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LIPA Laserama Topics on Laser Illuminated Projectors

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1 LIPA Laserama Topics on Laser Illuminated Projectors
February 19, 2014

2 LIPA Membership LIPA represents the voice of the majority of projector manufacturers and suppliers of laser illuminated projectors (Less than 1 minute) Contact LIPA at 2/19/14

3 Today’s Agenda Regulatory Update: Are they legal?
Radiance is the same – lamps and laser projectors IEC standards updates Understanding speckle …and how to measure it Laser Color Primary Selection Impacts on Gamut, Image Quality and Efficiency Do you see what I see? Color Matching and the Single Observer Any Questions? Here are the topics covered today Contact LIPA at 2/19/14

4 Regulatory update Pete Ludé
LIP light output = Lamp projector light output Pete Ludé Mission Rock Digital, LLC

5 Study conducted LIPA Commissioned Study: Tested optical characteristics of 35mm film projector Current Xenon short-arc digital cinema projectors Prototype laser projectors Lead Researcher: Dr. David Sliney Casey Stack, Laser Compliance Jay Parkinson, Phoenix Laser Safety David Schnuelle, Dolby Laboratories Eight projectors tested in various locations over 7 months. Contact LIPA at 2/19/14 5

6 Hot off the press! Published in Health Physics, March 2014
Radiation Safety Journal Official Journal of the Health Physics Society Peer review complete Cover story! Additional analysis presented at Society of Motion Picture & Television Engineers Conference – October 22, 2013. Contact LIPA at 2/19/14

7 Laser Brightness (Radiance)
LARGE FOCAL SPOT (FILAMENT IMAGE) LENS MICROSCOPIC FOCAL SPOT (“DIFFRACTION LIMITED”) LASER LENS From Sliney DH and Trokel, S, 1993 Contact LIPA at 2/19/14

8 Comparison of Radiance Values
Light Source Radiance Value Units 5mW laser pointer 70 MW/m2 sr The SUN (visible λ) 7 30,000 lumen cinema projector 2 Contact LIPA at 2/19/14

9 Comparing Radiance: Lamp vs. Laser
Measured Radiance (W • cm-2 • sr -1) Normalized Laser Xenon Xenon Laser Laser Actual Luminance Power (Lumens): 5,000 17,000 30,000 55,000 2,000 Normalized Luminance Pwr (Lumens): 5,000 5,000 5,000 5,000 5,000 Contact LIPA at 2/19/14

10 and new laser-illuminated projectors, when of equal luminance power,
Conclusion Traditional lamp projectors and new laser-illuminated projectors, when of equal luminance power, emit almost identical radiance. Contact LIPA at 2/19/14 10

11 IEC Regulatory Changes

12 Laser Projector Regulation under IEC
All laser product requirements are defined in Medical Industrial Laboratory use Laser Welding Laser Illuminated Projectors IEC Ed 2 (2007) Safety of Laser Products Part 1: Equipment classification & Requirements Contact LIPA at 2/19/14

13 Laser Projector Regulation under IEC
IEC Ed 3 (2014) Safety of Laser Products Part 1: Equipment classification & Requirements IEC Ed 1 (2006) Photobiological safety of lamps and lamp systems Carve-out for devices with radiance < (1 MW•m-2 •sr -1)/α Contact LIPA at 2/19/14

14 Laser Projector Regulation under IEC
IEC Ed 3 (2014) Safety of Laser Products Part 1: Equipment classification & Requirements IEC Ed 1 (2015?) Photobiological safety of Lamp Systems for Image Projectors Contact LIPA at 2/19/14

15 US State Laser Regulations
100 Km 100 Miles 500 Miles 500 KM 500 Km HI AK AL AZ AR CA CO CT DE FL GA ID IL IN OA KS KY LA ME MD MA MI MN MS MO MT NB NV NH NJ NM NY NC ND OH OK OR PA RI SC SD TN TX UT VT VA WA WV WI WY No relevant laser regulations Some relevant laser regulations Most involved & potentially burdensome Contact LIPA at 2/19/14

16 Speckle

17 What is Speckle? Interference pattern that occurs when coherent light is scattered off an optically rough surface (i.e. screen) Visible noise on uniform areas of scene Decreases perceived contrast Most visible on uniform, bright scene elements (e.g. sky) More visible when you move your head back and forth (“subjective” speckle) Figure of merit: Speckle contrast ratio Source: K.O. Apeland (5) SCR= standard deviation / mean intensity in % Between 0 and 1 0 means “no speckle” Can be expressed as percentage Here are the basics. You can learn a lot more from the book “Speckle Phenomena in Optics” by Joseph Goodman. See item (8) in the references listed at the very end of this presentation. The figure of merit is simply the standard deviation divided by mean intensity – often expressed as a percentage. For example, a 0.1 speckle contrast ratio may be referred to as 10%. Source: Goodman (8), Curtis (7) Contact LIPA at 2/19/14

18 Methods to reduce speckle
In Theory: • Polarization diversity • Temporal averaging • Wavelength diversity • Angle diversity • Temporal coherence reduction • Spatial coherence reduction In Practice: Array of multiple emitters Slightly different frequencies (wavelength diversity) Spatially separated (angle diversity) Rotating diffusers Vibrating diffusers Hadamard matrices Vibrating screen Other methods… There are many ways of reducing speckle, some well documented and some proprietary. Any measurement method should be able to quantify the results of any of these methods. Source: Goodman (8) Contact LIPA at 2/19/14

19 Speckle Metrology Considerations
Source (Laser) Projector Focal plane (≠ screen?) Reference light source (coherent) Luminance power (brightness) Based on the many proposals for laser speckle measurement, here is a summary of the key variables. First, the device under test is considered. Some proposals specify a de-focusing of the image projector from the screen to remove image attributes such as LCoS or DLP pixels from interfering with SCR measurement. It may be useful to have a (nearly) “speckle free” reference source for calibration. It should be determined what luminance flux should be used. Contact LIPA at 2/19/14

20 Speckle Metrology Considerations
Source (Laser) Projector Focal plane (≠ screen?) Reference light source (coherent) Luminance power (brightness) Camera Clear aperture / f-number Pixel size (relative to speckle size) Focal length (related to distance) Shutter speed / Integration time Focus point (= screen?) Spectral filtering (high/low-pass) The camera system has many variable that must be considered. Examples are listed here. One key point is the effect of shot noise in the image sensor. Contact LIPA at 2/19/14

21 Speckle Metrology Considerations
Source (Laser) Projector Focal plane (≠ screen?) Reference light source (coherent) Luminance power (brightness) Camera Clear aperture / f-number Pixel size (relative to speckle size) Focal length (related to distance) Shutter speed / Integration time Focus point (= screen?) Spectral filtering (high/low-pass) Image Processing Gamma (Optical-Electrical transfer curve) Exposure Compression algorithm Bit depth / dynamic range Digital Image Processing After the image is captured, the processing must be carfully controlled. Adequate bit-depth must be provided in order to preserve subtle difference in SCR readings. Contact LIPA at 2/19/14

22 Speckle Metrology Considerations
Source (Laser) Projector Focal plane (≠ screen?) Reference light source (coherent) Luminance power (brightness) Camera Clear aperture / f-number Pixel size (relative to speckle size) Focal length (related to distance) Shutter speed / Integration time Focus point (= screen?) Spectral filtering (high/low-pass) Image Processing Gamma (Optical-Electrical transfer curve) Exposure Compression algorithm Bit depth / dynamic range Digital Image Processing Screen Screen gain Total Integrated Scatter Objective (second) screen As discussed earlier, the projection screen plays a critical role in measurement results. One proposal calls for a second screen (“objective screen”), placed in the viewing area of the primary projection screen, to reflect speckle into the camera. Contact LIPA at 2/19/14

23 Speckle Metrology Considerations
Source (Laser) Projector Focal plane (≠ screen?) Reference light source (coherent) Luminance power (brightness) Camera Clear aperture / f-number Pixel size (relative to speckle size) Focal length (related to distance) Shutter speed / Integration time Focus point (= screen?) Spectral filtering (high/low-pass) Image Processing Gamma (Optical-Electrical transfer curve) Exposure Compression algorithm Bit depth / dynamic range Digital Image Processing Screen Screen gain Total Integrated Scatter Objective (second) screen Room Geometry and Environment Projection and camera capture angles Viewing distance / Ambient light Ratio of image area to average speckle size The projection through, camera capture angle, viewing distance ambient light and ration of image area to average speckle size will all have some influence on the SCR measurement results. Contact LIPA at 2/19/14

24 To learn more… LIPA Speckle Metrology Working Group
Update report at: Technology Summit on Cinema at NAB April 5-6, 2014 Las Vegas Convention Center https://www.smpte.org/tsc2014 Contact LIPA at 2/19/14

25 Laser Color Primary Selection Options and Tradeoffs
Impacts on Gamut, Image Quality and Efficiency Bill Beck BTM Consulting, LLC

26 Primary Selection: Lumens vs. Watts
545 nm, 669 lm/W 532 nm, 603 lm/W 462 nm, 45 lm/W 445 nm, 20 lm/W 640 nm, 120 lm/W 618 nm, 277 lm/W System A “Native DCI” (P3) System B “Available Lasers” nm lm/W lm/Color Req’d W 618 277 17,880 65 640 120 18,391 154 545 669 64,529 96 532 603 65,985 109 462 45 3,289 74 445 20 1,321 366 85,697 235 261 328 Bill Beck BTM Consulting, LLC February 19, 2014

27 First Pass Observations…
“Infinite” number of RGB combinations and “Spectral Power Distributions” (SPD) to achieve desired gamut, white-point and primaries - requires design TRADEOFFS Desired color-space can be produced with native RGB wavelengths and balance delivered from the laser engine… …or via color correction in the projector, which always reduces overall brightness and sometimes bit depth Likely ideal solution will be a bit of both Contact LIPA at 2/19/14

28 Single line vs. Multi/Wide-band Primaries
Narrow band RGB laser “lines” FWHM ≤ 1 nm Simple modeling and supply chain … but Massive Speckle Potential for “Observer Metameric Failure” (OMF) Multiple RGB lines per primary - n x FWHM ≤ 1 nm Wavelength options depend on physics and availability Little impact on speckle if narrowband Unknown impact on OMF Spectrally broadened RGB bands FWHM nm Replicates incoherent white light Low speckle and OMF Hard to achieve with available lasers Contact LIPA at 2/19/14

29 Single line vs. Wide-band Primaries
Wide, “filled in” primary bands are ideal but… Very difficult to procure laser sources At the right wavelengths Fill in the bands of interest Exhibit the same good beam quality, i.e., low étendue Have similar lifetimes …all, at a reasonable cost Let’s look at the tradeoffs Contact LIPA at 2/19/14

30 Primary Selection vs. Gamut
Rec 709 DCI P3 Rec 2020 Narrowband primaries “on locus” Wider gamut and more saturated But higher speckle and OMF Longer Reds and shorter Blues are commercially available Shorter Green adds Magenta but cuts Yellow saturation Wider gamut primaries reduce luminous efficacy (lm/watt) Contact LIPA at 2/19/14

31 Primary selection vs. Speckle Contrast Ratio (SCR)
Benchmark is Xenon illumination – Incoherent and Lambertian RGB pass bands for DCinema installed base ~60 nm wide System f# ~2.4 (fast) to maximize angle and usable lamp output SCR for Xenon ~ 1% - hard to measure Single wavelength, narrow line (≤1 nm) RGB primaries SCR ~20% UNWATCHABLE in Green and Red; speckle noticeable even in Blue Multiple emitters of the same wavelength – little reduction in SCR Multiple beamlines that “fill” nm reduce speckle to Xenon levels ***Each Laser Primary should fill 10 – 40 nm band*** Contact LIPA at 2/19/14

32 Primary Selection vs. Observer Metameric Failure (OMF)
Three factors to consider: Spectral Bandwidth of each primary Spectral Power Distribution (SPD) i.e., flat vs. peaky Color point of primary (wavelength or x,y) Bandwidth is first order – wider is better for OMF and Speckle Smooth SPD is better than peaky Wide band primaries reduces saturation and gamut slightly Wavelength is important, especially for narrow band primaries Intersection with the tri-stimulus curves determines impact More work is needed here – computational and observational See: Wiley Periodicals Vol. 34, Number 5, October 2009 Rajeev Ramananth Contact LIPA at 2/19/14

33 Primary Selection vs. Luminous Efficacy
Luminous Efficacy = White balanced lumens / RGB watt Ideal is to use “native” laser primaries: Rec 709 : 613/550/463 nm = 362 lm/W DCI P3 : 618/545/462 nm = 366 lm/W Rec 2020 : 630/532/467 nm = 288 lm/W Readily available lasers: 640/532/445 nm Rec 709 : Raw 249 lm/W Correction reduces lm/W DCI P3 : Raw 261 lm/W Correction reduces lm/W Rec 2020 : Raw 261 lm/W Very slight reduction in lm/W Contact LIPA at 2/19/14

34 Primary Selection vs. Wall Plug Efficiency (WPE)
Projector + Engine WPE is a very complex function of: RGB wavelengths – sets luminous efficacy ( lm/RGB watt) Étendue at the PJ input – determines PJ throughput Aggregation and delivery efficiency – set gross RGB watts required Laser Device WPE – drives engine efficiency and cooling required Ranges from 3% for some Greens to >30% short Blue Laser Source Speckle Contrast Ratio – if low, no additional losses in projector for downstream speckle reduction Contact LIPA at 2/19/14

35 Current Laser Primary Options
Color Wavelength (nm – FWHM) Device Type Watts per Device Lumens Per watt Lumens per Device étendue Diode ~1 73 med Diode; Bar ≤ 8 131 1,048 high DPSS + OPO 10 301 3010 low 550 – 0.1 VCSEL SHG 2 679 1358 DPSS wide spectrum 20-40 671 >20K 532 – 0.1 DPSS; VCSEL; FL SHG 2-100 603 >60K range 1 542 50 3 20 60 For reference ~ 85,000 RGB lm input to the projector for 30,000 lm output VCSEL=Vertical Cavity Surface Emitting Laser SHG=Second Harmonic Generation DPSS=Diode Pumped Solid State FL=Fiber Laser Contact LIPA at 2/19/14

36 A few words on Optical Fiber Delivery
Watts / beamline and beam quality determine the number and size of fibers required Best case: high power per color - with some redundancy Fewest fibers per kilo-lumen on screen Smallest diameter (cheapest) fibers Worst case: lots of low power devices with bad beam quality Requires large number of large diameter fibers Cable ends up too big, too stiff and too expensive Don’t worry about the fibers Single fiber cables can deliver kilowatts of laser power Attenuation is very low - up to 100 meters or more Contact LIPA at 2/19/14

37 Summary and Conclusions
Primary wavelengths + BW impact: Gamut, Speckle, Observer Metameric Failure (OMF), Luminous Efficacy (LE), Wall Plug Efficiency (WPE) Wide band primaries, where possible, reduce speckle and OMF Difficult to achieve in practice Slight tradeoff with saturation and gamut (smaller triangle) Wide Gamut laser options are available, but less efficient than DCI P3 Optimum primary wavelengths and bandwidths do no coincide with mature, low cost laser offerings, especially for Green and Red RED: too long and narrow; high speckle and low lm/W GREEN: is too narrow; high speckle and low electrical efficiency BLUE: can fill the band at low cost but power per device is still low Contact LIPA at 2/19/14

38 Do you see what I see? Color Matching and the Single Observer
Matt Cowan Entertainment Technology Canada Ltd.

39 Metamerism Metamerism is the matching of apparent colour of objects with different  spectral power distributions. Colors that match this way are called metamers. (wikipedia) Observer metameric failure can occur because of differences in colour vision between observers. …….. In all cases, the proportion of long-wavelength- sensitive cones to medium-wavelength-sensitive cones in the retina, the profile of light sensitivity in each type of cone, and the amount of yellowing in the lens and macular pigment of the eye, differs from one person to the next. This alters the relative importance of different wavelengths in a spectral power distribution to each observer's colour perception. As a result, two spectrally dissimilar lights or surfaces may produce a colour match for one observer but fail to match when viewed by a second observer. (Wikipedia) Contact LIPA at 2/19/14

40 Raises 2 Issues With color science we should be able to calculate different spectral distributions that give an exact “average” color match. (Metamers) The population of observers will have differing sensitivity to the degree of the average match. (Observer Metameric Failure) Contact LIPA at 2/19/14

41 What we see, What we measure (100 years of color science in 1 slide)
Metrics established through: Deriving observer’s sensitivity to color through Cone Sensitivity Functions Choosing a representative observer as the “standard observer” Transforming cone functions to “color matching functions” (CMF) Determining spectral power distribution (SPD) of stimulus Integrating the SPD across the CMF to achieve 3 numbers (X,Y,Z) to describe the stimulus color Normalize the X,Y,Z values to achieve the familiar x,y,L coordinates XYZ x,y,L SPD CMF Contact LIPA at 2/19/14

42 Color Matching Functions
Cone functions are basic HVS characteristic CMF is linear transform of cone functions CIE 1931 Color matching functions Contact LIPA at 2/19/14

43 The Real World – we are all different
Standard – singular response Figure 3: Cone spectral responses for 1000 simulated individual observers randomly sampled from the Tl, Tm, L, M, and S values of Equation 1 (Fairchild et al 2013). (Plot is 1000 narrow lines on same plot) Contact LIPA at 2/19/14

44 Standard Observer – did we get it right in 1931?
Contact LIPA at 2/19/14

45 Try a Different CMF – fix offset
Offset is failure of 1931 CMF. Scatter is observer metamerism From Sony white paper “Color Matching between OLED and CRT” v1.0 Feb 15, 2013 Contact LIPA at 2/19/14

46 Observer Metamerism failure
How significant is differences in observers? Occurs with all illuminations – even daylight Contact LIPA at 2/19/14

47 Figure 7: The metameric pairs for each of the 24 XRite Color Checker patches as seen by the standard observer on the left and the 95th percentile simulated observer on the right. (Fairchild et al 2013) Contact LIPA at 2/19/14

48 Conclusions Color matching using instruments will be better if we use CMF’s updated from 1931 Observer Metamerism failure is a fact of nature, we live with it every day Contact LIPA at 2/19/14

49 LIPA Laserama Questions??
LIPA Laserama Questions?? Pete Ludé Mission Rock Digital, LLC Bill Beck BTM Consulting, LLC Matt Cowan Entertainment Technology Canada Ltd.


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