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DMX Control of cinematic lighting

DMX Control of Cinematic Lighting

Just recently I've been learning Black Magic's Fusion software using the recently released MacOSX version. It led me to think about how scenes can be composited and made to look believeable.


I've found lots of weird behaviour in the CookTorrance and re-lighting tools. In addition although you can make materials glow, they don't actually emit light as they do in other software, for example Cheetah3D.

Black Magic Fusion Interface

This led me to the conclusion that one would need to light the scene to be added to a composite in a way that matches the overall movement of the rest of the elements in the scene. Should those elements were moving and changing, then one would need to control the lights accordingly. Hence I set to work to find out how my lights behaved under DMX control.


I've used MyDMX software with the DMX buddy as a USB to DMX interface. This is simple to use and quick to get going although mildy frustrating in that it will crash if it can't find the USB interface. This means that you can't just work on a few scenes without a connection. This us a real pity since they have the virtual stage concept which allows pre-visualisation of scenes. This would be pretty useful for getting thing about right before you get on set.

MyDMX has a very large library of 'fixtures', although its very unlikely to have any cinematic lighting. You can used the supplied Scan Library utility to define the behaviour or your lights. This seems pretty simple to me, although I notices that the MyDMX forum is full of posts asking the developers to do it for them!

You can operate the software without defining any 'fixtures', you just set the faders for the DMX channels and away you go. However it may well bend you head trying to remember what channel does what. It makes life much easier to drop the 'fixtures' onto the grid of channels. Now you know where the fixtures are, and when you move the sliders for say a RGB fixture, the colour display above the sliders will mimic what the fixture is doing.

MyDMX 2.0 controling cinematic lighting

Scenes etc.

You can define scenes and associate them with a keystroke, in general I've been using the 1,2,3,4 keys for the scenes and the space bar for the 'All Off' scene. This is OK if you have cuts between angles, but not so useful if you need to fade between one scene and another. Here's the first bit of odd, although you can define a fade time for a scene, it won't actually fade, for that your scene needs to have more than one step, and now the fade defines fade between this step and the next. The first time I used this was for a music video where I wanted the lights to pulse on particular beats, so I arranged the scene and the trigger key and set the next scene to 'All Off'. Then I had an assistant tap the key intime with relevant downbeats.

To make the scenes work for the Fusion compositing I needed slower fades and more steps. MyDMX allows for all this, but you have to keep a mental model of where you are time wise and you'll need your actors to anticipate and response to changing light cues.

It's an iterative process

Well it is for me at the moment. Maybe when I have 100+ Fusion hours I'll be able to estimate scenes and levels etc. So far I've found the easiest way to deal with DMX controlled lights and green screen is something like this:

  • Define an 'All Off' scene and associate it with the space bar
  • Define a scene 'Green Screen' that sets just the green screen lights to a level where you are confident that you can pull a key from it
  • Copy the above for as many scenes as you feel you are likely to need. In this way the background green screen levels will remain constant
  • Now define the scenes as you need them and then shuffle them into order
  • Now associate the scenes with the 1,2,3,4,5,6 keys as you need them
  • This is the point to set the Fades and the Holds along with the 'Next Scenes'
  • Rehearse and adjust timings
Cinematic Lights

Take some footage then scurry away to do a quick key, this gives you a good idea of where the lighting effects are overpowering or wrongly timed, then 'rinse and repeat' as they say.

Issues

You seem to get what you pay for, I guess that is no surprise. When fading between scenes I found some lights ('Fixtures') behaved much better than others. For example the Celeb 200's were exemplery, But the Dyancore Elf2 flickers dreadfully during a fade (it has three settings for modulation - none helped). You might expect 'disco' and stage lighting to fare better, after all they are designed for this stuff, however this wasn't the case. My 'LEDJ Stage Wash 16' were much flickering wheras the 'ADJ HEX12P' lights were super smooth.

Since you can only define a fade per scene step it will affect all 'Fixtures' equally. Therefore its worth a quick test to see which lighting you can dim and which should be left to the green screen lighting duties

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