Hi Steve,
I’m not certain if Matt Johnson is monitoring the forum.
So I like to answer as I know you do a class, and everyone likes to get this done. The example has shortcomings, which I will explain below!
I have attached a material with a short set up how I would do it, based on the final frame of that tutorial.
Please keep in mind that he is simulating how it would like. This is from my point of view a common set up and it ignores some parts of the Capture Pipeline.
As the light sabers would normally,well they do not exist—but if, they would create a full saturated color, beyond most camera capture options if hold still. First, most laser-light is way out of the typical Color Space (e.g.,Rec 709), such as a green laser. As we see them mostly on film/video, we are used to the short comings of those capture methods. To copy then these short-comings back into the scene is not preferable. Secondly, the energy of the laser is so “hot” that any color renders to white. Hence most CG artists set a single color-channel back, and all channels equal—to white with a low “energy”. Like a common mistake to “retrieve highlights” in LightRoom. It is then re-establsihed from the color channel that contains some data. in that way, highlights are normally recognized as white. Which is just wrong as a general rule.
Again, nothing wrong as he did it in the tutorial, but it leads to short comings if you go further.
There are several points to note:
Motion Blur
Bokeh and its blooming
Refraction and the effects in optical media
Reflections
In these four main areas, you might find that anything that isn’t resembling the “real” brightness and achromaticity of the laser, leads to a more or less unspectacular presentation of the light saber. ILM has certainly understood how to do it.
It might goes beyond the four points, if you use Global Illumination methods. Anything that is done in linear space, should be related to a brighness vlaue that simulated a rolled out high light as film emulsion (e.g., Kodak, Fuji) would have done it. During production we need an more real world scenario, to keep it in the storytelling dramatic that we like to have—if light sabers become the center of the scene.
I might have gone beyond your question, but I think your students like to have that impact they know from the movies, right?
All the best
Sassi
