01 Aug 2014

Predicting color under lighting just got a lot easier

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Index

Here’s how it works

• You initially select the Camera Sensitivities Parameter. A specific camera sensor or Standard Human Observer) to set the spectral sensitivity for your imaging device.
• You set the Camera Filter. A modification for any filters that you may or may not have added to the front of the camera lens.
• You set the Reference Light Source. This is the light source you’re comparing to. You can select any parameter, but the most common ones would probably be Tungsten, or ISO Studio Daylight as they’re the most familiar. You can even chose theoretically perfect sources like 3200K and 5500K black bodies to see how the real world stacks up to the ideal.
• You then set the Test Light Source, which has all the same choices as the Reference Light Source. You could choose HMI, or Cool Fluorescent for example.
• The Light Source Filter is then added if you have one, signifying any gels that you may or may not have put over your lights.
• Then you select your Target Reflectances, which are representations of different commonly used color reference charts.

The White Balance parameter allows you to simulate what would happen if you white balanced for a mix of the two lights in the same scene (Off), or if you white balanced for each light separately, for example one scene shot in two locations with different lights (On).

Then take a look at the results. The top half of each square of the color chart is the Reference Light Source, and the bottom half of each square is the Test Light source. You can now see where and what colors will be different between the two sources, and more importantly: exactly how they differ.

Each of the parameters above can be plotted in a spectral power curve in the lower part of the app. The Y axis of the curve represents the luminance value (how much of each color is in the light) vs the X axis which is the color itself. These plots can be laid on top of each other to visualize where in the color spectrum the light sources match up and where they diverge.

It’s fascinating to be able to scan through all the different lighting technologies and see what parts of the spectrum they excel at, or what parts they’re lacking altogether. It would also help in deciding which brand of light to purchase or rent. Those cheap LED’s may be tempting, but are they are missing an entire part of blue-green? Maybe a fluorescent is a better choice for this set? After playing around with this app a bit, I’ll be damned if after all the advances in lighting technology, heating up a tungsten filament still doesn’t give you the best skin-tones. It makes me want to get those power-hungry, finger-burning, explosively-bulbed monstrosities out of storage and give them a go again.

While this is an interesting app to explore color, the Academy Color Predictor is not yet exactly a production ready tool. It’s still very much a theoretical proof of concept, but a very promising one. In order to make this a magnitude more useful it definitely needs work on both scope and specificity. Scope in the amount of cameras, lights, and filters it can model; and specificity in exact model numbers. DSLR1 and DSLR2 are useful in theory, but I want to know Canon 5D mark III or Panasonic GH4 instead. Likewise Warm LED’s 1-4 need to be LightPanels, Arri, and Kinoflo, etc..

What’s the difference between shooting with fluorescents and LED lights both at 5600K? What happens to the colors when you bring a tungsten light with an 80A gel out into the daylight? Now you will know, and not only do you know in general, you will see how the light reacts based on your individual camera’s sensor! This is the promise of the Academy Color Predictor, and with a fair amount more effort from the Academy, this could be come a standard tool in everyone’s production kit.

You can download it to your iPad for free here: http://www.oscars.org/science-technology/council/projects/colorpredictor/

 




John Burkhart

John Burkhart has been working in the TV and Film industry for 20 years in a series of varied and curious roles. Enthralled with film and video technology from the beginning, he hopes to share some insight from his experiences from no-budget student shoots, to multi-million dollar Hollywood productions, to filmmaking in Southeast Asia.

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