All posts by s.westland@leeds.ac.uk

What colour is the sky on mars?

nature, news, technology, , , , , , ,

mars_originalmars_red

The cameras never lies. Or does it? Recently I had to take a photo for a medical case and before submitting it I had to sign to say that the photo had not been modified. I did this – but it was ridiculous of course. Many people have this idea that the cameras faithfully captures what the scene looks like and that, unless we intentionally manipulate the images (in photoshop, for example), then we have captured the truth. Nothing could be further from the truth – as the recent image of #TheDress showed.

The top photo above was taken and released by NASA in 1976 and shows a Martian landscape. The sky is blue. However, at the time, Carl Sagan said “Despite the impression on these images, the sky is not blue…The sky is in fact pink.”

You see the original image had not been colour corrected. Colour correction is a process that takes place on most cameras these days without the user being aware of it but in 1976 was not automatic. The process can compensate for the spectral sensitivities of the camera sensors (which may differ from one camera to another) or for the colour of the light source. The second picture (above) shows the colour-corrected image. Some people are now arguing, however, that the amount of colour correction applied by NASA is wrong and that the sky should not be as red as it appears on the second photograph. For the full story including some other nice images of Mars see here.

get it right in black and white

design, , , ,

A student was asking me about use of colour in a design (that showed text on a background) today and one of the things I said to her was “Get it right in black and white”. Prof Lindsay MacDonald taught me this. The idea is to make sure there is contrast in lightness and that you are not relying on a contrast in hue for people to read the text. So, for example, if you must put red text on a green background – I don’t advise this particularly, but if you do – then make sure it is a dark green and a light red or a light green and a dark red.

text1

text2

In the above two images, one is easier to read than the other. In both cases the hue of the red and green are the same. But in one case there is a large lightness difference and in the other there is not. if you were to print these out in black and white, one would be more readable than the other. That is what, “Get it right in black and white means.” It’s sensible if for no other reason than it increases the chance that someone who is colour blind (most are red-green colour blind) would be able to read it. Of course, maybe red and green would be not great colours to use in the first place – but that is a longer story.

I have come across a really lovely interactive website that helps with this. It is called colorable. It allows you to enter two colours (in hex format) – or use slider bars to control hue, lightness and saturation – and then it gives you a WCAG contrast ratio and even a pass/fail decision about whether you meet the minimum guidelines. Please try it – it’s great fun.

how colour vision works

knowledge, opinions/rants, , , , ,

yellow

Really super article by Ana Swanson in the Washington Post about colour vision and how it works. As she explains, it is not really correct to think of the long wavelength visible light as being red. It is better, as Newton knew of course, to say that the long-wavelength light has the ability to cause the sensation of redness in us. She gives a nice visual example of how the spectrum looks to a dog, something (by coincidence) that I was only talking about in a lecture last week. As she says:

Is what I see as “blue” really the same thing as what you see as “blue”? Or have we both learned the same name for something that looks different to each of us?

Her article is really worth reading.

There is just one thing I take issue with. It may be ‘nit picking’. But she says “A green leaf, for example, reflects green wavelengths of light and absorbs everything else.”

My image, at the top of this post, shows the reflectance of a typical yellow object. At each wavelength the reflectance is between 0 and 100 per cent. But notice that it is not zero at any wavelength in the range shown (400-700nm). That means that the object reflects light at every wavelength. And it is not 100 at any wavelength meaning that it also absorbs to some extent at every wavelength. It’s just it absorbs more at the shorter wavelengths than at the longer wavelengths and it reflects more at the longer wavelengths than at the shorter ones. But notice one other remarkable thing – the yellow object reflects more light at 700nm (a wavelength we would normally associate with red) than it does at 580nm (a wavelength we might normally associate with yellow).

Yes, the reflected light does look yellow. But, the notion that a “A yellows object reflects yellow wavelengths of light” is misleading. It suggests that the yellow object only reflects, for example, the wavelengths in the spectrum we would normally think of as yellow (around 580nm) and absorbs the rest. This is just not how things are.

What colour is your office?

culture, design, opinions/rants, , , , , , ,

Decorating-GOMIX-new-office-2

I just saw an interesting article by Kim Lachance Shandrow about how the colour of your office can affect productivity. The article refers to a paper (2007) in Color Research and Application (CRA) by Nancy Kwallek entitled Work week productivity, visual complexity, and individual environmental sensitivity in three offices of different color interiors. The paper suggests that the influences of interior colours on worker productivity were dependent upon individuals’ stimulus screening ability and time of exposure to the interior colours. CRA is a top quality academic journal that is peer reviewed and so I am respectful of the findings.

However, in Kim’s online article there is a lot of stuff that I am highly sceptical about. For example, she writes that “Red … increases the heart rate and blood flow upon sight.” Is this true? Is there really any evidence for this. I have two PhD students working in this area right now and I am far from sure that colour does affect heart rate and, if it does, the effects are probably tiny. And yet we can read statements like this all over the internet as if it is a fact beyond doubt. Other things she says that I take with a pinch of salt is that “green does not cause eye fatigue” and that “yellow triggers innovation.” Don’t get me wrong – I am very interested in how colour can be used to affect us emotionally, psychologically and behaviourally; it’s just there is a danger that if some things are said often enough (such as red increases your blood pressure or heart rate) then people start believing them even though there may be little evidence.

That said, you might find the infographic fun and it is well done. See the original and full article here.

On CIE colour-matching functions

advanced stuff, knowledge, , , , , ,

In 1931 the CIE used colour-matching experiments by Wright and Guild to recommend the CIE Standard Observer which is a set of colour-matching functions. These are shown below for standard red, green and blue primaries. These show the amounts – known as tristimulus values – of the three primaries (RGB) that on average an observer would use to match one unit of light at each wavelength in the spectrum. Why are these so important? Because they allow the calculation of tristimulus values for any stimulus (that is, any object viewed under any light as long as we know the spectral reflectance factors of the surface and the spectral power of the light).

650px-CIE1931_RGBCMF.svg

I gave a lecture this week about these and so they are fresh on my mind. I wanted to use this blog post to explain two things about the colour-matching functions that may be puzzling you. The first was stimulated after the lecture when one of the students came up to me with a question. You will note that for some of the shorter wavelengths the red tristimulus value is negative. Hopefully you are aware that no matter how carefully we choose the three primaries we cannot match all colours using mixtures of those three in the normal sense. What we have to do is to add one of the primaries to the thing we are trying to match and then match that with an additive mixture of the other two primaries. The question from the student was, wouldn’t that change the colour of the thing that is being matched? The answer is that it would of course. But it’s ok.

We normally represent this matching with an equation:

S ≡ R[R] + G[G] + B[B]

which simply means that the stimulus S is matched by (that is the symbol ≡) R amounts of the R primary, G amounts of the G primary, and B amounts of the B primary. The values R, G and B are the tristimulus values. I put square brackets around the primaries themselves to distinguish them from the amounts or tristimulus values of the primaries being used in the match.

Now when we add one of the primaries to the stimulus (the thing we are matching) itself, we can write this equation:

S + R[R] ≡ G[G] + B[B]

The new colour, S + R[R], can now be matched by an additive mixture of the other two. Hmmmmmm? You may ask. How does that work? Well, we can rearrange this equation to make:

S ≡ -R[R] + G[G] + B[B]

In other words, matching the additive mixture of the original stimulus S and some red with some green and blue, means that – if it were possible – we could match the original stimulus S with the same amount of green and blue and a negative amount of the red. I appreciate that this is mathematical but I hope that it is maths that anyone could understand. It’s not rocket science. Just simple adding and subtracting. This is how we arrive at the colour-matching functions above. No matter what RGB primaries we use one of them will have to be used in negative amounts to match some of the wavelengths. In practice, this is done by adding it to the stimulus as described above. Of course, you may also know that the RGB colour-matching functions were transformed to XYZ colour-matching functions. These are the XYZ values everyone is familiar with. But that is another story I will devote another post to one day.

The second question though, is isn’t this just arbitrary? If we used a different set of RGB primaries wouldn’t we get a different set of colour-matching functions? Again, the answer is yes, but again it doesn’t matter. The whole point about the CIE system was to work out when two different stimuli would match. If two stimuli are matched by using the same amounts of RGB then by definition those two stimuli must themselves match. If we used different RGB primaries the amounts of those tristimulus values would change, of course, but the matching condition would not. Two stimuli that match would also require the same RGB values as each other to match them, not matter what the primaries were (as long as they were fixed of course). So the key achievement of the CIE system was to define when two stimuli would match. However, it was also useful for colour specification or communication but that does indeed depend upon the choice of primaries and requries standardisation.

I hope people find this post useful. Post any questions or comments below.

Do women use more colour names than men?

culture, fun, , , ,

I just came across this funny cartoon about the difference between men and women in terms of colour names.

doghouse_color_wheel_altered

But on the same page I found the results from an actual colour survey where over five million colours were named across 222,500 user sessions. One aspect of the results is shown below:

doghouse_analysis

It does seem that there is some evidence that women use more colour names than men – though generally there was agreement between how the names were used. For further details see the original article.

Press coverage of #TheDress

culture, design, , , ,

Whatever anyone thinks about the colour of dress and the attention it is received there is one undeniable fact – this story had received huge attention from the public and from the media. That in itself is probably more interesting than the debate itself.

The Daily Mirror story covered the angle that we are all right whatever we see because colour exists only in our heads. According to Dr Paul Knox, a reader from the University of Liverpool’s department of Eye and Vision Science, “Colour isn’t something that exists in the world. Different wavelengths of light exist and can be observed but colour is something we make up inside our heads.”

ITV also took the view that the explanation is that colour doesn’t exist. I broadly agree with this view, but the interesting thing is that that doesn’t explain why there was so much disagreement about the colour in this particular case whilst normally we barely notice any disagreement. If it is simply that colour doesn’t exist then why do we ever agree about colour at all?

On the other hand, in the Guardian an article by Bevil Conway considers cognitive processes in our colour vision and visual strategies that may vary from one person to the next. Of course, Bevil Conway is a super scientist and I agree with almost everything he says. Certainly, cognitive strategies could have something to do with this phenomenon. However, when he says that “By accident or design, the dress is a carefully created composition of orange and blue that confounds our visual systems,” I have to disagree. If you look at a properly taken photograph of the dress or the dress itself in real life what you see is shown below:

dress_original

The dress is not a carefully crafted composition of orange and blue – the dress is blue and black. However, Bevil is probably talking about the image that was circulated not the one shown above. To understand this phenomenon you need to understand colour imaging and the fact that colour images are sometimes not faithful reproductions. One of the reasons why this story has run and run is that there is no simple answer, no 10-second soundbite that can put the story to bed. It is a complicated phenomenon.

Extraordinary facts relating to the vision of colours

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In 1794 John Dalton presented a lecture to the Manchester Literary and Philosophical Society about colour vision. The first two sentences are shown below:

It has been observed, that our ideas of colours, sounds, tastes, etc. excited by the same object may be very different in themselves, without our being aware of it; and that we may nevertheless converse intelligibly concerning such objects, as if we were certain the impressions made by them on our minds were exactly similar. All, indeed, that is required for this purpose, is, that the same object should uniformly make the same impression on each mind; and that objects that appear different to one should be equally so to others.

It is interesting to reread this sentence again in the light of the recent controversy about the blue and black dress.

Dalton

colour and language

culture, opinions/rants, , , , ,

One of the things that #TheDress controversy has highlighted is that colour is not as fixed as the majority of people believe. We tend to think that objects have a single colour and that we all see that colour the same way. However, in the image below you can see two central grey patches that are physically identical but probably look different in colour to you. My experience is that the majority of people would explain this as the two grey patches being the same colour but looking different in colour because of the background. An illusion.

90

I don’t agree with this way of thinking however. The colours we see when we look at something do depend upon the other colours around it but this is not a a special case. It’s not unusual, as Tom Jones would say. It’s how colour works. If it is an illusion then it’s happening all of the time, almost whenever you are looking at colour. So what is the real colour of something? Is it even sensible talk about an object having a single fixed real colour?

There is a body of research emerging that suggests that the language that we use influences how we see things. Jules Davidoff, a Professor at Goldsmiths University, went to Namibia where he conducted an experiment with the Himba tribe, who speak a language that has no word for blue or distinction between blue and green. When shown a circle with 11 green squares and one blue, they couldn’t pick out which one was different from the others. But the Himba have more words for types of green than we do in English. When looking at a circle of green squares with only one slightly different shade, they could immediately spot the different one, even when the difference was so small that we would find it very difficult to see the odd one out. See below for an example.

davidoff

In the image above – a screenshot from one of Davidoff’s experiments – the Himba tribe can easily see that the green patch at about 1 o’clock is different from the others.

In fact, some people even think that in ancient times we could not see blue at all because we had no word for it. In the Odyssey, Homer famously describes the “wine-dark sea.” But why “wine-dark” and not deep blue or green? It turns out that most ancient languages (including Greek, Chinese, Japanese and Hebrew) did not have a word for blue. Does this mean that they didn’t see blue? Is blue a relatively modern phenomenon? There is a thought-provoking article about this by Kevin Loria at Business Insider. Read more here.

final word on the dress

culture, design, news,

Yesterday, I posted about The Dress that people see as either blue and black or white and gold. Following several radio and telephone interviews I wanted to have a final attempt to explain what is happening with the dress. It is quite an extraordinary phenomenon – yesterday the dress looked blue and black to me but my PhD student (looking at the same dress on the same screen) said it looked whitish and gold. When I came home last night and looked at the photo on my mac book, the same image that had looked decidedly blue and black to me before now looked whitish and gold. So what is happening?

The first thing is that it is nothing to do with the dress. The problem is with the photo of the dress. I believe that anyone looking at the dress in real life would certainly call it blue and black and also anyone looking at the manufacturer’s photo of the dress would also call it blue and black.

The second thing is that there is more than one phenomenon going on. The reasons why my PhD student and I saw different colours in my office may be a little different from the reasons why I saw it one colour on my pc in my office during the day and another colour during the evening on my mac. So, although people might like a simple answer and a soundbite, in my opinion the explanation is necessarily a little detailed. But I will try to avoid too much technical jargon below.

The camera does lie
I think many people believe that when they take a photograph and put in on the internet and people look at, what people are seeing is a faithful rendition of the original scene. People take this for granted, I believe, without giving it much thought. Unfortunately, this is not guaranteed. There are many reasons why the colour someone might look at in an image might not be the same one that was in the original scene. Different cameras capture colour in different ways depending upon the type of camera, the settings on the camera, and the light under which the image is taken, to name just three factors. In The Dress image, the image looks over-exposed and the colours are washed out. The black is quite pale and has a colour tint and the blue is very washed out and insipid. Hopefully you can see where this is going already.

Different displays show colour differently
You can put the same image on a PC, a mac, a smart phone and a tablet and look at it. The colours will probably not be identical. Reds will probably be red and blues will be blue. But the colours are likely to be not exactly the same on the different devices. If you are looking at your screen from an angle, the colours may change radically. Also, if you are looking at your screen in bright sunlight the colours may look more washed out – though some smart phones and tablets try to ‘intelligently’ correct for this which might make the problem better or worse. The fact that I saw the colours differently in my office than at home could be due to differences in the devices I was using or could be due to the lightening environment, The lighting in my office is quite different to that in my home, for example.

People see colour differently – a little bit
About 1 in 12 men are colour blind. Very few women are afflicted. But even for the rest of us – so-called normal observers – there is variability in our colour vision. One factor for this could be that there are known to be differences in our eyes from person to person. This effect could be small but may be a factor in this story. More important is probably the fact that if sit in a dark room for a while and get used to the dark our vision will be different to it would be if we were outside in bright sunshine. This so-called ‘adaption’ is one way our visual systems deal effectively with such a wide range of brightness from dark rooms to brightly illuminated outdoor scenes. Someone coming into a room from outside (where the sun and sky are very bright) might very well see different colours on the screen than some who had been in the room for a much longer period. These adaption factors are well known in science.

People don’t always agree on colour names
There are at least 3 million different colours in the world. How many colour names can you think of that we could broadly agree on? Words like, blue, black, red etc. There are others like beige and taupe where we might agree less well. But include these and how many do you have? 30? 50? 100? And these names have to cover 3 million colours!! So each name is a category that covers quite a large range of colours. Last year I published a paper where we gradually moved a colour from yellow to green and asked people to tell us when the colour went from yellow to green. Not surprisingly, the point at which people told us the name changed varied from person to person. So there are some colours that some people will call yellow and other people will call green. Correspondingly, just because two people are calling a colour by different names does not necessarily mean that they are seeing it as a different colour.

My final explanation
Variabilities in displays, viewing conditions, observers and colour-naming boundaries can cause disagreement in how to name colours. Normally, this would not shift a black to a gold or a blue to a white. However, in this case, the image that has caused the controversy is not a faithful reproduction of the original. Because of the way the image was taken the black has shifted considerably away from the centre of the category that we would call black. And likewise for the blue. In my office today I would still call it black. But it was not a strong convincing black. It was a little pale and had a bit of colour in it. To be honest, I could understand why someone else might call it gold. The colour was on the boundary between black and gold and now differences between people could cause it to be classified as one colour or the other. When I came home, the colours had shifted for me. I don’t think my colour naming boundaries had shifted. Rather, I think this was to do with the lighting I was viewing the colour in, or the screen (a mac rather than my pc) or the angle I was viewing my screen at. Any or all of these factors could have shifted the colour so that it passed from the category I call black to the one that I would call gold.

Maybe the surprising thing is that these controversies do not happen more. Colour imaging scientists have been phenomenally successful in delivering colour imaging devices that satisfy consumers. Part of this work is done at the University of Leeds where I work but there are other places around the world who make great contributions including RIT in Rochester USA. And then there are some super bright scientists in places like Samsung, Apple, HP and LG who have worked hard to understand the complexities of colour perception and colour communication to the extent that people barely even think about these issues. However, there is more work to be done. Colour is still a major factor in people being dissatisfied when they buy something over the internet. When the product arrives it is sometimes not the colour they expected it to be. And colour fidelity is still not good enough for many medical applications. If you want to get involved in colour science please contact me. My email is s.westland@leeds.ac.uk and you can also find me @stephenwestland