Embed Size (px)
Citation preview
1
color
rein van den boomgaard
2
color images
3
color images
4
color images
5
the physics of color
Light is electromagnetic energy
6
spectral color vs object color
Lamp
objectcolor
beamcolor
7
light source
sensor
object
object color
l(λ)
c (λ)
l(λ)c (λ)
8
object color
e(λ )=m l(λ) c (λ) variation due to geometry
9
photoreceptors in the retina
10
photoreceptors in the retina
In the retina photoreceptors measure the light
11
photoreceptors in the retina
Rodsfor low light levels (only B/W)
Conesfor normal light levels
for color detectionThree types of cones sensitive to different wavelenghts
12
sensitivity of the cones
300 400 500 600 700 800 9000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
L
M
S
13
example
14
'calculate' SML
S=∫e (λ )s s(λ)d λ
M=∫e (λ)sm(λ)d λ
L=∫e (λ)sl(λ)d λ
15
color blindness (see Wikipedia)
Protanopia: Lacking the long-wavelength sensitive retinal cones, those with this condition are unable to distinguish between colors in the green-yellow-red section of the spectrum. They have a neutral point at a wavelength of 492 nmthat is, they cannot discriminate light of this wavelength from white.
Deuteranopia: Lacking the medium-wavelength cones, those affected are again unable to distinguish between colors in the green-yellow-red section of the spectrum. Their neutral point is at a slightly longer wavelength, 498 nm.
16
color blindness
about 10 percent of males is colorblindit is wise to check your colors in design to see whether
colorblind people can distinguish the important colors
http://colorfilter.wickline.org/
17
colorimetrie
De SML gevoeligheidscurves zijn pas enige tientallen jaren met enige nauwkeurigheid bekend.
Kleursystemen zijn veel ouder
Colormatching: gebruik menselijk oog als meetinstrument
om zoveel mogelijk de subjectiviteit van de menselijke beoordeling uit te sluiten 'vragen' we de mens alleen over gelijkheid van kleuren te oordelen
18
a 1 1pa 2 2pa 3 3p
t
color matching experiment
19
rgb color matching functions
20
xyz color matching matrix
21
XYZ color system
22
chromaticity coordinates
23
xy – chromaticity diagram
24
color reproduction
Faithfull color reproduction is possible using any three colorimetric independent light sources.
a1
a2
a3
25
color reproduction
26
color reproduction
a1a2 a3
27
color gamut
28
color gamut
29
different color gamuts
30
RGB cube
31
RGB to XYZ
32
the RGB color cube
33
the RGB color cube
34
the RGB color cube
35
color camera’s
a color CCD camera is either:3 ‘parallel’ camera’s, one for Red, one for Green and one
for Blue, or
3 ‘interwoven’ camera’s (Red, Green and Blue pixels mixed on the CCD: this is a lot like the human retina)
36
3 CCD color camera
37
Bayer color mosaic
38
finding Waldo
39
punctal COLOR observations
40
skin color
41
skin pixels, not-skin pixelsRGB - space versus rgb - space
skin color
42
skin color
43
hue – saturation – value
hue: the dominant color (red/green/blue/...)
saturation: pure color (saturation = 1) or almost colorless (mixed with grey: saturation = 0)
value: the intensity (what you would see with a black and white camera)
44
hue – saturation – value
45
hue – saturation – value
BB
GG
RR
HH SS
46
hue
BB
GG
RR
HH SS
47
color (hue) histogram
