Tag Archives: colour

two cultures?

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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 🙂

subtractive mixing – why not RGB?

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In a previous post I spoke about the difference between additive and subtractive mixing and why the additive primaries are red, green and blue or RGB for short – http://colourware.wordpress.com/2009/07/13/additive-colour-mixing/

The chromaticity diagram – see http://colourware.wordpress.com/2009/09/28/colourchat-audiovisual-guide-to-the-chromaticity-diagram/ – has a very useful property. If you plot the chromaticities of two lights, then the straight line that joins the two points on the chromaticity diagram show you the additive mixtures that can be obtained by mixing together the two lights. If we take three lights, then the additive mixtures that can be obtained are defined by the triangle that is formed if the chromaticities are the vertices of the triangle. Ok – that’s a bit of a mouthful so let’s have a practical example. The triangle in the diagram below shows the gamut that can be achieved when we have three additive primaries that are positioned at the corners of the triangle.

rgb_gamut

 From this diagram it should become obvious why the additive primaries are RGB. Say, we chose, two reds and a cyan as the three additive primaries – well, the triangle would be tiny. In other words, the gamut would not be very big. The biggest triangle in the chromaticity is one whose vertices are formed by a red, a green and a blue. WhichRGB will give the biggest triangle? I don’t know – it’s been something that has been puzzling me for the last few days and I’ll come back to this in a later post. But certainly any RGB triangle is pretty large as long as the red, green and blue primaries chosen are reasonably saturated.

So what happens if we choose RGB as the subtractive primaries? Subtractive colour mixing describes how inks and paints mix together to form colours. The first thing to point out is that subtractive colour mixing is not additive and linear – you remember I said that when you mix two lights together the colour mixtures all fall on the straight line that joins the  two points in the chromaticity diagram that represent the two lights? Well, this is only true for additive colour mixing. So to work out the gamut for subtractive systems is not an easy thing to do. However, if you do select the three subtractive primaries as RGB you’ll get a gamut that looks something like this:

rgb_subgamut

Notice that the gamut is concave. Mixing red and green lights produces a nice yellow. You can test this by going into your colour-picker in software such as Photoshop or Powerpoint and setting the RGB values to be 255:255:0. You’ll get a nice yellow. But mixing red and green paints – it will give you a similar hue to yellow but you’ll get something quite desaurated; most likely you’ll get a brown. So using RGB as the subtractive primaries would not be a very good thing at all.

It turns out that additive and subtractive colour mixing are very related. The best subtractive primaries are the ones that control the amount of red, green and blue light reflected. A yellow dye applied to textiles, for example, mainly absorbs short wavelengths in the blue section of the spectrum, allowing the other wavelengths to be reflected by the textile. The “other wavelengths” that are reflected give yellow. But the important point is that the yellow dye absorbs blue. Similarly, a magenta dye absorbs green and a cyan dye absorbs red. This leads to the idea of the optimal subtractive primaries being those that are cyan, magenta and yellow or CMY. This leads to a gamut somewhat like this:

cmy_gamut

The biggest gamut for subtractive mixing is obtained by using CMY as the primaries. But weren’t you taught at school that the subtractive primaries are red, blue and yellow? Almost certainly you were – and this is because it is accepted dogma at most art colleges and in many art and design textbooks. But it is quite easy to show that the optimal primaries – those giving the largest gamut – are CMY not RBY. If you were building a colour-reproduction system using only three colours such as a printer you would come to the conclusion – as companies such as HP, Xerox, and Epson have done – that you get the largest colour range with CMY. So why has it become commonplace for artists to refer to red, yellow and blue as the primaries? Could it be a colour naming and language issue – that they really mean cyan when they say blue and it’s just a naming error. Possible, but not likely in my opinion.  I think it is more likely that most artists are not overly concerned that RYB gives a smaller gamut than CMY because they rarely restrict themselves to three primaries. An artist would typically use 6 or more primaries. For example, they might use two blues (one that is reddish and one that is greenish), two reds (one that is yellowish and one that is bluish) and two yellows (one that is greenish and one that is reddish) in order to easily be able to mix a wide range of colours. The (mis-)identification of RYB as the subtractive primaries has much to do with colour wheels. I like to keep each of these blog posts reasonably concise – if I start writing about the problems of colour wheels now I will be writing for another 2 hours. And it’s nearly midnight now so colour wheels will need to wait for another day!

silver still the most popular car colour

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Pittsburgh-based PPG Industries Inc. said silver has been the number one colour for nine straight years, accounting for 25 per cent of vehicle paint choices in the U.S., 35 per cent in Europe and 34 per cent in the Asia-Pacific region.

In the U.S., silver rose from 20 per cent of the market a year ago. White finished second at 18 per cent and black was third with 16 per cent. Red was a distant fourth at 12 per cent. See http://www.google.com/hostednews/canadianpress/article/ALeqM5gi9WBgK8rDlLWiq1EGAWASLjOwPA

However, it would be interesting to see a more detailed analysis by car type and model. I used to have a Mazda MX5. It was bright red. Although the dark grey MX5 looks nice, for the MX5 you really have to have red in my opinion. It’s iconic.

Having said that, I just searched for MX5 on Google images. It produced, on page 1, 10 silver cars, 5 red cars, and 2 blue cars. So the power of the iconic little red sports car could be weakening and silver could be reigning supreme.

My longing – like that of many others of my age – for a little red sports car probably goes back to The Graduate and Benjamin Braddock’s red Alfa Spider (see picture below).

Thegraduate

Colour by words

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By chance, another Xerox story. Xerox have introduced a method for making colour adjustments to images based on natural langauge. There is a nice demo you can try out – http://open.xerox.com/xeroxproject/natural-language-color

The technology is available in the Xerox Phaser 7500 colour printer. Interesting.

red-blue flicker causes epilepsy

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In 1997, more than seven hundred children in Japan suffered an epileptic attack while watching an episode of Pokemon cartoon. This was later diagnosed as a case of photosensitive epilepsy (a kind of epilepsy caused by visual stimulus) triggered by a specific segment of the cartoon containing a colourful flickering stimulus. However, despite the ubiquitous presence of colourful displays and materials, very little is known about the relationship between colour-combinations (chromaticity) and photosensitivity. A new study has recently been published that suggests that certain colour combinations, for example, red-blue flickering stimuli, cause larger cortical excitation than other colour combinations such red-green or blue-green stimuli – http://www.goldsmiths.ac.uk/press-releases/pressrelease.php?releaseID=749

solid ink printers in UK

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As an alternative to laser or inkjet technology, Xerox offers solid-ink technology printers. A solid-ink printer uses solid sticks or blocks of ink instead of toner or inkjet cartridges. Xerox claims that solid-ink printers offer better colour consistency, are less expensive per sheet of printing and are more environmentaly friendly, producing less waste than lasers and inkjets – http://www.office.xerox.com/solid-ink/enus.html. The technology uses solid inks that are melted and sprayed onto the page as droplets, in a manner not dissimilar from inkjet printing. But because the inks are solid at room temperature, they can be supplied in blocks that are simply dropped into the printer, rather than being contained in a cartridge.

Now solid-ink technology is available in the UK with the launch of three Xerox ColorQube printers. However, they are out of the reach of the home user, costing around £13K each.

Colourchat audiovisual guide to the chromaticity diagram

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I have discovered a nice plug-in to powerpoint that allows me to synch voice and animations – this is my first attempt. An audiovisual guide to the chromaticity diagram:

http://www.colourware.co.uk/steve/chromaticity/

yellow transport

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In the UK, official taxis run by the council tend to be black. However, Derby – a city in the UK – introduced a new regulation in 2001 that all the official taxis should be yellow. Presumably this was to make them more distinctive so that members of the public would be more certain that they were getting into an official taxi rather than an illegal one. One of the taxi drivers – John Kirkham – painted his car yellow to comply but was then shocked to have his application for the renewal of his licence refused because he had used the wrong shade of yellow!

 yell_taxi

The council backed down after adverse publicity. If only they had specified the colour tolerance as part of their specification they would have had a much stronger case.

Another reason for choosing yellow could be safety. Many school buses in USA are yellow – presumably for reasons of safety. A number of regions in the UK have recently been trialling the use of yellow buses. Getting more school children to travel to School by bus is seen as being good for the environment and would free up the congested roads. In the USA more than half of all chidren travel to School by yellow buses according to the BBC – http://news.bbc.co.uk/1/hi/uk_politics/7610933.stm

yellow bus 

The use of yellow for school buses in the USA was introduced in 1939. The colour – National School Bus Chrome Yellow – was introduced for reasons of consistency and also for safety because of its high visibility. Cost was also a consideration since manufacturers charged extra for special colours. In addition the black lettering was easily visible by contrast on the yellow background (as you can see in the picture below).

yellow bus usa

The approximate colour can be obtained by #FFD800 or [255 216 0] in RGB values.

What is a colour space?

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In my job I probably use the phrase “colour space” every day and have done for the last 20 years. So imagine my surprise when I was talking with a colleague recently and after a few minutes he said “Can I stop you for a second there Steve – when you say colour space, what exactly do you mean?”.

A colour space is like a map. A map of New York, for example, shows the location of various landmarks with reference to the xy coordinates (the position in horizontal x and vertical y units on the map). A colour space or colour map does the same thing with colours. Perhaps the simplest colour space is the spectrum, see below:
 myspectrum

As we look from right to left on the spectrum the wavelengths changes from around 700nm on the far left to about 400nm on the far right. So this map shows colour with reference to wavelength. Although it is a commonly used colour space it is limited because it only really describes how hue changes with wavelength. Hue is only one of three ways in which colour can change or vary.

The most well-known really useful colour space then is the CIE chromaticity diagram – see below.

chromdiagram

The CIE chromaticity diagram shows colours arranged on a 2-D plane. We can easily refer to any colour by how far from the left it is (the x coordinate) and how far from the bottom it is (the y coordinate). This space only shows two of the dimensions of colour; the hues are arranged in a somewhat circular way and the colourfulness increases as we move outwards from the white point (a position near to the centre of the diagram). However, we can also consider the third component of colour (brightness) if we imagine a dimension coming out of the page towards you (http://colourware.wordpress.com/2009/07/18/cie-system-of-colorimetry/). The CIE defines several different colour spaces; the CIELAB colour space, for example, is another 3-D space that defines a colour by its L*, a* and b* values.

It is useful to think of an image-display device as also having a colour space. Consider the display on which you are probably reading this blog. The display shows colour by changing the amount of the red, green and blue light emitted at each point on the screen. The diagram below is a representation of what the RGB colour space of your display device may look like.

 

rgb

In the RGB cube, black is in the bottom left. As the RGB values increase colours are created and white results from each of the RGB primaries at full strength. So the RGB colour space defines the relationship between RGB values and colour. However, here’s the really interesting thing: The colour space for different display devices is very different. Even if we take a single device – such as the one that you are reading this blog on – then as we change settings (the brightness, the contrast, the gamma, the colour temperature, etc.) then the colour space changes. That is, the relationship between RGB and colour changes as you change those settings. This is a huge problem. Imagine if there were many maps of New York and each showed the position of, say, the Empire State Building to be in a different position. How confusing would that be? Well, that’s the problem with colour-display technology. If we didn’t do anything about this problem then every time we looked at a colour image on a different display device the colours could change markedly. This is why we need colour management. Colour management can make compensations to the RGB values that are sent to each display device so that the colours always appear the same (well, nearly the same). To make this compensation the colour management software (which is embedded in your Windows or Apple operating system) needs to know about the colour space of each device connected to the computer. Each device needs to have a profile that describes the relationship of its own colour space with respect to some standard colour space. 

How good is colour management? Well, that depends upon many factors. Most printers, cameras, scanners, and screens (LCD, CRT, etc.) come with a driver that includes a crude colour profile. This ensures that there is a basic level of colour management and for a great majority of users this is more than adequate. However, if you want better performance then you need to think about making some measurements that will allow a more accurate colour profile to be built. In a recent blog I described a new device that you can buy to enable you to do this – http://colourware.wordpress.com/2009/07/29/colormunki-colour-management/. There are many such devices on the market. I highly recommend Andrew Rodney’s book Color Management for Photographers which is both clear and accurate (though the edition I have works on Adobe’s CS2 package whereas the latest package is CS4).

514PWPFTKXL__BO2,204,203,200_PIsitb-sticker-arrow-click,TopRight,35,-76_AA240_SH20_OU02_

However, no matter how hard you try, colour management is never likely to be perfect. This is because different devices have different colour gamuts; a printer is likely to be able to display some colours that your display physically cannot and vice versa.

cure for colour blindness

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One of the reasons I enjoy travelling by train is that it gives me an opportunity to read a newspaper from front to back (something I very much enjoy but rarely have time to do). Yesterday I was travelling to Bristol where I was delivering a lecture at the IMPACT6 Printmaking conference on colour management and took the train from Leeds to Bristol during which I was able to read The Times. I couldn’t fail to notice the story about a potential cure for colour blindness – http://www.timesonline.co.uk/tol/news/science/medicine/article6837392.ece

Congenital red-green colour blindness occurs when either the L- or M-cone class is either missing (making the sufferer a dicromat) or shifted in terms of peak wavelength of sensitivity (resulting in anomalous trichromacy) – see http://colourware.wordpress.com/2009/07/04/colour-blindness-news/.

Scientists working at the universities of Seattle and Florida have restored normal colour vision to two colour-blind monkeys by injecting a virus with a modified gene (called L opsin) that is known to be responsible for red-green colour blindness. The success of this work is remarkable in that it suggests that the brain is able to rewire itself to take advantage of the new receptors. 24 weeks after the injection the monkeys were able to correctly distinguish patterns of grey, green and red dots that they had previously been unable to distinguish.

colour_385x185_615124a

Jay Neitz, professor ophthalmology at the University of Washington, is now looking to start work that could lead to a similar treatment for humans.

The work has just been published in Nature – http://www.nature.com/news/2009/090916/full/news.2009.921.html