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Masking of image

martin b

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I got a little problem. Soon I am going on a Theater-tour, and we are bringing a projector to make a snow-effect. The procetor has to hang/stand @ FOH, or some other place in front of the stage. The thing is that it is not always possible to place the projector right in front of the stage, somtetimes it has to be placed in one of the sides or something like that, due two the conditions in the venues...


So I need a way to mask the image so I dosnt spill all over the proscenium etc. It has to be easy and it is going to be done every day.

The optinal would be something like having knifes to do it with, like in a profile! We have also considered the possibility to do it through a media server, like the pandoras box mediaplayer, can that be done?


Any sugestions appreciated!




ps. sorry for the spelling, I am danish...

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To do as you ask, you would have to put the mask inside the projector at the point where the image is focused as per the shutters (knives) in a standard spot, if you try to rig a mask in front of the lens it will appear as being soft or out of focus. Depending on the type of image you are projecting you may be able to add a mask in software (such as PowerPoint) which is not ideal as you still get some light projected even in Black!


The other way is to use a digital media server type fixture which does have adjustable shutters such as (I think?) the High End DL1 or DL2 but you need a big budget for these.

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have you look at Hippotizer media server?

you could do your desired effect a couple of ways with Hippotizer.


1. Full realtime keystoning which would allow you to position your projector to the side of the are you need to project onto and keystone the image so it looks like you are projecting from the front


2. Using a black and white image in hippotizer you can use this in the mask effect on the same layer and mask off a certain area of the screen.


3. there is an effect called shutter which allow you to shutter in each side of the images.


Hope this helps


Let me know if you need more infomation


Green Hippo's website is www.green-hippo.com


Best Regards



Moderation: We feel we should point out that Tom works for Green Hippo, so while it will no doubt fulfill the OPs question, he is a bit biased.

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My first thought when you mentioned a media server was that this was a bit overkill for your application if all you want to do is mask the image.


I have had to do a similar thing in the past and every time I have used a different option.

  • Some projectors come with the ability to mask and move certain sections in the menu. You can adjust these in the projector setup, however this is often limited in how much control you have.

  • Use a separate computer to create a mask which you then key through a vision mixer. This is probably the easiest if you have a spare vision mixer and pc to hand which I often do. All you do is output an image to the monitor with the black areas where you do not want to display an image and everything else in a keying colour like magenta. Then you set the vision mixer to key using your mask. This will mean the magenta areas will display the video and everywhere else will be black. Simply update the image to change the mask.

  • I needed to display video on a round screen so I wrote a plugin for my Screen Monkey software that masked the image with a circle. I can give you this plugin but my point is you may find a similar plugin for VLC and alike.

You have not said what your source is, is it a DVD player or PC etc?

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I know your saying this has to happen every day and has to be simple I would suggest


1.Use a media server with keystoning such as High End Axon,this can keystone and has the ability to change the image aspect which can can be helpful when shooting off centre.

Other media servers I'm sure will do the same.


2.Create a digital mask or a few PNG(photoshop)file to mask off the sections of the image you don't want.


3.Use a projector that has keystoning ability.


4.Get a real snow machine.



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You might want to have a look at Radlites Video Drive, a basic media server, priced close to archaos, It has one mask layer and one play back, the mask layer has full 3D key stoning, in one extreme instance have used this 50 degrees off centre for projection,


will play back most video files and jpegs can be put in a show order and single button play back or multiple DMX control,







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