Getting a white edge on a mask?
  • barringgaffner
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    Getting a white edge on a mask?

    by barringgaffner » Mon Aug 09, 2010 8:09 pm

    I export an RGBA image from photoshop with the rgb the same as the alpha.. just black and white with a soft edge.

    When I bring it into modul8 and use an alpha mask filiter it seems only the 100% white pixels are transparent... anything between 0 and 1 seems to make a white edge.

    any ideas? I'm sure i'm just using the wrong filter or something?

    thanks!
    bg
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    deepvisual
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    by deepvisual » Tue Aug 10, 2010 2:06 pm

    you shouldn't need a filter.
    it could be your antialias settings... see preference.
  • vj furure
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    by vj furure » Tue Aug 10, 2010 2:59 pm

    it a known bug since years.
    a workaround is using aftereffects.
    its explained in this thread:
    http://www.garagecube.com/forum/viewtop ... ight=alpha
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    sigmasix
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    by sigmasix » Wed Aug 11, 2010 9:59 am

    it's not really a bug… it's just metaphysics hehe

    your alpha channel and your image are exactly the same which means when the pixels goes from black to white on the alpha, it will make appear the image that is also going from black to white. so it will make appear the greyish pixels in between.
    To avoid that, you image should be all black and the alpha as is.
  • barringgaffner
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    by barringgaffner » Thu Aug 12, 2010 2:34 am

    ah, now that makes sense. thanks sigmasix! So you really don't need after effects at all, just make sure your RGB are black in Photoshop. I should have thought of that myself! I didn't think it was actually using the RGB part of the image though.

    Side question about mattes...

    let's say I have to quickly set up a matte based on two screens on stage. Would a fast way to create two layers, use perspective transforms to match each screen by eye, then export that image(using file> output or something, forget what menu it's under.
    Then quickly create an alpha for that in photoshop using that outputted image
    THEN
    Bring in that image and use it as a mask?

    It would be cool if they introduced rotoshapes or something!

    Is the 'painter' module reliable?
  • ilan

    by ilan » Thu Aug 12, 2010 11:36 am

    @barringgaffner from my tests applying this method in Photoshop does not work. Somehow only After Effects can create a clean mask. If you find otherwise please let me know.
  • vj furure
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    by vj furure » Sat Aug 14, 2010 2:40 pm

    its definitly a bug. or lets say a very special behaviour of modul8 ;-)
    in any other program i use, alpha channels were handled different.

    a simple test you can make is:
    make a image with a mask, which only has black and white inside the alpha
    channel. if you use it in modul8, you will get a white greyish border.

    use the same mask in other programs, you will not see this white line.
    even, if you are not scaling the image.
    so come on, it could not be that dificult to interpete an alpha properly :-)

    f.
  • barringgaffner
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    by barringgaffner » Sun Aug 15, 2010 2:07 am

    it's not really a bug at all, it does make sense if you think about it. The edge area needs to be the same colour values otherwise the slightly transparent portions will bring through whatever colour is there. although I guess some programs will fix it for you.

    ILAN: And yeah, this does indeed work straight from photoshop... no need for After FX! :D

    the RGB channels needs to be black, with the alpha channel being the only one with the mask shape. I had it so that everywhere except the areas I want my video to play through are white and that worked. Now I am only using it to sort of 'look through' a mask so that the video is only projected into certain parts of the stage.. but yes that works. I haven't tried things like logos yet though.

    thanks all.
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    deepvisual
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    by deepvisual » Sun Aug 15, 2010 11:41 am

    an easy fix in photoshop is to apply image/adjustments/threshold to the alpha channel, which will remove any anti-aliasing.
  • Goldberg7
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    white lines in alpha

    by Goldberg7 » Sun Sep 26, 2010 9:28 pm

    I´ve got it by simply:

    Choose Layer > Matting > Defringe

    in ps.
    http://www.eccecello.com

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  • Barbara11
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    by Barbara11 » Tue Oct 26, 2010 11:21 am

    Hmm...thats interesting !! :D
  • cycloptic
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    by cycloptic » Fri Dec 10, 2010 3:36 am

    turn off bi-linear filtering on the media you are using as a mask, this is processing that modul8 applies internally to all media by default to smooth edges.
    on an edge of transparency (alpha) the minimum smoothing that can be done is 1 pixel, this is the 1 pixel white line you see.
    alternatively, turn the modulateRGB sliders to zero if you want to maintain bi-linear filtering

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