External alpha channel [solved]

  • Hi,

    i can't find a solution to make something that seems quite simple for me :
    i want to apply the alpha channel resulting from a ChromaKey actor to a separate foreground...
    Both AddAlphaChannel and AlphaMask actors use a grayscale source as mask, not the alpha,
    and i read [this](http://troikatronix.com/troikatronixforum/discussion/comment/759), but the output of the Threshold actor is unusable.
    i worked several years as digital compositor for tv and cinema,
    and working separately on key and foreground is essential to me...
    any ideas ?

  • Dear Spidflinch,

    You say that the output of the "Threshold" actor is unusable. But why?
    I just created this test patch, and it most certainly gives a black and white mask. You can easily invert it by changing the 'invert' input of the Chroma Key actor to change the "polarity."
    Best Wishes,


  • as said here :

    _Still, there is some mystery about the result. While the output of the Colorizer was still ARGB and showing a proper transparent image when holding the mouse on the connection, the output of the Threshold was RGB only and holding the mouse on the connection you see a plain white image. Furthermore, the output of the Threshold can not be used for further processing, apart from projectors._
    - newbie issue : i just can't post the screen capture of my test patch !! the insert image button ask me for an url, and the file's attachement keeps uploading without result !... -

  • Well, the Threshold actor does not pay attention to the alpha channel. The point is, that you end up with an RGB mask that is black and white, and this can be passed on to a Add Alpha Channel actor.

    I've made an example patch for you, including sample pictures and many comments.
    Best Wishes,


  • Works perfect ! (especially with ChromaKey's Alpha turned off...)
    Thank you so much !