Focal length

Vision system components
Strobecontroller
Camera
Illumination
PC system
Sample
Presentation and
sorting mechanics
PLC
Light
• Light is electromagnetic energy
conveyed through particles called
photons and though waves
• Quantum mechanics unites the two
types of behavior in the wave-particle
duality assertion
• The field concerned with the study of
light is called optics, a major research
area in modern physics.
Light properties
• The speed of light in vacuum denoted c
is 299,792,458 m/s
• The photon is a mass-less particle that
carries an energy E=h ν
• h=6.6262*10-34Js is called Planck’s
constant
• The spatial period or wavelength of the
light wave λ is found – in vacuum – by
the relation c=λν
Wavelength bands
VUV
10 nm -200 nm
Vacuum ultraviolet. Absorbed by oxygen.
UVC
200 nm – 280 nm
Very harmful to most forms of life. Absorbed by ozone layer.
UVB
280 nm – 315 nm
Over exposure causes sunburn and can damage the DNA in
the skin. May cause skin cancer. Induces vitamin D
production in the skin.
UVA
315 nm – 400 nm
Causes tanning. ―Black light‖.
Violet
380 nm – 450 nm
Blue
450 nm – 495 nm
Green
495 nm – 570 nm
Yellow
570 nm – 590 nm
Orange
590 nm – 620 nm
Red
620 nm – 780 nm
NIR
780 nm – 1400 nm
Near infrared.
SWIR
1400 nm – 3 µm
Water absorption 1450 nm
MWIR
3 µm – 8 µm
Used in heat-seeking missiles
LWIR
8 µm – 15 µm
Thermal infrared
FIR
15 µm – 1000 µm
Far infrared
Visible light
ultraviolet
(UV)
near-infrared
(NIR)
nm
200
300
400
500
600
700
800
900
1000
Illumination
• Light source
• Illumination geometry
Light sources
• Incandescence
– Light emission from hot bodies
– Continuous spectrum
– Wolfram lamps, halogen lamps, sun
• Luminescence
– Light emission from relatively cool bodies
– Flourescent lamps, CRT displays, LED
Luminescence
• Flourescence
– Instantaneous conversion of higher energy
light to lower energy light
• Phosphorescence
– Delayed conversion of higher energy light
to lower energy light
• LED
• Electroluminescence
• Cathodoluminescence
Luminosity
• Lux is a photometric term that
represents the amount of light per area
that falls on a surface
•
•
•
•
•
Bright sunlight: 100,000 lux
Cloudy day:
10,000 lux
Twilight: 5 lux
Full moon: 0.05 lux
Overcast night: 0.00005 lux
• Human eye is sensitive to this range!
Light source
• Choice based on
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–
–
–
–
–
Spectrum
Intensity
Stability
Lifetime
Heat
Cost
Light source
• Choice based on
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–
–
–
–
–
Spectrum
Intensity
Stability
Lifetime
Heat
Cost
Brightfield/darkfield
Brightfield frontlight
Darkfield frontlight
Darkfield backlight
Darkfield frontlight
Darkfield backlight
Brightfield backlight
Brightfield diffuse
backlight
• Easy to make
• Dependent on clean
surface
• Useful for count, size
shape, orientation and
transparency
Brightfield diffuse backlight
Brightfield collimated
backlight
• Dependent on clean surface
• Useful for precision
dimensional measurements
and more precise
transparency measurements
• Examples
• Direct sunlight
Brightfield collimated backlight
• Overhead projector
•Distant backlight
Light/material interaction
Specular reflection
Incoming light
Refraction
Diffuse reflection
Scattering
Absorption
Fluorescence / phosphorescence
Translucent transmission
Transparent transmission
Reflection
Source:graphics.cornell.edu
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•
•
•
Specular reflection – mirrorlike
Lambertian reflection
Combination
Gloss
BRDF
• bidirectional reflectance distribution function
• 4-dimensional function used in vision and
computer graphics
• Ratio of incident irradiance and reflected
radiance
• Units are 1/sr
Gloss
Refraction
Incoming light
1 n
n
Snell’s law
1
2
2
sin 1 2

sin  2 1
Refracted light
Air-glass-water interface
3
2.5
2
1.5
Air
1
0.5
Glass
0
-0.5
Water
-1
-1.5
-2
-2
-1
0
1
2
3
4
5
Water-glass-air interface
3
2.5
2
1.5
Water
1
0.5
Glass
0
-0.5
Air
-1
-1.5
-2
-2
-1
0
1
2
3
4
5
Carpules in water
Carpule without air
Carpule with air
Absorption
Incoming light

I0
 l 
I (l )  I  
N
N
Transmitted light I  I 0 exp    l 
Beer-Lambert’s law
l
Absorption
Interaction between light and matter
Atomic nuclei
Outer electrons
Bond vibrations
Molecular vibrations
Chromophores
• Often conjugated pi systems or metal
complexes.
• Four pyrrole rings
– Metal in the center – porphyrin e.g. heme,
chlorophyll
– No metal - phytochrome, phycobilin,
bilirubin
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•
•
•
Flavone e.g. anthocyanins
Quinone e.g. cochineal pigment
Triarylmethane
Diaryl azo
Human and animal pigment
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•
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•
•
Hemoglobins
Myoglobins
Melanins
Bilirubin
Non-pigments (for visual light)
– Water
– Collagen
– Fats
Heme
• Heme is a special ring-shaped molecule
that is found in haemoglobin and is
essential to the oxygen-carrying capacity
of blood.
• There are three biologically important
kinds of heme. The most common type is
heme b. The others are heme a and heme
c.
Heme b
Hemoglobins
• Four globular protein subunits each contaning a heme group
• Three main states
– Deoxyhemoglobin (red)
– Oxyhemoglobin (green)
– Carboxyhemoglobin (blue)
• Blood pigment
70
60
50
40
30
20
10
0
440
460
480
500
520
540
560
580
600
620
640
Myoglobins
• Muscle pigment
• Myoglobin / Oxymyoglobin
– is a single-chain protein containing a
heme group in the middle.
– It is the primary oxygen-carrying
pigment of muscle tissues
• Metmyoglobin
– is the oxidized form of the oxygencarrying protein myoglobin.
– Metmyoglobin is the cause of the
characteristic brown coloration of
meat that occurs as it ages.
– This has important consequences for
the meat packing industry, as brown
meat is less aesthetically appealing,
and in order to be sold, it is usually
downgraded and minced, at a reduced
price, resulting in a substantial
economic loss.
– Spectrum depends on pH
Source: W. Bowen, 1948.
Bilirubin
• Bilirubin is a yellow
breakdown product of heme.
• Absorps light from 390 to
500 nm with peak at 453 nm.
• Jaundice is caused by
increased levels of bilirubin
in the human body.
Melanins
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•
•
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•
•
Skin pigments
Melanin is a biopolymer pigment
that is responsible for the color of
hair, skin and eyes.
Dermal melanin is produced by
melanocytes, which are found in
the bottom layer of the epidermis.
Two distinct classes of melanin
Eumelanin is dark brown to black
and it is the most abundant
melanin in humans. Lacks the
amino acid cysteine.
Pheomelanin is red to yellow and
is found in the skin of people with
red or blonde hair. Contains
cysteine.
T Sarna, HM Swartz, The physical melanins, in "The Pigmentary System", ed. JJ
Nordlund et al., Oxfoproperties of rd University Press, 1988
Water
0.25
0.2
0.15
0.1
0.05
0
500
600
700
800
900
1000
1100
Biscuit with wet spot
Humidity detection on biscuit
Water absorption
Water has significant absorption peaks in NIR
Kilder: Indigo Systems, http://www.indigosystems.com/
Thermo Galactic Spectra Online, http://spectra.galactic.com/
Collagen
• Collagen is the main
protein of connective
tissue in animals and the
most abundant protein in
mammals.
• Along with soft keratin, it
is responsible for skin
strength and elasticity.
• In histology, the dye
methyl violet is used to
stain the collagen in
tissue samples.
Chlorophyll
•
•
•
•
Common structure of
chlorophyll α, b and
d
Chlorophyll is a green photosynthetic pigment
found in plants, algae, and cyanobacteria.
most abundant photosynthetic pigment , other
pigments are carotenoids and phaeophytin.
absorbs mostly in the blue and to a lesser extent
red portions of the electromagnetic spectrum,
hence its intense green color.
typically covers up the yellow carotenoids except
in autumn, when the chlorophyll decomposes
Carotenoids
organic pigments that are naturally occurring in plants and some
other photosynthetic organisms like algae, some fungi and bacteria,
large (35-40 carbon atoms) polyene chain, sometimes terminated by
rings, 600 known
Carotenes
un-oxidized carotenoids
Xanthophylls
Oxycarotenoid, some double
bonds have been oxidized
α-carotene
β-carotene
Lycopene
Lutein
Zeaxanthin
Astaxanthin
Carotenes
• Carotene is an orange photosynthetic
pigment important for photosynthesis.
• It is responsible for the orange colour
of the carrot and many other fruits and
vegetables.
• It contributes to photosynthesis by
transmitting the light energy it
absorbs to chlorophyll.
• It comes in two primary forms: α and
β-carotene. γ, δ and ε-carotene also
exist.
• β-carotene can be found in yellow,
orange, and green leafy fruits and
vegetables. These can be carrots,
spinach, lettuce, tomatoes, sweet
potatoes, broccoli, cantaloupe, orange,
and winter squash. As a rule of
thumb, the greater the intensity of the
color of the fruit or vegetable, the
more beta-carotene it contains. It is
also found in some animal products
such as egg yolk.
Lycopene
• Lycopene is a bright red
carotenoid pigment found in
tomatoes and other red fruits.
• Lycopene is the most common
carotenoid in the human body
and is one of the most potent
carotenoid antioxidants.
• The highest natural
concentrations of lycopene in
food are found not in
tomatoes, but in watermelon.
• Almost all dietary lycopene
comes from tomato products,
however.
Lutein
• Lutein absorbs blue light and
therefore appears yellow at low
concentrations and orange-red at
high concentrations.
• Lutein is found in green leafy
vegetables such as spinach and
kale.
• Lutein is found in the retina, and
dominant in the peripheral part
• Lutein is employed by organisms
as an antioxidant and for blue light
absorption.
Zeaxanthin
• Zeaxanthin is an orange-red carotenoid
• Like lutein found in the retina, and
dominant within the macula.
• Zeaxanthin and lutein are isomers.
• It is the pigment that gives paprika,
corn, saffron, and many other plants
products their characteristic color.
• Zeaxanthin breaks down to form
picrocrocin and safranal, which are
responsible for the taste and aroma of
saffron.
Anthocyanins
• Anthocyanins are water soluble red
and blue pigments often observed in
plants, where they serve to color
anything from fruits to the autumn
leaves.
• Act as powerful antioxidants helping
to protect the plant from UV damage.
• They can be used as a pH indicator
because they change from red in
acids to blue in bases.
• They are considered secondary
metabolites and allowed as a food
additive with E number 163.
Approximately 250 different
anthocyanins are known.
Cochineal pigment (carminic acid)
• Cochineal is an expensive
carmine dye derived from the
cochineal insect (Dactylopius
coccus).
• Current health concerns over
artificial food additives have
renewed the popularity of
cochineal dyes.
• it is used as a fabric and
cosmetics dye and as a natural
food coloring, as well as for
oil paints, pigments and
watercolours.
• When used as a food additive,
carmine is labelled as E120.
• Cochineal is one of the few
water-soluble colourants that
resist degradation with time.
Triarylmethane dyes
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•
•
•
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Methyl violet / crystal violet
Malachite green
Fuchsine
Patent blue V
Bromocresol green (BCG)
Triphenylmethane
Methyl violet
• Methyl violet is the name given to a
group of similar chemicals used as
pH indicators and dyes.
• Tetramethyl (four methyls) is known
as methyl violet 2B, and this specific
chemical finds uses in chemistry and
medicine.
• Pentamethyl (five methyls) is known
as methyl violet 6B, and is darker (in
dye form) than 2B.
• The hexamethyl (six methyls) is
known specifically as crystal violet
or methyl violet 10B. This is much
darker than 2B, and often darker
than 6B.
• The main use of methyl violet (by
sheer volume used worldwide) is to
dye textiles purple and give deep
violet colors in paints and printing
ink.
Malachite green
•
•
•
•
Malachite green is used to dye
materials like silk, leather, and
paper. The chemical known as
malachite green does not actually
contain the mineral malachite —
the name comes from the
similarity of color.
Malachite green is used as a
biological stain for microscopic
analysis of cell and tissue
samples.
Malachite green is also found to
be especially active against the
fungus Saprolegnia, which infects
fish eggs in commercial
aquaculture. It is also a very
popular treatment against Ich in
freshwater aquaria.
The use of this substance has been
banned in many countries due to
its suspected carcinogenicity
effect.
Fuchsine
• Fuchsine, fuchsin, rosanilin, or
rosaniline hydrochloride is a
magenta dye.
• It becomes magenta when
dissolved in water; as a solid,
it forms dark green crystals.
• As well as dying textiles,
fuchsine is used to stain
bacteria and sometimes as a
disinfectant.
Patent blue V
• Patent Blue V, also called
Food Blue 5 or Sulphan Blue,
is a dark bluish synthetic dye
used as a food coloring.
• As a food additive, it has E
number E131.
• It is not widely used, but can
be found in e.g. Scotch eggs.
Patent Blue V is banned as a
food dye in Australia, USA,
and Norway.
• In medicine, Patent Blue V is
used in lymphangiography as a
dye to color lymph vessels.
Indigo
• Indigo is an important dye
with a distinctive blue color.
• The natural dye comes from
several species of plant, but
nearly all indigo produced
today is synthetic.
• Among other uses, it is used in
the production of denim cloth
for blue jeans.
• Also name for a color between
blue and violet, 420-440 nm.
Azo dyes
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•
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Para red
Direct blue 2B
Tartrazine, E102
Sunset yellow, E110
Azorubine, E122, red
Trypan blue, dead tissue
dye
• Congo red