Tag Archives: technology

The future of colour is quantum

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image-20150105-13827-1uj9moe

Although our digital displays can show literally millions of colours in fact they show us less than half of the possible colours in the world. This is partly because of the reliance on trichromatic devices – what you probably know as RGB. No matter how we choose them, it is impossible to mix together three colours and make all of the other colours. This is despite this embarrassing statement on the BBC website:

Red, yellow and blue are primary colours, which means they can’t be mixed using any other colours. In theory, all other colours can be mixed from these three colours.

This is just plain wrong. It is not the case that in theory, all other colours can be mixed from these three colours. In theory, and in practice, they cannot.

But I digress. The point is that using a three-colour primary system – a trichromatic system – is never going be able to reproduce all of the possible colours in the world. But even if we do use three, we could do better than the current TVs, phones and tablets on the market if we could improve our technology. The problem is that the red, green and blue lights in these displays are not as bright and colourful as they could be. That is where quantum dots come in.

Quantum dots are tiny crystals that can be precisely tuned to efficiently produce very specific colours. The crystals are grown from a mixture of various semiconductor materials and liquid solvents. By carefully controlling the conditions, engineers can adjust the size of the crystals, which determines the wavelength of the light that the crystals emit. Smaller quantum dots, with a diameter of two nanometres (two billionths of a metre) or so, emit short-wavelength, or blue, light. Bigger dots, with diameters closer to eight nanometres, produce light that’s nearer the long-wavelength, or red, end of the spectrum. We can expect to see new technology on the market soon offering brighter and more colourful displays.

colour physics 101

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kindle_colourphysicsfaq

Download my colour physics FAQ e-book for the Kindle here.

Also available as a physical book from Amazon.

  • What is colour?
  • How does colour vision work?
  • Why is the sky blue?
  • What is the colour spectrum?

The answers to these and many other related questions about colour physics are each provided in a short and easy-to-understand form. Will delight and entertain colour professionals and curious members of the public.

measure colour with your smartphone

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node

This looks interesting. Node is a way to add sensors to your iOS device. It allows you to measure all sorts of things, including colour if you have the node+chroma combination. The node costs about £100 and the additional sensors cost about £50 each. I am not sure how much the chroma sensor costs.

You can find further details here – http://variableinc.com/chroma-contact/

accurate colour on a smartphone or tablet

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Electronic displays can vary in their characteristics. Although almost all are based on RGB, in fact the RGB primaries in the display can vary greatly from one manufacturer to another. Colour management is the process of making adjustments to an image so that colour fidelity will be preserved. In conventional displays – desktops and laptops – the way this is achieved is through ICC colour profiles. Colour profiles store information about the colours on a particular device that are produced by RGB values on that device. So to make a display profile you normally need to display some colours on the screen and measure the CIE XYZ values of those colours; you then have the RGB values you used and the XYZ values that resulted. The profiling software can use these corresponding RGB and XYZ values to build a colour profile so that the colour management engine knows how to adjust the RGB values of an image so that the colours are displayed properly. Building a profile often requires specialist colour measurement equipment – though this can often be quite inexpensive now. If you are using your desktop or laptop display and you have never built a profile then you are probably using the default profile that was provided when your display was shipped. The default profile will ensure some level of colour fidelity but particular settings (such as the colour temperature or the gamma) may not be adequately accounted for. If you want accurate colour then you should learn about colour profiling.

It all sounds simple except for the fact that ICC colour profiles are not supported by iOS or Android operating systems on mobile devices. I find this really surprising but that’s how it is for now. Maybe it will be different in the future.

This means that ensuring colour fidelity on a smartphone or tablet is not so straight forward. So what can you do?

Well, there are two commercial solutions to this problem that I am aware of. They are X-rite’s ColorTrue and Datacolor’s SpyderGallery. ColorTrue and SpyderGallery are apps that will use a colour profile and provide good colour fidelity. These are great solutions. Perhaps the only drawback is that the colour correction only applies to images that are viewed from within the app. Having said that, they allow your standard photo album photos to be accessed – but the correction would not apply, for example, to images viewed using your web browser. This is why a proper system implemented at the level of the operating system would be better, in my opinion.

There are two alternatives. The first would be to implement your own colour correction and modify the images offline before sending them to the device. This would not suit everyone – the average consumer who just wanted to look at their photos for example. But it is what I typically do here in the lab if I want to display some accurate colour images on a tablet. But if you were a company and you wanted to display images of some products for example – it might be a reasonable approach. It has the advantage that the colour correction will work when viewed in any app on the device because the colour correction has been applied at the image level rather than the app level. But it does mean you need to do this separately for each device and keep track of which images are paired to each device. This is ok if you have one or a small number of devices but maybe not so good if you have hundreds of devices.

The second alternative would be to build your own app. If you want to do things with your images that you cannot do in ColorTrue or SpyderGallery or if you have lots of devices and you can’t be bothered to manually convert the images for each device, then you could install your own app that implements a colour profile and then does whatever else you want it to do.

On CIE colour-matching functions

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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.

#TheDress

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I was asked to comment on the radio today about a dress which is topping the trends of social media in the USA in particular today.

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The dress has sparked controversy because different people say that it is different colours. There is a group who say it is blue and black and another group who say that it is white and gold. What do you think?

I will give my explanation but it is not simple so …

Now, about 1 in 12 of all men in the world are colour blind. But if we consider the rest of the population you may be surprised to know that there is variability in our colour vision. This is mainly due to the colour receptors in our eyes. Put simply, some people have more red receptors and some people have more green receptors, for example. So we know that we don’t all see colour in the same way.

There is a second complexity and that is just because we use different names for a colour doesn’t mean we see it differently. This most often happens with brownish colours where some people will refer to it as more of a green and others will be adamant that it is definitely a brown. So words – colour names in particular – are not always very precise. We can see at least 3 million colours in the world and how many names do we have? A few hundred at least.

There is a third complexity which is that people think the camera never lies – that is, that they take an image of something using their phone and put it on the internet and everyone is seeing a faithful reproduction of the thing they took a picture of. Sadly, the camera does lie. Variability in the light that is used to capture the image, the settings on your display (whether you have a warm white or a cool white, for example) and how bright the light is in the room when you look at your screen – these can all dramatically affect the colour. Take a look at the picture below:

dress_original

This is the manufacturer’s photo of the dress. Taken professionally, I think most people would see it as blue and black. But the image that is on the internet is very different. I suspect it was taken in a very bright light and the colours are consequently a bit washed out.

So, in summary, the camera does lie. I think the lighting conditions under which the photo was taken were far from ideal and have changed the colours from how they would have appeared if you had been there. However, that is only half the story. Since people looking at the same image on the same screen are disagreeing with the colours. To fully explain what is going on you need to invoke the knowledge that we can sometimes see colours differently (because of variability from one person to the next) and even if we see the colour the same we might give it a different name (because colour names are crude ways to communicate colour).

Of course, fundamental to this is the idea that things are not coloured at all but your brain constructs a colour from the signals it receives in the eye. This allows us, for example, to discount changes in colour that may occur when the light source changes (this is known as colour constancy). We have evolved to discount the effect of light being bluer or yellower, for example, so that we normally see the colours that the object would have in neutral daylight. In the case of the dress image it may be that people are using different processing strategies and discounting the effect of the light source in different ways.

Which all goes to show that colour is complex. But if you have been reading my blog you already know that, don’t you?

grab colour – use it

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colour pen

Many of you will have seen the Scribble Pen which uses a colour sensor to detect colours. The sensor is embedded at the end of the pen opposite the nib. The pen then mixes the required coloured ink (cyan, magenta, yellow, white and black) for drawing, using small refillable ink cartridges that fit inside its body. The device can hold 100,000 unique colours in its internal memory and can reproduce over 16 million unique colours.

But wait. Don’t think that means you will be able to use the pen to write in 16 million different colours. You won’t. A typical phone screen can display about 16 million unique combinations of RGB (red, green and blue). But many of the RGB combinations are indistinguishable. Open up powerpoint and make two squares. Set the RGB values of one to [10 220 10] and of the other to [10 220 11]. I would be amazed if you could really tell the difference between them. And anyone who has read much of my blog will know that I believe that if two colours look the same then they are the same. So the pen might be able to create 16 million combinations of cyan, magenta, yellow, white, and black – but that doesn’t mean 16 million different colours.

The second problem is that just because your pen can grab a colour (using its sensor) doesn’t mean it can create it. There are lots of colours out there in the world that are outside the colour gamut of an ink-based system (even one using five primaries – cyan, magenta, yellow, white and black).

Read more: http://www.dailymail.co.uk/sciencetech/article-2647129/Forget-crayons-Multicolour-pen-lets-pick-colour-draw-16-million-shades.html#ixzz35gJ0racJ
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check your urine colour!

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urine

Just key urine colour chart into google images and prepare to be amazed. There are so many different charts and blogs and experts. Who would have thought it!! Today I saw an article in The Guardian that inspired to be to make this search. It turns out that there is a new urine colour chart from a clinic in USA that allows you to make a self diagnosis of your health based on the colour of your wee. A case of cross-media colour reproduction if ever I saw one (a poor joke that, for colour imaging scientists who may come across this blog).

I’m not sure it’s news though since there are a plethora of interesting charts for this already in existence and according to The Guardian the philosopher Theophilus noted the medical value in looking at the colour of urine as long ago as 700AD. However, if you have strangely coloured urine you might want to have a quick peek at The Guardian article to put your mind at rest (or not, as the case may be). Mine, for those who are interested, is sometimes clear but sometimes yellow verging on orange which is, I believe, because I don’t drink enough water. If you have blue urine it’s time to worry apparently.

3D colour printer

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3d-printer_0

An article in Stuff reveals what 3D Systems claims to be the world’s first continuous-tone full colour 3D plastic printer, called the ProJet 4500.The ProJet 4500 offers full-colour parts with colours that are able to blend into each other with gradient transitions.