a brief history of color y measurement in tomato
TRANSCRIPT
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A Brief History of Color yMeasurement in Tomato
David Slaughter University of California, Davisy
Window withwith Narrow Opening
Red
Glass PrismOrangeYellowGreenBlueBlueViolet
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Electromagnetic Radiation
• We use a ruler to measure length, g ,and a scale to measure mass. I ’t th t• Isn’t there a way to measure color?
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A Tale of Two CitiesRi h d HRichard Hunter & USDA
PTAB & MagnusonEngineers, Inc.
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Karl Ewald Hering(1834 1918)(1834-1918)
German Physiologist• When viewing a mixture of psychologically
pure red and pure green lights,a person will see: red• a person will see: red, green, or white,
• never yellow.y
• Hering created a theory of l i i b d th
Humancolor vision based on three opposing pairs:
• Red – Green
Eye
• Yellow – Blue, and • Black - White
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Afterimage Example• Stare for ~30s at center, then
switch to white slide.
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Richard S. HunterOptical EngineerOptical Engineer
• In 1948, he developed the Hunter L, a, b color space
– Based upon the Hering’s p gred-green, yellow-blue opponent color axes
• Hunter’s Objective:– Create a “Uniform”
color space• A one-unit change in a or
b is consistent with humanb is consistent with human perception of the amount of color change.
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Hunter L, a, b color spaceSi l i th• Since color is the principal attribute that
iconsumers use in purchasing decisions, th H t & b lthe Hunter a & b color scores were adopted b th i d tby the industry as a measure of quality.
– USDA Processed Tomato Juice Color ScoreUSDA Color = 25.715 +K1 * [a –K2*b] K1 = 0.956, K2 = 1.828
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S. R. Whipple, 1955. COLOR INSPECTION—FRESH FRUITS AND VEGETABLES
• First electronic instrument to measure tomato ripeness was developed in the early 1950’sdeveloped in the early 1950 s.
• Designed to measure the color of the surface of two halves of a t ttomato.
• Color score was the G/R ratio of green reflectance (546nm) to red reflectance (640 nm).
• Initially used to train inspectors and to determine the grade ofand to determine the grade of “doubtful” tomatoes.
• Modified in the 1970’s to measure the color of demeasure the color of de-aerated juice.
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Measuring T t RiTomato Ripeness
reen
ker
Red R
ed
• Kader & Morris, 1978
atur
e G
Bre
ak
Pin
kLi
ght R
– Used an Agtron E5-W Ma
urni
ng
• Agtron score was well correlated with ripeness
Tu
correlated with ripeness stage.
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Agtron E5-MC l i P i T t I tiColor in Processing Tomato Inspection
Red Neon &Red Neon & Green Mercury LampsLamps
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Tomato Juice Reflectance35
30 20
PTAB Color
(502
nm
)
25
(%)
26 31 33 so
rban
ce
15
20
ctan
ce 33
35 43
open
e A
bs
banc
e
10
Ref
lec
Lyco
yll A
bsor
b
70 n
m)
0
5
Chl
orop
hy (67
0 400 450 500 550 600 650 700
Wavelength (nm)
C
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INTERINTER--INSTRUMENT AGREEMENT OF AGTRON & LED INSTRUMENT AGREEMENT OF AGTRON & LED MACHINES READING A SINGLE TOMATO JUICE SAMPLEMACHINES READING A SINGLE TOMATO JUICE SAMPLE
100LEDAGTRONR
ER
E
80AGTRON
HIN
ES
HIN
ES
LO
R S
CO
LO
R S
CO
60
OF
MA
CH
OF
MA
CH
ME
CO
LM
E C
OL
20
40
RC
EN
T O
RC
EN
T O
TH
E S
AM
TH
E S
AM
0
20
PER
PER
GIV
ING
G
IVIN
G
024 25 26 27 28 29 30 31 32
COLOR SCORECOLOR SCORE
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UC Davis LED Tomato Color MeterTEMPERATURECONTROLLEDCHAMBER (110 oF)
LED LAMP ARRAYCHAMBER (110 oF)
REFLECTEDLIGHTLIGHT
DETECTOR
TOMATO JUICE
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CIE L*, a*, b* color system• “Uniform” color
systemsystem– Developed in
1976 by the yInternational Commission on Illumination
– “Improved”i f H tversion of Hunter
L, a, b color space
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Hunter L,a,b vs. CIE L*, a*, b*Hunter L,a,b vs. CIE L , a , b
HUNTER CIE1
L 10 Y L* 116 * YY
1316
a 17.5 * 1.02X Y
Yn
X 13 Y
13
a
Y
7* Y 0 85Z a* 500 * X
Xn
3
YYn
3
b 7* Y 0.85Z
Y
b* 200 * Y
13 Z
13
b 200 *
Yn
Zn
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Comparison of Color Space Uniformity
Hunter Lab CIE L*a* b*
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Albert MunsellAmerican PainterAmerican Painter
1915The original Munsell
system is almost f tl if
• Hue = name of color(e g purple green yellow)
perfectly uniform.
– (e.g., purple, green, yellow)
• Value, (or lightness)Divided into 11 equal steps– Divided into 11 equal steps
• (black=0, white = 10)
– Value ~ √ave reflectanceValue √ave. reflectance
• Chroma, purity, or saturation
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Konica Minolta CR-10
CIE L* C* H*CIE L ,C H Color Meter
• Over 13,000 peaches evaluated for maturity with the CR-10 in 2006.
• Operated by SPI p yinspectors in 2006.
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Hue Color Wheel80
45
90
8080 degrees
45
0180
270Standard Illuminant: D65Standard Illuminant: D6510 Degree Observer
UC Davis
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PTAB Color Situation• The current LED technology is
beginning to require increasedbeginning to require increased maintenance and will require replacement.
• The opportunity exists to make a significant change in how maturity/color is determined at har estdetermined at harvest.
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PTAB Color Proposal for 2012• PTAB would start
using the Minolta CR-410 Colorimeter for
l i i icolor inspection in 2012.
• CIE H* (Hue Angle) would become the
ffofficial grade.• Hunter L, a, b, and• CIE L*, a*, b* could
be provided at no
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PTAB Color vs. USDA Color
45
UC Davis 2006 Color Study Results
35
40
co
re
30
35
Co
lor
Sc
25
PTA
B C
15
20
10 20 30 40 50Hunter / USDA Processed K1*(a - K2*b) Color Score
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PTAB Color vs. Hue Angle
45
ore
UC Davis 2006 Color Study Results
35
40
Co
lor
Sc
30
35
d J
uic
e C
25
Sc
ree
ne
d
15
20
PTA
B S
10 20 30 40 50CIE H* (Hue Angle) Unscreened Juice
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PTAB Color vs. L*/a* Ratio
45
ore
UC Davis 2006 Color Study Results
35
40
Co
lor
Sc L* ≈ Green
a* ≈ Red
30
35
d J
uic
e C
L*/a* ≈ G/R = Agtron
25
Sc
ree
ne
d
15
20
PTA
B S
0 0.5 1 1.5 2 2.5 3CIE L*/a* Unscreened Juice
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2011 Prototype Flow-Through Color Grading SystemGrading System
• Blends juice sample,• Measures Color, pH,
and Soluble Solids,• Self-cleaning.