Defining Image Quality In Digital 3D Playback

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Wed, 03/25/2009 - 20:00 -- Nick Dager

A Conversation with Louis Eales Louis Eales is the senior director of worldwide technical operations for products and services at Dolby Laboratories. He recently spoke via email with Digital Cinema Report about the challenges inherent in successfully bringing 3D movie content from the studio to the screen. Digital Cinema Report: Please give an update on Dolby’s involvement in digital 3D in exhibition. Louis Eales: Dolby Laboratories was a key contributor in the onset of digital 3D exhibition back in 2005 with the movie Chicken Little 3D by providing the Dolby Digital Cinema server technology. What we discovered from speaking with exhibitors was the polarized 3D solution provided didn’t match some of the fundamental challenges they were experiencing.  They wanted to use their existing white screens.  Replacing their current screen with a silver screen was not only expensive but produced a hot spot that decreased image quality for both 2D and 3D. Upon further research Dolby also learned that exhibitors weren’t enthralled with the active glasses solution – they cited replacing batteries or recharging the glasses as two issues. The possibility that the shutter glasses could turn off in the middle of a 3D feature also made this an unattractive solution. So Dolby looked to do what it does best solve these problems. In 2007 Dolby launched Dolby 3D Digital Cinema providing exhibitors with an innovative solution that uses a standard white screen and passive glasses. I am pleased to say that in less than two years Dolby has shipped over 1000 Dolby 3D systems around the globe.
  DCR: Film digital 2D and digital 3D are all here for the foreseeable future in most markets. What is the ideal kind of screen for exhibitors to consider when showing all three types of content? 
 LE: Back in the old days of Hollywood the silver screen was necessary to get a brighter image reflecting back off the screen due to the inefficient projector light sources. As lamp power increased the use of a silver screen decreased. Exhibitors got a brighter more even image on a white screen which by the way is cheaper and easier to maintain. This is still true today. A white screen is the ideal screen for exhibitors looking for the flexibility to show both 2D and 3D content. The high gain of a silver screen creates “hot spots” and reduces the number of seats in the sweet spot. This is due to the limited amount of lumens (or light generated off the screen) in off axis seating (to the left and right of the screen). Seats directly in front of the screen or in the sweet spot receive a brighter image where seats on the sides will get a duller and less impressive image off the silver screen.  Although a high gain silver screen is necessary for a polarized 3D system exhibitors need to dedicate an auditorium to 3D movies.  Unfortunately playing back 2D content in those auditoriums is compromised with the hot spot and does not present a great viewing experience. In addition silver screens can add discoloration and are more prone to showing scuffmarks fingerprints dirt and are difficult to clean. DCR: How can the Dolby 3D system enhance a cinema screen’s capabilities? LE: Dolby 3D utilizes the standard white screens minus the added costs and image quality compromise associated with the use of a silver screen delivering a superior 3D experience from every seat in the auditorium. Dolby 3D also supports both 3D and 2D presentations without the need for a dedicated 3D auditorium. The system switches effortlessly between 2D and 3D in the same projector and auditorium. Patrons can see a 2D movie in the afternoon and a 3D movie can be shown that evening using the same auditorium which is a tremendous benefit. DCR: What is color correction and ghost busting and why is it necessary for 3D playback? LE: Color correction is necessary in 3D. The process of delivering a stereoscopic image through a left eye and right eye filter offsets the color parameters of the image due to the amount of light being filtered. Color correction adjusts the colors to compensate for the light that is lost in the process. Once the movie content goes through the color correction process the system delivers a more precise image to the audience. In addition each 3D system introduces its own color offset.  With the Dolby 3D Digital Cinema system color correction for the latter is processed automatically in the servers. Ghost busting is mainly necessary for polarized systems since these systems tend to have increased ghosting. Specifically the left and right-eye image required for a stereoscopic 3D movie can leak into each other’s image causing a ghosting effect. Ghost busting can be conducted in the creation of the digital cinema package. However this requires another preprocessing step for studios delivering a 3D movie for a polarized 3D system. The Dolby 3D Digital Cinema system has inherently lower ghosting. The 3D specification from the studio's DCI consortium recommends a single 3D deliverable standard that doesn't involve preprocessing so that 3D files can play on any system.  Since Dolby 3D is not a polarized system studios don’t need to address ghost busting in this preprocessing step.   DCR: What is Dolby doing to make 3D image quality better from the studio to the screen?  
 LE: Dolby works through the entire entertainment chain making solutions easier and better for implementation for both the studio and the exhibitor. For the studios both color correction in the Dolby 3D system and the lack of ghost busting ensures the content will be the best image quality possible creating a premium viewing experience. For the exhibitors Dolby’s solution uses a unique patented full-spectrum color-filter technology that provides realistic color and extremely sharp images from any seat in the house. Having the Dolby 3D filter inside the projector allows for higher lamp power. Because the filter is applied to the light before the image is formed it delivers stable and sharp images as well as no modulation of the actual image. As a result viewers see the most precise colorful picture with no degradation to the image. In addition Dolby 3D glasses use curved lenses to minimize reflections from auditorium lights and exit signs creating a better viewing experience. Patrons may also like the fact that the Dolby 3D system uses reusable passive 3D glasses which are more environmentally friendly.