New to colour? Here are some basic colour concepts you need to know.

Sensing colour is a natural process in our lives, so we tend to take for granted that its simple and never think there is a lot more to colour than just what meets the eye.

As colour has become ubiquitous not only in our natural world, but now also in our food and beverages, automotive, plastic, paint and built environments. In almost every imaginable application, colour and consistent colour is now a standard requirement.

Colour is sensed when light is reflected from an object, when light shines through and object, or indeed if the object diffuses or emits coloured light. We discuss how colour is sensed in more detail in some of our other blogs.

 

Antoni Gaudí – the famous architect and craftsmen who moved to Barcelona in 1868 to study. He combined his studies with working as an assistant in an architectural practice, as well as in the workshops of a carpenter, a glassmaker and a locksmith where he learned these crafts.

He stood out in the subjects of design, drawing and mathematical calculation.
In 1878, after qualifying in Architecture, he received his first official commission. As his professional reputation grew he undertook larger projects and in 1883 he took over the design of the Sagrada Familia, a new and technically challenging Cathedral while also working on other projects.

He worked for 43 years on the building until 1926. In 1914 he left all other work to concentrate exclusively on this sole project until his death on 10 June 1926, the result of a tragic accident three days earlier.

Through out his life Gaudi was fascinated with colour, its properties under varying conditions, its relation to nature and its part in setting our moods and emotions.

The image below is just one tiny part of the immense work of colourful art and architecture he brought to this project.

Here are some facts you need to know about colour measurement:

If you are going to enter into the business of measuring light or colour, it is important to first be clear on a few facts. These facts are often misunderstood or not taken into account because people believe that they understand how colour works, when this is often not the case.

As humans, we sense colour and light automatically and we therefore we pay little attention to the complex mathematics and optics at play.
Whether it is in manufacturing, R&D or simply trying to repaint your house, dealing with colour is not always simple unless some basic rules are understood and followed.

• Light is not visible but its effect are – Our modern understanding of light and colour begins with Sir Isaac Newton (1642 – 1726) and a series of experiments that he publishes in 1672. He is seen as the first to understand the rainbow by refracting a ray of white light through a prism which splits the light into it’s component colours: red, orange, yellow, green, blue and violet. This understanding has been the basis of colour measurement and colour perception ever since.
• Data captured by the eye is basically meaningless – There are always some constraints and pitfalls when dealing with colour. The best way to get a sense of these pitfalls is by watching this video which speaks to how light works and how humans sense light in different ways.

As this diagram below illustrates, light from the sun or artificial light, may fall onto an object made up of different coloured components. The data is transmitted to the eyes as our suitable optical tools capable of sensing the wavelengths found in the visible light rwavelength range from about 360 – 780nm on the electromagnetic spectrum.

This data is sent to the brain where it is processed, and the sense of colour or colours is “decided” by the brain based on our past experience with that object, and we then “see” whatever it is that our brain has decided the object is, including what colour it is.

As an example, if you compare two colours for the purpose of trying to colour match one to the other, you may look at the two objects and “see” some differences in the colour and appearance between the two objects. However, you may not know what those differences are or how to communicate them. If on the other hand, the two colours match perfectly, the first thing that you will sense is that they “Feel” right. No amount of discussion or technical jargon will convince you that the colours are the same or not. It is a sense that we feel and can discern whether they are the same or different.

• Colour is difficult to remember and recall – Once we have seen a colour, it can be very difficult to even picture that colour in our minds again. If we no longer have the object in hand, it can be extremely difficult to try and colour match or even determine whether two objects are the same colour without a side-by-side comparison.
• Colour is challenging to describe and communicate – Verbal descriptions of colour can be vague and misleading. Even if you have two samples for side-by-side comparison, it can be difficult in communicating the difference in colour between the two samples. If asked to describe the colour ‘Royal Blue’, how would you go about it?
• Colours look different under different conditions – This point seems fairly obvious, yet many customers confuse the issue that the colour of an object is NOT the property of that object, but rather the perception of the observation under defined conditions. Picture this, you have a bright red apple in front of you in a room with great lighting. The apple looks bright, shiny and it’s clearly a red apple. Now what would happen if you switched off the lights? Is the apple still red? Probably not.
  It is crucial that conditions of observation are kept constant for accurate colour measurement.

Here’s the question then, how do we measure colour?

While nearly any object can be measured in almost any form, the rules of measurement and the conditions of measurement might change depending on the application or situation.

Using precise instruments to measure colour is made possible by the fact that when light is split by a prism, the different wavelengths result in different colours. This gives us a least ONE axis or mathematical tool to start to calculate colour. Each wavelength has a distinct colour.

If we collect Spectral Data, we can at lease see which group the colours fall into, although little data is given about the quality of the colour. It is either Red or Yellow, but whether its bright or dark, pail or intense, has to be calculated further. This is where we apply the CIE norms like the algorithm CIE L*a*b.

The picture above shows the results from a typical colour difference measurement where we can see the colour as defined by the C.I.E L*a*b* colour space.
L*a*b* describe the precise coordinates of a colour on a three-dimensional colour space. This “GPS” of the colour on the colour space can be used to compare two colour together using the Delta values (dL*, da* db* and dE*ab).

This information is often used to set Tolerances, which can be used to define the outer limits of colour acceptance. This data is simple and accurate and allows colour to be easily communicated using colour difference. Based on the data received in the image above, it would be easy to see that the sample colour is LESS RED or MORE GREEN than the target colour. We could also say that the sample is MORE BLUE or LESS YELLOW than the target.

Using this information we can understand exactly what needs to change in the sample to get the colour more closely matched to the target.
While this method is simple and reliable, you sometimes need to know more about colour and Full Spectral data is required.

 

Above we see, in addition to the CIE L*a*b values, there is also a Red Spectral Curve or Reflection Curve which shows the percentage of colour reflected at different wavelengths. In this case we could see we are at a Green colour, as most of the reflectance is in the middle of the curve, in the Green spectral area.

This reflectance curve is less like a GPS position as we discussed with L*a*b*, and more like a precise fingerprint of that colour that is unique to that sample. This gives you a clearer idea of the chemcial or colourant components.
If you compare reflectance curves between two samples and you notice that although the L*a*b* and Delta L*a*b* are within tolerance, the spectral reflection curves are not the same, it would be safe to say that the chemistry of the one sample does not match the other sample. This can be used to understand whether the chemical or colourants within the sample have changed indicating adulteration or a change in recipe.

We can see this with the graph below where two samples have very different spectral curves indicating that they are not the same based on the chemistry of the sample.

Want to take your colour measurement further?

Before embarking upon a new colour measurement process, whether that be for quality control and pass/fail judgements or for more advanced applications like colour formulation and prediction, let’s have a detailed discussion about your application and the potential benefits you can get by implementing precise colour control.

We can help you in this regard by assisting you with:

• Select the correct solutions for your application and budgets
• Understand how to get the most value from your colour measurement device
• Implementing an effective colour measurement to improve quality control and guide production decisions
• Offering local service and support for all our solutions
• Technology Transfer training packages to ensure optimal instrument usage.