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Screen selection-for-digital-cinema (1)
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 431-1-2006.
• 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.
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 screens reflect more light back to the
audience than matt white screens
Gain Screen Matt White Screen
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
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
2.20
2.40
2.60
7o 10o 20o 30o 40o 50o 60o
GAIN
VIEW ANGLE
Harkness Screens
Perlux 220 Perlux 180
Perlux 140 Matt Plus
13. Picture formats / masking
2 most common movie formats are:
• Cinemascope 2.35:1
• Flat 1.85:1
Screen size can be adjusted by
• keeping screen height constant
• largest picture is „scope‟
or
• keeping screen width constant
• largest picture is „flat‟
1
1
2.35
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
12 15 18 22 30
1.0
1.4
1.8
2.2
9200 14400 20800 31000 57700
6600 10300 14800 22200 41200
5100 8000 11500 17200 32100
4200 6600 4400 14100 26200
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
12 15 18 22
1.0
1.4
1.8
2.2
11700 18300 26400 39400
8400 13100 18800 28200
6500 10200 14700 21900
5300 8300 12000 17900
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
Based on 4000 hours annual use.
Examples of operating cost savings € p.a.
Using 2 kw instead of 3 kw lamp : 1940
Using 3 kw instead of 4 kw lamp : 4625
Using 4.5 kw instead of 6 kw lamp: 6300
1.8 gain screen costs including install €
11m flat 4000
14m scope 5000
18m scope 7000
There may also be initial investment savings if a smaller model projector can be used by reducing
required lamp power.
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
1000
600
1.7 1360
2.9 2900
5.7 7125
4.0 4800
6.7 10500
800
1200
1600
1800
2400
2160
4100
8725
6600
12900
0.54
1.03
2.18
1.65
3.23
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.
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
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. efficiency
Real D 15%
Real D XL 28%
Dolby 12%
Xpand 18%
3D Cinema light efficiency
“Acceptable” screen brightness level 4.5 fl. (14 fl. 2D)
All 3D systems absorb a large amount of light compared
with 2D mode because of filters and eyewear
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. •This theatre has most
seats with an acceptable
viewing experience.
•Seats outside the half-gain
angle will have an inferior
viewing experience.
Viewing Angle
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.
