1. Screen Selection for Digital 2D & 3D Cinema
Andrew Robinson
Managing Director
Harkness Screens
ICTA June 2009
Amsterdam

2. This presentation will cover the following topics:
Brightness standards for digital cinema.
Differences between digital and 35mm projection.
Screen selection for digital projection.
Use of “gain” screens.
Digital 3D – screen implications.
Mixed digital 2D/3D applications.

3. Standards for screen luminance
SMPTE luminance standard for digital cinema is:
14 fl in screen centre +/- 3fl.
75% of centre brightness at the sides, minimum 9 fl. SMPTE
Luminance standard for 35mm projection is 16 fl.

4. Differences between digital and 35mm projection
Digital projectors use short arc, high-pressure Xenon lamps which are more costly than 35mm Xenons.
Light distribution from digital projector is more even than 35mm.
Setting up and changing film formats on digital projectors can result in significant reduction of available light.

5. Digital Cinema Projectors
Light outputs of up to 30,000 lumens are quoted by projector manufacturers.
Achieving maximum lumens requires optimum set-up and operating conditions:
- this may be costly in terms of operating costs
- in reality, incident light on screen may be significantly less
Screen selection is important to achieve recommended light levels and to moderate operating costs.

6. Screen light efficiency
Screens cannot create light; but they can optimise the reflection of it.
Reflectivity of a screen is measurable and is usually called “gain”
Gain is measured by comparing reflectivity of the screen with a reference standard and is expressed as a factor (e.g. 0.8 or 1.2).
There is a British Standard for gain measurement (BS 5550), which uses a reference standard to compare screen materials.
There are other measurement standards, but the BS is widely recognised and is used by Harkness to classify screen gain.
This enables screen materials to be compared in the laboratory.

7. Measurement of gain Projector Light meter Magnesium carbonate block
Screen surface
Gain is measured according to British Standard BS 5550

8. Types of cinema screen
Screens are available with various gain levels:
matt white: 'gain' typically 0.8 – 1.0
'gain' screens: up to 2.0 or more
: typically mid gain (~1.4)
: or high gain (~1.8)
: above 1.8 gain there is a risk
of 'hot spotting'

9. Light reflectance
Gain Screen
Matt White Screen
Gain screens reflect more light back to the audience than matt white screens

10. Measurement of viewing angle
Gain is measured at intervals of 10° by comparison with reference standard

11. Gain vs. viewing angle
with all screens, perceived brightness reduces as viewing angle increases
brightness of gain screens reduces more than matt white as viewing angle increases

12. Gain curves of typical screens

13. Picture formats / masking
2 most common movie formats are:
Cinemascope 2.35:1
Flat :1
Screen size can be adjusted by
keeping screen height constant
largest picture is ‘scope’ or
keeping screen width constant
largest picture is ‘flat’ 1
2.35 1
1.85

14. 2k digital projectors : film formats
Native ‘scope’ screen
The full resolution of the DMD is 1080 x 2048.
Changing film formats with “constant height” can be done electronically by reducing the area of DMD that is used.
Up to 37% loss of available light. Using motorised lenses reduces this significantly.

15. 2k digital projectors : film formats • alternatively using an anamorphic lens for ‘scope’ picture
this maximises the use of available light – 10% light loss from lens
requires activation of anamorphic lens
these anamorphic lenses are expensive
this is the only practical approach on large cinemascope screens

16. 2k digital projectors : film formats
Native ‘flat’ screen
Changing film formats on ‘constant width’ screens.
This is easily achieved electronically.
With digital projection, light is reduced changing from 1.85 screen to 2.35 screen, but so is the screen size. Brightness levels are maintained. (This is an advantage over 35mm when the opposite happens).

17. Xenon lamp light losses
Digital projectors use high performance Xenon lamps.
Usually more expensive, and have shorter warranty lives than 35mm lamps.
Light loss at warranty life can be up to 40%.
Running beyond warranty life further reduces light.

18. Screen light levels
Light losses from set-up and life-point of lamp can be as much as 50% of theoretical maximum.
Screen gain level can make a big difference to screen brightness or lumens required.
Medium to high gain screens (1.4 to 1.8) will reduce lamp power needs and can significantly reduce operating costs.

19. Screen light levels Lumens required to achieve 14 ft lamberts
Screen gain
Screen width (m) / cinemascope format
1.0
1.4
1.8
2.2
The above lumens are for incident light on the screen (after losses).

20. Screen light levels cont’d Lumens required to achieve 14 ft lamberts
Screen gain
Screen width (m) / flat format
1.0
1.4
1.8
2.2
The above lumens are for incident light on the screen (after losses).

21. 2k digital projectors : film formats
Optimum aspect ratio for digital projection is 1.90:1 (2048:1080).
If movies were made in this format and cinema screens were this format, there would be significant benefits with digital projection
use all the DMD (no set-up losses)
use all the available screen
no need for anamorphic lens
no “blockbusters” on a smaller screen
no need for moving masking
Many modern US theatres have “constant width” screens 1.85:1 which is very close to 1.90:1; less common in Europe
Could 1.90:1 become a new standard?

22. Operating Savings Lamps kw user price € warranty life (hrs)
lamps lamp cost
p.a € p.a.
power
cost
€ p.a.
operating cost
€ p.a. € per hr 2 3 4
4.5 6
800
1000
1250
1200
1500
2400
1400
700
600
1600
1800
2160
4100
8725
6600
12900
0.54
1.03
2.18
1.65
3.23
Based on 4000 hours annual use.
Examples of operating cost savings € p.a.
Using 2 kw instead of 3 kw lamp :
Using 3 kw instead of 4 kw lamp :
Using 4.5 kw instead of 6 kw lamp:
1.8 gain screen costs including install €
11m flat
14m scope
18m scope
There may also be initial investment savings if a smaller model projector can be used by reducing required lamp power.

23. Practical Implications
New installations of digital projectors
- consider projector / lamp options together with screen gain level
potential operating cost savings
capital cost savings if can use smaller projector
Existing installations of digital projectors
by changing to high gain screens, may be able to reduce lamp size and operating costs

24. Measuring screen gain in existing theatres
Relatively easy to do this using light meter and reference card.
Gain = L1 / L2
Worthwhile also to measure absolute light levels in foot lamberts.

25. Gain screens and viewing angles
Perlux 140 (1.4 gain)
half-gain angle = 50° (0.7 gain)

26. Gain screens and viewing angles cont’d
Perlux 180 (1.8 gain)
half-gain angle = 34° (0.9 gain)

27. Viewing Angle
In this typical theatre almost all seats have better than half-gain level even with 1.8 gain screens.

28. Screen shape
A curved gain screen reflects more light back to the audience

29. Screen shape •Gain screen curvature
Harkness guideline is 5% curve
R.O.C. = 5% of chord
20m screen width
1m screen depth

30. 3D Cinema Stereoscopic 3D is growing fast, particularly in US.
Over 2,500 3D screens operational worldwide end 2008.
Forecast of 6,000 3D screens by end 2009 and 9,000 by end 2010.
17 3D titles releasing in 2009; more in 2010/11.
Single digital projector gives economic 3D performance.
High quality of digital 3D images.

31. 3D Cinema Technologies Polarised light systems
There are 3 main technologies used in digital 3D cinema:
Polarised light systems
polarising filter / silver screen / passive eyewear
e.g. Real D, Master Image, Imax
Colour filters
colour filter wheel / white screen / passive eyewear
e.g. Dolby
“Active” eyewear
white screen / electronic “shutters” in eyewear
e.g. Xpand

32. 3D Cinema light efficiency
All 3D systems absorb a large amount of light compared with 2D mode because of filters and eyewear
efficiency
Real D
15%
Real D XL
28%
Dolby
12%
Xpand
18%
“Acceptable” screen brightness level 4.5 fl. (14 fl. 2D)

33. Screen implications for 3D Cinema
Polarised light systems (e.g. Real D)
Screen must maintain polarisation on reflection.
“Silver” screens (aluminium flake coatings).
>130:1 signal:noise ratio to maintain quality 3D images.
Silver screens are intrinsically high gain (typically 2.4).
Compensates light losses from 3D.
Screens up to 14m with a single projector (22m with Real D ‘XL’ system is possible).

34. Screen implications for 3D Cinema
Colour filter wheels (e.g. Dolby 3D)
Use white screens (do not need to maintain light polarisation).
Gain screens required to overcome light loss
- up to 2.2 (maximum gain available)
Up to 14m wide screen possible with single projector / 2.2 gain screen.

35. Screen implications for 3D Cinema
Active eyewear (e.g. Xpand)
White screen.
Gain screen needed for larger screens.
Screen up to 15m with single projector / 2.2 gain screen.

36. Mixed 2D / 3D applications
Acceptable brightness level with 3D is 4.5 fl
efficiency level 15%
Recommended brightness level for 2D is 14 fl
Switching 2D / 3D modes
2D image too bright
change lamp / reduce power in 2D mode
Real D ‘XL’ system 2D / 3D modes in balance
Increased risk of visible defects due to high gain
All Harkness 3D screens will support 2D content
useful for mixed programming

37. Theatre shape 3D systems use high gain screens.
High gain screens have reduced viewing angles:
Spectral 240 half-gain angle 24º
Perlux 220 half-gain angle 25º
Best to use theatres for 3D which are long relative to width
throw minimum 1.5 x screen width
With 3D, curving the screen is strongly recommended.

38. Viewing Angle
This theatre has most seats with an acceptable viewing experience.
Seats outside the half-gain angle will have an inferior viewing experience.

39. Summary For digital projection, it is recommended to use gain screens.
Benefits in power use/lamp life can give big operating cost savings.
Screen must be consistent with 3D technology chosen.
For 3D digital screens, it is usually necessary to change the screen for the highest possible gain.