the footage is in fact interlaced? I've run into issues with Vegas correctly recognizing progressive files, to the point where I've gone in and changed the file properties manually.

  4. #4

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    Quote Originally Posted by TimStannard View Post
    OK
    I'm assuming you understand that in interlaced footage, the camera alternately records odd and even scan lines In other words filming at 1080/50i The image is split into 1080 lines and in the first 50th of a second the camera records 540 "even" lines with the image in position "A", then in the next 50th of a second it will record the "odd" lines of the image in position "B", so if you superinpose the first image onto the second you will get a very fine "comb" effect.

    But, in the normal course of events, we don't superimpose one on top of the other we show them alternately and our eyes are tricked into seeing a nice smooth motion image.

    Now imagine what happens if you zoom in - lets say to double height.
    Each one of your lines now takes up the height that two lines previously took up so your "odd" line is now split across one odd and one even "output" line (for want of a better way of describing it). In other words half of the image from the lines that were in "position A" are now being replaved on the second 1/50th of a second. Depending on how much you zoom in, you can see that the effect of doing this will differ which is exactly the phenomenon we can see above.

    You need to de-interlace any footage if you are going to zoom even if your output will be interlaced.

    (It took me a while to understand this as well as it sounds contrary to what we are trying to do).

    You do this in File | Project Properties - in "Deinterlace Method". Set it to Blend Fields or Interpolate Fields. Experiment to see which works best for your footage.I believe that this is "smart" in that it will only deinterlace footage which requires it (ie footage you zoom into or out of)

    Some will advise going outside of Vegas and deinterlacing first in something else

    Hope this helps.

    Hi Tim,
    Thank you very much for the response. That explains a lot. Whereas I had some knowledge of what interlaced footage is, i didn't know how it is affected by what we do to it. That really helps.
    Could I also ask you then, when normally viewing the interlaced footage in the workflow timeline (or via any other player actually) on a PC monitor or laptop can I expect to see the combing effect on the the lines in movement? I mean is that going to be normal as it is not broadcast on a TV? I am going to to render two versions a de-interlaced version and interlaced for this possible reason of broadcast. I am currently seeing the combing effect when looking closely or rendering a clip as interlaced to see what it is like....and on my laptop and PC monitor there are the field lines visible. So is this quite normal?

    Thanks very much
    Martin

  5. #5

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    Quote Originally Posted by bouldersoundguy View Post
    Are you sure the footage is in fact interlaced? I've run into issues with Vegas correctly recognizing progressive files, to the point where I've gone in and changed the file properties manually.
    HI bouldersoundguy,
    Thanks for the response. Yeah I'm sure it is, I shot 50i on c100 and when checking properties of the footage itself it's 25 frames upper field first. To double check I also allowed Vegas to match media for me and the project property settings were the same also.

    Thanks
    Martin

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    Quote Originally Posted by Trapdoor View Post
    Could I also ask you then, when normally viewing the interlaced footage in the workflow timeline (or via any other player actually) on a PC monitor or laptop can I expect to see the combing effect on the the lines in movement?
    That is exactly what I see. Some software will deinterlace the footage (so you won't see the combing - I think VLC does) and your TV will do this as well (or maybe it's the DVD/Bluray player)

    Here's a little experiment you can do to prove what's going on.
    Drop a piece of interlaced footage onto the timeline.
    Set the deinterlace method to "none"
    Open pan and crop and move a few seconds along and zoom in to create a second keyframe. (You should now have footage that zooms in)
    Set your monitor (or second monitor if you have one) to be the preview device so you have full screen playback and scrub through the piece (or place the cursor in different places along teh timeline)
    You will see differing amounts of "waviness" like your photos above.
    Now set the deinterlace method to "Blend" or "Interpolate" and do the same - the waviness/combing has disappeared!

    Delighted to have helped.
    Tim

  7. #7

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    Hi Tim,
    Thanks for the tips, and yes that is the case.
    I did another test and burnt a dvd with a rendered interlaced clip. The rendered clip had the combing lines as mentioned. However, the dvd did not ....and it played fine on my pc without the lines. So I am presuming that these field lines are fine in my work flow as they will not show if broadcasted etc? And any zooming/cropping I do will have to be deinterlaced.

    Thanks Tim
    Martin

  8. #8

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    Good response Tim, my settings have been Blend for years after I came to the same conclusion as you

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    Quote Originally Posted by Z Cheema View Post
    Good response Tim, my settings have been Blend for years after I came to the same conclusion as you
    Hey, Good to hear you're still dropping by this forum Z!
    Tim

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