Category Archives: knowledge

SimCity for the Colour Blind

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A while ago I posted about whether colour blindness was something that designers should take more seriously. After all, about 8% of all the men in the world are colour blind. Of course, this does not mean that they cannot see colour (the term, colour blindness is a bit of a misnomer) but it does mean that they have difficulty discriminating between colours that the rest of us can easily tell apart. In my original post I was referring to the computer game, Call of Duty, and whether the gameplay could be reduced for colour blind players who may have difficulty telling the various colour tags apart that appear on the screen.

Sim_City_1

So it was quite interesting that I just came across news that the developers of SimCity have added three special colour filters that make adjustments to the colours on screen so that colour blind players can better discriminate. A great idea – but about time!!

new colour blogs

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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.

Race for colour

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The films were made by a young British photographer and inventor called Edward Turner, a pioneer who can now lay claim to being the father of moving colour film, well before the pioneers of Technicolor.

The footage will be shown to the public from 13 September at the museum in Bradford. And a BBC documentary, The Race for Colour, will be broadcast on 17 September in the Yorkshire and south-east regions on BBC1. I will feature in the film for a minute or two. Exciting.

For further details see the story in the Guardian.

on-line test for colour blindness

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Quite a lot of people are colour blind and have poor colour discrimination. There are tests that can be carried out and these include the Ishihara test (which is a screening test that I certainly remember from School) and the Munsell 100-hue test (where people have to arrange a number of coloured discs in order). These tests need to be performed whilst being viewed in daylight. There are online tests but these are less reliable – partly because the viewing conditions vary such a lot. I recently came across a new online test provide by X-rite. It seems to be based on the 100-hue test (or, at least, something similar) and I can see how it could work, despite being an on-line test). I just had a go. It gave me a score of 34 and suggested that for my age group (and gender) the best score was 0 (perfect colour acuity) and the worst was 99 (low colour acuity). Hmmmmmmmmm. I have a version of the 100-hue test and I can perform it perfectly. My real score should be 0. I have perfect colour discrimination. So, much as I like the X-rite test, I have not changed my opinion that on-line tests like these should be used for fun and should be understood to not provide an accurate assessment of your colour vision. On the other hand, it could just be bitter because I only scored 34. 🙁

special females

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Our colour vision results from the fact that our eyes contain three types of light-sensitive cells or cones that have different wavelength sensitivity. Some people (called anomalous trichromats) are colour blind and this is usually because one of their cones is mutated and has a different wavelength sensitivity compared with those in so-called normal observers. Colour-blind is a misnomer really because anomalous trichromats can still see colour; they just have less ability to discriminate between colours than normals. Some people are missing one of the cone classes altogether and are referred to as dichromats; they have even poorer colour discrimination but can still see colour. Only monochromats are really colour blind and they are extremely rare.

For a long time I have known that some females have four cones classes (this makes them tetrachromats). Dr Gabriele Jordan, a researcher at the Institute of Neuroscience (Newcastle University) has spent the last 20 years working on human colour vision. She has discovered that tetrachromatic females exist and that although this gives them the potential for colour discrimination much better than normal trichromats in practice most have normal colour discrimination. However, in a recent report she has found a tetrachromat who really does have enhanced colour discrimination. This is really exciting news!

The report in the Daily Mail suggest that a functional tetrachromat could be able to see 99 million more hues than the average person. Personally I am skeptical of this claim even if, as I suspect, it means 99 million more hues than the average person. The number of colours that an average person can see is debatable but I think may be about 10 million (see my previous blog post).

UK goes red, white and blue mad!

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This was a picture taken whilst shopping in Tesco today. There are union jack flags everywhere you look at the moment in the UK. The Olympics has not even started yet – the reason there are so many flags already is, of course, the sixtieth anniversary of the Queen taking the throne of the UK. The red, white and blue colours of the union flag – red = Pantone 186 (C), blue = Pantone 280 (C) – derive from a combination of the three flags from England, Scotland and Ireland.

The English flag dates from 1194 when Richard I introduced the cross of St George as the national flag of England.

The Scottish flag was a diagonal white cross on a blue background.

When Queen Elizabeth I died, the scottish king James (King James VI of Scotland) inherited the throne of England and became James I. James I proclaimed himself King of Great Britain and essentially unified England and Scotland. But which flag to use? A new flag was created that was a combination of the previous two and known as the Union flag. A white boarder was added around the red cross because the rules of heraldry demanded that two colours must never touch each other.

The union flag was used at sea from 1606 but became the national flag of Great Britain in 1707 under the reign of Queen Anne. We now had the United Kingdom of Great Britain. In 1801 Ireland became part of the United Kingdom. The Irish flag had been a diagonal red cross on a white background.

The combination of all three flags resulted in the familiar Union Jack.

The name was later changed to United Kingdom of Great Britain and Northern Ireland when the greater part of Ireland left the United Kingdom in 1921.

Why is Wales not represented in the Union Jack? To read why this is please visit here.

why I don’t like the colour wheel

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There are many reasons why I don’t like colour wheels of the type shown below:

The first reason is because it perpetuates the myth that the subtractive primaries are red, yellow and blue whereas the fact is that red, yellow and blue produces a rather small gamut of colours. It is certainly not the best choice of subtractive primaries though it is taught as dogma in many art and design schools and throughout children’s education. The problem is that whenever two colours are mixed together there is saturation loss; that is, the resultant mixture ends up being more desaturated than the two components were. The saturation loss is greatest when mixing colours on the opposite side of the colour circle where the resultant mixture can be almost grey. However, for certain choices of primaries, the saturation loss is greater than for others. If red, yellow and blue are used as the primaries then of course it is possible to generate any other hue. However, there is significant saturation loss and the above colour wheel gives completely the wrong impression. It suggests that mixing blue and yellow together, for example, results in a really bright vivid green.

The reality of pigment mixing is much more like the triangular colour wheel shown below:

In the above diagram it can be seen that mixing together yellow and blue results in a really muddy dark green. The purple resulting from mixing blue and red is almost black!! Now it is possible to mix together a blue and a yellow to get a better green. For example, mixing a greenish blue with a yellow will give a much more vivid green. Mixing a bluish red with a greenish blue will result in a lovely purple. We have a name for a greenish blue and a blueish red – we call them cyan and magenta. A much better colour gamut is obtained if we start with the primaries, cyan, magenta and yellow.

Footnote: Some people may look at the triangular colour wheel and think that the reason the colours are dull is that the red, yellow, and blue primaries used are not ‘pure’ enough. Nothing could be farther from the truth. If it was possible to make really vivid and bright red and blue pigments then the resultant colour gamut would be even smaller. Fundamentally, red, yellow and blue just don’t make good subtractive primaries.

what colour is indigo?

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Seems to be a lot of people typing

what colour is indigo

into google. Why all the fuss about indigo?

In case you are one of those people I can tell you that in the spectrum indigo was generally considered to be associated with wavelengths in the range 420nm – 450nm though many would argue that it is not in the spectrum at all and that light below about 450nm is considered to be violet. Have a look at my earlier post about why indigo is generally not considered to be in the spectrum by modern colour scientists.

In terms of RGB (sRGB for the techies) it can be approximated as R=75, G=0, B=130 and this looks like this:

Though of course, the RGB on-screen representation is not the same colour as the indigo in the colour spectrum since every colour in the spectrum is outside the gamut of your RGB display and therefore cannot be properly shown.

The word indigo is named after the blue colorant obtained from plant indigofera tinctoria.

Colour Physics FAQ

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In the 1990s I used to host a colour physics FAQ on the web. The FAQ was bite-sized answers to the most common questions I used to get in those days about colour physics.

Really, this FAQ was the precursor to this blog. I much prefer the blog format because it allows a greater degree of interactivity and also fluid evolution of content. But the FAQ was quite popular. Even some university libraries used to ask me about it (I noticed a few days ago that a website in India had ‘stolen’ the content and presented it as theirs – these things happen I guess).

I had to move the location of the the Colour Physics FAQ quite a few times on the web and it became quite painful trying to maintain it. So I decided to make it available as an e-book and as a physical book via Amazon. I spent quite a few days working on the e-book format. To be honest I am not sure I got the format ready. I used the epub format and there are things I don’t like about it. Displaying greek characters is difficult and images are often converted to black and white, especially for display on the kindle or similar devices. Also, footnotes are not allowed and I am a big fan of footnotes. So I am not 100% impressed. We’ll see how it goes. But Amazon’s CreateSpace allows you to create a physical book. This seems much better. The book is printed on demand as far as I can see and I am looking forward to how it looks.

To see the e-book go to amazon. I’ll add a comment below when the physical book is available.

Roy G Biv

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We all know that Newton wrote about the colour spectrum having seven colours. As a child I wrote the mnemonic – Richard Of York Gave Battle in Vain. The sentence makes reference to Richard III, an English king who was defeated by Henry VII in 1485 at the battle of Bosworth. In order to avoid reference to this defeat, people from Yorkshire developed the alternative Rowntrees Of York Gave Best In Value, apparently. Rowntrees was a chocolate factory formed in York in 1862 (exactly one hundred years before I was born).

When I was young I naively thought that everyone would know the Richard of York line. I was surprised, later in life to learn that in the USA a different mnemonic is normally used: Roy G Biv (the name of a person). I find this American mnemonic a little bizarre to be honest; are there really people whose surname is Biv? If your surname is Biv, or you know someone called Biv, please comment below. Only recently I came across a small rhyme that goes:

Red for the rainbow, orange too.
Yellow says, ‘how do you do’.
Green is the next one, green for go.
Then comes blue and indigo.
Number seven, we must not forget, is pretty violet.

Since children learn these mnemonics from an early age most people never question whether there really are seven colours in the spectrum despite the fact that we often see the spectrum in the form of a rainbow in the sky. However, if most people look closely at the spectrum they will likely state that they can only discriminate between six bands of colour; that indigo and violet are really one colour band. So why is it that we teach children that there are seven colours in the rainbow?