七 色度與 CIE 色度座標之測定 - 發光學術語與基本概念 1. 輻射束 (joule/sec) 2. 光束 / 光通量 (lumen) 3. 光度 (Candela, cd) 4. 輝度 (cd/m 2 ) 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 Φ (Radiant flux, 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 Watt F = KΦ (K 為視覺度, 其大小依波長而異, 其最大值為 100, F 為光束 2. 光束 / 光通量 (luminous, 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, 可用照度計加以量測
3. 光度 I (Luminous intensity, 單位為燭光 Cd, candela) 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 = df/dω 所以 df = I dω 此立體角內所有方向之光度 I 則為 I = df/dω 對均勻的點光源而言,F (lumen) = 4πI ( 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 或 nt = cd/m 2 或 stilb (sb), sb = cd/m 2 由一特定的光源發出強度相同時, 其發光的面積越大者, 則其輝度值越小 某一截面的輝度 L (nit) 值, 為其該方向的光度值 I (cd), 以該截面的視面積 A (m 2 ) 除得之值, 以 L 表示 L = I (cd)/a (m 2 ) = nit or cd/m 2 or stilb 各種光源的輝度值 (nit) 太陽 165 x 10 7 蠟燭 1 x 10 4 水銀燈 14 x 10 4 納氣燈 (200W) 8 x10 4 月亮 26 x 10 2 藍空 8 x 10 3 日光燈 6x 10 3-1x 10 4
5. 照度 E (Illumination Intensity, 單位為 Lux 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/m 2
彩色分析儀 - 輝亮度 (cd/m 2 ) 對比度對比度 閃爍閃爍 色度 (x,y) 值之測定
Anatomy of Human Eyes 3 視網膜 4 Rods 5 Cones 視神經 玻璃體 玻璃體.7 瞳孔 2 角膜 1 虹膜 6 水晶體
Cones ( 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 )
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 types of cones) Human eye Problems with difference between individuals and memory characteristics Tristimulus method 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 )
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 1951 年根據亮 暗適應條件下, CIE 對 200 多位觀察者視覺的測定結果, 分別推薦了標準的明視覺 (V(λ): 峰值 555 nm, 光譜光效能最高值 K m (λ)= 683 lm/w) 與暗視覺 (V (λ); 峰值 507 nm, 光譜光效能最高值 K m (λ) 1699= lm/w) 函數曲線 S1 函數曲線的標準化與 K m (λ) K m (λ) 值測定, 在全球光度量測上有了統一的基礎! Scotopic (low light) vision system V (λ): Driven by rod cells; unable to differentiate different λ s; provides no saensation of colors Phototopic (daytime) vision system V(λ) : Driven by cone cells; can differentiate different λ s: ctreate sensation of colors 視覺函數 V(λ), V (λ) 曲線 507 nm 555 nm
投影片 18 S1 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 2 o field of view, hence the name "2 o Standard Observer" In 1964, the CIE defined an additional standard Observer, this time based upon a 10 o field of view and this is referred to as the "10 o Supplementary Standard Observer The 2 o standard Observer should be used for viewing angles of 1 o to 4 o and the 10 o supplementary standard Observer should be used for viewing angles of more than 4 o.
七 色度與 CIE 色度座標之測定 - specification and measurements of colors 1. The human eyes 2. The nature of chroma ( 色度 ) 3. The standard observers ( 標準觀查者 ) 4. Color space ( 色域 ) - chromaticity diagram/coordinates - color temperature http://home.wanadoo.nl/paulschils/10.02.htm
CIE 1931 RGB r 10 (λ), g 10 (λ), b 10 (λ) color matching functions The r 10 (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 zz, 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 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 the spectral power distribution of the light emitted from a colored object and are factored by sensitivity curves which have been measured for the human eye. The CIE Color Space
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-u o v = v-v o
CIE 色度座標圖 色調 CIE(Commission Internationale de l'éclairage ) 飽和度 x x
Mixing of Colors of light Sight of human Eyes Mixing of Colors of pigments Mixing paint pigments Additive mixing Simple subtractive mixing MAGENTA, YELLOW and CYAN pigment of proper intensities are known as The Subtractive Primary Colors.
Additive mixing Simple subtractive mixing Additive color mixtures are always lighter than any of the individual components! 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 ).
P22 CRT phosphors ZnS:Ag (blue) (Zn,Cd)S:Ag (green) Y 2 O 3 :Eu 3+ (red) Y 2 SiO 5 YAG Y 2 SiO 5 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: E R = Σ(Idλ) R E G = Σ(Idλ) G E B = Σ(Idλ) B 1. Take the spectral curves. 2. Multiplying by the overlap of each tristimulus curve. 3. We obtain Tristimulus Values. Emittance X = xσi R dλ Y = yσi G dλ Z = zσi B dλ Reflective (scattering) X = xσ I R R R dλ Y = yσ I G R G dλ Z = z Σ I B R B dλ x, y, z are the stimulus response of red, green, and blue; 而 X, Y, Z 則稱之為 tristimulus values
Because each color gives a set of tristimulus values 但 each set 之間並未有相互 correlation 因為 I R I G I B (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)
Measuring Emissive Colors 之過程 ( 如何將光譜轉換成色度座標?) 1) Obtain emission spectrum ( 利用 spectrofluorimeter) 2) 利用 利用 energy of RGB spectral curve: E R = Σ(Idλ) R E G = Σ(Idλ) G E B = Σ(Idλ) B 等公式, 將 (Idλ) 積分, 以獲得 RGB 三原色色光之能量 3) 因為 X = xσi R dλ Y = yσi G dλ Z = zσi B dλ 故可以利用 X Y Z x = y = z = X + Y + Z X + Y + Z X + Y + Z 求取 (x,y x,y) 值 green, and blue 上述 x, y, and z 為 the stimulus response of red,
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 2856 K 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. Light source A Light source B 6774 K 6504 K Light source C D 65
Any hue ( 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, 能完全吸收任何入射波長輻射的熱輻射體, 稱之為黑體 (black body) 1900 年 Planck 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, 在波長 λ 處的光譜能量分布為 P λ = (c/λ 5 )(1/e c /λt-1 ) 黑體總能量 P = P λ dλ = σt 4 (Stephen-Bosemann law)
Lava sun Sirius 天狼星 1000K 5000K 色溫 10000K