Color is an aspect of visual perception dependent on the spectral composition of observed radiant energy.

Color is physical impression of human mind. It is impossible to measure.

According to Colorimetry of the optical society of America.

“Color is the general name for all sensations arising from the activity of the retina of the eye and its attached nervous mechanism, this activity being in nearly every case in the normal individual, a specific response to radiant energy of certain wavelength and intensity”

Physics of colorElectromagnetic radiation is characterized by its wavelength (or frequency) and its intensity. When the wavelength is within the visible spectrum (the range of wavelengths humans can perceive, approximately from 390 nm to 700 nm), it is known as "visible light".Most light sources emit light at many different wavelengths; a source's spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species.

Color of objectsThe color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain. Physically, objects can be said to have the color of the light leaving their surfaces, which normally depends on the spectrum of the incident illumination and the reflectance properties of the surface, as well as potentially on the angles of illumination and viewing. Some objects not only reflect light, but also transmit light or emit light themselves, which also contribute to the color. A viewer's perception of the object's color depends not only on the spectrum of the light leaving its surface, but also on a host of contextual cues, so that color differences between objects can be discerned mostly independent of the lighting spectrum, viewing angle, etc. This effect is known as color constancy.

Basic norms of Color ScienceColor: The visual effect that is caused by the spectral

composition of the light emitted, transmitted, or reflected by objects.Color Temperature

A color temperature meter measures the color temperature of an incident illuminant.The temperature, in Kelvin, of a Planckian black body

radiator whose radiation has the same chromaticity coordinates as that of a given stimulus. Fluorescence

The process whereby colors absorb radiant power at one wavelength and immediately re-emit it at another (usually longer) wavelength, as in "day-glo" or black-light paints. Hue

The attribute of a visual sensation according to which an area appears to be similar to one, or to proportion of two, of the unique hues: red, yellow, green and blue.

LightA universal and essential attribute of all perceptions and sensations that are peculiar to the visual system. In other words, an optical radiation capable of directly causing a visual sensation.Luminescence

Luminescence may occur either during or after the absorption of light energy at another wavelength. Emission which occurs only as long as the exciting input is being received is specified by the term fluorescence; emission which continues for some time after the energy input has ceased (as on the dial of an alarm clock) is said to exhibit 'afterglow' or the attribute of so-called phosphorescence.

MetamerismAn effect created when objects having different spectral distributions look alike under one light source but appear different when viewed with a dissimilar light source. Metameric Pair

Objects which exhibit the following:They have different spectral reflectance factors (spectral curves).They match under at least one combination of illuminant and observer.They do not match under at least one combination of illuminant and observer.Phosphorescence

Light emission which continues for some time after illumination has ceased – "glow-in-the-dark" phenomenon.

SpecularityAlso specular component or gloss. Reflection as in a mirror without deviation by scattering, diffraction or diffusion.Spectrum

Specification of the monochromatic components of the radiation considered. Unique Hue

A perceived hue that cannot be further described by the use of hue names other than its own; there are four unique hues: red, green, yellow and blue.

All color is due to light: radiation in the visible portion of the electromagnetic spectrum. Visible, to us, means the range of wavelengths that can be processed by the human optics and brain. The sensation of an object's color is produced by the combination of: A light source - illuminating an object

An object - reflecting light to an observer

An observer - sensing the reflected light

A simplistic explanation of how color is perceived involves white light, "a mixture of all the colors of the rainbow", falling on a red object, which absorbs all the colors except the red portion of the spectrum, which is reflected back to the viewer.

The wavelengths of the complete visible

spectrum, between infrared and ultraviolet,

range from approximately 390 to 750 nm

(nanometers, billionths of a meter). Spectral

wavelengths are also frequently given in Å

(angstroms, 10 nm) or °K (degrees Kelvin).

While active upon the human body, ultraviolet

and infrared are invisible to the human eye.

These are the wavelengths for the traditional

visible "seven colors of the rainbow", VIBGYOR:

430-390

Violet

450-440

Indigo

480-460

Blue

530-490

Green

580-550

Yellow

640-590

Orange

750-650

Red

Color, wavelength, frequency and energy of light

Color(nm) (THz) (μm−1) (eV) (kJ mol−1)

Infrared >1000 <300 <1.00 <1.24 <120

Red 700 428 1.43 1.77 171

Orange 620 484 1.61 2.00 193

Yellow 580 517 1.72 2.14 206

Green 530 566 1.89 2.34 226

Blue 470 638 2.13 2.64 254

Violet 420 714 2.38 2.95 285

Near ultraviolet 300 1000 3.33 4.15 400

Far ultraviolet <200 >1500 >5.00 >6.20 >598

Electromagnetic radiation with a wavelength of over 750 nm is called

infra-red, and radiation under 350 nm is ultra-violet. Each color on the

spectrum can vary in saturation, lightness and darkness, and it's

estimated that a human eye can distinguis about 10 million color

variations.

Color in the eye

The ability of the human eye to distinguish colors is based upon the varying sensitivity of

different cells in the retina to light of different wavelengths. Humans being trichromatic, the

retina contains three types of color receptor cells, or cones. One type, relatively distinct from

the other two, is most responsive to light that we perceive as blue or blue-violet, with

wavelengths around 450 nm; cones of this type are sometimes called short-wavelength cones, S

cones, or blue cones. The other two types are closely related genetically and chemically:

middle-wavelength cones, M cones, or green cones are most sensitive to light perceived as

green, with wavelengths around 540 nm, while the long-wavelength cones, L cones, or red

cones, are most sensitive to light we perceive as greenish yellow, with wavelengths around

570 nm.

Color in the brainThe mechanisms of color vision at the level of the retina are well-described in terms of tristimulus values, color processing after that point is organized differently. A dominant theory of color vision proposes that color information is transmitted out of the eye by three opponent processes, or opponent channels, each constructed from the raw output of the cones: a red–green channel, a blue–yellow channel, and a black–white "luminance" channel. This theory has been supported by neurobiology, and accounts for the structure of our subjective color experience. Specifically, it explains why we cannot perceive a "reddish green" or "yellowish blue", and it predicts the color wheel: it is the collection of colors for which at least one of the two color channels measures a value at one of its extremes.

Cone cell

Cone cell structure

Cone cells, or cones, are one of two types of photoreceptor cells in the retina of the eye. They are responsible for color vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. There are about six to seven million cones in a human eye and are most concentrated towards the macula.

Cones are less sensitive to light than the rod cells in the retina (which support

vision at low light levels), but allow the perception of colour. They are also

able to perceive finer detail and more rapid changes in images, because their

response times to stimuli are faster than those of rods. Cones are normally

one of the three types, each with different pigment, namely: S-cones, M-

cones and L-cones. Each cone is therefore sensitive to visible wavelengths of

light that correspond to short-wavelength, medium-wavelength and long-

wavelength light. Because humans usually have three kinds of cones with

different photopsins, which have different response curves and thus respond

to variation in colour in different ways, we have trichromatic vision.

Being colour blind can change this, and there have been some verified reports

of people with four or more types of cones, giving them tetrachromatic

vision. The three pigments responsible for detecting light have been shown to

vary in their exact chemical composition due to genetic mutation; different

individuals will have cones with different color sensitivity.

Destruction of the cone cells from disease would result in

blindness.

Color optics of HumanThe human eye detects color through light-sensitive cells called cones. Current understanding is that the 6 to 7 million cones can be divided into red cones (64%), green cones (32%), and blue cones (2%) based on measured response curves. The three different types of cones, named red, green, and blue for the portion of the spectrum each type is best at absorbing. They provide the eye's color sensitivity. The green and red cones are concentrated in the fovea centralis. The blue cones have the highest sensitivity and are mostly found outside the fovea, leading to some distinctions in the eye's blue perception. Yet just these three types of cones let you see all the colors you can see -- roughly 7 million colors. That's somewhat less than half the number of colors computers offer for "true color." Computer systems need the much larger number of colors, because the eye is more sensitive to changes in some parts of the spectrum than in others, but computers distribute the steps evenly across the spectrum.

In essence, when you see a color, it's because the three kinds of cones contribute to a sensation that your brain recognizes as a particular color. When you see a frequency of yellow light, say, (as measured by its wavelength), your red, green and blue cones absorb the light in particular proportions. When you see a combination of red and green (as measured by the wavelengths of the light once again), your red, green, and blue cones absorb light in the same proportion, and your visual system once again senses yellow. In fact, there are an infinite number of combinations of light frequencies that will register the same way on your visual system to produce the same sensation -- which is to say, the same color. All of which brings us back to the jacket and pants problem. If the jacket and pants you look at in the store are made from the same bolt of cloth -- which means they are part of the same dye lot -- they will almost certainly both reflect each wavelength of light the same way.

Regardless of the light source, then, they will always reflect the same combination of wavelengths, and you'll see them as being the same color regardless of the light source. If they're made from cloth that came from different dye lots, however, odds are that they won't reflect each wavelength of light the same way. The mix of wavelengths they reflect from one light source – the light source in the store – will produce

the same color, because the dyes were mixed to look the same under a light source that matches the light source in the store. But because different dye lots usually reflect and absorb different wavelengths differently, it's highly unlikely that the mix of wavelengths they reflect from a different light source will also look the same.

Move to a different light source, in short, and the colors won't match. As you might guess, you can run across problems with metameric pairs in all sorts of situations – a set of furniture with fabric from

different dye lots, wall paper produced in different runs, paint mixed to match a color from a different brand of paint, and so on. More important, metamerism is something you need to keep very much in mind when dealing with color on a computer system. When you're working hard to match colors of a scanned photo to printed output for example, you need to think in terms of matching the colors in a given light. What matches at home under incandescent light may not match at the office under fluorescent light.

Spectrophotometer:The spectrophotometer is a physical tool which is eminently suited to measurethe most important variable of all, the shade and strength of the dyestuffsthemselves, whether they be in solution or on the fiber. Spectrophotometerused by dyeing factory and colorant manufacturers all over the world.Normally Color lab manager analysis the color of swatch with the help ofspectrophotometer.

Types of Spectrophotometer

Spectrophotometers measure reflected or transmitted light across a light spectrum. The resulting data creates a visual curve. Spectral data is invaluable to anyone in the printing trades. Spectral measurements ensure that color is consistent across varying substrates and production processes. A densitometer checks density but does not see color, and this can often result in color variations that might not meet customer expectations.

Spherical Spectrophotometers

0º/45º (or 45º/0º) Spectrophotometers

This is simply because a human viewer does everything in his or her power to exclude the “specular component” (gloss) when judging color. When we look at pictures in a glossy magazine, we arrange position so that the gloss does not reflect back to the eye. A 0º/45º instrument, more effectively than any other, will remove gloss from the measurement dynamics and measure the appearance of the sample exactly as the human eye would see it. Because 45° instruments perceive color in the same way as the human eye, they are generally preferred for applications such as measuring color on smooth or matte surfaces. They are not necessarily the best choice for measuring color on glossy and reflective surfaces.

Multi-Angle Spectrophotometers

Automotive manufacturers have created and refined automotive

coatings to present a unique experience when viewing a vehicle.

They have experimented with special effect colors using special

additives such as mica, pearlescent materials, ground-up seashells,

specially coated pigments in order to produce a surface that shifts in

color when viewed from different angles. Large and expensive

goniometers were traditionally used to measure these colors until X-

Rite introduced a battery-powered, hand-held, multi-angle instrument.

Color measurement procedure consists of 5 steps:

1.Prepare samples to make colored compound

2.Make series of standard solutions of known concentrations

and treat them in the same manner as the sample for making

colored compounds

3.Set spectrophotometer to l of maximum light absorption

4.Measure light absorbance of standards

5.Plot standard curve: Absorbance vs. Concentration,

Spectrophotometers measure reflected or transmitted light

across a light spectrum. The resulting data creates a visual curve.

Spectral measurements ensure that color is consistent across

varying substrates and production processes. A densitometer

checks density but does not see color, and this can often result in

color variations that might not meet customer expectations.

Instruments for Measuring Transmittance

The measurement of dyes in solution to verify the color quality and strength is the most

common application, although the measurement of transparent films is also used. Most

spectrophotometers for measuring liquids are designed such that a transmission cell or

cuvet is inserted between the detector

Dual- beam spectrophotometer

Functions of spectrophotometer: 1.Color difference 2.Metamerism 3.Pass/fail operation 4.Fastness rating 5.Shade library 6.Cost comparison 7.Color match production 8.Reflectance curve.

Flow Chart of Color Matching Process with Spectrophotometer:

Color measurements The human eye has a spectral sensitivity that peaks at around

555 nm, which means that the color green gives an impression of

higher brightness than other colors. At 490 nm the sensitivity is

only 20% compared to the sensitivity at 555 nm. Furthermore,

the human eye can only distinguish about 10 million different

colors which is actually quite limited relative to the needs of

color measurement applications. Spectrometers are designed to

measure exact wavelengths, and are therefore ideal for color

measurements.

Color measurements may be applied to a variety of industrial applications such as color of textile, paper, fruit, wine, and bird feathers. Avantes has developed a variety of custom probes to meet the specific demands of the color measurement application. Color measurements are manifested in the L*a*b* color model which includes parameters for brightness and hue.

Colorimetry, the science of color measurement, is widely employedin commerce, industry, and the laboratory to express color innumerical terms and to measure color differences betweenspecimens. Applications include paints, inks, plastics, textiles andapparel, food and beverages, pharmaceuticals and cosmetics,displays, and other parts and products that reflect or transmit color.

While the term colorimetry often is used in a general sense to

mean color measurement, it differs from spectrophotometry, a

related but distinct method of color measurement.

In colorimetry, the quantification of color is based on the three-

component theory of color vision, which states that the human

eye possesses receptors for three primary colors (red, green,

and blue), and that all colors are seen as mixtures of these

primaries. In colorimetry, these components are referred to as X-

Y-Z coordinates. Colorimeters, based on this theory of color

perception, employ three photocells as receptors to see color in

much the same way as the human eye.

Spectrophotometry, on the other hand, uses many more sensors (40 or more in some spectrophotometers) to separate a beam of reflected or transmitted light into its component wavelengths. It measures the spectral reflectance of an object at each wavelength on the visible spectrum continuum. Spectrophotometry provides high accuracy and is generally used in research and color formulation applications. Colorimeters are generally used in production and quality control applications.

A number of mathematical models and graphing methods have been

developed under the auspices of the Commission Internationale de

lÆEclairage (CIE).

Figure 2: 1931 X,Y chromaticity diagram

Hue is the term used for general classification of color—the region

of the visible spectrum (380 to 700 nm)—in which the greatest

reflectance of light occurs. Hues perceived as blue tend to reflect

light at the lower end of the spectrum, greens in the middle region,

and reds toward the higher end. Above slide shows spectral

sensitivity corresponding to that of the human eye.

Lightness/darkness can be measured independently of hue. For example, the lightness of a lemon can be compared with the lightness of a cherry. Saturation describes the vividness/dullness of a perceived color and, like lightness, can be measured independently of hue.Among the most widely used color spaces for defining and mathematically expressing these attributes are the CIEÆs Yxy color space, established in 1931; the 1976 L*a*b* color space; and the L*C*h color space. Other color spaces, such as CIELUV, Hunter Lab, developed by Richard S. Hunter, and the Munsell color notation system, also are in use.Since then, color space representations have been refined to more closely correspond to the color difference perceptions of the human eye as defined by continued experimentation and statistical averaging.

X-Y-Z values and Yxy color spaceOne of the earlier color space representations is the CIE 1931 X,Y chromaticity diagram, as shown in figure 2. The diagram is used for 2-D graphing of color, independent of lightness. X and Y are the chromaticity coordinates calculated from the tristimulus values X-Y-Z. In this diagram, achromatic colors are toward the center, and chromaticity increases toward the edges. A colorimetrically measured red apple whose chromaticity coordinates are X = 0.4832 and Y = 0.3045 can be located in this color space at position A (the blue circle).

Also referred to as CIELAB, L*a*b* color space was promulgated in

1976 to adjust for one of the problems of the original Yxy color

space. Equal distances on the X,Y chromaticity diagram did not

correspond to equally perceived color differences. In the L*a*b*

diagram, a spherical color solid, L* indicates lightness, and a* and

b* are the chromaticity coordinates. Here the a* and b* indicate

color directions (+a* is the red direction, -a* is the green

direction).

L*C*h color space uses the same diagram as L*a*b* color space, but employs cylindrical rather than rectangular coordinates. L* is the same as the L* of the L*a*b* diagram. C* is chroma, and h is the hue angle. The value of C* is zero at the center for an achromatic color, and increases according to the distance from the center. Hue angle (h) is defined as starting at the +a* axis and is expressed in degrees as the chroma axis rotates counterclockwise.

Measurement output from a colorimeter is expressed in terms of X-Y-Z values for the measured sample, as well as in units of other accepted uniform color spaces. By comparing measurements of target colors with sample specimens, the user obtains not only a numerical description of a color, but can also express the nature of a color difference between two measured specimens. The colorimeter pinpoints the difference in lightness, chromaticity, and hue between the target and the sample.

Figure 3: a*, b* chromaticity diagram

Color measurements taken in one location and expressed in units of a given color space then can be compared with measurements taken in another location or at another time and communicated in an internationally accepted language. In this manner, colorimetric measurement eliminates subjectivity in color perceptions and color difference judgments.

Color space A system for ordering colors that respects the relationships of similarity among them. There are variety of different color spaces, but they are all three dimensional.The two most widely known's of these methods are the Yxy color space, devised in 1931 based on the tristimulus values XYZ defined by CIE, and the L*a*b* color space, devised in 1976 to provide more uniform color differences in relation to visual differences. Color spaces such as these are now used throughout the world for color communication.

The Munsell Scale

In 1905, artist Albert H. Munsell originated a color ordering system — or

color scale — which is still used today. The Munsell System of Color

Notation is significant from a historical perspective because it’s based on

human perception. Moreover, it was devised before instrumentation was

available for measuring and specifying color. The Munsell System

assigns numerical values to the three properties of color: hue, value and

chroma. Adjacent color samples represent equal intervals of visual

perception. The model in Figure 4 depicts the Munsell Color Tree, which

provides physical samples for judging visual color. Today’s color

systems rely on instruments that utilize mathematics to help us judge

color.

Three things are necessary to see color:

• A light source (illuminant)

• An object (sample)

• An observer/processor

We as humans see color because our eyes process the interaction of

light hitting an object. What if we replace our eyes with an

instrument —can it see and record the same color differences that

our eyes detect?

Theory of Color Mixing

Additive or Light theory

Subtractive or pigment theory

Three dimensional color system

AZMIR

DYE PICK UP TEMPERATURE OF DIFFERENT HUE

Yellow-60-65 ˚C temp increase shade will be more yellowishRed-70 ˚C temp increase shade will be more reddishBlack- 60-65 ˚CBlue-60-65 ˚CTurquoise- 85 ˚COBA- 80 ˚C

CMC-Color Measurement CommitteeCMC is not a new color space but rather a tolerance system. CMC Tolerance system

is a modification of CIE LAB which provide better agreement between visual assessment. Color is measure by spectrophotometer(data color) by reflectance

value.Reflectance means= intensity of reflected light/intensity of incident light

For perfect black-reflectance=0For perfect white-reflectance=1

Color Difference E=( C*2 + H*2 + L*2)1/2

WHERE, L=LIGHTNESS/VALUE(BRIGHT OR DULL)C=CHROMA(DEEPNESS OF COLOR)H=HUE(FIRST APPEARANCE OF COLOR)

Color difference in CIE L*,a*,b* space, the color difference between a standard and trial sample is expressed numerically DE

DE=(DL*2 + Da*2 + Db*2)1/2Where,DL*=Lt* - Ls*

Da*=at* - as*Db*=bt* - bs* T-trial

S-standardPartially (0) color difference is impossible.CMC Commercial factor =1.Acceptable limit of color difference DE, (0-1)-Da=more green / less red +Da=less green / more red-Db=more blue / less yellow+Db=less blue / more yellow-DL=darker+DL=lighterDC*=The distance between sample and L* axis(value axis)DH*=The angle made by the chroma line and a* axis

Light Source Specification Color Temperature

Day light D65 International standard Artificial daylight-400-700nm

6500K

Incandescent Light A Cool White Fluorescent.USA shop light source-405,436,546 and 578nm

4200K

Department store light-CWF /F2 Fluorescent Lamp 4230K

Department store light-TL84/F11 Fluorescent Lamp 4o00K

Ultraviolet Light-UV Ultraviolet lamp;365nm -

Light source F Sun setting light .Yellow light Source 2700K

The most Popular Norm lights

Light Source Descriptions:

D75 (7500K) - A bluish colored light source originally used for grading cotton and other

evaluation applications. It has been replaced by D65 as the standard source for these

applications. It accentuates blue and subdues green and red. It is derived from the

light coming in a north facing window in the northern hemisphere at noon at various

times throughout the year. It is commonly called “North Sky Daylight.”

D65 (6500K) - A light bluish colored light source used in color matching applications of

paints, plastics, textiles, raw inks, and other manufactured products. It is the only

daylight source that was actually measured. The other daylight sources (D75 and D50)

were mathematically derived from these measurements. It accentuates blue and

subdues green and red. Commonly used as a primary light source in color

measurement instrumentation. It is derived from the average of measurements made

of light coming in a north facing window in the northern hemisphere on an

overcast day at various times through the day at various times throughout the year.

D50 (5000K) - A near white light source used in the evaluation of graphic arts and

imaging applications. It has similar amounts of red, green, and blue energy. It neither

accentuates nor subdues color, a prime requirement when viewing press sheets and

original images (i.e., photographs) since they usually have many colors within the

product to be evaluated.

Ultra Violet - Light energy not normally visible to the human eye, but which is present

in natural daylight. UV energy has the ability to excite certain substances

(dyes/pigments/chemicals) within a sample causing them to emit light in the visible

spectrum, usually in the blue region. These substances are used in various products

to “brighten” colors, particularly whites. It is necessary to include correct amounts of

UV energy in a color matching system to allow for optimum simulations of natural

daylight.

Cool White Fluorescent (CWF) - A wide band single phosphor fluorescent source commonly used in commercial lighting applications in North America. It is characterized by emitting high amounts of green energy, with a color temperature of approximately 4100K. It has a CRI or approximately 62.

Warm White Fluorescent (WWF) - A wide band single phosphor fluorescent source used in commercial lighting applications in North America. It is characterized by emitting high amounts of yellow/red energy, with a color temperature of approximately 3000K. It has a CRI of approximately 53.

TL84 - A narrow band tri-phosphor fluorescent source originally designed for commercial lighting applications outside North America. It is characterized by emitting high amounts of green energy, with a color temperature of approximately 4100K. It has a CRI of approximately 86.

TL830 - A narrow band tri-phosphor fluorescent source originally designed for commercial lighting applications outside North America. It is characterized by emitting high amounts of yellowish red energy, with a color temperature of approximately 3000K. It has a CRI of approximately 86.

TL835 - A narrow band tri-phosphor fluorescent source originally designed for commercial lighting applications outside North America. It is characterized by emitting high amounts of reddish yellow energy, with a color temperature of approximately 3500K. It has a CRI of approximately 86.

Ultralume 30 (U30 or 30U) - A narrow band tri-phosphor fluorescent source originally designed for commercial lighting applications in North America where energy savings is required. It is characterized by emitting high amounts of yellowish red energy with a color temperature of approximately 3000K. It has a CRI of approximately 85.

Ultralume 35 (U35 or 35U) - A narrow band tri-phosphor fluorescent source originally designed for commercial lighting applications in North America where energy savings is required. It is characterized by emitting high amounts of reddish yellow energy with a color temperature of approximately 3500K. It has a CRI of approximately 85. It must be understood that not all fluorescent sources are available in all lamp sizes. Additionally, as was stated previously, certain retailers will specify which light sources or fluorescent lamps must be used for color matching applications if product is to be supplied to their stores. Your GTI representative will be happy to assist in the process of choosing the right compliment of sources and lamps for your applications. Please contact GTI or your local representative for further information. Daylight source lamps supplied by GTI are specifically designed to provide the necessary light output, at the various visible and non-visible wavelengths and maintain the proper viewing environment within the GTI fixtures and color matching systems. If commonly available commercial lamps are used, even lamps from another standardized lighting manufacturer, the viewing system may not conform to specified standards. To assure consistent quality, always replace GTI lamps with GTI replacement lamps.

Incandescent and Tungsten IlluminationA typical light bulb found in the home is an incandescent tungsten lamp. It uses a tungsten filament that will glow when electricity is passed through it. A quartz halogen lamp is also a tungsten incandescent lamp, but has specialcharacteristics to give the lamp a more even output over its life cycle. These lamps are very common and are used incolor match applications where a yellowish to red source is required. The most common tungsten filament sourcesavailable, with their applications, are given below:

3200K Tungsten A Red/Yellow Photographic imaging applications.2865K Illuminant A Yellowish Red Standardized source and illuminant for color matching.2300K Horizon Reddish Source described in older specifications and used for color matching applications. Replaced by Illuminant A.

Tungsten A - is used primarily in the photographic, film and video industries where a “whiteish” source andcontinuous light output are required. It is not commonly used for color matching applications.

Illuminant A - is a standardized illuminant described in the international standard, CIE Publication 15.2 and specified for use in color matching applications in ASTM D1729-96. It is used where a yellowish-red source is required. It is the predominant source/illuminant used for both instrumental and visual color matching applications. Another source is not used in instrumental color matching applications. Described as Horizon in an outdated standard as an “Incandescent illumination of low correlated color temperature…”

When CMC value pass

When CMC value warn

When CMC value is Fail

FOR MEASURING CMC VALUE THERE ARE TWO MEASURING SOFTWARE

Color Tools : Shade Measurement + Set new Standard + set new batch

Dci Match : Recipe Adjust + Data batch (self shade for using dyes )

Mainly Data color gives three types of result

-Pass { When DE =(0-.7)}-Warm { when DE =(.71-.99)}- Fail {when DE =( 1 above)}

Color difference also depends on light source (D65,TL84,TL87,TL83) but its show the average value i.e CMC DE

Metamerism is a psychophysical phenomenon commonly defined incorrectly as "two sampleswhich match when illuminated by a particular light source and then do not match whenilluminated by a different light source." In actuality, there are several types of metamerism,including sample, illuminant, observer, and geometric. The first two are most commonlyreferred to and also most commonly confused.

Types of Metamerism

Illuminant metamerism: Illuminant metamerism is witnessed when there are a number ofspectrally matched — exactly the same — samples, but when each is independently yetsimultaneously illuminated and viewed under lights whose spectral power distributions differ,significant variations of the color can be perceived. This phenomenon is rarely witnessed,unless a light box that allows the observer to see both lights separated by a divider is used, andthe two identical samples are illuminated by the different light sources.

Observer metamerism: Every individual perceives color slightly differently, assuming theindividuals possess adequate color matching aptitude. This can be demonstrated in manyways.

Metamerism (color)

Geometric metamerism: Identical colors appear different when viewed at different angles,

distances, light positions, etc. It can be argued that one reason men and women often perceive

color differently is that the distance between a woman's eyes is, on average, slightly less than a

man's. This slightly different angle of stereoscopic viewpoint falls under the category of geometric

metamerism.

Sample metamerism: When two color samples appear to match under a particular light source

but do not match under a different light source, this is "sample metamerism." One can conclude

that the spectral reflectance distributions of the two samples differ slightly, and their plotted

reflectance curves cross in at least two regions. By illuminating them with lights with

considerably differing spectral power distributions, the visual differences between the two

samples can be witnessed and even exaggerated.

Graphic arts and color reproduction considerations metamerism: In the printing industry,

metamerismis the source of great frustration. It is perceived as a negative characteristic of color;

if it did not exist, many believe, color reproduction problems would be eliminated. In actuality,

however, it is this phenomenon that allows for mass color reproduction of an artwork. Inks used

to create a color reproduction can be combined to simulate an artwork, but can only be made to

accurately match the reproduction under only one (D50 or D65) light source.

Metamerism

You know you have an instance of metamerism if two paper sheets look identical under

one set of lighting conditions, but they appear to have a different shade from each other

under a different illuminant. The major causes of metamerism problems are (a) poor

selection of dyes when the same grade is made on different paper machines, (b) different

effective levels of fluorescent whiting agent especially in white grades, and (c)

attempting to make the same grade with very different types of fiber furnish.

Metamerism in color paper grades usually can be avoided by making sure that the red,

yellow, and blue dyes each have a similar hue to the dye used when making the standard

that was approved by the customer.

Metamerism Index

Metamerism, the situation where two color samples appear to match under one condition but not under another, is the result of differences in object surface composition. The dyes and pigments used to create the color of objects such as textiles, paints and so on, have different spectral reflectance curves. Color perception is a combination of the spectral reflectance of the pigment or of the dye (and its substrate) and the spectral distribution of the light source. The color you see is influenced by the emission spectrum of the source of the light available to be reflected by the object.

The most common light sources are fluorescent, incandescent, ultraviolet and sunlight, which have different spectral distributions. Incandescent lighting is generally considered warm compared to cooler fluorescent lighting, famous for sucking the life out of beige. Other colors that are likely to have metameric problems include taupe, mauve, lilac, tan, celadon, gray-blues, and grays. While metamerism is normally a light-source effect, it can also arise from differences in the physiological optic structure of observers, e.g. color-blindness.

Test for MetamerismThere are two basic tests available that are useful for evaluating whether or not two objects (that match) are metameric.Visual Test for Metamerism

1.Confirm that the objects match, by viewing (in a light booth) under the reference (primary) light source.

2.Change the light source to a test source that is significantly different from the reference source.

3.If the objects still match, then it is likely that they will match under any source, and are thus probably not metameric. If the objects do not match under the test source, then they are a metameric pair. Repeating this test under a third (different) source (whenever there is a match under the reference and test sources) should be done whenever possible, as there are exceptions to this rule.

Instrumental Test for Metamerism1.Using a spectrophotometer, measure the objects, and confirm that the objects match under a specific illuminant/observer combination.

2.Compare their reflectance spectral curves. If the curves differ, and cross each other at least three times, then the objects are metameric.

3.Confirm the metamerism and compute its amount, by calculating color differences under different illuminant/observer combinations.