The Stothard Group Colour & Appearance Specialists
Opacity Gloss Gardner Appearance Haze Matt Darkness Yellowness Colour Whiteness APHA Metamerism
An Introduction to
Colour & Appearance
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The Stothard Group Colour & Appearance Specialists
When the Appearance of your product matters...
Our Vision On the 1st September 2005 my father passed me his vision to create a business that contained the worlds best professionals, instruments and knowledge to bridge a gap that would see companies from around the world receive the correct solutions whether it be a colorimeter, spectrophotometer or vision system in a timely and efficient manner and with the support to keep working for many years to come. After 30 years he crafted an organisation that contained these experienced professionals, the highest quality tools for measuring, colour, appearance and vision and ensure we stayed on top of giving the customer exactly what their application needed. I am proud to lead our business into the next 30 years with strong links with leading solution manufactures including Hunterlab (the colour measurement experts) and continued knowledge and support from a network of professionals. I would like to take this opportunity to thank you for finding The Stothard Group. I hope my team can welcome you to our way of doing things and provide you with the service you deserve.
Tom Stothard
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The Stothard Group Colour & Appearance Specialists
Contents Page 4
The Basics of Colour & Appearance
Page 6
The Language of Appearance - Hue, Chroma, Value
Page 8
The Language of Appearance - Surface
Page 10
The Language of Appearance - Haze
Page 12
The Language of Appearance - Light, Object, Observer
Page 14
The Language of Appearance - Communicating by Numbers
Page 16
Using Appearance Data to control our process
Page 18
What can be used to measure the appearance of our products
Page 22
Select the right instrument for you - Quick Guide
Page 24
What we do
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The Basics of Colour & Appearance
The Stothard Group Colour & Appearance Specialists
What words would you use to describe the appearance of the pool ball? Yellow or slightly reddish yellow or perhaps orange? You might add the words shiny or maybe even glossy. But could the person on the end of a telephone be expected to make a gallon of this paint for touch up based on these words? Most likely not!
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The Language of Appearance
Value (Lightness)
Hue (Chromatic Tone)
Chroma (Saturation, Purity)
The Stothard Group Colour & Appearance Specialists
Colour
Hue
Chroma
Value
Colour is a three dimensional characteristic of appearance consisting of a lightness attribute, often called “Value” and two chromatic attributes, called Hue and Chroma. Colours can be distinguished from one another by specifying these three visual attributes. The Figure on the left hand side shows the characteristic of the three facts necessary for a three-dimensional representative colour space.
Hue is often the first attribute of colour that is mentioned. Consider the pool ball. The most obvious thing about it is, that it is a shade of Yellow rather than Blue or Green. Hue is the attribute of Colour perception by which an object is judged to be red, yellow, green, blue and so forth. The colours of the rainbow arranged in a circle would make a hue circle such as that shown on the left.
A colour specification requires more than just a designation of hue. How concentrated is the blue? That is, how much colour does there appear to be? Words such as depth, vividness, purity and saturation have been used to convey how different the colour is from grey. Chroma is the more accepted term and is used to specify the position of the colour between grey and the pure hue.
A third dimension is necessary to complete our specification. This is a luminous or lightness attribute which distinguishes “light” colours from “dark” colours. Value is the term commonly used to express this attribute and is shown as the vertical axis on the left.
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The Language of Appearance Effect of Surface Characteristic on Perceived Colour
textured matte
Light Distribution From Different Surfaces
matte surface
semi-gloss surface
high-gloss surface
The Stothard Group Colour & Appearance Specialists
Surface Texture
When light strikes an opaque object the total amount of reflected light is characterized as two distinctly different light reflections from the surface: specular reflection and diffuse reflection. Specular reflection is light that is directed at an angle opposite to the incident light and is perceived by the observer to be glare caused by the shininess or glossiness of the sample. To see the apparent colour of the sample, observers must move their eyes away from the glare (specular) and concentrate on examining the diffuse (scattered) reflectance from the sample. When the smoothness of a surface changes (lower gloss or increased texture, for example), the light-reflection characteristics from that surface become much more complicated. For a medium-gloss sample, the amount of specular reflectance decreases in one direction, then spreads out and becomes mixed with the diffuse reflected light. Â A matte or heavily textured specimen scatters almost all the specular light that mixes with the normally scattered diffuse light, causing an apparent dilution of the perceived colour. Since the specular light is normally white, the appearance is a lighter colour with less chroma when it is mixed with the coloured diffuse light. Therefore, the appearance of the colour has been affected by the scatter of the specular light. Â To the average observer, a high-gloss specimen would appear to have more chroma and be a darker colour than an identically pigmented specimen with lower gloss or increased surface texture.
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The Language of Appearance
Quite often, companies want to make sure that there is NO Haze in their product at all. Other applications require a certain Haze Value, which is set.
The Stothard Group Colour & Appearance Specialists
Haze
Haze is cloudiness of a product that is caused by scattering of light. Light may be scattered by particles suspended in the substance, such as pigment particles or contaminants, or by an imperfect surface caused by dirt, oil, or a fine texture. Haze is an important appearance attribute which can be quantified and then used to assess the quality of objects such as liquids, glass, plastics, painted panels and even metals. Types of Haze The type of haze you see when you look at an object is determined primarily by the way in which you view the object. You view a transparent or slightly translucent material by looking at the light which is transmitted through it (transmission haze). You view an opaque material by looking at the light reflected from it (reflection haze). Hazy appearance is described as either transmission haze or reflection haze.
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The Language of Appearance Object 1
Light Visible Spectrum
Ultraviolet 300
550
450
Infrared 650
1000
2
400 500 600 700
Wavelength - Nanometers (nm)
The CIE Standard Observer
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3 10째 2째
Specimen
Spectrophotometric Curve
2째 Standard Observer and 10째 Standard Observer
The Stothard Group Colour & Appearance Specialists
Putting numbers on what we see The typical visual observing situation shown in Figure 1 employs three important components: light, object, observer. To develop a more objective way to specify colour, quantification of the three elements is a necessary first step.
Light
Visible light is a small part of the broad electromagnetic spectrum as shown in Figure 2. An instrument known as a Spectroradiometer can be used to measure how much of the various wavelengths are present in any source of light. All sources of light, sunlight or manmade can be expressed as tables of numbers called spectra power distributions.
Object
Light REFLECTED or TRANSMITTED by objects can be measured by an instrument known as a Spectrophotometer and plotted as spectral curves as shown in Figure 3. Spectral curves represent the amount of light either reflected or transmitted by objects relative to a reference. This again can be represented by a table of numbers.
Observer
Early colour matching experiments using mixtures of coloured lights led to the standardization of a human observer. The CIE have specified two Observers. The CIE 1931, 2 degree and the CIE 1964, 10 Degree supplementary standard observer. This summed up the way a human views an object. For example through a pair of binoculars (2 degree) or a larger area (10 degree) as shown in Figure 4. This information gets mathematically combined and turned into three easy to understand values: X (Red) Y (Green) and Z (Blue).
But is there any easier way to discuss how the product looks? Yes!
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The Language of Appearance
L=100
+b -a
+a -b
L=0
L= Lightness/Darkness a= red (+)/green (-) b= yellow (+)/blue (-)
The Stothard Group Colour & Appearance Specialists
Communicating Appearance by Numbers In 1942, Richard S. Hunter applied the opponent-colours theory of human vision and invented what eventually become known as the Hunter L, a, b Colour Scale. The XYZ system was being used but it was quite difficult to interpret. The Hunter L, a, b Colour/Appearance scale is more visually uniform than the XYZ Colour/ Appearance scale and makes it a lot easier to communicate what we see. The Hunter L, a, b is interpreted as follows (and shown on opposite page): The L-Axis runs from top to bottom. The maximum for L is 100, which would be white or a perfect reflecting diffuser. The minimum for L would be zero, which would be black. The a- and b-Axes have no specific numerical limits. Positive a is red. Negative a is green. Positive b is yellow. Negative b is blue. In 1976 the CIE recommended two new uniform methods of describing Colour and Appearance: CIE L*, a*, b* and CIE L, C, h The CIE L*, a*, b* is interpreted in the same way as the Hunter L, a, b space. The CIE L, C, h is interpreted as follows: The L-Axis runs from top to bottom. The maximum for L is 100, which would be white or a perfect reflecting diffuser. The minimum for L would be zero, which would be black. C would be the “chroma� and/or saturation and the h would be the hue and/or dominant colour. The communication of Colour/Appearance by numbers can remove the subjectivity often involved in the discussion of Colour/ Appearance. It must be remembered, however, that numbers alone have no meaning unless the specifics of the measurement process are included.
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Using Appearance Data to control our processes
The Stothard Group Colour & Appearance Specialists
Colour/Appearance Differences Comparisons between specimens or between a standard and a sample can be easily expressed as Colour/Appearance differences in terms of Delta L*, Delta a* and Delta b*. Using this information, one can interpret both the size of the difference (large or small numbers) and direction of Colour/Appearance difference (+ or -). For judging acceptability, we can see if these numbers fall within predetermined limits (tolerances). For example in the baking process: Based on the information obtained from consumer testing a leading bakery produces its product with an L value (how light or dark) of 60. If the L value were to be 40 it could suggest the following: • The temperature of the oven is too high • The product is being cooked for too long • Too much moisture in the product If the L Value were to be 70 it could suggest the following: • The temperature of the oven is too low • The product is not being cooked for long enough • Too little moisture in the product In the Plastic Industry, manufacturers can use the difference from a standard to work out how much of a certain pigment has to be added to make the target appearance for example: Based on the information obtained from their customer a leading plastic manufacturer has to make a red product that has an a value of 20. If the a value were to be 10 it could suggest that the company have not added enough “red” master batch. If the a value were to be 50 it could suggest that the company is adding too much “red” master batch. Overall if the company can stay within the tolerances they tend to: • Keep customers happy • Save money on production and raw material costs • Prevent returns • Optimise product processes
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What can be used to measure the Appearance of our products
The Stothard Group Colour & Appearance Specialists
Light Booths
Appearance Cards / Standards
Gloss Measurement
We need to ensure we physically see our products under the same “light”. As different light sources can make the product appear different it is advisable to standardise the way you look at the product using a light booth. Light booths can have different light sources installed for different situations.
When matching products it is a good idea for everyone involved to work from the same standard. Appearance standards can be made and mass produced for everyone working on the product to work to the same standard.
The surface texture of our products can change the overall appearance and the way people perceive the item. It is best to control the amount of “gloss” by using a Gloss Meter. Gloss meters can give you one value that relates to the level of gloss.
To help you cover and ask all the right questions when deciding on a solution please see our quick guide on page 24/25!
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What can be used to measure the Appearance of our Products Spectrophotometers & Colorimeters
Online-Systems
Bench-Top Spectrophotometers
Portable Instruments
The Stothard Group Colour & Appearance Specialists
The most Accurate Method Handheld & Portable Spectrophotometers and Colorimeters. Our eyes cannot create, store and remember numerical appearance data such as the Hunter L, a, b Scale. So a Spectrophotometer and/ or Colorimeter is the most accurate tool of choice.
Online Colour/Appearance Measurement The online measurement of appearance is ideal as you can generate and store data of a production run 24 hours a day, 7 days a week without having to remove samples from the line. Online sensors can provide the Hunter L, a, b scale as well as other useful information.
Defect Detection and Imaging Vision & Microscope Systems are used to detect missing parts, detect anomalies and also photograph and set standards. The correct system must be used with the right line speed and suitable camera system.
To help you cover and ask all the right questions when deciding on a solution please see our quick guide on the following page!
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Select the right instrument for you Your Industry - Your Application - Our Instruments
CHEMICAL
BIO-PHARMA
PLASTICS
FOOD
PAINT & COATING
TEXTILE
PAPER
BUILDING PRODUCTS
COSMETICS
The Stothard Group Colour & Appearance Specialists
There are many suppliers on the market today but how can you be sure you are purchasing the correct tool for the job? Our guide is designed to help you ask all the right questions when deciding on a solution. What technology is most up to date? What features will give me at least 10 years worth of use and will give me the best return on investment? What technology and setup will simulate what the human eye sees the closest? How easy is the instrument to use? What will give me the most repeatable measurement? How easy and fast is it to take a reading and get the results out of the instrument? How does the instrument deal with darker appearances (appearances that give little reflection as they absorb the light)? How durable will the instrument need to be? What maintenance is required each day, week and year? How much will it cost in year 1, 2, 3 and 4 etc.? How quickly can I talk to somebody on the end of the phone? If it is an important piece of QC equipment does the vendor have facilities to service and repair the instrument from within the UK and on site? (As an installed unit may not be able to leave site) If we start a new project and/or need some advice how available is the vendor and how much knowledge do they have? Am I getting a new, current instrument that will have parts available in at least 4 years from purchase? Does the instrument/software allow you to have the usual colour scales, differences and indices for this and future applications? What else can the instrument realistically be used for?
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The Stothard Group Colour & Appearance Specialists
So... You have a problem with appearance? We can help you on your journey with the following options:
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Training
Learn about the theory behind appearance to help you understand what could be causing your issues or to help you put your own controls in place. Comprehensive training is carried out on site and provides you with all the information needed to establish effective controls and methods.
Fact finding and method development service
We can fast track the process and have one of our consultants understand the issue and/or requirement and solve the problem by putting together an easy to understand method and a plan to implement a solution.
Already know what you need?
We stock a vast range of optical equipment including Spectrophotometers and Colorimeters, Gloss meters, Lighting cabinets and Vision Systems with full service, calibration and technical support.
Use our Lab!
We have a purpose built laboratory located in Leicestershire, East Midlands and it is kitted out with a variety of optical tools to carry out the measurements for you. All of our reports provide the method, the data and an explanation.
The Stothard Group Colour & Appearance Specialists
Visit our brand new website
www.colourmeasure.com Our website is an information resource dedicated to answering your colour measurement & appearance questions.
The Stothard Group Colour & Appearance Specialists
The Mews, 15B Town Square Syston, Leicestershire LE7 1GZ + 44 (0) 116 269 1240