Recent research from Prof Pettigrew – University of Queensland, Australia – has shown that one of the reasons that some cave paintings have apparently retained their colour for so long is that the original pigments in the paint have been replaced by living organisms that are themselves coloured. This makes dating cave paintings difficult and also makes it hard to know what the original paint colours were. The story is reported by the BBC – http://www.bbc.co.uk/news/science-environment-12039203
It’s often thought that black, white and grey are mature and sophisticated colours and that saturated reds and yellows are childish colours. Part of the reason for this is that the Romans and Greeks didn’t use colour. All those classic statues we see in museums are achromatic. However. this may be all based on a misunderstanding. At a CREATE conference in Italy last year I first came across the idea that the Romans and Greeks used colour quite extensively but that over the centuries the colour faded. Today I saw this story in the popular press.
An exhibition of work – Gods In Colour: Painted Sculpture of Classical Antiquity – recoloured as it is believed to have originally been features more than 20 full-size colour reconstructions of Greek and Roman works. Currently on show at the Pergamon Museum in Berlin, Germany.
Human colour vision under normal lighting levels is mediated by three cones (light-sensitive cells) in the retina. Each class of cone has peak sensitivity at a different wavelength and thus the cones are known as L (long-wavelength sensitive), M (medium-wavelength sensitive) and S (short-wavelength sensitive) cones or (sometimes) as red, green and blue cones. Both colour and luminance are captured by the same cone mechanism. The L and M cone responses are combined to give luminance and various cone responses are compared to give rise to hue and chroma. Interestingly, the distribution of L, M and S cones in the retina is not uniform but is random.
A recent paper – http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0008992 – by scientists at Washington University School of Medicine (St Louis, USA) reveals that chickens have five types of cone. Interestingly, one of these types of cones (so-called double cones) seems to encode luminance, whereas the other four cones (red, green, blue and violet) give rise to tetrachromatic vision. The cones are very regulary spaced in the retina.
The spacing of cones in the human retina may result from a compromise – the same cones need to encode colour and luminance. The avian colour vision system seems to be more sophisticated. One can only wonder at what benefit was bestowed in avians by separating the processing of colour and luminance information.
Everyone is familiar with the colour spectrum. If you pass white sunlight through a prism then it splits into the component wavelengths. The shorter wavelengths appear blue, the longer wavelengths appear red, and in between we have the familiar colours that I learned as school as Richard Of York Gave Battle In Vain, for the sequence red, orange, yellow, green, blue, indigo and violet, and that I have since understood is taught in the US as a person: Roy G Biv. I wonder if there are any other mnemonics that people know of? Of course, many people believe that Newton was in error when he identified 7 colours in the spectrum – he was probably influenced by Aristotle who wrote about there being 7 fundamental colours as there are 7 tones in the musical octave. I’ve posted about the indigo issue before – http://colourware.wordpress.com/2009/07/20/indigo-a-colour-of-the-rainbow/ – so won’t repeat that here.
Newton was probably the first person to create a hue circle (others, such as Forsius, created colour cicles but often included white and black in the circles). Newton created a true hue cirlce where he took the colour spectrum and wrapped it around, noticing that the two ends of the spectrum (where the reds become bluish and the blues become reddish) look rather similar.
Of course, there was a gap because the two ends of the spectrum did not quite match and thus Newton had to add in some purplish colours – these are hues that are never seen in the spectrum (and are sometimes called extra-spectral hues or non-spectral hues). The hues in the spectrum can be created by a single wavelength; however, the extra-spectral hues only occur when we see several wavelengths at the same time. For example, when we see short and long wavelengths together we can see purple.
In my lecture at the University of Leeds (www.leeds.ac.uk) this week someone asked “Why do the two ends of the spectrum look similar at all when the light is so different physically (at one end the waves are short and high energy and at the other they are long and low energy)?” Very very good question – if changes in wavelengths change the hue why should wavelengths that are so different look so similar?
So, why is hue circular? The answer is that it has very little to do with wavelengths and physics and more to do with human physiology. The human visual system captures light with three classes of cell (called cones) in the retinae of the eye. The signals from these cones are processed by the human visual system to create opponent signals (red-green and yellow-blue). This puts red and green opposite each other and yellow blue opposite each other and results in the perception of hue being circular. It also explains why some hues particularly contrast – sometimes called complementary colour harmony.
For several decades there has been a great interest in understanding how we use colour names. Do we use the same colour categories (even though they may be called different things in different languages) irrespective of language and culture; in other words, is our perception of colour the same across all cultures and this shapes our use of colour names? Or, is our perception of colour shaped by our language. A well-known study by Berlin and Kay in the late 1960s suggested that language is shaped by perception. But the alterantive hypothesis – known as the Sapir-Whorf hypothesis – that perception is shaped by language also has support. We may soon know more about this issue because of an interesting on-line colour experiment being carried out by a scientist at Hewlatt-Packard. California-based Nathan Moroney’s multi-lingual colour-naming experiment uses a clever design that allows each participant to perform a small part of the experiment; but when lots of people take part – from all parts of the world and using different languages – some interesting and valuable data is collected. I won’t say any more about the work here because it is not complete yet; but I urge you to go and take part in the experiment. It only takes a minute or less to do it. And there is a debriefing document that you can read about the results obtained so far. Please visit http://www.hpl.hp.com/personal/Nathan_Moroney/mlcn.html.
Meanwhile a study by Skirinko (at the University of Virginia) and colleagues at Rice University reveals that the colour names that companies such for their products can have a big effect on sales. Consumer reactions are more positive to fancy names such as mocha as opposed to simple and generic names such as brown. The explanation for this is based on categorical perception; people use categories and a name such a mocha maps to a more positive cataegory than the simpler brown. So it is perhaps not jsut the colour of a product that affects sales; sales may also be affected by the langauage used to describe the colours of products.
The work by Skirinko et al. was published in Psychology and Marketing in 2006.
Carrots are orange because they absorb certain wavelengths of light more efficiently than others. Beta-carotene is the main pigment and is mainly absorbs in the 400-500nm region of the visible spectrum with a peak absorption at about 450nm. Carotenoids are one of the most important groups of natural pigments. They cause the yellow/orange colours of many fruit and vegetables. Though beta-carotene is most abundant in carrots it is also found in pumpkins, apricots and nectarines. Dark green vegetables such as spinach and broccoli are another good source. In these the orange colour is masked by the green colour of chlorophyll. This can be seen in leaves; in autumn, when the leaves die, the chlorophyll breaks down, and the yellow/red colours of the more stable carotenoids can be seen.
However, the properties of beta-carotene are not what prompted me to make this blog. Last night I was watching the 4th in the series of Christmast Lectures by Prof Sue Hartley – the Royal Institution Christmas Lectures are a series of lectures given by a prominent scientist each year to an audience of children and broadcast on TV – http://www.rigb.org/registrationControl?action=home.
Prof Hartley’s lecture was about selective breeding and how humans had used this technique of thousands of years to make food safer and easier to eat. The section about wheat was particularly good.
However, she also talked about the colour of carrots and said that not all carrots are indeed orange at all. They come in many varieties including white and purple.
Prof Hartley said that it was the Dutch who selectively bred wild (white) and cultivated (purple) carrots to create the orange ones that we all know today. The orange was popular because it is the Netherland’s national colour and, at the time, the Dutch were fighting for independence. It was this story that has led me today – yes, Christmas Day – to make a virtiual visit to the British Carrot museum to research this story. You can follow my tracks at – http://www.carrotmuseum.co.uk/. Yes, such a place really does exist! 🙂
It turns out the story is not so clear as that told by Prof Hartley (though I am sure she is aware of this and was simply making it interesting to the children). Certainfly the first cultivated carrots – in the Afghanistan region – were purple and orange carrots were cultivated in Northern Europe about 500 years ago. However, some scholars dispute the Dutch story about breeding orange carrots because orange was the national colour. Indeed, there is, apparently, a Byzantine manuscript from as long ago as 512AD that depicts orange carrots. So the mystery deepens and I have far better things to do on Christmas day than to research this further. Perhaps if any experts in carrot technology come across this page they can add an informative footnote?
A paper in the journal Alchoholism: Clinical and Experiment Research by researchers at Brown University reveals that the colour of alchoholic drinks really does affect how bad you feel the next morning. Darker drinks (such as whisky) contain more chemical by-products than do lighter ones (such as vodka). However, how you feel (in terms of hangover) does not necessary correlate with performance loss the next day. So you may feel better drinking vodka but you would be just as incapable of driving or using heavy machines etc than if you drank whisky – though the latter may make you feel worse.
See http://www3.interscience.wiley.com/journal/123216970/abstract
One of my favourite movies – especially at Christmas – is It’s a Wonderful Life; a 1946 American movie directed by Frank Capra and starring James Stewart, a man who is financially ruined and is about to commit siucide on Christmas Eve until he is visited by a guardian angel.
Today I saw a new colorized version of the movie being advertised on DVD (or maybe Blu-Ray, whatever that is). It turns out that it is not the first colorized version of this movie. The first was introduced in 1986 and improved upon in 1989. The process of colorization is a difficult and time-consuming process; essentially an artist adds colour to each frame of the movie (obviously this is usually done digitally on a computer). There are two interesting properties of the world and of colour vision that makes the process a little easier than it might otherwise be.
Firstly, colour varies slowly over the scene so that it is not necessary to individually colour each pixel; the artist can define an area an add a single colour to that area with a single mouse click. The importance of luminance for detecting edges and defining form allows some error in this process with the knowledge that it probably wouldn’t be noticeable to most observers. However, in addition to spatial smoothness, there is also temporal smoothness. So, most adjacent frames are very similar. This allows the artist to colorize every, say, 10th frame, and use interpolation to do the rest.
The results of colorization are sometimes disappointing, especially for flesh tones. However, the process is improving all the time and I look forward to seeing the latest results.
You may well have seen a typical diagram showing the chromaticity diagram and the gamut of an RGB monitor. The gamut is a triangle, of course, with the vertices formed by the chromaticities of the RGB primaries. See, for example, http://colourware.wordpress.com/2009/10/04/subtractive-mixing-why-not-rgb/.
However, that triangle is a little misleading. One problem is that we are only looking at the maximum chromaticities available – this does not imply that all of these chromaticities are available at every luminance level. Take the very vertices of the triangle – these occur for the RGB values [255 0 0], [0 255 0] and [0 0 255]. The luminance of the pure red [255 0 0] might be 27 cd/m2, of the pure green [0 255 0] 56 cd/m2, and of the pure blue [0 0 255] might be 6 cd/m2. (These are luminance values for a typical RGB monitor – your monitor will vary a little from this and depending upon your settings.) This means that the chromaticities of the points of the triangular gamut are only available at these respective luminance levels.
For the monitor just described the maximum luminance would be obtained when RGB = [255 255 255] and the luminance of this white would be 89 cd/m2. So for very high luminances the gamut is tiny since to achieve these high luminance values you need to have all three RGB guns firing and hence by definition the colour is going to be very desaturated.
For the typical monitor described above I have calculated the gamut of colours available at three luminance levels: 10 cd/m2, 40 cd/m2 and 70 cd/m2. I have plotted these below and coloured bright red the chromaticities that cannot be obtained at that luminance. So, for example, at 10 cd/m2 you can obtain most chromaticities but not the pure blue. The reason for this is the pure blue [0 0 255] would be only 6 cd/m2 – to get 10 cd/m2 you need to add a little red or green and this desaturates the blue.
At 40 cd/m2 you can obtain a much smaller gamut and at 70 cd/m2 the gamut obtainable is very limited. To get such high luminances on this typical RGB monitor you would need high R and G values and that gives you yellows and yellowish whites.
The point of all this is that gamuts are three dimensional and looking at the gamuts in a 2-D chromaticity diagram can be very misleading.
This week I was honoured to be the invited speaker at the 5th National Conference of the Italian Colour Group. I decided to address the meeting about two of my research projects that to some extent attempt to bridge the gap between art and science.
In 1959 CP Snow – a Cambridge University academic – delivered a famous lecture entitled The Two Cultures that led to heated and widespread debate. Snow argued that the lack of communication between the sciences and the humanities was a problem that inhibited solution to the world’s major problems.
I believe that Snow’s argument is still valid today. Interestingly I bought The Times to read on the plane to Palermo – where the colour conference was being hosted – and to my surprise that very day’s edition had a substantial article about The Two Cultures – http://www.timesonline.co.uk/tol/comment/columnists/guest_contributors/article6862299.ece
The Times writes that Snow said “There is something wrong with a civilisation, he said, where knowledge is so compartmentalised that people can count as highly educated and yet be wholly ignorant of huge swaths of what other highly educated people know. How could scientists not read Shakespeare? How could literary people never have heard of the second law of thermodynamics?”
In terms of colour, I believe there was more cross-over between the sciences and the humanities in the 18th and 19th centuries than there is now. I am not convinced that the problem that Snow articulated has gone away. Perhaps the divergence between the two fields is an inevitable result of specialisation? Possibly, but I don’t think so. I think there is room (indeed, a requirement) for specialists. However, we also need to find a way for people working in colour to in the arts and humanities and in the sciences to communicate more effectively to each other. Because, we have much to learn from each other.
In my experience some scientists do not want to communicate outside of their narrow discipline. Others, would like to but seem unable to do so without recourse to specialist language (e.g. mathematics). In the arts, if anything the willingness to communicate “across the gap” is even less.
One organisation that has worked hard for many decades to encourage debate across the science-art divide is the AIC (the International Color Association”. You can find their website here – http://www.aic-colour.org/
I know from the nice stats that wordpress provide that a lot of people read my blog. But not many people leave any comments 🙁
It would be rather wonderful if – having read this – you left your view at the bottom. Is there a gap? Is it a good or a bad thing? How can we bridge it?
ps. I am not holding my breath waiting for the responses 🙂