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  1. I am using Blur(0,0.5) in avisynth for my lowpass filter, is it a good idea to sharpen afterwards? If so, what is the best thing to add to my code to sharpen my footage again after the blur?
    Last edited by katieburchett; 3rd Sep 2015 at 06:20.
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    I'm assuming we are talking about low-passing to reduce so called interline-twitter caused whenever a video is run through an interlaced playback chain.


    Originally Posted by katieburchett View Post
    is it a good idea to sharpen afterwards?
    Yes, because otherwise you are just, well, blurring.
    Think of it like this: the purpose of low-passing is to make vertical details thicker so that they are not completely absent in either of the fields. That's not really the same as blurring vertical details.


    Originally Posted by katieburchett View Post
    If so, what is the best thing to add to my code to sharpen my footage again after the blur?
    Sharpen(0, 0.x, false)


    Here is what I've been using for years for DVD menus, CG renderings and HD to SD conversions.
    Code:
    Blur(0, 0.6, false).Sharpen(0, 0.4, false) #mild, not for very detailed sources
    Blur(0, 0.7 false).Sharpen(0, 0.4, false) #medium, works well with almost any source in my experience
    Blur(0, 0.9 false).Sharpen(0, 0.5, false) #strong, try medium first
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  3. Originally Posted by Skiller View Post
    I'm assuming we are talking about low-passing to reduce so called interline-twitter caused whenever a video is run through an interlaced playback chain.
    Yes I am referring to interline Twitterr! (jaggies?) But I'm not familiar with the term 'interlaced playback chain' - my footage is progressive so does this still apply?


    Originally Posted by Skiller View Post
    Sharpen(0, 0.x, false)

    Here is what I've been using for years for DVD menus, CG renderings and HD to SD conversions.
    Code:
    Blur(0, 0.6, false).Sharpen(0, 0.4, false) #mild, not for very detailed sources
    Blur(0, 0.7 false).Sharpen(0, 0.4, false) #medium, works well with almost any source in my experience
    Blur(0, 0.9 false).Sharpen(0, 0.5, false) #strong, try medium first
    This is absolutely perfect, thank you!

    EDIT: I've just researched interline twitter, my footage is PROGRESSIVE (down-converted from HD to SD) but it definitely is exhibiting jagged Twitter along the horizontal lines. Is this normal for progressive material because Wikipedia suggests interline Twitter is caused by interlacing only? Should I still be using this low pass filter and sharpen? Thank you!
    Last edited by katieburchett; 3rd Sep 2015 at 07:55.
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    Originally Posted by katieburchett View Post
    But I'm not familiar with the term 'interlaced playback chain' - my footage is progressive so does this still apply?
    Yes, it most often does still apply even with progressive footage. Reason is: interlaced playback chain – it means at some point in the playback chain the information of the video being progressive might get lost and it is therefore assumed to be interlaced and treated as such by whatever comes next in the playback chain. When this happens it does not matter whether the video is actually really interlaced or progressive – the jaggies will show up if it hasn't been low-passed.


    Originally Posted by katieburchett View Post
    EDIT: I've just researched interline twitter, my footage is PROGRESSIVE (down-converted from HD to SD) but it definitely is exhibiting jagged Twitter along the horizontal lines. Is this normal for progressive material because Wikipedia suggests interline Twitter is caused by interlacing only?
    As explained above, this can happen with progressive video because it is treated as if it were interlaced. The Wikipedia article is somewhat ignoring the interlaced playback chain issue here: it is not certain for progressive video on DVD (even when properly flagged as such) to be treated accordingly throughout the entire playback chain.


    Originally Posted by katieburchett View Post
    Should I still be using this low pass filter and sharpen? Thank you!
    Yes, I highly recommend to do so.
    Last edited by Skiller; 3rd Sep 2015 at 09:10.
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  5. Originally Posted by Skiller View Post

    Originally Posted by katieburchett View Post
    Should I still be using this low pass filter and sharpen? Thank you!
    Yes, I highly recommend to do so.
    Great! Thanks for all the info!
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