Balancing brightness, limiting hot spots are goals
If you’ve been to a 3D movie, you may have noticed — or heard others comment — that the picture looked dark.
It’s not your imagination.
Between the light filtered out by 3D glasses and exhibitors’ notorious proclivity to nurse projector lamps long past their recommended lifespan, 3D images can be downright murky.
Most of the efforts toward solving this problem have gone into throwing more light on the screen with brighter projectors. But the brightness of the image also depends on the screen itself. A screen that reflects more light — or has higher “gain,” in tech parlance — gives a brighter picture.
The last great era of innovation for screens was the 1950s, but with the current 3D revival, this long-sleepy tech sector is suddenly getting some big attention. Exhibitors have proven their willingness to spend money on 3D gear, and manufacturers are seizing the opportunity to improve their product and boost sales.
The key issue is balancing gain with its unwanted side effect, the “hot spot.”
“Silver screens,” necessary for RealD and MasterImage 3D systems, give the highest gain, but they have a bright “hot spot” in the center, with noticeable falloff toward the edge of the screen. Silver screens are also expensive, difficult to manufacture, delicate and relatively short-lived.
Standard white screens reflect light more evenly across the surface, but they generally have low gain.
“The gain issue is a compromise. You are trying to retrieve some of the light that is being lost, but if you are too successful, you become more conscious of the hot spot,” says John Galt, senior VP of advanced digital imaging at Panavision, whose 3D system uses a white screen.
Harkness is among the screen-making firms working to reduce this tradeoff.
“Any high-gain screen is going to be less and less bright as you move toward the edges,” says Jeff Samitt, group director of sales and marketing for Harkness. “We are working on flattening the gain curve, which means viewers at an extreme angle still get a bright, attractive image.”
Harkness is working to apply paint on screens more smoothly, and to improve the signal-to-noise ratio for 3D on silver screens, which can create ghosting. Stereoscopic images show separately to each eye. “We want to minimize the amount of noise that comes through one lens that is intended for the other eye,” Samitt says.
Meanwhile Stewart Filmscreens recently filed for a patent on its Daily Dual, a single product that allows the operator to switch between white and silver surfaces, using an electrically operated roller screen. The Daily Dual is targeted to sell to screening rooms, as well as postproduction houses such as EFilm that may need to view images on both types of screens.
EFilm already has both silver and white screens in its postproduction operations, and it has had problems with the former. “We had to reject a couple of silver screens during installation because of the unevenness of the surface,” says Kevin Dillion, executive VP and general manager at EFilm. “Our rejection rate on matte screens is almost non-existent.”
EFilm’s problems with silver screens extend to color grading and quality control; there’s a need for the highest- quality, most consistent image possible in order for filmmakers to make creative choices, for instance adjusting color on the work itself.
“When you look at 2D on a silver screen, you are going to have that hot spot,” Dillion says. “EFilm’s perception is (that) the better screen for color timing (2D and 3D) is a white screen. Our concern is with the hot spot.” If center of the image is too bright only because of the screen, the colorist can be misled.
Not everyone agrees. Oculus 3D president Lenny Lipton, who developed some of the key technology behind the RealD system, rejects this often-cited complaint about watching 2D on silver screens. “They are completely wrong,” he argues. “It is just a prejudice. I think (silver screens) look better; they have higher contrast.”
As screenmakers bring their new products to market, awakening new demand, they also need to grow their plant capacity. Said Bruce Olson, president of Markus Theaters, “There are a lot of orders and there is a waiting time, at least three months, maybe longer.”