change background without chromakey, but using empty picture as a reference?

  • Hi, 

    some visual soft, like photoshop or after effect, use an alternative way than chromakey to change background,
    they use an empty picture (where the character doesn't appear), and memorize it to be able to cut moving objects (like character) in the screen. 

    Is it possible in Isadora to use a background image ( with no character on) and set it as the background,
    and therefore being able to get the character or object moving as a cut contoured layer? 

    hope I'm clear, 

    all the best

  • @bennnid



  • Beta Platinum


    @jfg suggestion is good. There is also a patch by @Mark that demonstrates ‘difference’ here:

    Best Wishes 


  • @bonemap @jfg  thanks to both of you  ! 

  • @jfg I like the difference mixing effect, but the new object is still affected by the back ground colors, I'd like the new object to be always in it s original  color, on a black background,... tried with alpha mask too  but not really what I need...  I think it's more a depth think as for filter, any idea? 

  • Just expanding slightly on @jfg example, I've had good results with something along these lines before. It's only been successful with certain criteria being met though.

    1 - a really steady camera - no wobble as dancers jump around!

    2 - really consistent lighting - doesn't work if the sun goes behind a cloud or if the projection in the space is bright enough to impact the camera for example.

    Having said that, I have used it a number of times in shows and it's been okay. Generally more as a 'tracking' technique or with more abstract work than as a cinematic chromakey replacement but I have done that with it a few times. Tweeking the contrast pre-Freeze and then playing with threshold and blur as needed post-Effect-Mixer makes a big difference.

    The other one to consider is Luminance Key. It can be great in really well controlled environments - ie theatre with black floor, black drapes and really well lit performer (preferably with side light). Or if you can get a really bright white background. In both instances a bit of contrast, threshold and blur before the key can be a big help. Again, I'd take what comes out of the key, adjust it and run it back through an Alpha Mask rather than use it straight. You can also key it multiple times with a bit of blur in-between each key to get rid of the 'holes' that sometimes appear but there's obviously potential performance issues with lots of repeated blurring/thresholding.

  • Tech Staff


    Also see Scenes ~11 to ~15 in this Motion Tracking tutorial file for using Freeze or an empty reference photo as a method for background removal

    Best wishes,


  • @woland thanks a lot I follow it but it seems hard to freeze and get only the "new" pixels, without being affected by color or lightning...

  • Tech Staff

    @bennnid said:

    it seems hard to freeze and get only the "new" pixels, without being affected by color or lightning...

     it is hard. It takes some clever lighting and camera placement to get a good effect.

  • @dusx

    i see, so with time and good choices ;-)  I have plenty to test now ....

    Although I'm not sure I can get the same smooth effect around the character that some background do... digging with alpha mask seems a good solution !