The most desirable quality of xenon light is the uniformity of its visible spectrum. In film systems, the entire visible spectrum is used, with only filters for infrared and ultraviolet wavelengths. In digital projectors, the visible spectrum is filtered into overlapping color bands of Red, Green, and Blue. The advent of laser illumination, however, introduces a new wrinkle. Instead of starting with a full visible spectrum and deriving component colors for the digital projector, lasers are used to either directly generate the primary colors, or the primaries are derived from a higher frequency laser. The full spectrum is never recreated in laser illumination, setting the ground for visible artifacts in color perception referred to as metamerism. This subject was discussed at length in my May 2012 report. The American Society of Cinematographers is now taking steps to better understand the effects of metamerism caused by laser illumination with the formation of a Laser Illumination committee.
The impact of this study could be far reaching, making it one of the most important studies undertaken in the cinema community since the compression evaluation tests conducted in 2001. The study could validate the work of current laser development, reducing one more barrier to entry. At worst, it could provide guidelines for the development of laser illuminators that meet the visual standards of cinematographers.
The need for this study is self evident. Sessions are now given in trade show demonstrating the not-obvious and often unexpected effects of narrow band RGB lighting on sets, educating the industry as to the impact of new light sources. Many people who have closely observed laser illuminated images report color casts in the images. Notably, the color cast is not observed by all attendees, indicating that metamerism is at work.
Eric Rodli, a past COO and Vice President of Entertainment Imaging at Kodak, is taking the lead, along with Steve Schklair of 3ality Digital. Your author, of course, decided to join the fun. Mr. Rodli is a consultant to Laser Light Engines, which holds significant patents in this area. Assuming LLE will be a source of laser illuminated projectors, it’ll provide a close working relationship between technology provider and cinematographers. Knowing how these things develop, it will likely take until the end of the year to organize a test screening comparing xenon and laser illumination with the same source material.
