Ill do my best to help This Week C o l o r amp Images Next Week Depth Kevin Ponto Image Compositing Perry Kivolowitz This Week Optics amp Physics of Color ID: 292883
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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
) Slide3Slide4Slide5Slide6
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)Slide24Slide25
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: RGBSlide31Slide32Slide33
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)