Circular matte/mask

  • Hello. what's the best way to mask all video so its inside a circle? i'm projecting onto the floor (via a mirror and a fair amount of keystoning in the projector and in Izzymap) and my rectangular image is only slightly distorted - i can work with that.

    now i need to create a circular image, but i'd like to keep everything as GPU as possible, so i'm trying to avoid alpha masks.

  • Tech Staff


    you can do a circular mask with the mapper. See attached image.

    Best Michel

  • Hello,

    You can use Shapes and FFGLAddAlphaChan to have a variable mask (square to round and ellipse).
    Here is a quick sample.

    b74de9-roundmask01.jpg 60c196-roundmask01.izz

  • thanks Michel and Jacques. i shall experiment with your solutions.


  • @Michel

    I like the way we find very different way to do the same task. I hope to see you in Berlin this summer.

  • Tech Staff


    I will be there. Looking forward seeing you too, it's long time since last time.

    Best Michel

  • hi all,

    is there a way to soften the edges of the mask with Michels solution inside the mapper?

    ciao Bodo

  • Tech Staff


    Within the mapper there is no method of blurring the mask.

  • @DusX this really turns out to be a "feature" in bad need ;)

  • It's the reason I proposed the shapes way, you can blur the mask…

  • @jhoepffner very nice example indeed (i also use it this way at the moment) but if you need more of a complex mask (composite/ strange shapes/ sculptures ect.)

    the only option at the moment is to build, scale and adjust an alpha mask from within photoshop. 

  • @gapworks

    I agree with you, but there is another way, on which I am preparing a tutorial (in french first…).
    That's to use processing, with all the possibilities to draw and move lines interactively by OSC and receive it by Syphon. I hope it in 2 weeks.

  • @jhoepffner looking forward to this :) and if its in french i hope google is my friend :)

  • @gapworks

    I made a first sample for a quadrangular mask. In Isadora, you can activate the mask, move the corners, activate the blur and adjust blurriness.
    With a little bit of coding in Processing, you can have more corners and even beziers vertex.
    I tried to comment in Processing and Isadora.
    Feel free to give comments, it's a prototype.

  • And just for the fun, the same with 2 bezier curves.

    You can move the 2 points, the 4 tangents, change the blur and change the quality.
    Hope you appreciate

  • I just forget to say that you need:

    Processing (3.0.3)
    Syphon library (2.0-RC2)
    It's possible to make an app but it's heavier and platform exclusive

  • Hello again,

    I'm currently in the studio with a projector and a white dance mat. my projector is rigged horizontally  in the grid, with a mirror reflecting the image down onto the floor - causing massive keystoning. i've used Izzymap (tweaking the corners of a rectangular slice in the output screen) to correct this keystoning and produced a rectangular image that looks great.
    in a separate Projector, i've used @Michel's method above to add a mask - and the circle is nicely round, but the image inside the circle is keystoned.
    How can i combine the two to create a circular mask of a mapped image?
    (i've been through the manual, but i can't find out how to solve this particular problem)

  • Tech Staff


    Can't you correct the keystone on the output side of the mapping?

    Best Michel

  • @Michel - i'll have another look tomorrow.

  • ok. i found the problem. when projected, the circle mask wasn't really circular, but looked circular from where i was sat (underneath the projector) so i dropped a grid image in and mapped it so that the grid was square. it will be much easier when i've cut the floor to a perfect circle.ef5085-marjo05w.jpg

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