Transparency Questions
  • jnevin
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    Transparency Questions

    by jnevin » Tue Sep 28, 2004 7:06 pm

    All,

    First and foremost, thank you for Modul8 -- an innovative, valuable tool with many uses!

    Using Modul8 transparency or possibly an alpha channel, we are trying to insert a live performer, who is being video'd live with a bluescreen background, over other background movies. Luma-key is not appropriate here, but Modul8's "R-G-B"option works, partially. The performer's layer places what looks like a translucent, dark film over the background.

    Does this mean that the blue of our performer's background is not blue "enough?"

    For total transparency using one of the R-G-B transparency options, what value does the chosen color channel need to be? For example, if we choose "B" (blue), then for total transparency, does the blue in the video need to be "0-0-255" in RGB terms? (BTW, we have some external control over this -- we can run the performer's live video first through a mixer that puts a solid color background behind the performer.)

    Our other option is to live-encode the live video with Sorensen 3.1's masking feature (thus create an alpha channel) before feeding it to Modul8 -- but this introduces additional overhead and a time delay.

    Any suggestions would be appreciated!
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    yves@garagecube
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    Re: Transparency Questions

    by yves@garagecube » Wed Sep 29, 2004 12:10 pm

    jnevin wrote:Does this mean that the blue of our performer's background is not blue "enough?"


    Well, yes. The color lumakey in the current version is pretty straightforward: 100% blue = 100% transparent. It works well with very pure colors, but not that well for live. This is an area that we plan to improve in future versions.

    In the meantime, you can use the saturation and the contrast to improve the precision of the color lumakey (saturation and contrast are applied before the lumakey filter).

    Best Regards,
    Yves.
  • jnevin
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    by jnevin » Wed Sep 29, 2004 8:59 pm

    Thanks, Yves.

    So, then, what does Modul8 define as "100% blue"? Is it the RGB value of "0-0-255"?

    Regarding your comment -- "It works well with very pure colors, but not that well for live. This is an area that we plan to improve in future versions. " For people using bluescreen who need a solution now, -- I suggest feeding the live video first through a video mixer with keying capabilities (the Videonics MX-1 is on Ebay for about $100), and keying the actor to a fixed color background (the actual bluescreen varies in color values). Then feed this to Modul8.
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    boris
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    by boris » Thu Sep 30, 2004 2:48 pm

    jnevin wrote:Thanks, Yves.
    So, then, what does Modul8 define as "100% blue"? Is it the RGB value of "0-0-255"?


    That's right.
    One example w/saturation and a full blue background...


    Image
    Boris * garageCube team
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    sigmasix
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    by sigmasix » Thu Dec 02, 2004 2:17 pm

    Maybe for the version 2.0 you could add a "pipette" (is that english?!?) to select a color to make transparent and with this option, choose the range of the selected color (as the magic wand in photoshop). That would make a very powerful transparency tool!!

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