lipa laserama topics on laser illuminated projectors february 19, 2014

LIPA LaseramaTopics on Laser Illuminated Projectors

February 19, 2014

LIPA Membership

2Contact LIPA at [email protected] 2/19/14

Contact LIPA at [email protected] 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?

2/19/14

Regulatory update

LIP light output = Lamp projector light output

Pete LudéMission Rock Digital, [email protected]

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.


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 atSociety of Motion Picture & Television EngineersConference – October 22, 2013.


Laser Brightness (Radiance)

LARGE FOCAL SPOT (FILAMENT IMAGE)

MICROSCOPICFOCAL SPOT(“DIFFRACTION LIMITED”)LASER

LENS

LENSFrom Sliney DH and Trokel, S, 1993


Comparison of Radiance Values

Light Source Radiance Value Units

5mW laser pointer 70 MW/m2 sr

The SUN (visible λ) 7 MW/m2 sr

30,000 lumencinema projector 2 MW/m2 sr


Comparing Radiance: Lamp vs. Laser

Proj 6 Proj 2 Proj 1 Proj 4 Proj 50

5

10

15

20

25

30

35

40

Laser Laser LaserXenon Xenon

Nor

mal

ized

Mea

sure

d R

adia

nce

(W •

cm-2

• sr

-1)

30,00017,0005,000 2,00055,000Actual Luminance Power (Lumens): 5,000 5,0005,000 5,000 5,000Normalized Luminance Pwr (Lumens):


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Conclusion

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Traditional lamp projectorsand new laser-illuminated

projectors,when of equal luminance power,emit almost identical radiance.

Contact LIPA at [email protected] 2/19/14

IEC Regulatory Changes

Laser Projector Regulation under IEC

IEC 60825-1 Ed 2 (2007)Safety of Laser Products

Part 1: Equipment classification & Requirements

• All laser product requirements are defined in 60825

• Medical

• Industrial

• Laboratory use

• Laser Welding

• Laser Illuminated Projectors





IEC 62471 Ed 1 (2006)Photobiological safety of lamps and lamp systems

Carve-out for devices with radiance < (1 MW•m-2 •sr -1)/α





IEC 62471-5 Ed 1 (2015?)Photobiological safety of Lamp Systems

for Image Projectors


US State Laser Regulations

15

00 100 Km

100 Miles

500 Miles

0 500 KM0

0 500 Miles0 500 Km

HI

AK

AL

AZ

AR

CA CO

CT

DE

FL

GA

ID

IL IN

OA

KSKY

LA

ME

MD

MA

MI

MN

MS

MO

MT

NBNV

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


Speckle

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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

SCR= standard deviation / mean intensity in % • Between 0 and 1

• 0 means “no speckle”• Can be expressed as percentage

Source: K.O. Apeland (5)

Source: Goodman (8), Curtis (7)


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Methods to reduce speckle

In Theory:

• Polarization diversity

• Temporal averaging

• Wavelength diversity

• Angle diversity

• Temporal coherence reduction

• Spatial coherence reduction

Source: Goodman (8)

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…


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Speckle Metrology Considerations

• Source (Laser) • Projector Focal plane (≠ screen?)• Reference light source (coherent)• Luminance power (brightness)


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• 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)


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• Image Processing• Gamma (Optical-Electrical transfer curve)• Exposure• Compression algorithm• Bit depth / dynamic range

•

Digital Image Processing


22





•

• Screen• Screen gain • Total Integrated Scatter• Objective (second) screen



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•

• 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•




To learn more…

Technology Summit on Cinema at NAB

April 5-6, 2014

Las Vegas Convention Center

https://www.smpte.org/tsc2014

2/19/14

LIPASpeckle Metrology Working Group

Update report at:

Laser Color Primary Selection Options and Tradeoffs

Impacts on Gamut, Image Quality and Efficiency

Bill BeckBTM Consulting, [email protected] +1 617.290.3861

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System A - “Native DCI” (P3) System B - “Available Lasers”

nm lm/W lm/Color Req’d W 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 65

366 85,697 235 261 85,697 328

545 nm, 669 lm/W 532 nm, 603 lm/W

462 nm, 45 lm/W445 nm, 20 lm/W

640 nm, 120 lm/W

618 nm, 277 lm/W

Primary Selection: Lumens vs. Watts

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


28

Single line vs. Multi/Wide-band Primaries

Contact LIPA at [email protected]

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 10 - 40 nm• Replicates incoherent white light • Low speckle and OMF• Hard to achieve with available lasers

2/19/14

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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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Primary Selection vs. Gamut


Rec 709 DCI P3Rec 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)

2/19/14

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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” 10 - 40 nm reduce speckle to Xenon levels

***Each Laser Primary should fill 10 – 40 nm band***


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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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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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Primary Selection vs. Wall Plug Efficiency (WPE)

Projector + Engine WPE is a very complex function of:

• RGB wavelengths – sets luminous efficacy (200 - 350 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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Current Laser Primary OptionsColor Wavelength

(nm – FWHM)

Device Type

Watts per Device

Lumens Per watt

Lumens per Device

étendue

650 - 1 Diode ~1 73 73 med

638 - 1 Diode; Bar ≤ 8 131 1,048 high

615 - 8 DPSS + OPO 10 301 3010 low

550 – 0.1 VCSEL SHG 2 679 1358 med

546 - 12 DPSS wide spectrum

20-40 671 >20K low

532 – 0.1 DPSS; VCSEL; FL SHG

2-100 603 >60K range

525 - 2 Diode 1 542 542 med

462 - 2 Diode 1 50 50 med

445 - 2 Diode 3 20 60 med


For reference ~ 85,000 RGB lm input to the projector for 30,000 lm outputVCSEL=Vertical Cavity Surface Emitting Laser SHG=Second Harmonic Generation DPSS=Diode Pumped Solid State FL=Fiber Laser

2/19/14

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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


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


Do you see what I see?

Color Matching and the Single Observer

Matt CowanEntertainment Technology Canada [email protected]

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)



Raises 2 Issues

1. With color science we should be able to calculate different spectral distributions that give an exact “average” color match. (Metamers)

2. The population of observers will have differing sensitivity to the degree of the average match. (Observer Metameric Failure)

2/19/14

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

SPD CMF x,y,L



Color Matching Functions

Cone functions are basic HVS characteristic

CMF is linear transform of cone functions

CIE 1931 Color matching functions

[ ¿ ]

2/19/14

The Real World – we are all different

Figure 3: Cone spectral responses for 1000 simulated individualobservers randomly sampled from the Tl, Tm, L, M, and S valuesof Equation 1 (Fairchild et al 2013). (Plot is 1000 narrow lines on same plot)

Standard – singular response


Standard Observer – did we get it right in 1931?


Try a Different CMF – fix offset

From Sony white paper “Color Matching between OLED and CRT” v1.0 Feb 15, 2013

Offset is failure of 1931 CMF.

Scatter is observer metamerism


Observer Metamerism failure

How significant is differences in observers?

Occurs with all illuminations – even daylight


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 [email protected] 472/19/14

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


LIPA LaseramaQuestions??

Pete LudéMission Rock Digital, LLC

[email protected]

Bill BeckBTM Consulting, [email protected] +1 617.290.3861

Matt CowanEntertainment Technology Canada Ltd.

[email protected]

www.LIPAinfo.org

lipa laserama topics on laser illuminated projectors february 19, 2014

Documents

laser laser xenon

contact lipa

new laser

safety of laser products

laser projector regulation

iec iec

laser product requirements

mw laser pointer