How New Methods for Evaluating Color Rendering Will Affect The CIE Color Rendering Index (CRI) What

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Transcript of How New Methods for Evaluating Color Rendering Will Affect The CIE Color Rendering Index (CRI) What

  • 1

    May 5–7, 2015

    Lightfair

    How New Methods for Evaluating Color Rendering will Affect You

    Michael Royer, PNNL

  • 2

    Color Fidelity: A Partial Picture

    Reference Image

  • 3

    The CIE Color Rendering Index (CRI)

    What CRI conveys:

    • Average color fidelity/color shift (but with limitations) – Outdated color science

    – Few samples

    – Only pastel Munsell samples

    – Can be selectively optimized

    What CRI doesn’t convey:

    • Direction/type of color shifts

    • Increases or decreases in chroma

    • Information about specific hue regions

    • Human preference

    • Color discrimination potential

    • Difference in color for any specific object

    • How one source will make things look compared to another

  • 4

    One Index is Not Enough. But how many are needed?

    And what should they be?

  • 5

    A Path Forward: IES Color Metrics Task Group

    • Technical Memorandum (i.e., calculation procedure), TM-30

    • Currently in final stage of balloting

    • It draws from a variety of other color perception research

    • Based objective/mathematical approach

    • Two-metric system (fidelity [Rf] and gamut [Rg]) for quantifying average color rendition

    • 99 color evaluation samples (CES) with color space and wavelength uniformity – Excellent correlation to much larger sets of color samples

    • Improved color science

    • Many additional tools (e.g., color distortion icon) for better understanding rendition of specific hues.

    TM-30 IS NOT YET A FINAL DOCUMENT!

  • 6

    The CIE Color Rendering Index (CRI)

    What CRI conveys:

    • Average color fidelity/color shift (but with limitations) – Outdate color science

    – Few samples

    – Only Pastel Munsell Samples

    – Can be selectively optimized

    What CRI doesn’t convey:

    • Direction/type of color shifts

    • Increases or decreases in chroma

    • Information about specific hue regions

    • Human preference

    • Color discrimination potential

    • Difference in color for any specific object

    • How one source will make things look compared to another

  • 7

    Summary of Notable Features

    Calculation Engine

    • 99 color evaluation samples – Real objects

    – Color space uniformity

    – Wavelength uniformity

    • Calculations in CAM02-UCS – CIECAM02 chromatic

    adaptation

    – Most uniform color space

    – Stability over CCT

    • Mixed reference (4500 K to 5500 K) eliminates discontinuity

    Outputs

    • Average Color Fidelity: Rf • Average Color Gamut: Rg • Rf Versus Rg Plot

    • Color Distortion Icon / Color Saturation Icon

    • Color Fidelity by Hue Angle (16 Groups)

    • Chroma Change by Hue Angle (16 Groups)

    • Skin Tone Color Fidelity

    • Color Fidelity by Sample

  • 8

    A Two-Metric System for Average Characterization

    0 < Rf ≤ 100

    When Rf > 60:

    60 < Rg ≤ 140

  • 9

    Hue shift

    Rf Versus Rg Plot

    Increasing

    saturation

    Decreasing

    saturation

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  • 10

    What does it all mean…

    For Specifiers?

    For Manufacturers?

    For Researchers?

    For Energy Efficiency Programs/Utilities?

  • 11

    Specifiers

    1. Learn about the new metrics – Presentations, Journal Articles, TM-30 (Pending), DG-01 (Pending)

    – What they do and don’t characterize; limitations

    2. Examine values for existing sources, understand your preferences in applications where you commonly specify

    3. Use additional information for better specifications

    • Case study: Museums

  • 12

    Comparing Rf and Rg

    60

    70

    80

    90

    100

    110

    120

    130

    140

    50 60 70 80 90 100

    G am

    u t

    In d

    ex , R

    g

    Fidelity Index, Rf

    Halogen Neodymium Incandescent F40T12WW/RS/EW F32T8TL830 CDM 830 Hybrid LED RAGB LED Phosphor LED

  • 13

    Color Distortion Icon

    Rf = 83 | Rg = 112 Rf = 83 | Rg = 99

    Increased Saturation

    Decreased Saturation

    Hue Shift

    13

  • 14

    Manufacturers

    1. Learn about the new metrics – Presentations, Journal Articles, TM-30 (Pending), DG-01 (Pending)

    – What they do and don’t characterize; limitations

    2. How do your products measure up against others?

    3. Does your product have distinguishing features that are marketable?

    4. Use tools for future optimizations – Balance between efficiency and color rendition

    • Case study: Neodymium Lamps

  • 15

    Communicating Performance

    (Live Calculation Tool Demo)

  • 16

    Beyond Averages

    Rf = 82

    Rg = 95

    LER = 342

    Rf = 82

    Rg = 95

    LER = 318

    0

    0.5

    1

    1.5

    2

    2.5

    380 430 480 530 580 630 680 730 780

    R ad

    ia n

    t P

    o w

    e r

    (n o

    rm al

    iz e

    d t

    o Y

    =1 0

    0 )

    l (nm)

    0

    0.5

    1

    1.5

    2

    2.5

    380 430 480 530 580 630 680 730 780

    R ad

    ia n

    t P

    o w

    e r

    (n o

    rm al

    iz e

    d t

    o Y

    =1 0

    0 )

    l (nm)

  • 17

    Beyond Averages

    50

    55

    60

    65

    70

    75

    80

    85

    90

    95

    100

    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

    R f b

    y H

    u e

    Hue Bin

    -20%

    -15%

    -10%

    -5%

    0%

    5%

    10%

    15%

    20%

    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

    C h

    ro m

    a Sh

    if t

    B y

    H u

    e

    Hue Bin

    50

    55

    60

    65

    70

    75

    80

    85

    90

    95

    100

    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

    R f b

    y H

    u e

    Hue Bin

    -20%

    -15%

    -10%

    -5%

    0%

    5%

    10%

    15%

    20%

    1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

    C h

    ro m

    a Sh

    if t

    B y

    H u

    e

    Hue Bin

  • 18

    EE Programs/Regulators

    1. Learn about the new metrics – Presentations, Journal Articles, TM-30 (Pending), DG-01 (Pending)

    – What they do and don’t characterize; limitations

    2. How do existing thresholds for color rendering relate?

    3. Should all sources that previously qualified still do so? Should the numerical value stay the same?

    • Case study: Triphosphor Fluorescent

  • 19

    Comparing Rf and Ra

    ~16 point spread in

    Rf scores at Ra =

    ~80 70

    75

    80

    85

    90

    95

    100

    70 75 80 85 90 95 100

    R f

    CRI Ra

    Filament Daylight Models Narrowband Fluorescent Broadband Fluorescent HID Hybrid LED Color Mixed LED Phosphor LED

  • 20

    Researchers

    1. Learn about the new metrics – Presentations, Journal Articles, TM-30 (Pending), DG-01 (Pending)

    – What they do and don’t characterize; limitations

    2. New information can improve characterization (but averages shouldn’t always be used to establish correlations)

    3. What new investigations are warranted?

    • Case study: Preference by Application

  • 21

    WHY ADOPT?

    • With two average numbers and other visualization tools, TM-30 provides a more complete characterization of color rendition than a fidelity metric alone (e.g., CRI).

    • With a greater number of samples, the values are harder to selectively optimize and should provide a better representation of average color rendering.

    • The method can help manufacturers optimize spectral designs, as well as accurately weigh tradeoffs between color rendition and other characteristics.

    • The color rendition characteristics of products can more easily be differentiated (and marketed).

    • The method can help specifiers and purchasers to select products that are more appropriate for their needs.

    • Thresholds, design guidance, and preconceptions will need to be re- evaluated.

    TM-30 IS NOT YET A FINAL DOCUMENT!

    Cover Slide Color Fidelity: A Partial Picture The CIE Color Rendering Index (CRI) One Index is Not Enough A Path Forward: IES Color Metrics Task Group The CIE Color Rendering Index (CRI) Summary of Notable Features A Two-Metric System for Average Characterization Rf Versus Rg Plot What does it all mean… Specifiers Comparing Rf and Rg Color Distortion Icon Manufacturers Communicating Performance (Tool