Bright ideas: Making onscreen presentation even better
Cast your minds back to the not-too-distant past (or present day, depending on where you are in the world) when the switch from 35mm to digital projection was in overdrive. The entire industry seemed to be running around sourcing and installing any and all available equipment to make the switch and take advantage of early VPF deals. Such was the demand that lead times on equipment such as projectors and screens exceeded six months for quite some time!
At that time keen to meet the new DCI industry standards which accompanied the digital rollout, exhibitors looked at every conceivable affordable equipment permutation (projectors, lamps, screens, 3D systems, etc.) to deliver suitable presentation results. Given the newness of the technology at the time, some of the permutations to achieve suitable center-screen brightness performance must have in truth been little more than a best estimate. After all, how could anyone have truly known how any projector with a xenon lamp and gain screen would perform beyond the theory? The upshot was that whilst many theatres did and still do end up meeting the industry standard of 14fL (for center-screen brightness), many did and still do not and even some of those that did may have either over- or under-specified the equipment necessary to achieve suitable brightness levels.
Now bring yourself back to today and to established markets such as the U.S. and Europe where digitization is near to complete, the education process has evolved dramatically, and the industry as a whole has become much more scientific in the ways of digital cinema. The manufacturers, dealers, installers and indeed the exhibitors have become so much more knowledgeable and are now looking at ways to improve upon existing set-ups in theatres; in essence, there’s a significant and growing retrofit program gearing up, all aimed at delivering the paying customer with the very best experience.
But retrofitting a theatre with new projectors, lamps, 3D systems, etc. is expensive, and to perhaps do that on a scale of 1,000-plus theatres might stretch the budget line just a little, even if long-term cost savings can be realized. So exhibitors are turning to more cost-effective tried and tested means to increase presentation quality.
One of the hot topics within the industry at the moment is brightness uniformity. Exhibitors have up until now been focused on achieving the required center-screen brightness levels for 2D (14fL) and 3D (4.5fL) in order to achieve industry-standard compliance (and guidance); however, this has in many cases inadvertently compromised brightness uniformity, which is of course a key element of DCI compliance (for 2D).
For 2D presentation, DCI standards dictate that edge brightness should be between 70 to 90% of center-screen brightness to achieve compliance.
Where matt white screens (with a gain of 1.0) are used, brightness uniformity is unlikely to be a such a significant issue (assuming there are no unusual geometric issues such as large offset port holes). However, these screens do by definition endure substantially higher operational costs given the projector and lamp size needed to light the screen sufficiently to achieve suitable and acceptable brightness levels. So even the very thought of stripping out a higher-gain screen for a low-gain screen, which one might think is the solution to solving brightness uniformity issues, is almost the worst solution, unless spiralling lamp costs and projector capability are not a concern.
Gain screens by their very definition reflect more light back to the center of the seating area and the higher the gain of the screen, the more directional the light becomes. So in terms of meeting DCI compliance for center-screen brightness, it remains a winner; however, the edges of the screen become less bright and uniformity falls away.
So where’s the happy medium? Well, this is where screen optimization really comes to the fore. The ability to curve and tilt gain screens to use all of the available light, achieve both the maximum center-screen brightness and improve overall uniformity is not just a sensible option but in most cases the most cost-effective.
Let’s look at an example of a 3D comparison:
8m flat screen, 12m throw, 4.5fL in Z-Screen 3D
Clarus 170 screen: 3kw lamp size; 53% power setting; 60% center-to-edge brightness uniformity; 92% center-to-edge uniformity with 5% curve
Spectral 240 screen: 2kw lamp size; 67% power setting; 30% center-to-edge brightness uniformity; 64% center-to-edge uniformity with 5% curve
We can see in the example the effects of using a lower-gain screen—Clarus 170 (Harkness’ new lower-gain, wider viewing angle passive screen) versus Spectral 240—in terms of center-to-edge uniformity. However, the compromise required here to achieve sufficient center-screen brightness (with the Clarus screen) is a larger and more expensive lamp with shorter lamp hours, hence an additional operating cost. Those additional costs could be easily as much as $1,700 per annum, which over the course of the screen’s lifecycle could be significant, especially when multiplied by many theatres. So, yes, you can have a more uniform screen by choosing a lower-gain option, but there is a financial trade-off.
What we can see, however, in both cases is the dramatic effect of curving a screen in terms of achieving brightness uniformity, a 32% increase with the Clarus screen and a 34% increase with the Spectral screen. Now, in both of these cases it could be argued that DCI compliance has not been met due to center-to-edge brightness of both screens being above and below the recommended guidelines; however, in both cases a shallower or deeper curve could be used to meet the industry guidelines.
Curving the screen deals with the sides, but what of the top and bottom of the screen? In some cases there is a significant difference between the brightness at the top and the bottom of the screen and in almost every case this is due to the geometry of the auditorium.
Tilting a screen either forwards or backwards can achieve one of two objectives, either to bring the maximum light falling on the center of the screen to the DCI measuring position (in the exact middle of the seating area), or to bring uniformity to the screen. In some cases the two objectives can be achieved concurrently, in others there is a trade-off that has to be realized.
Navigating through the optimization minefield
Screen optimization is an exact science, though; it’s one of those things that if you get right can have a dramatic effect not just on operating costs but on overall presentation quality. It’s not just as simple a process as adding a 5% curve to a screen and expecting all the problems to be solved; seldom are two theatres ever exactly the same. Guidance should always be sought and we at Harkness always recommend that our customers discuss screen optimization plans with us prior to purchase so that we can best advise them on how to meet their specific requirements.
Indeed, screen selection and optimization are the most cost-effective ways of improving presentation both in terms of center-screen brightness and uniformity in retrofit situations. That’s why more and more exhibitors around the world are looking at retrofit screen optimization and replacement programs over the next 12 months. Of course, cost-effective improvements which yield a return on investment mean happy shareholders and an improved presentation means happy customers.
If you require assistance with screen optimization programs, e-mail firstname.lastname@example.org.