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Color
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Colors combine by adding color spectra

Light adds to black.

Source: W. Freeman

Slide 12

Examples of additive color systems

Examples of additive color systems

CRT phosphors

multiple projectors

Slide 13

Superposition

Superposition

Additive color mixing:

The spectral power distribution of the mixture is the sum of the spectral power distributions of the components.

Figure from B. Wandell, 1996

Slide 14

Subtractive color mixing

Subtractive color mixing

Colors combine by multiplying color spectra.

Pigments remove color from incident light (white).

Source: W. Freeman

Slide 15

Examples of subtractive color systems

Examples of subtractive color systems

Printing on paper

Crayons

Photographic film

Slide 16

Today: Color

Today: Color

Measuring color

Spectral power distributions

Color mixing

Color matching experiments

Color spaces

Uniform color spaces

Perception of color

Human photoreceptors

Environmental effects, adaptation

Using color in machine vision systems

Slide 17

How to know if people perceive the same color?

How to know if people perceive the same color?

Important to reproduce color reliably

Commercial products, digital imaging/art

Only a few color names recognized widely

English ~11: black, blue, brown, grey, green, orange, pink, purple, red, white, and yellow

We need to specify numerically.

Question: What spectral radiances produce the same response from people under simple viewing conditions?

Slide 18

Color matching experiments

Color matching experiments

Goal: find out what spectral radiances produce same response in human observers.

Slide 19

Color matching experiments

Color matching experiments

Foundations of Vision, by Brian Wandell, Sinauer Assoc., 1995

After Judd & Wyszecki.

Observer adjusts weight (intensity) for primary lights (fixed SPD’s) to match appearance of test light.

Slide 20

Color matching experiments

Color matching experiments

Goal: find out what spectral radiances produce same response in human observers.

Assumption: simple viewing conditions, where we say test light alone affects perception

Ignoring additional factors for now like adaptation, complex surrounding scenes, etc.

Slide 21

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