Principles of Color Measurement - Radiant Vision Systems...Radiant Vision Systems engineers imaging...
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Principles of Color Measurement 460 480 500 520 540 560 580 600 620 Kelvin ( K ) 10000 6000 4000 3000 2500 3000 2000 1500 100 % 50 % 0 % Spectral Locus Colors at maximum saturation. Dominant Wavelength Intersection point on the spectral locus by a line originating at white and then projected through a given color. Purity (Excitation Purity) The ratio of the distance of white to a stimulus with respect to the distance of white to the dominant wavelength on the spectral locus (expressed as a percentage). Planckian Locus Color of light emitted by a black body at a given temperature. Used to calculate Correlated Color Temperature (CCT) of white light sources in Kelvin (K). 0.0 400 500 /nm 600 700 0.5 1.0 1.5 2.0 CIE Color Matching Functions MacAdam ellipses indistinguishable to the human eye (ellipses shown here at ten times their actual size). Color gamut illustrates the RGB limits reproducible by digital displays. Calculating CIE color coordinates of a stimulus: For a spectral power distribution (SPD), given as , the XYZ tristimulus values are computed as: 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 CIE 1931 CIE 1931 sRGB DCI-P3 Rec.2020 CIE 1976 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.6 0.4 0.5 sRGB DCI-P3 Rec.2020 Radiant Vision Systems engineers imaging colorimeters and photometers, application software, and goniometric systems to critically evaluate light, color, and surface quality. Calibrated to www.RadiantVisionSystems.com Copyright ©2019 Radiant Vision Systems LLC. All rights reserved. 2019/03/21 Anatomy of the CIE Chromaticity Diagram CIE 1931 CIE 1976 v’ u’ y x 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.6 0.4 0.5 v’ u’ CIE 1976 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 y x Example Stimulus 490
Transcript of Principles of Color Measurement - Radiant Vision Systems...Radiant Vision Systems engineers imaging...
Principles of Color Measurement
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Kelvin ( K )
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100%50%0%
Spectral Locus Colors at maximum saturation.
Dominant Wavelength Intersection point on the spectral locus by a line originating at white and then projected through a given color.
Purity (Excitation Purity) The ratio of the distance of white to a stimulus with respect to the distance of white to the dominant wavelength on the spectral locus (expressed as a percentage).
Planckian Locus Color of light emitted by a black body at a given temperature. Used to calculate Correlated Color Temperature (CCT) of white light sources in Kelvin (K).
0.0400 500
𝜆𝜆/nm600 700
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2.0 𝒙𝒙𝒙𝒙𝜆𝜆𝒙𝒚𝒚𝒙𝒙𝜆𝜆𝒙𝒛𝒛𝒙𝒙𝜆𝜆𝒙
CIE Color Matching FunctionsMacAdam ellipses define areas of color on the CIE chromaticity diagram that are indistinguishable to the human eye (ellipses shown here at ten times their actual size).
Color gamut illustrates the RGB limits reproducible by digital displays.Calculating CIE color coordinates of a stimulus:
For a spectral power distribution (SPD), given as 𝑃𝑃𝒙𝜆𝜆𝒙, the XYZ tristimulus values are computed as:
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Radiant Vision Systems engineers imaging colorimeters and photometers, application software, and goniometric systems to critically evaluate light, color, and surface quality. Calibrated to simulate human visual perception, Radiant cameras perform scientific measurement of displays and illuminated components to ensure quality that accurately reflects human experience.
www.RadiantVisionSystems.com Copyright ©2019 Radiant Vision Systems LLC. All rights reserved. 2019/03/21
Anatomy of the CIE Chromaticity Diagram
𝑋𝑋𝑋𝑋𝑃𝑃𝒙𝜆𝜆𝒙𝒙𝒙𝒙𝒙𝜆𝜆𝒙𝑋𝑋𝜆𝜆𝑌𝑌𝑋𝑋𝑃𝑃𝒙𝜆𝜆𝒙𝒚𝒚𝒙𝒙𝜆𝜆𝒙𝑋𝑋𝜆𝜆𝑍𝑍𝑋𝑋𝑃𝑃𝒙𝜆𝜆𝒙𝒛𝒛𝒙𝒙𝜆𝜆𝒙𝑋𝑋𝜆𝜆
Cx𝑋X/𝒙𝒙X+Y+Z𝒙𝒙
Cy𝑋Y/𝒙𝒙X+Y+Z𝒙𝒙
u′𝑋4X/𝒙𝒙X+15Y+3Z𝒙𝒙
v′𝑋9Y/𝒙𝒙X+15Y+3Z𝒙𝒙
CIE 1931 CIE 1976
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ExampleStimulus
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Principles of Color Measurement
460
480
500
520
540
560
580
600
620
Kelvin ( K )
10000
6000
4000
3000
25003000
2000
1500
100%50%0%
Spectral Locus Colors at maximum saturation.
Dominant Wavelength Intersection point on the spectral locus by a line originating at white and then projected through a given color.
Purity (Excitation Purity) The ratio of the distance of white to a stimulus with respect to the distance of white to the dominant wavelength on the spectral locus (expressed as a percentage).
Planckian Locus Color of light emitted by a black body at a given temperature. Used to calculate Correlated Color Temperature (CCT) of white light sources in Kelvin (K).
0.0400 500
/nm600 700
0.5
1.0
1.5
2.0
CIE Color Matching FunctionsMacAdam ellipses indistinguishable to the human eye (ellipses shown here at ten times their actual size).
Color gamut illustrates the RGB limits reproducible by digital displays.Calculating CIE color coordinates of a stimulus:
For a spectral power distribution (SPD), given as , the XYZ tristimulus values are computed as:
0.1
0.2
0.3
0.4
0.5
0.6
0.7
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
CIE 1931
CIE 1931
sRGB
DCI-P3
Rec.2020
CIE 1976
0.1
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0.3
0.4
0.5
0.6
0 0.1 0.2 0.3 0.60.4 0.5
sRG
BDCI-P
3Rec
.202
0
Radiant Vision Systems engineers imaging colorimeters and photometers, application software, and goniometric systems to critically evaluate light, color, and surface quality. Calibrated to
www.RadiantVisionSystems.com Copyright ©2019 Radiant Vision Systems LLC. All rights reserved. 2019/03/21
Anatomy of the CIE Chromaticity Diagram
Cx=X/((X+Y+Z))
Cy=Y/((X+Y+Z))
CIE 1931 CIE 1976
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x
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y
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ExampleStimulus
490
Radiant Vision Systems engineers imaging colorimeters and photometers, application software, and goniometric systems to critically evaluate light, color, and surface quality. Calibrated to simulate human visual perception, Radiant cameras perform scientific measurement of displays and illuminated components to ensure quality that accurately reflects human experience.
www.RadiantVisionSystems.com Copyright ©2019 Radiant Vision Systems LLC. All rights reserved. 2019/03/21
The Language of Light
Human Photopic Response
The human eye is not equally sensitive to wavelengths of light across the visible electromagnetic spectrum. Sensitivity of the human photopic response is given by the CIE 1931 luminosity function for a standard photopic observer (aligns with the 𝒚𝒚 color matching curve), peaking at around 555 nanometers. Thus, green wavelengths are typically brightest to the eye.
Spectral Power Distribution Every light source is defined by its unique spectral power distribution (SPD), which is the radiant power (Watts) emitted by the light source at each wavelength in the visible electromagnetic spectrum.
Units of Measurement: Photometry
Photometry vs. Radiometry
Luminance(candela per meter squared)
Luminous Intensity(candela)
Illuminance(lumens per meter squared)
Luminous Flux(lumens)
Lumen (lm)lm = cd * sr
Luminous Flux
Candela (cd)cd = lm/sr
Luminous Intensity
Lux (lm/m2)
Illuminance
cd/m2
1 cd/m2 = 1 nit
Luminance
Total output of a lightsource in all directions
Luminous flux emittedper unit solid angle
Light incident on asurface per unit area
Directional lightemitted or reflectedback from a surfaceper unit solid angle
AB
PhotometricHuman Visual Perception
RadiometricAll Radiation
LUMINOUS FLUXlumens (lm)
1 Im = 1 cd * 1 sr
RADIANT FLUXWatts (W)
LUMINOUS INTENSITYcandela (cd)1 cd = 1 lm/sr
RADIANT INTENSITYW/sr
ILLUMINANCE
LUMINANCE
IRRADIANCEW/m2
RADIANCEW/sr * m2cd/m2
1 cd/m2 = 1 nitfoot-lambert (fL)
1 fL = 1/π * cd/ft2
lux1 lx = 1 lm/m2
foot-candle (fc)1 fc = 1 lm/ft2
Total light output
Light froma direction
Light incidenton a surface
Brightness
Wavelength 𝜆𝜆 (nm)
Wavelength 𝜆𝜆 (nm)cd = candela sr = steradian lm = lumen W = Watt fc = foot-candle fL = foot-lambert
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SpectralSensitivity of
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D65 (Sunlight)
Illuminant A
LCD Blue
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HeNe Laser
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