Alpha masking / moving or resizing a mask

  • Hi,

    I'm working on a patch that reveal a picture, the idea is to have a picture revealed under a black layer, moving the mouse the user can see a portion of the image...
    I've started combining an alpha mask actor with a foreground black layer, a background with the choosen image and a mask that is a PNG file, a little circle on transparent. Unfortunately, this doesn't work, it gives me unexpected results and I'm not able to move the mask "revealing" the image layer: if I de-zoom or move the image mask, the results it that moves also the wireframe around the mask! So the image is already revealed and the result is very bad! I am quite sure that is possible to have my goal done, and the only issue is that... I can't find the solution! someone out of there can help me?

  • Thanks for any ideas or suggestions :)

  • Try the Shapes actor!



  • Ill second Hugh's suggestion. The shapes actor plus the alpha mask actor is going to do what you need.

  • Yes, I've tryed now and it works. Thanks :)

  • Tech Staff

    And use a bit of gaussian blur to give it a smooth edge (if needed).

  • Yeah Graham, of course I've used also Gaussian Blur... it looks fine!

    Going on next level: I'd like to use the mask like an "eraser" that reveal the photo, until is completely visible. 
    I am experimenting with and the mask moves motion blur is giving me the best results, but still isn't what I would to do, mainly because the current position of the "viewing hole" is burned and, of course, because because motion blur "viewing tray" is temporary... (I've also tried with Video Delay and Sprite actors put on a second projector, but it seems more bad...). Any suggestions?
    as usual, thanks to any ideas...

  • Tech Staff

    You might be best looking at something like the buffer actor and freeze?

    I made something a while ago but it's not on the machine I am using at the moment. I used it for erasing part of a mask for video mapping.

  • Freeze in a loop of sorts with a pulse generator is one good possibility. Some clever use of the Particle system actor is also a viable approach.

  • Tech Staff


    Attached is a patch that does what you want.


  • that is nice @Michel , maybe with the gaussian blur between shapes and effect mixer,  I was trying to get the final video with a black BKG but cannot find the way to make it work... suggestions please?

  • Tech Staff


    if you want the same starting with black instead of white, see the attached patch.


  • @Michel

    thanks, that works fine, I added a Table to change mode on the Effect Mixer in order to go to black together with the intensity in the projector so to make it a loop

    best regards

  • Hi everyone,

    sorry I am away from computer for some days... I'll try next week :)
    For now, thanks in advance!

  • Hello,

    this is from a patch I was working on a few weeks ago; it's fairly similar to the one posted by Michel above. We were trying to recreate the effect of a long exposure picture taken with a stills camera but the principle is similar. Swap out the 'Video In Watcher' for a combo of the 'Stage Mouse Watcher' & 'Shapes' as in Michel's patch. It will give slightly different results to the motion blur patch, try playing with the frequency of the pulse generator to get different effects.


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