Chroma Key: Jagged Edges?! (FCP & Motin 3)

Discussion in 'Digital Video' started by lilnyc, Feb 11, 2008.

  1. lilnyc macrumors 6502a

    lilnyc

    Joined:
    Jun 5, 2007
    #1
    I chroma keyed a video using Motion's Primatte RT filter. The green was removed, but there are (white?) jagged edges around the subject. I have attached two screen grabs so that you can help me:

    I have these apps if you feel I should try another way:
    Final Cut Studio (w/Motion 3)
    After Effects CS3
    Shake

    I was advised to use Shake by one person. Please let me know what you recommend.

    Thanks in advance!
    Contact me faster at NYImport@gmail.com
     

    Attached Files:

  2. killmoms macrumors 68040

    killmoms

    Joined:
    Jun 23, 2003
    Location:
    Washington, DC
    #2
    Shake also has a Primatte filter (although its more advanced one is keylight's). You should be able to get a good result with Primatte in Motion, perhaps tweaking the falloff/softness of the mask would help some.
     
  3. lilnyc thread starter macrumors 6502a

    lilnyc

    Joined:
    Jun 5, 2007
    #3
    Hi Killmoms,

    I used the Matte Magic filter in Motion 3 (thanks to Ripple Training) and adjusted the Shrink and Feather settings. That resolved the white around the jagged edges. It looks better, but I worry that the edges are not perfectly smooth yet. So I'll try your suggestion as well as a tutorial on Lynda.com for Shake.
     

    Attached Files:

  4. LethalWolfe macrumors G3

    LethalWolfe

    Joined:
    Jan 11, 2002
    Location:
    Los Angeles
    #4
    What is the source footage? If it's DV then you are going to run into the limitations of the codec pretty fast. Also, if you work in an uncompressed environment (even if you are working w/DV footage) you'll get a little more headroom w/regards to tweaking the footage.


    Lethal
     
  5. lilnyc thread starter macrumors 6502a

    lilnyc

    Joined:
    Jun 5, 2007
    #5
    I believe it's HDV. The source file ratio is 1440x1080, Animation codec. They are on a hard drive, so I don't know much other than what info I can pull from the metadata.
     
  6. ppc_michael Guest

    ppc_michael

    Joined:
    Apr 26, 2005
    Location:
    Los Angeles, CA
    #6
    HDV has a relatively low color resolution so you probably will run in to limitations.

    Can you output the alpha channel from your key as a grayscale clip? That way you could add a slight blur and choke it a bit and stuff, then re-apply it as a travel matte.
     
  7. MovieCutter macrumors 68040

    MovieCutter

    Joined:
    May 3, 2005
    Location:
    Washington, DC
    #7
    What Lethal said
     
  8. killmoms macrumors 68040

    killmoms

    Joined:
    Jun 23, 2003
    Location:
    Washington, DC
    #8
    I was under the impression that all operations in Motion were performed outside of the limitations of the codec and simply rendered back down to the codec of choice when done. In other worse, the key operation would be working on a 4:2:0 color space image but the operation itself would be free of said limitations, and only the rendered result would be crunched back down to 4:2:0 on output.
     
  9. lilnyc thread starter macrumors 6502a

    lilnyc

    Joined:
    Jun 5, 2007
    #9
    I'm almost there. Thanks, everyone.

    Here's my latest issue -- lumpy edges. I found a way to get rid of the green around th edges, and the key actually looks fantastic compared to what I did earlier. But now I'm concerned about this slightly rough edge (right). The original looks very sharp (left), and I want to emulate that:
     

    Attached Files:

  10. bigbossbmb macrumors 68000

    bigbossbmb

    Joined:
    Jul 1, 2004
    Location:
    Pasadena/Hollywood
    #10
    That is correct, but that original image is highly compressed and doesn't hold very much color information compared to an uncompressed (4:4:4) source.
     
  11. AviationFan macrumors 6502a

    AviationFan

    Joined:
    Jan 12, 2006
    Location:
    Cedar Rapids, IA
    #11
    Actually, the edge on the left appears softer to me than the edge on the right, which I think is why the one on the right looks unnatural. Have you tried feathering the edge? Just use a tiny little bit of it, you don't want it to be too soft. Other than that, don't expect perfection with DV/HDV footage.

    Oh, and if you have Shake, check out this tutorial with Andrew Shanks:
    http://library.creativecow.net/articles/shanks_andrew/preprocessing_for_keying.php
    I've used this with good results in the past.

    - Martin
     

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