SpectraCal on 3D Viewing and Active Shutters

What follows is a very good article from SpectraCal—we buy our video calibration equipment from them.

“With the advent of the 3D display we have all been left wondering: What is relevant in a 3D display? How do active shutter glasses affect viewing? What should we look for in a 3D display? What procedure should we use to set one up?  This Tip is designed to answer these questions. 

Why is it relevant to calibrate a 3D Display? First let’s understand the concept of 3D. We have been bombarded with 3D imagery for years. In the beginning there was just the shift of two colors, usually Red and Green, offset at just enough left and right eye creating a pseudo-depth of field. This was great for the motion picture industry. This craze filled drive-ins and movie theaters with people willing to put on cheap paper glasses with two separate pieces of colored Mylar for lenses. Why did this work? The human eye can’t see depth of field! It’s the placement of both the left and right eyes (roughly two and a half inches apart) seeing two separate images that is processed by our brain and perceived as depth of field. A 3-D display emulates this same concept by showing each eye the same image but from two separate perspectives. This, in essence, tricks our brain into thinking it’s seeing a real image.   

How do active shutter glasses affect viewing? When we are watching a 3D movie we are effectively looking through sunglasses. Whether active or polarized passive (or anaglyph), the glasses not only cut a substantial amount of light, but they may create a measurable color shift. Active 3D glasses rely on liquid-crystal shutter elements. These elements will vary in transmission efficiency and color transparency based on the quality of the materials employed. For active 3D viewing, the display should operate at a minimum of 120Hz, alternating between right and left eye, to eliminate any perception of flicker, This means that for 1/120 of a second, the left eye will be dark and the right eye will be “on,” and for 1/120 of a second, the left eye will be “on” and the right eye will be dark. This shuttering creates the high-quality 3D effect: During every 1/60 of a second, both the left eye and right eye will be presented with two distinctly different images, separated by a very brief “dark time.” This alternating presentation of left eye and right eye content is another big factor that impacts the brightness of 3D imagery. Specifically, 50% of the time, your right or left eye will be viewing a dark field, thus reducing the effective light output by about 50%. In addition, active 3D glasses are only   80-90% efficient in their transmission of light. This leaves a 10 - 20 % of light being lost to the viewer. The color loss is directly related to the lenses color, usually a slightly greenish/blue and the display pushing red to compensate! As one would guess, this imagery isn’t calibrated to proper specifications!

So now that we understand how and where the problems of light loss and color shift are created, we need to compensate for these losses in our calibration.

What should we look for in a 3D display?While there are increasing libraries of 3D content coming online, 3D HDTV's will still need to display a lot of 2D material. Thus, having multiple memory locations is imperative, since we will need to calibrate for both 2D and 3D modes. Most HDTVs are capable of retaining dual calibration presets for color temperature, light output and basic calibration settings, as well as provide enough additional light output (maximize backlight and contrast on LCD-LED) to overcome the substantial loss of perceived brightness when viewing 3D content. For the best 2D and 3D experience, select an HDTV with ISF Day and Night modes or other discrete memory locations. This allows you to store calibration settings for both 2D and 3D in their own memories.”

Please visit www.spectracal.com for more information on HD and calibration.