Alpha Channel

  • Hello there,
    thank you for help in advance!

    I am having a video which has a white backround and moving hand (scale from grey to blue/violet) and I would like to achieve that which color becomes totally transparent, while having hand in tact. I manage to get transparencies, but in total frame (including hand was getting transparent, which I do not want).

    Down I tried one patch, however I doubt that is good, since I am still getting white background.


  • Here its how it looks. I will clear out that FX, recorded output, after I do Aplha Channel, so I keep it on GPU. Its just a test. Thanks.

  • Tech Staff


    Did you try it with the chroma key actor? There is also a FFGLChromaKey actor, I think it's in the TroikaTronix FreeFrameGL Plugin Collection.

    Best Michel

  • HI Michel,
    I have partial success with traditional Chroma Key - but there is bit too much of a noise. FFGL gives me control only over entire frame. Regardless of FX what is there before, I just trying to get that blue hand on transparent background.
    Maybe its not work for Isadora, but some editing/FX software.
    Thank you anyway.

  • Dear @em_tx,

    Given that you have a white background, I would suggest the Luminance Key actor, which is based on brightness not color. Try that... you might have better success.
    Best Wishes,

  • Dear @mark, dear @Michel,

    I did not really succeed with complete isolating hand that its stays and everything gets transparent. With Luma I am able to get hand transparent (and insert content there), however not a background. Video file I am using is an output of Isadora. I am getting solid white. Its also quite rough.

    With Chroma key I can get subject floating while background (even white) is transparent, but its very rough.

    I tried with After Effects, just I would like to ask which format/codec takes Isadora, that I can import video, where I am able to maintain color and texture while having transparent background and keep the detail.

    Thank you very much!


  • Tech Staff

    I like "hap alpha" for video with an alpha channel.

  • Screenshot:

  • Tech Staff


    the screen capture looks like the correct sort of setup, except that you will gain much in performance using Vid_gpu rather than cpu and,
    I suggest using the native isadora plugin "Luminance Key". It offers more control and, includes help text that can help you understand the inputs.


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