Salee Colour Public Company Limited

1 . Factors That Enable Color

Light Source : 1. Daylight – Natural lights illuminated by the sun

2. Illuminant – Artificial lights generated by manmade devices such as fluorescent lamps of light bulbs

Object : Color Object and visible by our eyes

Observer : Human Eyes

Human eyes contain sets of cells that together make up human eyes nerve system

1. Cone cells: Cone cells recognize color spectrum range of 400-700 nm

There are three sets of Cone cells:

- Red cone cells recognize red color spectrum range

- Green cone cells recognize green color spectrum range

- Blue cone cells recognize blue color spectrum range

Rod cells : Rod cells recognize brightness (black or white intensity)

* Rod cells do not recognize colors

Color Spectrum of Sun Light

2. Light Effect

What happens when lights fall on objects (Lights reflection phenomena)

-When lights fall on opaque metal or gloss objects

- When lights fall on translucent objects (Translucent material)

- When lights fall on transparent objects (Transparent material)

- When lights fall on metallic surface (light scattering phenomenon)

3. Color Visibility :Theory and Measurements

To eliminate inconsistency in color theory and measurement and to create an international level understanding, a method of color measurement is developed.The method define numeric value measurements for the three factors that affect color visibility.

Color Visibility :Theory and Measurements

CIE : CIE is an international organization for the development of science and technology involving light and lighting. The CIE developed a CIE System for creating equation standards in determining the values of the three factors affecting color visibility.

CIE : Commision International de l’ Eclirge.

or ICI : International Commision on Illuminants.

In addtition to CIE there are other organizations, for examples: Hunter Lab, ANLab, Muncells,ect. Hunter Lab, ANLab, Muncells,ect.

Illuminants : Stand light sources

Because color perception of natural lights can change due to day, time, geographical location, weather and environment, standard light sources (illuminants) must be defined.

Standard Illuminants.

D65 gives thermal illumination energy of 6,500 K

A(Tungsten) gives thermal illumination energy of 2,856 K

CWF (F2) gives thermal illumination energy of 4,200 K

TL84 gives thermal illumination energy of 4,000 K

C gives thermal illumination energy of 6,700 K

These values are defined by measuring energy reflected of black body illuminated by various illuminants

These Color Temperature values are later defined as Power distribution energy (P) which can be plotted against wave lengths to obtain Cure Relative, Spectral energy distribution curves for various light sources

Object : Object measurement can be measured by a Spectrophotometer which gives a curve called Spectral curve.

Spectral curve which shows the relationship between the amount of reflection in the wave range of 4400-700 nm. The refection is measured in %R in various wave lengths.

Blue is in the wave length of 400-500 nm.

Green is in the wave length of 500-600 nm.

Red is in the wave length of 600-700 nm.

**Notice where the peak is located. The peak can have a maximum value of 100%

- An ideal w hite object can have reflectant values of 100% in all wave lengths

Today BaSo4 and MgO can give reflectant values of 96-98% which is very close to those of ideal white

- A Black object has reflectant values of 0% across all wave lengths. Ideal white objects do exist.

In addition %R that is close to upper of lower limit can indicate color density.

%R :

Refactant (%) = Refactant Light from (colored) Surface x 100

Refactant Light from Standard White Surface

Benefits of Spectral Curve

1.Indicate the color of the object by the location of the peak.

2.Indicate the color density of the object by observing if the peak is closer to the upper or lower limit.

3.Indicate if the Metamerism Phenomenon by observing where the curve intersects.

Standard Observer :

In human eyes, there are three sets of color sensitive cells but we cannot measure the values that these cells read. Instead we measure the average values of responses by human eyes that respond to red green and blue colors and we call the collected values Standard Observer.

X, y, x values can be plotted as Relative, Spectral energy distribution in the spectral range 400-700 nm

Tristimulus Values :

The values of standard color elements that create a given color under the same illuminant within the spectral range 400-700 nm. Can be calculated.

X = S (Pi . Ri . xi) indicating value of Red

Y = S (Pi. Ri . yi) indicating value of Green

Z = S (Pi. Ri. zi) indicating value of Blue

But X, Y, Z are values of color elements in the objects, we need to use these values to calculate Chromaticity Co-ordinate so we can construct Chromaticity Diagram which can better represent color values.

Chromaticity Co-ordinate Calculation.

x = ____X____

X + Y + Z

y = ____Y____

X + Y + Z

z = Z or Y

X + Y + Z

In theory z will not be used but the value of Y from Tristimulus Values will be used to indicate brightness

The values x, y, and Y are used as coordinates to define the color space of given colors. This color space is called Chromaticity Diagram

Because the values given by both Tristimulus Values and Chromaticity Co-ordinate are still not good enough in communicating colors, some improvements are made.

CIE L*a*b* and L*C*h

Parameter Color Co-ordinate of color Color Space by

L* : Lightness บอกความมืด ความสว่าง จะอยู่บริเวณจุดกึ่งกลางระหว่างแกน a*,b* ใน ลักษณะแนวดิ่งลึกลงไป

a* : ค่าที่ใช้กำหนดความเป็น สีแดง สีเขียว ตามแนวระนาบ

+ a* = Red

- a* = Green

b* : ค่าที่ใช้กำหนดความเป็น สีเหลือง สีน้ำเงิน ตามแนวตั้งกับ a*

+ b* = Yellow

- b* = Blue

C : Chroma, Saturation, Strength, Intensity.

The value of the color density is defined by the length of the radius. and the color shade (color hue) is indicated by the angle the radius makes on the a – b axis.

h : Hue, Shad ค่าความเป็นแม่สี วรรณะของสี จะแสดงค่าในลักษณะเป็นมุม องศา ระหว่าง

รัศมีกับแกนในแนวนอน

The value of the angle h needs to be calculated before used in calculation.

C* = ( a* + b* )

h = tan ( b*/ a*)

L* = 116( Y/ Yn ) - 16

a* = 500[ (X/Xn) - (Y/Yn) ]

b* = 200[ (Y/Yn) - (Z/Zn) ]

X, Y, Z = Tristimulus Values

Xn, Yn, Zn = Tristimulus Values for Ideal white

Color Difference : color difference between Standard and Batch by

หาจากกรนำค่า Color Co-ordinate ที่ได้มาคำนวนหาค่า DL*, Da*, Db*, DC* และ DH แล้วนำค่าทั้งหมดมาหาค่า DE ( Total Color Difference ) ค่าความแตกต่างของสีโดยรวมเป็นลำดับสุดท้าย

ในระบบ CIE จะมีค่า Color difference อยู่ 2 ระบบ คือ

1. CIE L*a*b*

Ex : Difference between Batch with Standard

L* a* b*

Batch 70 8 15

STD. 68 10 10

D(L*a*b*) 2 -2 5

DE = [ (2) + (-2) + (5) ] = 5.75

if DL* is + Lighter

is - Darker

Da* is + Redder

is - Greener

Db* is + Yellower

is - Bluer

2. CIE L* C*h

Ex : ความแตกต่างของ Standard กับ Batch

L* C* h

Batch 68 30 45

STD. 70 32 60

D (L* C* H*) -2 -2 4

DE = [ (-2) + (-2) +(4) ] = 4.9

if DL* is + Lighther

is - Darker

DC* is + Stronger, Brighter

is - Weaker, Duller

DH* จะความเป็นสีต่างๆโดยเปิดตารางตรีโกณดูค่ามุม h

ในทิศทวนเข็มนาฬิกา

Metamerism : Metamerism is a phenomenon where two objects of the same color under one illuminant but show different colors under another illuminant. This phenomenon can be observed from the spectral curve. If there are three or more intersecting points, the objects have Metamerism.

ตัวอย่างกราฟที่เกิด Metamerism