Tag Archives: blue

What colour is the sky on mars?

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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.

colour and language

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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.

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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.

new British flag

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Some of you may recall that last year – a big year for the UK with the Olympics in London and Queen’s jubilee – there was a lot of waving of British flags. I posted about how the flag was derived historically and noted the absence of any representation by Wales. For those who are less familiar, the United Kingdom is a union of four countries (England, Scotland, Wales and Northern Ireland). By contrast Great Britain is just England, Scotland and Wales (not including Northern Ireland) and the British Isles is a geographical feature that includes the United Kingdom and the Republic of Ireland. Simple?

Next year the Scottish people be asked if they want to be independent. If they vote yes (in my opinion this is not very likely, but possible) it will signal the end of the union of Great Britain and Northern Ireland. Today the BBC ran a feature about possible new designs of the new flag. I wasn’t very impressed by any of them, including the horrible one below. Try reading my post first and then the new BBC article.

flag

eyes change colour?

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reindeer

I didn’t realise how sophisticated reindeers are. It turns out they have two layers of fur to help them keep warm, are able to shrink the pads on their hooves to give then better grip, and can detect ultraviolet light which enables them too see in very dim light. And it also turns out that their eyes can change colour in winter so that their vision is more sensitive. Reindeers, like cats, have a reflective layer behind the retina (which is the inside of the eye ball where all the light-sensitive cells are) that helps them to see in dim light. This is why, if you see a cat at night, you might see the eyes shining; you are seeing light being reflected back at you from the cat’s tapetum lucidum (which is the technical term for the layer behind the retina). The light that shines back in most animals with this layer is golden but in reindeer it apparently shifts to blue in the winter. The shift to blue allows more light to be scattered and improves the vision of the animal.

The full paper can be read in the Proceedings of the Royal Society.

good reasons to use colour

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I just came across this nice article – http://understandinggraphics.com/design/10-reasons-to-use-color/ – entitled 10 reasons to use color.

The article lists 10 good reasons to use colour in design. Number 10 is using colour for metaphor and taking advantage of the associations that are inherent in phrases such as feeling blue or green with envy. There is no doubt about the meaning in the image below; that the woman is filled with envy.

color-for-metaphor

Where is colour mixing?

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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:

ColourMixing

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

This is called additive colour mixing as I am sure you know. 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). So 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. When I sat down with a couple of students last week and asked then what they though they said that the red and green light mixed together to create yellow light and when I pressed them, they went further to say that the yellow light was at about 575 nm.

visible-a

If we measure 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. 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. It also makes me think that additive colour mixing, if it can be said to occur anywhere in particular, occurs in the eye. And I do mean eye, not brain.

We all live in a turquoise submarine

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Apparently this week the Iranian navy revealed their latest submarine, resplendent in bright turquoise paint. Why would the navy use this colour since I would think it could make it easy to spot? Could they have thought that it would blend in with the sea and be hard to spot? Surely not.
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jaws

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“Wearing a light blue wetsuit that matches the colour of the sea will make you less likely to become the victim of a shark attack, according to researchers.
Sharks are completely colour blind and only see things clearly if they are mostly light or dark, scientists have claimed.”according to the Daily Mail.

This does not make a lot of sense – if sharks are colour blind then it wouldn’t matter what colour you wear. But later in the article the point is put better by Professor Nathan Hart, from the University of Western Australia: ‘It’s the high contrast against the water rather than the colour itself which is probably attractive to sharks. So you should wear perhaps more muted colours or colours that match the background in the water better.’

Apparently sharks really are monochromats – so colour blind in the popular understanding of the word – and so it’s really a case of matching the yoru swim suit with the lightness or brightness of the surrounding water. Don’t wear a very bright or a very dark swim suit, in short. Maybe this can lead to better designed swimwear!

Whitehall colour branding

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The UK government is set to rebrand its departments with bold new colour schemes. The new colours include lots of blues and greens; for example, navy blue for the Foreign Office, bright blue for the NHS and green for the Department of Energy and Climate Change. However, the The Department for Culture, Media and Sport, which is purple at the moment, is reassigned bright pink.

Read more here.