A new study by academics at the University of Colorado suggests that the colour ink you use when providing comments and feedback to students can alter their perception of criticism and place unnecessary blame on the teacher for bad marks or feedback. According to the researchers teachers should use a blue pen if they want their comments to be taken in a constructive manner. The full research paper is available online here.
Readers may be interested in a new colour-related blog by the SDC’s Chief Executive Graham Clayton. The SDC – the Society of Dyers and Colourists – is the world’s leading independent educational charity dedicated to advancing the science and technology of colour worldwide. It is a professional, chartered Society and becoming a member gives access to SDC’s professional coloration qualifications. I have been a member since about 1982 and I am a Chartered Colourist and a Fellow of the SDC.
I also recently came across another colour blog called chromatic notes. It’s not clear from the web site who runs this blog but there is a great deal of technical information there.
There are two phrases I keep seeing written down all over the internet that cause my blood pressure to increase.
The first is that the colour primaries are red, yellow and blue (RYB). And the second is that the primaries are colours that cannot be made by mixing other colours. Neither of these statements are true, of course.
The first statement makes no distinction between additive colour mixing (of lights) and subtractive colour mixing (of paints and inks) but subtractive colour mixing is normally implied. However, RYB is a relatively poor choice for three colour primaries. The range of colours that can be produced is actually quite small. For most painters and artists it doesn’t matter because very few work in just three primaries – if they did so they would probably be frustrated by the small gamut of colours achievable. Many artists (painters) will use 10 or more basic colours to mix their palette. However, there is a group of people who care passionately about the gamut of colours that can be obtained by mixing three colour primaries – that is the people who work for companies such as HP and Canon. These companies make CMYK printers for the consumer market and their jobs depend upon consumers liking their printers. They understand that the largest gamut (in subtractive mixing) can be obtained if the primaries are cyan, magenta and yellow (CMY). The teaching of RYB as the (subtractive) primaries should be stopped. It’s already gone on for far too long.
One reason I don’t like the teaching of RYB as being the subtractive primaries, in addition to the fact that it is wrong, is that it confuses people who are trying to learn colour theory. This is because red, yellow and blue seem to be quite pure colours and this encourages people to hold the second belief I don’t like which is that the primaries are pure colours that cannot be mixed from other colours. If people understood that the primaries were CMY it would be less tempting to hold this belief about the purity of the primaries. Of course, if you make a palette of colours of three primaries then it is true that no mixture of two or more colours from that palette can match any of the primaries. However, there are other colours (that are outside the gamut of the primary system) that could be mixed together to match the primaries. This false notion of purity confuses the real issue – that is, that the subtractive primaries are cyan, magenta and yellow because the additive primaries are red, green and blue. Look at this picture below:
The additive primaries are red, green and blue and the secondaries are cyan, magenta and yellow. Correspondingly, the subtractive primaries are cyan, magenta and yellow and the subtractive secondaries are red, green and blue. Simple.
I wrote about this before so for a slightly different perspective see my earlier post.
Perhaps I am so agitated about it today because I am just watching England getting trounced by Ireland at rugby when the Grand Slam was so tantalisingly close. Or maybe I will feel just the same tomorrow.
It’s possible to say that everything is designed. When we think of design we often think of fashion design or graphic design, or perhaps automtotive design or software design. But everything is designed. When we put a meal together, couldn’t you say we are designing? A chef is a food-designer!! When we are arrange our furniture, aren’t we engaging in interior design? Isn’t a chemist engaging in design at the moulecular level? Thinking like this leads to the idea that design is everything. However, if design is everything and everywhere then it is no thing and nowhere in particular. So if design is everything then it is also nothing. Discuss.
Though this is a blog about colour I can’t help but take this opportunity to announce that I recently had my first app for the iPhone accepted by Apple on the appstore – no mean feat I can assure you – and it is now available for download.
It’s a chess app called ChessTutor Lite. Most chess apps allow you to play the computer or even play your friends. Mine doesn’t allow either of those things. Booooooo! However, it does something equally exciting in my opinion – it allows you to step through a grandmaster game and predict the moves at each step. For each move you make you get a score (100% if you make the move made by the grandmaster – or as good as – right down to 0% if you make a game that results in a catastrophic defeat!!). You also get a natural language comment about why the move you made is good or bad. Huzzzzaahahah. So it allows you to assess how good your chess is and learn how to play better. It’s pretty unique I think. And it’s completely free.
You can find out further details about here – http://www.colourchat.co.uk/apps/chesstutor/ – or just put chesstutor into the search box an your iphone apps page.
As a Color Designer in Nike Sportwear, you’ll work under the direction of the Design and Color Leaders to lead a category to create innovative color design solutions for a line of footwear. You’ll collaborate with category cross-functional teams to create a merchandisable line from concept to retail presentation; build innovative, retail viable color solutions for category or gender-specific lines; create seasonal direction of color; and lead color merchandising strategies and stories seasonally. You’ll also research and deliver color, design, market and lifestyle trends that influence and impact the product category process from product briefing to product concept to salesman samples. You’ll plan and execute color designs; collaborate with Design, Product Marketing, Development and Material Designers to focus color solutions for market success; finalize product details; and proactively follow through on the execution of color on each product.
For about 100 years there has been an international system for colour specification – it’s called the CIE system. The acronym comes from Commission Internationale de L’Eclairage.
This system is based on the notion of additive colour mixing – http://colourware.wordpress.com/2009/07/13/additive-colour-mixing/
Since it is possible to mix together three primary lights and make a wide gamut of colours (though not, of course, all colours) the principle is that the amounts of these primaries that an observer would use to mix togther to match a colour is a useful specification of that colour. We refer to these amounts as tristimulus values. One could imagine a visual colorimeter whereby an observer would try to match a colour that is to be specified by adjusting the intensities of three primary lights that are mixed together – once a match is obtained then the tristimulus values would define or specify the colour. All that would be necessary would be to able to decide on a set of primaries and manufacture the visual colorimeters so that they are very consistent from one device to the next. It would be a little clumsy though to have to use one of these visual colorimeters. But in principle it could work.
Fortunately the CIE does not require the use of such visual colorimeters since in 1931 the CIE measured the trismumulus values that observers made when matching various colours. These were averaged to create the so-called CIE standard observer. And here’s the really clever bit. Having defined the CIE standard observer it is possible to calculate the tristimulus values (the amounts of the three primaries that an observer would use to match a colour) without any further observations. All that is required is that we know the amount of light at each wavelength reflected by a sample or (in some cases) emitted from a device such as computer display and then – by using our knowledge of the CIE standard observer – it is possible to calculate the tristimulus values.
So what were the primaries. If you have read my previous post, What is a colour primary – http://colourware.wordpress.com/2009/07/08/what-is-a-colour-primary/ - you’ll know that the choice of colour primaries is somewhat arbitrary. Well, in fact the original determination of the standard observer what carried out in England using red, green and blue primaries. But the data obtained were later modified to refer to a different set of primaries known as X, Y and Z. It was necessary to make this adjustment because using any set of real primaries it was impossible to match any colour with mixtures of the primaries; using RGB meant many colours could be matched, but not all. So a set of so-called imaginary primaries was conceived which could – in theory – be used to match all colours. So the tristimulus values of the CIE system are known as X, Y and Z.
In fact, it didn’t really matter which set of primaries was used; the CIE system was concerned with colour matching. If two samples have the same tristimulus values then they would be a visual colour match no matter which set of primaries was used. So the choice of primaries really was not critical.
Today many instruments are commercially available – colorimeters, reflectance spectrophotometers, radiometers) – that, with the use of software, allow the CIE XYZ values to be measured; these instruments are extremely valuable in many industrial and commercial applications. The CIE system is still very much alive today, though many users often prefer to use one of the more advanced colour spaces – such as the CIELAB colour space – which was defined by the CIE in 1976 and whose values are very easily calculated from the CIE XYZ values. For further information about the CIE please visit their web site - http://www.colour.org/
There are – broadly speaking – two types of colour mixing: additive colour mixing and subtractive colour mixing. Subtractive colour mixing relates to how inks, paints, dyes etc add together to form different colours; additive colour mixing refers to how light-emissive colour devices create colours. So we’re talking about how computer monitors work or how phone displays work.
The essential principle behind additive colour mixing is that we can mix together three colours – called colour primaries – and create a surprising range of colours. See my earlier post - http://colourware.wordpress.com/2009/07/08/what-is-a-colour-primary/ – for further details about colour primaries. The additive primaries are red, green and blue. Is there anything special about these three colours that justifies their use as the primaries? No, apart from the fact that if you use red, green and blue as the additive primaries you get a large gamut (range of colours that can be produced). There is no reason why you couldn’t use orange, purple and turqiose as the additive primaries – it’s just the range of colours that could be created would be unsatisfactorily small. And nobody would like that!
So, we have red, green and blue as the additive primaries. The figure below illustrates how additive colour mixing works. Imagine that we have three projection lamps at the back of a hall – one has a red filter and so produces a beam of red light, and the other two use filters to produce green and blue beams. We project these onto a white screen and get three circles of light (one, red, one green and one blue). We then move the angles of the projectors so that the circles of light overlap. We get something that looks rather like this:
Where the red and green light overlap we get yellow. We get magenta and cyan for the other two binary mixtures. So,
red + green = yellow
red + blue = magenta
green + blue = cyan
And if we mix all three primaries we can achieve white (or other neutral colours). The primaries could be single wavelengths of light – so we could use a primary at, say, 700 nm (for the red) and one at 450 nm (blue) and one at 530 nm (green). In practice, most devices (CRTs, LCDs etc) don’t use single-wavelength primaries since it would be hard to create bright screens (gamuts are 3-D not just 2-D) but in principle could do so. It’s also important to note that different devices and different manufacturers use slightly different primaries.
But let’s imagine for a second that the three primaries used in the pictuire above are at 450 nm, 530 nm and 700 nm. Green light (530 nm) and red light (700 nm) additively mix together and generate yellow. When this happens what is being mixed and where does this mixing take place? Take a few moments to consider this before reading on.
Notice I said that they additively mix to generate yellow – I specifically avoided saying that they mix to generate yellow light. If we look at the part of the screen that is yellow we would see that we have some light at 700 nm and some at 530 nm. The wavelengths are not mixed; they don’t mix together to generate some third wavelength of light such as 575 nm (I choose this wavelength since monochromatic yellow light is about 575 nm). So no physical mixing takes place other than – I suppose one could argue – that the red and green lights are mixed in the sense that they are spatially coincident. But that’s not really mixing, for me, and certainly doesn’t even begin to explain why we have the sensation of yellow when we look at these wavelengths together.
So when we say that the red and green lights are mixed together to create yellow we should be aware that no phsyical mixing takes place. Indeed, one could argue that mixing is really the wrong word to use. Though as I write this I am struggling to think of a better one – suggestions on a postcard please.
When we look at the mixture of red and green light we see yellow – but the eye is still receiving the indivual wavelengths of red and green light. However, the visual response to this is that yellow is perceived. Indeed, a carefully composed mixture of red and green light could produce a yellow that is visually indistinguishable from yellow monochromatic light; but physically the mixture would still consist of light at 530 nm and light at 700 nm. If mixing occurs at all in any real sense it is in the perceptual mechanisms of the visual system. Indeed, at the heart of this matter is the way in which our visual pigments respond to light …. more about that another time.
I try to keep my blogs short. But this is going to be difficult!
Let’s start with what a primary is not. The primaries are often quoted as being red, yellow and blue. And on the BBC website – of all places – it says “Primary colours are three key colours – Red, Yellow and Blue. They cannot be made from any other colour”. For the BBC site visit http://www.bbc.co.uk/homes/design/colour_wheel.shtml.
The statement that primary colours cannot be made from any other colour is simply not true. Further, it gives the mistaken impression that there is something special about these primaries (red, yellow and blue) that makes them stand apart from the other colours. Another false statement that one often sees even in quite scholarly work is that any colour can be made by the mixture of three primary colours.
What is true is that if we select three appropriate colours and mix them together we can make a suprising range of colours. These colours – let’s call them primaries – can combine to make a huge range of different colours but unfortunately there are no three primaries that can be selected such that in mixture they can create any other colour. Depending upon the choice of primaries the range (or gamut) of colours that can be created in mixture is larger or smaller. What makes a good set of primaries? Well, I think it is reasonable to say that a good set of primaries is one where the gamut of colours that can be created is large; indeed, I would argue that the optimal primaries are those that create the largest possible gamut.
There are certain sets of primaries that can easily be predicted to give a small gamut. For example, if any of the primaries are dull and desaturated then the gamut will not be very big. Also, if the three primaries are similar to each other then the primaries are not likely to be a good set. And finally, if it is possible to combine two of the primaries together to make the other one then the gamut will be tiny. This is where – I believe – the misleading statement on the BBC website comes from; for a good set of primaries it is important that the primaries are independent (that two cannot be mixed to match the other one) but this is a long way from the BBC statement. Once we havs selected three suitable priamries then it’s true that they cannot then be made by any other colours that the primary system can make – but to argue that this is why they are primaries is clearly a circular argument.
There is nothing special about red, yellow and blue. In fact, they are not even the optimal primaries! To say what the optimal primaries are we need to specify the type of mixing: additive or subtractive. Additive mixing describes the behaviour of light-emissive systems such as computer displays, subtractive mixing describes how paints and inks mix. For subtractive mixing the primaries are often quoted as red, yellow and blue, as in the BBC article. However, a larger subtractive gamut is obtained if we use cyan (instead of blue) and magenta (instead of red) – see figure below.
One of my current research interests is to understand why red, blue and yellow became known as the artists’ primaries when a larger gamut is obtained if a bluish red is used (something closer to a magenta) and if a greenish blue is used (something closer to cyan). One only has to look at the primary colours used in inkjet printers for example (where the manufacturers have a vested interest in being able to create a large gamut) to realise that cyan, magenta and yellow are the optimal subtractive primaries.
For additive colour mixing the optimal primaries are red, green and blue. The additive and subtractive primaries have an interesting relationship – but that’s for another blog, another day.
So when Newton wrote that the rays are not coloured, what exactly did he mean?
Well, he meant that even though we may say loosely that light at 400nm is blue and light at 700nm is red this implies that the blueness and the redness are properties of light. Although there are philosophical arguments that would support colour as a property of light (and we’ll get on to those arguments in a later post) for now I would like to put forward my view (which is, I believe, consistent with Newton’s) that colour is not the property of light.
The evidence that supports my view is that light at 700nm may look red to most people most of the time, it doesn’t look red to all of the people most of the time or even to most of the people all of the time. For a very striking example please consider the image below:
In this example, you will see some blue spirals and some green spirals. But physically the blue and green are the same. In terms of wavelengths, exactly the same wavelengths (in exactly the same proportions) are being reflected from the areas that you perceive as being green and the those you perceive as being blue. If you think in terms of digital (RGB) terms, the RGB values of the green areas and the blue areas are the same – both are about R = 9, G = 20, B = 160. We know now that the colour that you perceive for a wavelength of light or a group of wavelengths depends upon the colours that are close by. This is often expressed as contrast or assimilation. When contrast occurs colours become less like the colours that they are next to an image; when assimilation occurs colours become more like the colours that they are next to. Contrast and assimilation effects result in you seeing two colours, a blue and a green, when physically only one colour exists.
Straight away some of you can see that I am falling into loose language straight away because I am using colour in two different ways. On the one hand I am saying the two colours are physically the same and on the other hand I am saying that the two colours are perceptually different (blue and green). Which is it? It all depends upon how you define colour. My stance is that I define colour as a perceptual phenomonon – it’s something we see and experience. Others may argue that the two colours are really the same and that it is a mere illusion that they look different – I, on the other hand, would argue that the two colours are different. It’s not an illusion – you see a blue and a green, don’t you?
This is what Newton was referring to when he said that “to speak properly, the rays are not coloured” – I believe that Newton was aware of this problem with language – that colour can be used to represent several things. But when we speak properly we realise that the rays are not coloured.