Tuesday, June 10, 2008

Colour - a scientific perspective

What is colour? How do we experience colour? This post will focus on the science of colour – in simple terms:
  • The defining characteristics of colour
  • How colour is made
  • How we see and think about colour
Spectrum of Colour
Wikimedia Commons

The literature on the science of colour and the discovery of how it works is vast! As a result, art books explaining about colour have tended to take one of two paths. They either start with a hefty, very scientific chapter on the science of colour with lots of history, charts and graphs – or they ignore it completely and move straight to explaining the colour wheel.

Either way, I suspect a lot of artists have ducked the science of colour or not had access to the main messages. I’ve never been great at physics and I’ve certainly tended to be one of the former in the past! While writing this post, I’ve also been rather surprised by the number of books which ignore scientific colour basics - and how many gaps in my knowledge I've actually filled!

My personal view is that it’s very useful for artists to know about some of the basic scientific facts about colour – what it’s made up of and how it is created – but that it’s probably best to try and avoid a physics lesson!

What I'm trying to do is produce an outline of the science of colour which works for people who want to know more about colour (like me), mainly so we can avoid having incomplete or misconceived notions about colour. For example, one of the reasons I started this colour projects is that I didn't know what I didn't know!

In doing so, I’ll be focusing on what is known, rather than how it was discovered or by who or exactly how or why it works. So I'm not going to focus on the history of scientific development or the intricacies of the scientific background to the discovery of colour at all!


However for those who do find these things fascinating and/or want to know more after reading this and the more extended article on my website, I’ve included a number of references to technical articles relating to colour on the internet in a new information site called Colour science, systems and models - Resources for Artists.

I’ve also transferred most of the science references previously on the original information site Colour - Resources for Artists - which now leaves that looking a bit more straightforward.

I can also recommend Colour by Edith Anderson Feisner; Color – right from the start by Hilary Page and Colour Mixing Bible by Ian Sidaway.

For the rest of us, let's just assume that it's very useful to know about the end result without knowing too much about how it happened - and take the rest on trust!

What now follows is a shorter version of an article which I'm including on my website page Making A Mark Guide - Colour. I'm planning to work on the article some more as the project progresses. Do let me have any comments - particularly about aspects you find confusing or surprising - or that I've got wrong.

The Defining Characteristics of Colour - Hue, Value and Intensity

The most sophisticated machine for differentiating colours is the human eye. But how do we manage to tell one colour is different to another? What makes them different?

Hue, value and intensity are the three essential attributes of perceived colour – the colour we see with our eyes. These are also the defined ways in which the differences in colour can also be described and defined in a scientific way. These are described below. Both hue and value are also very important elements which contribute to the overall effectivess of any composition.

Hue, saturation, value

Hue

Hue is pure colour – one without tint or shade – and is used to describe the actual colour of an object or material. In everyday use, it’s another name for colour as we normally use the word in everyday language. Local colour is the term artists use to describe pure colour of a substance which is unaffected by the impact of light.

People have different views about what a colour is. If you asked 20 people to all produce a square coloured red, they’d all produce a slightly different colour of red. Color-Aid papers can be used to identify a hue correctly. Coloured paper was used by Josef Albers when he was developing his ideas about colour and writing Interaction of Color

Pigment/paint manufacturers sometimes use the word ‘hue’ when they’re replaced an original ingredient, which was used as the name for the paint, with a more modern (and often less toxic) substitute which achieves the same hue as the original paint. So for example, a paint may now be known as Cadmium Yellow (hue) even though it contains no cadmium.

Value

Value - otherwise known as lightness or luminance – is a measure of where a particular colour lies along the lightness–darkness axis. Value is also known as the tone (or tonal value). It’s often confused with but is not the same as brightness (which is actually about intensity).

Pure hues naturally vary in value and can be found in different places on the value scale. From light to dark they rank as follows: yellow, yellow-orange, orange, yellow-green-yellow, red-orange, yellow-green, green-yellow-green, red, green, red-violet, green-blue-green blue-green, blue-green-blue, blue, violet, blue-violet. To make hues of equal value they need to be adjusted using either white or black.

Intensity

Intensity is also known as colourfulness or saturation or chroma. A ‘saturated colour’ is the purity of a hue at its maximum intensity, at its most colourful. Thus, a highly colourful object is vivid and intense. In contrast, a less colourful object appears more muted, closer to gray. With no colourfulness at all, a colour is a “neutral” gray. I tend to think of intensity as being ‘in your face’ and its opposite as being about ‘subtlety’.

More technically,
  • colorfulness is the difference perceived between the color of an object and gray.
  • saturation defines the degree of purity of a colour relative to the brightness of a pure hue
  • chroma strength is a measure of a hue or colour’s relative purity or brightness – one to another and compared to white which is the most intense chroma.
  • lighter value hues have a stronger chroma than darker value hues.
How colour is made

The colour that we see is created from light. If there is no light, there is no colour.

The colour that we create on paper or canvas is different and operates in a different way. This is because it’s created from pigments or dyes.

The colour of light

Colour is actually a form of energy. The colour that we see is created from light. When light hits a surface, some of the light is reflected and some of it is absorbed. What we actually see is the colour produced by the light waves which are reflected.

Colour, in very simple terms is created through one of three processes:
  • Additive processing – which relates to all things visual and digital – which includes everything you are looking at right now).
  • Subtractive processing – which relates to pigments and paint
  • Partitive processing – which is based on a viewer’s reaction to colour when colours are placed next to one another. This is an important way of understanding colour because the reality is that the norm is that we always see colour in the context of other colours.
The important thing to know is that additive, subtractive and partitive processing of colours all produce different results when mixing colours.

Additive processing

Additive processing is used for mixing the different colours in light. Mixing colours increases brightness and lightness until it ultimately produces white light. White light is the colour of light at midday. It contains all the wavelengths in the visible range of the spectrum.

Additive processing is responsible for the colour of everything we see and the presentation of digital colour.

Additive processing colours
Wikimedia commons

Colour is made up of light waves. The colour that we actually see is what remains when light hits the particular materials in a surface. The light waves associated with that surface are reflected back and the rest are absorbed by the surface. So a pink surface is one which reflects pink light waves and a purple one is one which reflects purple light waves. Black is the colour created when all light waves are absorbed and white is created when all light waves are reflected.

Primary light colours are red, blue and green (RBG). More accurately, they are blue-violet, green and orange-red which all combine to make white light. Mixing the lightwaves of these three colours increases brightness and lightness and ultimately produces white light.

In simple terms, the human eye can physically see how additive processing works when stage lights with different coloured gels are mixed on one spot on a stage.

Subtractive Processing

The subtractive process is used for combining pigments and dyes, paints and printers inks. The bottom line is that mixing colours in a subtractive process absorbs light waves and diminishes lightness.

Subtractive processing - cyan, magenta, yellow
used in CMYK printing process

wikimedia commons

Primary colours are those which cannot be made by mixing other pigments and are red, blue and yellow - and cyan, magenta yellow for printers inks. However if all the primaries were mixed together they would create black. As more and more colours are mixed together they absorb more light waves and reflect less back – until the end result which is black. Although as we all know many of us have been known to take a long diversion making mud colours first!

Subtractive processing is one of the main reasons why artists often talk about trying to achieve ‘clean’ colours.

Partitive Processing

Partitive colour mixing is a perceptual process. The eye creates the colour based on the impression created when one colour is placed next to another colour. This is an important way of understanding colour because in normal circumstances we always see colour in the context of other colours – but in art we control that process.

Partitive processing is important to artists – because we choose how we place colours on canvas or paper and what we place next to them.

If dots of different colours are juxtaposed, your eye performs the mixing process and they can appear to be mixed in an additive process – which increases brightness and lightness. Seurat was famous for painting in dots – called pointillism. Partitive coloured dot mixing also occurs in colour printing where what is produced is made up of lots and lots of different coloured dots.

How we see and think about colour

Our experience is partly down to the physics of how light behaves (see above) and partly down to the physiology of how we physically perceive and register colour. I’m going to focus on two aspects of how we experience colour - colour vision (what our eye can see and brain can process) and colour memory (what our brain can remember).

Colour Vision - what the eye can see and the brain can process

You’ll know that vision is a function of both the eye and the brain and colour is perceived using your capacity for colour vision. You can have faults arise in either which can mean that your visual processing of what you can see is less than perfect (e.g. colour blindness). What you may be less clear about is that your vision is also a response to light waves – but you don’t need to know how that works – just that it does!

Example of an Ishihara colour test (numeral 2)
Philip Ronan
This file licensed under Creative Commons Attribution 2.5 License

Our capacity to perceive and notice colour is affected by a number of factors which include:
  • The level of illumination.
  • The nature of the media producing the colour (matte carpet; shiny metal)
  • Colours reflected by adjacent objects
  • A colour’s relationship to other colours present around and about an object
  • The way we choose to value a colour or not according to our culture (of which more later).
The combination of eye and brain produces the most sophisticated mechanism known to man for the perception of colour – in theory. In practice, most people probably don’t exercise their eyes and brain often enough to reach their full potential

Many a time I’ve heard painting tutors asking students (and me!) to describe the colour they can see – usually because the way we’ve represented it on paper is quite a long way from reality. I’ve learned over time that we can all get much better at both seeing colour and describing colour – but only if we practice! There are some tips contained in the paper on my website.

Colour memory - what the brain can remember

You only need to know one thing. People tend to have very poor memories for colour. This is the reason why we have to carry around a piece of curtain fabric or wall paper when trying to match colours when decorating!

For an artist, this means for the artist that unless you have a highly trained colour memory:
  • You won’t be able to carry the memory of a colour that you’ve seen in your head for very long. You certainly won’t remember all the nuances of colour that you can see.
  • It really doesn’t matter how many formulae for making colours that you read about, the reality is that you won’t be able to remember them.
It’s sad – but these are the physiological facts of life when it comes to colour! What you can do to improve is learn some basic principles which can then be more widely applied – more tips in the website paper.

Links:

14 comments:

Deborah Paris said...

Wow, Katherine-what a wonderful resource! Perhaps you have mentioned it elsewhere but I think that, in addition to value and intensity, temperature is one of the defining (and often overlooked) characteristics of any particular color/hue.
I look forward to more installments of your project!

Adam Cope said...

very good short summary/overview :-)

>>>>>>>>>>>

why are they changing the word 'saturation' for 'intensity'?

i guess because one colour such as red is more intense than another colour such as brown at it's max saturation?


HSL is a photoshop standard. there is no intensity button in photoshop, only saturation.

shame as nonemclature which changes regularly is confusing... guess we all have to periodically re-learn colour theory so as to keep up to date. there's so much too learn, personally i've done three concerted campaigns into learning colour theory over the years. wouldn't want more info than my painting/tecahing practice could handle/digest/put into practise.

BTW, painters need to know the three isihara scores of colourblindness... helps to know what colours people tend to be blind on & thus potentially explains some of the reactions of viewers towards one's painting (eg: people often don't know they're colour-blind towards turquoise, for instance)

stay colourful!

Katherine Tyrrell said...

As you say Adam - it's necessary to distinguish between
- whether a colour is operating at full saturation as that colour
- how a fully saturated colour compares in intensity to another fully saturated colour. The reality is at full saturation they aren't all the same.

Monday/Tuesday this week I found that the big big problem was not about trying to collect and share information about colour - but rather about finding neat ways to chunk it up and make it digestible. I still puzzled by why some books on colour give indepth history and physics lessons - and then go on to leave out hue value and saturation as key dimensions on colour!

Thanks for the note about PS and the colour blindness - I've always thought that some artist's palettes could probably be explained by a degree of colour blindness. Do you have any more info about where we could find the colour blindness test?

Speaking personally I have turquoise turned full on if not OTT!

Katherine Tyrrell said...

Deborah - I'm still debating how temperature fits in - it doesn't seem to feature in any of the scientific models which maybe means there isn't a scale of measurement for it?

Somebody commented a while back about temperature as a concept having fallen out of favour.

Certainly in the days of international standards for colour, hue, value and intensity seem to be the way forward in terms of classifying colours - with lightfastness being the next essential measure of importance for me!

Adam Cope said...

when i was researching this about four years ago on the net, i found some very good isihara sites as used by opticians for identifying the three scores of colour blindness.

the type with the coloured circles with a fure or a number emebedded in them.

don't know if there're still on the web?

>>>>>>>>>>>>

cobalt turquoise light...my favourite colour.

interestingly, i seem to remeber that most men can't see turquoise or don't know it's name. is colour perception gender based or is it nomenclature agin?

Katherine Tyrrell said...

I know that colour blindness is predominantly experienced by men and I believe some aspect of colour blindness is completely gender-related - but can't remember what exactly.

I'll have a look for the colour blindness tests.

Adam Cope said...

i've just posted about warm & cool colours in painting

Robby said...

As a painter, I've always had to work intuitively, since I have no formal art education. Things like technique and composition have been (relatively) easy to figure out, but color is definitely a subject that requires a certain amount of study, or a lot of study in my case. Thanks for your help.

Casey Klahn said...

My feeling on Temperature is that it is a subset "characteristic" or "property" after one considers hue, value, intensity. For instance, intensity is a more valuable tool (for me) than temperature.

One site says saturation is like the local color seen at different times of the day. That sounds like a muddle, because it describes perception.

I try to keep the intrinsic characteristics of a hue separate from the perceptual aspects. A pigment is red and, if "pure", it is at it's maximum intensity. Mix it with (not just green, but any other color[!]) and it looses intensity.

If this given red is mixed with some black, it's value changes, but the intensity will still (in theory and in good practice) be at it's max.

So, I see a problem with the use of the word "pure". Pure to me is an unadulterated pigment.

BTW, Katherine, I will insert here that your term usage in this series is spot on 99.999999% of the time. That is a huge challenge. I see these reference sites being muddled, and "pure" is one of those muddled terms.

Casey Klahn said...

That was a longish comment, eh? I had some instability on the computer and meant to preview it first!

Usually something that long deserves to be a post at my blog instead of a comment.

This is a great series, and I appreciate your precision in language here, Katherine. It is superior to the majority of sites I visit on the net "teaching" color.

Deborah Paris said...

Hi Katherine. I don't know how temperature might be treated scientifically, but I do know its an essential part of painting (at least for the representational painter). The old adage "break temperature, not value" goes to the very core of creating the illusion of 3-D form on a 2-d surface. Everything in painting is relative- that is, how light or dark (value), warm or cool(temperature), dull or bright (intensity) one color is compared to another in that particular painting. Being able to rate them on a scientific scale might be interesting but not too helpful when trying to solve a particular painting problem. Temperature can have a tremendous impact on how we perceive other attributes of color-for example, warm colors, particularly yellows, are generally perceived as being lighter in value than they actually are.

I have found in teaching that temperature is the one thing about color that is least understood and that, once understood, can have a dramatic effect on the quality of one's work.

So, I have to remain a resolute lobbyist for temperature as a key attribute of color...:)

Felicity said...

Wonderful post Katherine! I'm going to disagree with the last point though becuase my hubby is living proof that some people DO have colour memory. When we are out looking for things for the house, I know I can ask him if it's a match and he'll know exactly how it matches or if it's close but has too much yellow or too much blue, that sort of thing - 100% success. But at the same time we argue about names - I think I'm more accurate but he'd disagree!

fapj said...

Well put together and enjoyable to read! But....I don't agree with the global remark that no one can remember colour. I have a very long and strong colour memory. I certainly never need to take samples along to match a colour and I can reproduce colour mixes without the original in view! I think it's partly related to having a photographic memory or at least a very strong visual memory. Nothing to do with being an artist, of course. I also remember exactly where something I need is on a page in a book. That was very useful when I was working as an opera singer. If I had a rather nasty bit to negotiate musically, I would leave my vocal score in the dressing room open at the page, then just read it off if I needed it. Leaving the book closed was not the same psychologically. I needed the visual as a kind of insurance.
I think training the memory is the clue to all this. As a performing artist I had to! Now I run choruses and do all my directing from memory, too. My audial memory is also highly trained to pick out wrong notes in chords and be able to correct them just by listening! That isn't exceptional for musicians, of course!

Katherine Tyrrell said...

Jury is still out on temperature!

On the question of memory - I think it would be more accurate to say that normally people cannot remember colour.

People who can remember colour have trained their visual capacity and memory in some way for a practical reason - or they are just very exceptional people. Most people get it wrong. I've found I can retain the colours of a scene I've sketched for up to 24 hours - but no longer. Plus the memory deteriorates over that time. But I need to have looked and looked and looked first. After that it's the colours in the sketch that prompts the memory - and that's why i find sketching invaluable. I can't get the memory of the colours back from looking at photos as the colours in a photo are just wrong.

I've got a memory that errs slightly towards the photographic if it is something visual - insofar as I always used to be able to remember precise locations for things or what it said on an appointment card without needing to refer to a diary. Or should I say used to. Time has a terrible habit of reducing one's capacities! Now I sometimes can't remember what I went next door to get!

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