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)
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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
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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.
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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.
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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
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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
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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
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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.
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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
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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
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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
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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
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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)
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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)
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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.
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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.
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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.
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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.
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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
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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
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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
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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
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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)
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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***
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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
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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
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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
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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
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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
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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
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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)
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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)
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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
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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
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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)
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2/19/14

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

46. Observer Metamerism failure
How significant is differences in observers? Occurs with all illuminations – even daylight
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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)
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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
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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.