Presentation on theme: "Screen Selection for Digital 2D & 3D Cinema Andrew Robinson Managing Director Harkness Screens ICTA June 2009 Amsterdam."— Presentation transcript:
Screen Selection for Digital 2D & 3D Cinema Andrew Robinson Managing Director Harkness Screens ICTA June 2009 Amsterdam
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.
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.
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.
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.
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.
Measurement of gain Projector Light meter Magnesium carbonate block Screen surface Gain is measured according to British Standard BS 5550
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'
Light reflectance Gain screens reflect more light back to the audience than matt white screens Gain ScreenMatt White Screen
Measurement of viewing angle Gain is measured at intervals of 10° by comparison with reference standard
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
Gain curves of typical screens
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
2k digital projectors : film formats Native scope screen The full resolution of the DMD is 1080 x 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.
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
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).
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.
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.
Screen light levels Lumens required to achieve 14 ft lamberts Screen gainScreen width (m) / cinemascope format The above lumens are for incident light on the screen (after losses).
Screen light levels contd Lumens required to achieve 14 ft lamberts Screen gainScreen width (m) / flat format The above lumens are for incident light on the screen (after losses).
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?
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: gain screen costs including install 11m flat m scope m 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. power cost p.a. operating cost p.a. per hr
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
Measuring screen gain in existing theatres Relatively easy to do this using light meter and reference card. Gain = L 1 / L 2 Worthwhile also to measure absolute light levels in foot lamberts.
Gain screens and viewing angles Perlux 140 (1.4 gain) half-gain angle = 50° (0.7 gain)
Gain screens and viewing angles contd Perlux 180 (1.8 gain) half-gain angle = 34° (0.9 gain)
In this typical theatre almost all seats have better than half-gain level even with 1.8 gain screens. Viewing Angle
Screen shape A curved gain screen reflects more light back to the audience
Screen shape Gain screen curvature Harkness guideline is 5% curve R.O.C. = 5% of chord 20m screen width 1m screen depth
3D Cinema Stereoscopic 3D is growing fast, particularly in US. Over 2,500 3D screens operational worldwide end Forecast of 6,000 3D screens by end 2009 and 9,000 by end D titles releasing in 2009; more in 2010/11. Single digital projector gives economic 3D performance. High quality of digital 3D images.
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
efficiency Real D15% Real D XL28% Dolby12% Xpand18% 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
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).
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.
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.
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
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.
This theatre has most seats with an acceptable viewing experience. Seats outside the half-gain angle will have an inferior viewing experience. Viewing Angle
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.