4. 輝度(cd/m2)

七、色度與CIE色度座標
色度座標之測定
色度與
色度座標之測定之測定-發光學術語與基本概念
1. 輻射束 (joule/sec)
2. 光束/光通量
光束 光通量(lumen)
光通量
3. 光度 (Candela, cd)
4. 輝度 (cd/m2)
5. 照度 (Lux)
6. 光束發散度 (radlux)
7. 反射率 (reflectivity)
8. 電光源效率 (power eff.)
發光光度學常用單位與定義
1.輻射束
輻射束 Φ (Radiant flux, 單位為焦耳/秒
單位為焦耳 秒 Joule/sec)
電磁波於單位時間內所傳播的輻射能量 (J/sec)或
或 Watt
F = KΦ
Φ (K為視覺度
為視覺度,其大小依波長而異
為視覺度 其大小依波長而異,其最大值為
其大小依波長而異 其最大值為 100,
F為光束
為光束
2.光束
光束/光通量
光束 光通量 (luminous, 單位:流明
單位 流明 Lumen)
光源所發出的總光量或單位時間內所通過的光量,
光源所發出的總光量或單位時間內所通過的光量
可用照度計加以量測
3.光度
光度I
單位為燭光 Cd, candela)
光度 (Luminous intensity,單位為燭光
一光源在冇一方向所發出光的強度稱之為光度，假設dω
為一微小立體角，其包含的光束為dF，則此光源箭頭方
向的光度(I)為
I = 光束/立體角
ω
光束 立體角=
立體角 dF/dω
所以 dF = I dω
ω
此立體角內所有方向之光度I 則為 I = dF/dω
ω
對均勻的點光源而言，
πI (單位為燭光
單位為燭光)
對均勻的點光源而言，F (lumen) = 4π
單位為燭光
其中4π 為總立體角
點光源
I dω
4. 輝度 L (Brightness, 單位為nit
單位為 或nt = cd/m2 或stilb (sb), sb = cd/m2
由一特定的光源發出強度相同時，
由一特定的光源發出強度相同時，其發光的面積越大者，
其發光的面積越大者，則其輝度值
越小。
越小。
某一截面的輝度 L (nit)值
值，為其該方向的光度值 I (cd)，
，以該截面的
視面積A
除得之值，
表示
視面積 (m2)除得之值
除得之值， 以L表示
L = I (cd)/A (m2) = nit or cd/m2 or stilb
各種光源的輝度值 (nit)
太陽 165 x 107
月亮 26 x 102
蠟燭 1 x 104
藍空 8 x 103
水銀燈 14 x 104
日光燈 6x 103-1x 104
納氣燈 (200W) 8 x104
5. 照度 E (Illumination Intensity,單位為
單位為Lux
勒克斯)
單位為
勒克斯
(Spectra colorimeter)
380-780 nm
(Lux meter)
(color analyzer) 測量輝度值與色度值
0.2 – 999 cd/m2
彩色分析儀彩色分析儀- 輝亮度(
輝亮度(cd/m2)、對比度、
對比度、閃爍、
閃爍、色度(x,y)
色度(x,y)值之測定
(x,y)值之測定
Anatomy of Human Eyes
3 視網膜
玻璃體
.7 瞳孔
4 Rods
2角膜
角膜
5 Cones
玻璃體
視神經
1 虹膜
6 水晶體
Cones (解析度高有色彩分析能力
解析度高有色彩分析能力)
感光度高對低照暗輻極敏感)
解析度高有色彩分析能力 and rods (感光度高對低照暗輻極敏感
感光度高對低照暗輻極敏感
The distribution of cones and rods in the retina and
where the retina is most sensitive to light (blue graph).
Luminosity response of eyes
– yellow-green is brighter or stronger response to eyes, than R and B.
視網膜(3
視網膜 types of cones)
Human eye
Tristimulus method
Problems with difference between
individuals and memory characteristics
3 sensors
Small size and portability, used for color
difference measurements and QC inspection
Spectral sensors
Spectrophotometric method
Providing high accuracy and the ability to
measure absolute color, used in research area
Chromatic Adaptation（
（色彩的適應性 ）
Chromatic Adaptation (色彩的適應性
色彩的適應性 )
Block diagram of basic components of a spectrophotometer
Inventor: Brace DeWitt; In 1935 Arthur Cobb Hardy received a patent for the spectrophotometer.
A spectrophotometer is a device used to measure the intensity of radiation absorbed at
different wavelengths by looking at the spectral reflectance, transmittance or emission.
The spectral luminous efficiency curves
1942與
與1951年根據亮
年根據亮、
對200多
多位觀察者視覺的測定結果，
年根據亮、暗適應條件下，
暗適應條件下， CIE對
位觀察者視覺的測定結果，分別推薦了
標準的明視覺
峰值555
nm，
，光譜光效能最高值K
λ)= 683 lm/W)與暗視覺
與暗視覺(V’(λ
λ);峰值
峰值
標準的明視覺(V(λ
視覺 λ):峰值
峰值
光譜光效能最高值 m(λ
與暗視覺
S1
507 nm，
，光譜光效能最高值 Km’(λ
λ) 1699= lm/W)函數曲線
函數曲線。
函數曲線。
函數曲線的標準化與K
λ)、
、Km’(λ
λ)值測定
值測定，
函數曲線的標準化與 m(λ
值測定，在全球光度量測上有了統一的基礎!
在全球光度量測上有了統一的基礎
Scotopic (low light) vision system V’(λ
λ): Driven by rod cells; unable to differentiate
different λ’s; provides no saensation of colors
Phototopic (daytime) vision system V(λ
λ) : Driven by cone cells; can differentiate
different λ’s: ctreate sensation of colors
視覺函數V(λ
λ) 曲線
視覺函數 λ), V’(λ
507 nm
555 nm
投影片 18
S1
Steven, 2006/5/8
Color perception by eye and brain
The human retina has three kinds of cones. The response of each type of cone as
a function of l of the incident light.
The sensitivity between 700-800 nm is very low, only 380-700 nm is shown.
RGB-cones for the RED-GREEN-BLUE sensitivity also
called as the SML-cones for Short, Medium and Long wavelengths.
The RED sensitivity
for the R-cones
or the L-cones
The GREEN sensitivity
for the G-cones
or the M-cones
The BLUE sensitivity
for the B-cones
or the S-cones
The human retina has three kinds of cones. The response of each
type of cone as a function of λ of the incident light.
440
z
545 580
y
x
An Observer is a person or thing that observes. The sensitivity of each
individual's Eye is slightly different; even for people considered to
have "normal color vision" , there may be some bias toward red and blue.
Also, person's eyesight generally changes with age. Because of these factors,
colors will appear differently to each observer.
Standard Observer
In 1931, the CIE originally defined the standard Observer using a 2o field
of view, hence the name "2oStandard Observer"
In 1964, the CIE defined an additional standard Observer, this time based
upon a 10o field of view and this is referred to as the "10o Supplementary
Standard Observer“
The 2o standard Observer should be used for viewing angles of 1o to 4o
and the 10o supplementary standard Observer should be used for viewing
angles of more than 4o.
七、色度與CIE色度座標
色度座標之測定
色度與
色度座標之測定
- specification and measurements of colors
1. The human eyes
2. The nature of chroma (色度
色度)
色度
3. The standard observers (標準觀查者
標準觀查者)
標準觀查者
4. Color space (色域
色域)
色域
- chromaticity diagram/coordinates
- color temperature
http://home.wanadoo.nl/paulschils/10.02.htm
CIE 1931 RGB r10(λ
λ), g10(λ
λ), b10(λ
λ) color matching functions
The r10(λ
λ) curve is more than 3 times higher than the others because "red"
wavelengths have low luminance and moderate tinting strength, so more of the
R primary must be used to match the high luminance of the G primary and the
high tinting strength of the B primary.
Color-matching functions of the CIE
Standard Observer based on matching
stimuli of wavelengths
700.0 (R), 546.1(G), and 435.8 (B) nm.
C ≡ R (R ) + G ( G ) + B(B )
C ( 520 nm ) + R ( R ) ≡ G ( G ) + B ( B )
C ≡ − R (R ) + G ( G ) + B(B )
CIE 1931 XYZ standard Color matching functions
for 2°° observer
The three CIE color matching functions (CMFs) are called X, , Y,
Y and z
Z, and for
practical color matching and display applications. These can be treated as if they
were the spectral response curves for the cone-receptors in the human eye.
While it is convenient to think of X, Y and Z as red, green and blue, owing to
their wide band and substantial overlap (especially of X and Y), this is a crude
approximation. XYZ – tristimulus values; x, y, z : tristimulus response of
RGB
CIE Chromaticity Diagram (色品圖；
色品圖；色度座標圖)
This is an international standard for primary colors established in
1931. It allows all other colors to be defined as weighted sum of the
three "primary" colors. 1)There are no real three colors that can be
combined to give all possible colors. 2) Therefore, the standard
"primary" colors established by CIE don't correspond to real colors.
So the 3 "primary" colors are the virtual colors A, B, and C. Then
for a given real color, its components with respect to the
primaries are as follows:
x = A/(A+B+C)
y = B/(A+B+C)
z = C/(A+B+C)
Since x + y + z = 1, if x and y are known then z can be determined.
The CIE diagram is a plot of x vs. y for all visible colors
The CIE Color Space
• The CIE system characterizes
colors
by
a
luminance
parameter Y and two color
coordinates x and y which
specify the point on the
chromaticity diagram.
• the parameters are based on
spectral
power
the
distribution of the light
emitted from a colored object
and are factored by sensitivity
curves which have been
measured for the human eye.
CIE-1931 Chromaticity Coordinates as the Cartesian Coordinates used to
define color in the CIE color space. They are designated as x, y and z and are
the ratios of each of the tristimulus values X,Y and Z in relation to the sum of
the three.
z=1-(x+y)
CIE-1976 U.C.S. CHROMATICITY DIAGRAM
CIE-1976 Chromaticity Coordinates used to define color in the CIE color
space. They are designated as u' and v' u’ = u-uo v’ = v-vo
CIE色度座標圖
色度座標圖
色調
CIE(Commission Internationale de l'Éclairage )
x
x
飽和度
Mixing of Colors of light
Sight of human Eyes
Additive mixing
Mixing of Colors of pigments
Mixing paint pigments
Simple subtractive mixing
MAGENTA, YELLOW and CYAN
pigment of proper intensities are
known as ”The Subtractive Primary
Colors”.
Additive mixing
Additive color mixtures
are
always
lighter
than
any
of
the
individual components
!
Simple subtractive mixing
Subtractive color mixtures
are always darker than the
components separately.
Approximate color regions on CIE chromaticity
diagram (after Fortner, P. 5, Scien Tech J. 1996)
The C.I.E. Chromaticity Diagram
The
boundary
represents maximum
saturation
for
the
spectral colors, and
the diagram forms the
boundary
of
all
perceivable hues (色調
色調).
色調
Y2SiO5
P22 CRT phosphors
ZnS:Ag (blue)
YAG
(Zn,Cd)S:Ag (green)
Y2O3:Eu3+ (red)
Y2SiO5
YAG
YAG
The boundary of x, y diagram is bounded by the values of
monochromatic light, any color in terms of (x, y)
Tristimulus Fuilters Used in Defining Colors
The energy of any spectral curve:
ER = Σ(Idλ
λ) R
EG = Σ(Idλ
λ) G
EB = Σ(Idλ
λ) B
1. Take the spectral curves.
2. Multiplying by the overlap of each tristimulus curve.
3. We obtain Tristimulus Values.
Emittance
Reflective (scattering)
X = xΣ
ΣIRdλ
λ
X = xΣ
Σ IRRRdλ
λ
Y = yΣ
ΣIGdλ
λ
Y = yΣ
Σ IGRGdλ
λ
Z = zΣ
ΣIBdλ
λ
Z = z Σ IBRBdλ
λ
x, y, z are the stimulus response of red, green, and blue；
；
而X, Y, Z則稱之為
則稱之為tristimulus
values
則稱之為
Because each color gives a set of tristimulus values 但
each set之間並未有相互
之間並未有相互correlation
之間並未有相互
因為 IR ≠ IG ≠ IB (RGB spectral energy are not equal)
因此有必要將三刺激值 tristimulus values (XYZ) normalized，
並且定義一套 chromaticity coordinates (x, y, z)
Chromaticity coordinates x, y, z 可以定義為
x = X/(X+Y+Z)
y = Y/(X+Y+Z)
z = Z/(X+Y+Z)
其中 x + y + z = 1
(x, y, z) 稱之為色(度
座標 (chromaticity coordinates)
稱之為色 度)座標
Measuring Emissive Colors 之過程
(如何將光譜轉換成色度座標?
如何將光譜轉換成色度座標?)
1) Obtain emission spectrum (利用
利用spectrofluorimeter)
利用
2) 利用 energy of RGB spectral curve:
λ) R
ER = Σ(Idλ
EG = Σ(Idλ
λ) G
EB = Σ(Idλ
λ) B
等公式，
λ)積分，
三原色色光之能量
等公式，將(Idλ
積分，以獲得RGB
以獲得
λ
3) 因為 X = xΣ
ΣIRdλ
Y = yΣ
ΣIGdλ
λ
Z = zΣ
ΣIBdλ
λ
故可以利用
x=
X
X+Y+Z
y=
Y
X+Y+Z
Z
z=
X+Y+Z
求取(
上述 x, y, and z 為the stimulus response of red,
求取(x,y)
x,y)值
green, and blue
4) Draw vertical lines on each color function to obtain
“weighted functions” to calculate chromaticity
coordinates
x: 550-650 nm y: 510-600 nm z: 420-480 nm
One would have a set of lines whose spacing was
inversely proportional to peak height.
標準光源A The radiation emitted from an incandescent
tungsten filament operating at 3250K
標準光源 C
Daylight.
The northern skylight
at 11:30a.m. at
Greenwich, England
on Oct. 31, 1931.
Values Related to Color Specification
Comparison of Energy Distribution of Different Light Sources
An
approximation
of
noon
sunlight having a correlated color
temperature of approximately
4874 K and obtained by a
combination Light Source (A) and
a special filter.
2856 K
Light source B
Light source A
6504 K
6774 K
Light source C
D65
Any hue (色彩色調
色彩色調)
色彩色調 can be specified by (x, y). Illuminants can also be
specified.
標準光源
A: (0.420, 0.395)
B: (0.360, 0.360)
C: (0.315, 0.320)
Color Constancy
Different illuminants (shown in the above diagrams) have different
spectral energy distribution and therefore a given object can only reflect
different energy distribution.
Colored surfaces appear to retain their approximate daylight appearance
even when viewed under LIGHT SOURCES that differ markedly from
daylight.
Radiation Curve of Black body
任何溫度下，
body)。
。1900
任何溫度下，能完全吸收任何入射波長輻射的熱輻射體，
能完全吸收任何入射波長輻射的熱輻射體，稱之為黑體(black
稱之為黑體
年Planck提出光量子理論
提出光量子理論，
提出光量子理論，導出黑體輻射公式 (Planck equation)
– 處於絕對溫度T之黑體
λ5)(1/ec’/λλT-1)
處於絕對溫度 之黑體，
之黑體，在波長λ
在波長λ處的光譜能量分布為 Pλ = (c/λ
黑體總能量 P = ∫Pλdλ
λ = σT4 (Stephen-Bosemann law)
Lava
1000K
Sirius天狼星
天狼星
sun
5000K
色溫
10000K