Principles of Light and Color Measurement

Home , Colorimetry

PRINCIPLES OF LIGHT AND COLOR MEASUREMENT Presented By Shannon Roberts | June 26, 2018 Radiant Vision Systems | A Konica Minolta Company Light & Color Automated Visual Inspection Global Support TODAY’S AGENDA

• Light & Color Theory • What is light? • Quantifying Human Visual Perception • Photometry and colorimetry • CIE tristimulus curves • How to calculate CIE-matched color values • Light & Color Measurement Systems • Optical metrology devices for light measurement • Benefits of CCD imaging technology • Example Applications

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Light is made of photons: an electric field combined with a magnetic field, moving through space.

Gamma Rays Microwaves < 0.01nm  UV IR ➔ 0.0003 - 1mRadio Waves X-Rays 10 - 390nm 700nm - 0.0003m >1m 0.01 - 10nm

Ultraviolet Infrared (UV) Visible Light (IR)

Visible light is a tiny range of the electromagnetic spectrum to which our eyes respond.

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Every light source is defined by its unique Spectral Power Distribution (SPD) SPD = Light power (Watts) at each wavelength

D65 (Sunlight) Illuminant A LCD Blue LED Red HeNe Laser

390 430 470 510 550 590 630 670 710 Wavelength λ (nm)

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The human eye is sensitive to and

The human eye has three types of cones (S, M, and L) that are each sensitive to a range of wavelengths of light.

A cone cannot detect the individual light wavelengths. 2⁰ Cone Response Rather, a cone sees the sum L total of light from all wavelengths under that cone’s M spectral sensitivity curve. S

350 450 550 650 750

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Metamerism Different in spectral power All of these light sources distributions that appear as the appear ‘white’ to the eye same color to the human eye, but do not actually match.

Sunlight LED

Incandescent

CFL

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Would you design and test your products against values that do not match human visual perception?

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Photometry is the science of the measurement of as Visible Light perceived by the human eye. • Visible light spectrum only 2⁰ Cone Response

L Colorimetry is the science of the measurement of color as M S perceived by the human eye. Power

• How 3 cones in the human eye 350 450 550 650 750 respond (in terms of power) to Wavelength λ different wavelengths of light

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COLOR

A mathematical language is needed to quantify the brightness and the variations of color that are perceived by a standard human observer, so as to be used for measurement.

✓ Human photopic response at each ✓ Formula to quantify human eye’s wavelength. response to each SPD. ✓ Quantify light based on spatial ✓ Mathematical model to define area and direction of travel. visible colors (CIE color chart).

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SPD of Sunlight

The spectral limit of average human sight is: 380 – 830nm

Maximum luminous efficacy is: @ 555 nm (green) Spectral Sensitivity of

the Human Eye

390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650 660 670 680 690 700 Wavelength λ (nm)

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Mathematical way to determine human perception of color and brightness from different SPDs

풛ത

풚ഥ 풙ഥ

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Maxwell knew the additive nature of light in which mixing three primaries in equal proportions creates white. To test the eye’s response to colors, Maxwell presented various colored samples to an observer. The observer then adjusted the brightness levels of two primaries shining on the target until the resulting white matched a white target.

Red (615 nm)

Green (525 nm)

Blue (445 nm) Color Sample

White Target

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2.0 풛ത

1.5 풚ഥ 풙ഥ 1.0

0.5

0.0 380 430 480 530 580 630 680 730 780

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• Three curves multiply the SPD, and the integrals are Tristimulus X, Y, and Z. • Combinations of X, Y, and Z define color in spatial context.

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2.0 SPD 1 (Blue LED) 풙ഥ 1.5 풚ഥ 1.0 풛ത Shade of Blue 0.5

0.0 380 430 480 530 580 630 680 730 780

↓X ↓↓Y Cx = = 푠푚푎푙푙 Cy = = 푠푚푎푙푙푒푟 퐂퐱 > 퐂퐲 ↓X+↓↓Y+↑↑Z ↓X+↓↓Y+↑↑Z

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2.0 SPD 2 (Green LED) 풙ഥ 1.5 풚ഥ

1.0 풛ത Shade of Green

0.5

0.0 380 430 480 530 580 630 680 730 780

↓X ↑↑Y Cx = = 푠푚푎푙푙 Cy = = 푙푎푟푔푒 퐂퐱 < 퐂퐲 ↓X+↑↑Y+↓↓Z ↓X+↑↑Y+↓↓Z

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2.0 SPD 3 (Red LED) 풙ഥ 1.5 풚ഥ

Shade of Red 1.0 풛ത

0.5

0.0 380 430 480 530 580 630 680 730 780

↑↑X ↑Y Cx = = 푙푎푟푔푒 Cy = = 푚푒푑푖푢푚 퐂퐱 > 퐂퐲 ↑↑X+↑Y+↓↓Z ↑↑X+↑Y+↓↓Z

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2.0 SPD 4 (Sunlight) 풙ഥ 1.5 Mostly White 풚ഥ 1.0 풛ത

0.5

0.0 380 430 480 530 580 630 680 730 780

↑↑X ↑↑Y Cx = = 푚푒푑푖푢푚 Cy = = 푚푒푑푖푢푚 퐂퐱 = 퐂퐲 ↑↑X+↑↑Y+↑↑Z ↑↑X+↑↑Y+↑↑Z

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CIE Color Space Every visible color to the human eye.

Colors defined by coordinates (Cx, Cy) G

Color Gamut Producible colors using a device’s R primaries (a tristimulus color system via machine). B • Using a linear combination of primary colors (R,G, B) that occur at each y corner of the triangle R + G + B x

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A region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse.

*Ellipses at left are 10x their actual size

Images source: Wikipedia.org

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A region on a chromaticity diagram which contains all colors which are indistinguishable, to the average human eye, from the color at the center of the ellipse.

*Ellipses at left are 10x their actual size

Images source: Wikipedia.org

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Luminous Luminous Flux Illuminance Luminance Intensity

Amount of light Measure of the total Amount of light The amount of light emitted from a light luminous flux of a emitted in the range incident on a surface source or reflected light source by of a three- per unit area back from a surface in integrating its dimensional angular Illuminance a given direction intensity over its span (lm/m2 or lux) angular span Candela per meter Candela (cd) squared (cd/m2) Lumen (lm)

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Light & color measurement systems aim to replicate and quantify human visual perception of: color

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Light measurements systems include: ▪ Illuminance Meters ▪ Luminance Meters ▪ Spot Colorimeters ▪ Spectroradiometers ▪ Imaging Colorimeters

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Spot Imaging

Colorimeter Spectrometer

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Spot Imaging

Colorimeter Spectrometer

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풛ത

풚ഥ 풙ഥ

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Y-bar filter is used to accurately match the human photopic response to brightness.

Spectral Sensitivity of the Human Eye

390 430 470 510 550 590 630 670 710 750 790 830

Wavelength λ (nm)

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2.0 풛 ̅ Y-bar filter is used to accurately match the human photopic response to brightness.

1.5

풚 ̅ 풙 ̅̅ 1.0

0.5

0.0 380 430 480 530 580 630 680 730 780

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Spot Imaging

Colorimeter Spectrometer

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Spot Imaging

3 1 2 6 4 9

7 8

Colorimeter Spectrometer

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CCD-based imagers excel at: ▪ Contextual evaluation ▪ Measuring uniformity ▪ Identifying defects (pixels, blobs, artifacts) ▪ Measuring multiple spots (LED arrays) ▪ Rapid collection of multiple data points ▪ Advanced analysis

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Resolution – The number of pixels in an image translates into spatial resolution, which determines the ability to distinguish fine detail within an image.

1MP Resolution 29MP Resolution

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Higher-resolution CCD imaging enables: ▪ Easier detection of contrast variations ▪ Pixel-level defect detection and correction (displays) ▪ Detection of subtle defects

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Dynamic range: The ratio between the maximum possible signal and the “noise” level at the minimum signal of one

measurement WHAT WE SEE: SIGNAL Measured in dB (decibels)

▪ Calculates a signal-to-noise ratio (SNR) NOISE

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Large pixels have a greater storage capacity (electrons per pixel)

▪ This is called a pixel’s well capacity

The largest possible signal is directly proportional to a pixel’s full well capacity

Well Capacity has the strongest impact on Signal to Noise

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Original Image 217 216 215 214 213 212 211 Δ0 Δ1 Δ2 Δ3 Δ4 Δ5 Δ6 O% O.4% O.8% 1.2% 1.6% 2.0% 2.4%

Small Amount of Noise Added

A Little More Noise Added

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High Resolution Low Resolution With Noise Low Noise Radiant Image High Resolution & Low Noise Similar Level of Detail

➢ Noise lowers effective image resolution. ➢ Higher resolution offers little benefit if the image has noise.

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1. Electronically-controlled lens for any working distance 2. Precision tristimulus and neutral density filters

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Z Y X Lens Xb Each proprietary Radiant color filter precisely matches a CIE tristimulus curve; which allows for NIST traceable results.

Color images are a combination of images taken through each filter.

Color Filter Wheel ND Filter Wheel Greyscale CCD ✓ Precision made filters ✓ Bright Lights ✓ Scientific Grade with Large Pixels ❑ Xb Filter option ✓ Modulated Lights ✓ Cooled to 5⁰C & Precision Calibrated ❑ Radiometric option ❑ ND3 option ❑ 29-megapixel option

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1. Electronically-controlled lens for any working distance 4 2. Precision tristimulus and neutral density filters 3 3. Cooled CCDs reduce thermal noise and improve accuracy 4. Scientific-grade CCDs simultaneously capture 1 millions of data points

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Displays Backlit Symbols Lighting

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Brightness Color Offset Non-Uniformity Pixel & Line Offset (Color & Defects Brightness)

Light Mura Image Sticking View Angle Leakage

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Auto-detection of dark & bright blobs (mura)

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Contrasting anomalies like dead pixels, particles, and lines

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View Angle OLED Correction AR/VR Headsets

Head-up Displays IR Sensing Anti-Glare Layers

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(Above) Luminance and CIE color coordinates of a point on a panel under analysis.

(Right) Luminance and CIE color coordinates for all backlit symbols on panel.

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Lighting design file generation (IES) using luminous Light source evaluation using rotating imaging intensity distribution. goniometer to measure light from all angles in lab.

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✓ Imaging photometers and colorimeters have significant advantages for light & color and precise spatial measurement.

✓ By quantifying human visual perception, process improvements can be driven to ensure quality that accurately reflects customer experience.

✓ Imaging photometers and colorimeters meet a range of measurement applications; one system can meet multiple needs.

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