Any questions about the current assignment? - PowerPoint Presentation

Slide1

Any questions about the current assignment?

(I’ll do my best to help!)Slide2

This Week:

C

o

l

o

r

& Images

Next Week:

Depth

(Kevin Ponto)

Image Compositing (Perry

Kivolowitz

) Slide3
Slide4
Slide5
Slide6

This Week

Optics & Physics of Color

Color in DisplaysHow graphics people talk about colorImage Compression & Color ProfilesMisc (time permitting)Slide7

This Week

Optics & Physics of Color

Color in DisplaysHow graphics people talk about colorImage Compression & Color ProfilesMisc (time permitting)Slide8

Please

ask questions if you have them!!!Slide9

What is

C

olor?Slide10

“Color consists of the characteristics of light other than spatial and temporal

inhomogeneities

; light being that aspect of radiant energy of which a human observer is aware through the visual sensations which arise from the stimulation of the eye.”--OSA Committee on ColorimetryWhat is Color?Slide11

What is

C

olor?Both a physical quantity of light A wavelengthand a visual sensation.A perceptionSlide12

What is

C

olor?Both a physical quantity of light A wavelengthand a visual sensation.A perceptionSlide13

Color as a

wavelength

Light SourceSlide14

Color as a

wavelength

Light SourceLightSlide15

Color as a

wavelength

Light Source

Light is composed of photonsSlide16

Color as a

wavelength

Light Source

Photons have specific wavelengthsSlide17

Electromagnetic Spectrum:

All wavelengths of light

Visible Light (390-700nm):Light we can see (colors)Sun emits entire spectrumSlide18

Visible Light

Short Wavelength

Higher EnergyLong WavelengthLower EnergyWhite = All Visible WavelengthsBlack = No Visible WavelengthsSlide19

What is

C

olor?Both a physical quantity of light A wavelengthand a visual sensation.A perceptionSlide20

Vision is measuring visible light

Short Wavelength

Higher EnergyLong WavelengthLower EnergySlide21

Vision is measuring visible lightSlide22

Retina is a bunch of sensors

Rods

ConesSlide23

Rods:

Shades of grey

Sensitive to low-light Densest in the peripheryCones: Responsible for color vision Long (L), Medium (M), Short (S) Densest in the fovea (center)Slide24
Slide25

No blue cones

Cone Distribution

From M. FairchildSlide26

Measuring Visible Light

Short Wavelength

Higher EnergyLong WavelengthLower EnergySMRodLSlide27

Trichromacy

Color perception is a function of the relative stimulation of the three cone types (L, M, & S)

In graphics, this isRed, Green, & Blue!Slide28

L Cones

S

ConesNormalSlide29

This Week

Optics & Physics of Color

Color in DisplaysHow graphics people talk about colorColor SpacesImage Compression & Color ProfilesMisc (time permitting)Slide30

Blue

Red

Green“Cube” based on three primary colorsWhat (most) monitors useAttempt to stimulate each cone in isolationComputer Graphics: RGBSlide31
Slide32
Slide33

Monitors RGB

LCD

CRTFrom M. StoneSlide34

CRT MonitorSlide35

LCD MonitorSlide36

Two properties of monitors define what colors they produce

Gamma

maps intensity of light emittedGamut maps the space of possible colors generated by a displaySlide37

The amount of light emitted from a monitor is nonlinear

pixels

intensitySlide38

Gamma

parameter makes light intensity linearSlide39

Original

Small Gamma

Large GammaSlide40

Gamuts

Visible colors (grey) versus colors supported by the display (triangle)

Gamut: Colors that can be created using the three display primaries Slide41

Gamut Mapping

Moving an image from one devices’ gamut to anotherSlide42

How could you do gamut mapping when moving to a smaller gamut (e.g. less available colors)?Slide43

Clip

colors outside of the new gamut

Center the new colors with the old and then clipScale everything down towards the middle of the gamutScale just the primaries down towards the gamutOriginalSlide44

This Week

Optics & Physics of Color

Color in DisplaysHow graphics people talk about colorImage Compression & Color ProfilesMisc (time permitting)Slide45

Who talks about color?

Graphics people

PhysicistsPsychologistsArtists & DesignersSlide46

Physicists

Short Wavelength

Higher EnergyLong WavelengthLower EnergySlide47

Physicists: Spectral Distribution

From Stone’s

A Field Guide to Digital ColorSlide48

Blue

Red

Green“Cube” based on three primary colorsWhat (most) monitors useAttempt to stimulate each cone in isolationComputer Graphics: RGBSlide49

Why might choosing primaries that target cones (L, M, S) not work?Slide50

Different

cones respond to the

same wavelengthsMLSlide51

Different

cones respond to the

same wavelengthsMLSlide52

Metamerism

Colors with

different spectral distributions appear the sameFrom Stone’s A Field Guide to Digital ColorSlide53

Different

cones respond to the

same wavelengthsMLSlide54

How could we fix this?Slide55

Negative light

would need to shut down responses from a particular cone

MLImaginary Primaries!Slide56

Negative light isn’t a thing…

Hence, imaginary

Instead, psychologists look at how the brain interprets colorSlide57

An aside: aspects of color

Luminance:

How light something isSaturation: How colorful something isHue: What color something isSlide58

Psychologists: CIE XYZ

Intended to reflect perceptions based on cone primaries

Y: LightnessXZ: Hue/saturation planeFrom Stone’s A Field Guide to Digital ColorSlide59

Opponent Color

From M. StoneSlide60

CIELAB

L: Lightness

AB: Hue/saturation plane based on opponent responsesEuclidean distance is meaningful! Slide61

CIELCh

(Polar LAB)

Lightness

Hue

Colorfulness

Unique black and white

Uniform differences

Perception & design

From M. StoneSlide62

Psychologists’ way of talking about color is perceptually accurate, but difficult to understand & implement.Slide63

Artists

Think in terms of lightness/hue/saturation

Munsell Look-up TablesFrom Gretag-MacbethSlide64

HSV/HSLSlide65

Color Blending

Physical Pigments

CMYKMonitors & LightSlide66

Thursday

Optics & Physics of Color

Color in DisplaysHow graphics people talk about colorImage Compression & Color ProfilesMisc (time permitting)