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Advanced switcher modes

Here are a number of different ways to merge the input from the lightboard camera (showing the presenter + marks on the glass) together with input from graphics (e.g. powerpoint slides, movies) 

Let's call the two inputs CAMERA and GRAPHICS. In the examples below, the presenter and marks on the glass are part of the CAMERA input, and the tree is on the GRAPHICS input.

Ghostly sum: The simplest way is to just ADD the two inputs. On the Blackmagic Design ATEM Switcher, use ProgramInput=CAMERA and turn on the upstream keyer, putting it in Luma mode. In the upstream keyer settings, use KeySource=FillSource=GRAPHICS. Select "premultiplied key". That's all, there's nothing to adjust; the "clip" and "gain" sliders are deactivated. It looks like this, with both the graphics and lightboard semi-transparent:

Ghostly sum of lightboard and graphics




Lightboard and presenter preempt Graphics: Here the graphics appear to be BEHIND the presenter and marks on the glass. Around here we call this "weatherman mode".

Use ProgramInput= GRAPHICS. Put the upstream keyer in Luma mode. In the upstream keyer settings use KeySource=FillSource=CAMERA. Deselect "premultiplied key." Adjust the Clip threshold slider to a proper level at which the presenter shows up well, typically 5% - 10%. If you set the Clip threshold too high, the dim edges of your presenter will start to vanish, replaced with graphics. If you set the Clip threshold too low, smudges on the glass will preempt the graphics. Adjust Gain so it looks right, probably 50%.

Note that this mode can cause trouble if the presenter's face goes in front of non-black parts of the Graphics.  Dark parts of the face (mouth, pupils) may get replaced by graphics, which is very disconcerting.  If you want to use this mode extensively, consider chromakeying with a green screen, rather than lumakeying with a black background as we do here.

Lightboard in front of Graphics




Graphics preempts Lightboard and presenter: You can arrange that the graphics appear to be in FRONT of the presenter and the marks on the glass. 

Opposite the above, use ProgramInput=CAMERA. Put the upstream keyer in Luma mode. In the upstream keyer settings use KeySource=FillSource=GRAPHICS. Deselect "premultiplied key." Adjust the Clip threshold slider to a proper level at which the graphics shows up well, typically 5% - 10%. This works best if your graphics is all either bright or black, and does not have very dim parts. If you set the Clip threshold too high, dim parts of your graphics will start to vanish, replaced with lightboard. Adjust Gain so it looks right, probably 50%.

Graphics in front of Lightboard




Graphics preempts Lightboard and presenter, but with "pop through":

If the graphics are in front of the presenter, what if the presenter needs to point to something in the graphics? His/her hand is hidden. In this technique, the presenter can use a flashlight or other bright object as a "handheld cursor" to break through the graphics, even though the graphics is otherwise in front of the presenter.

Set this up just as above, graphics in front, but now also turn on the downstream keyer, and put it in Luma mode too. In the downstream keyer settings use KeySource=FillSource=CAMERA. Deselect premultiplied key. Now set the downstream keyer Clip threshold slider to a high value, typically 90%, so that only very bright spots in the lightboard input will replace the combined image from the upstream keyer.

Here you need to make sure that your videocamera exposure is not set too sensitive, because the flashlight must be brighter still. You don't want the lightboard material to drive the camera too near saturation.

As described above, the bright spot itself will pop through and be visible. You can also cause some other color or image to be substituted wherever the bright spot exceeds threshold. In the video below, I used KeySource=CAMERA and FillSource=Color (orange).

Graphics in front of Lightboard, but with pop through




Replacing live equipment with its image:

This was contributed by John Mocko at University of Florida. Here, real equipment is used behind the glass. In the example below a steel ball is rolled down the ramp. A frame is grabbed from the resulting video at a moment when the presenter is absent. The framegrab is uploaded to powerpoint or into the switcher's media pool, and the real equipment is removed from behind the glass. The image is used instead of the real equipment for further "fake" video. The live and fake segments are spliced together. To the viewer the equipment appears to remain in place, and the presenter can write on it. Below is a video done this way, starring Prof. Darin Acosta.
http://mediasite.video.ufl.edu/Mediasite/Play/7c44307b942f424c8bdde637b716dd021d



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