[Julien]

Julien Piaser  asked the Naked Scientists:

Hi Chris,

Wonderful work your team does ! I love it !

Here is my question : how can we make sure that the colours that we normally see are the same for everyone. How can we be sure that what we all call "blue" is really seen the same way by two distinct human beings? Is there any evidence to prove so?

This idea is pretty difficult to explain : I've always been wondering if the thing that we all call blue (for example) could be actually seen by someone as green (I mean in his brain) and by someone else as orange (again, in his brain). Still, as everyone's always been taught to call it blue, everyone calls it blue (even if our brains do not behave the same way)

Hope you can answer that one !
Cheers,

Julien

What do you think?

[Don_1]

This is not a matter of what your eyes see, but, as you rightly say, a matter of how your brain interprets the information it receives.

Your idea of a shade of blue and mine could be different.

Indeed what you see as blue and what I see as blue could be totally different.

Is there a way to compare conception? I rather doubt it.

[RD]

A person with Daltonism cannot differentiate colours which most people can.

[Kryptid]

Your question seems to be related to the "Inverted Spectrum" argument:

http://en.wikipedia.org/wiki/Inverted_spectrum

With sufficiently advanced neuoscience, we could probably determine if this is true for anyone or not. Proper analysis of the parts of the brain governing sight could reveal any structural similarities or differences that would result in specific perceptions of color qualia. I doubt that we are at that point today.

[dentstudent]

A person with Daltonism cannot differentiate colours which most people can.

A person who cannot differentiate living daylight colours has Timothy Daltonism

[Bored chemist]

It gets slightly more complicated with some people- most of the are women.
http://en.wikipedia.org/wiki/Tetrachromacy

[techmind]

Here is my question : how can we make sure that the colours that we normally see are the same for everyone. How can we be sure that what we all call "blue" is really seen the same way by two distinct human beings? Is there any evidence to prove so?
What do you think?

Although there are some exceptions (Daltonism, tetrachromacity etc), and we can never know if what I call blue has quite the same effect in your "mind's eye" to mine, Colour-Matching experiments (since the 1930's) prove that the physical part of our colour-discrimination is reasonably similar from one person to the next.

The "Colour Science" resulting from such experiments enable us to do such things as sythesise real-world colours from simple red/green/blue primaries on a TV or computer screen or from cyan/magenta/yellow in print. The majority of people perceive acceptable matches from the same synthesised colour to the original colour - even though the light spectrum is rather different.
We can give human-perceptual colours objective labels, such as the CIE x,y or CIE u,v system. Despite some arguing of the details, this works very well overall.

[RD]

While we are on the subject of colour perception, have a look at the centres of these crosses...


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http://despegando.blogspot.com/2007/10/logvinenkos-illusion-and-dales-color.html

[rhade]

Females have an extra red receptor in the eye, which we males don't possess. This information came from our own Dr. Chris himself. Yo! Chris! You out there?

[lyner]

Your 'average' person will produce a pretty similar match of a colour if they are given the controls of the brightnesses of three (red,green, blue)  lamps / projectors / Colour TV signal channels.
In that respect, you can say that they will agree about colours under fairly objective conditions. This is why paint pigments and colour tv and film work fairly well.
The Ishihara Colour vision test cards (patterns within multicoloured dot patterns) show if you are 'colour blind' - i.e. unable to distinguish between colours like the rest of us can. But they also reveal that there is a noticeable range of ability amongst people with normal vision. I have worked my way through an ancient book of tests and found that I and two colleagues preformed differently.
If someone hasn't been diagnosed as 'colour blind' they may well survive quite happily because they/ we also may use contextual information to judge colours. They are not cheating - they are just doing what they think everyone else must be doing; they just think they're not quite as good at it.

What they actually SEE, is personal, in the same way as they may interpret some music as noise and some noise as music.
Once, I told a really sweet woman that her piano needed tuning."How do you know?", she asked.

Chris - it's not a 'RED' detector, it's a 'RED SHOE' detector that women have.

[rhade]

Of course, the three colours of the TV/computer screen are the same as the colour receptors in the eye; red, green and blue. Print uses the similar four colour format of cyan, magenta, yellow and key, in which key is black. To obtain other colours, you need to consult a pantene colour chart, give the pantene number of the desired colour to the printer, and he then has to order the appropriate ink in.

[lyner]

Of course, the three colours of the TV/computer screen are the same as the colour receptors

They are not. The three ANALYSIS curves of the TV camera are more or less the same as the eye's analysis. The display phosphors are, line / band spectra, and are different for each display manufacturer and technology. The driver software / hardware adjusts the RGB signal levels to get the same percieved colour, whatever phosphors are used.
Analysing a scene using a phosphor type spectrum would be a dead loss.

To print a colour match using inks (subtractive mixing) the luminance gets less and less as you try to get a more and more saturated colour - so extra, special, colour pigments are needed for vivid, bright colours. Pantone is just a system for describing / matching printed colours.

[rhade]

Agreed. Which is why the colour you get back from the printer can vary so much and fail to match what you hoped for at the design stage. Likewise, the colour qualities of TV sets or computer screens can vary so much. I suppose what I should have said was that we aim for the closest approximation of the colours the eye perceives which our science can manage to produce at our current levels of knowledge.

[lyner]

That's what colour profiles are all about. With professional sensors and displays you should be able to rely on the final printed picture to look just like the picture on your monitor and the ink jet print you submitted to your client.
My photos, on the other hand . . . . . .. At least I use HP inks and good paper, though.

[rhade]

There are many variables, though. The difference between digital and litho printing, for instance. In a very real sense, no two printers will give exactly the same results.
If I may go off topic for a moment, in film it is thought better to have a good soundtrack and a poor picture, than a poor soundtrack with a good picture. This is because it is usually possible to follow the story from the soundtrack.

[lyner]

Poor lipsync is really disturbing, too. It happens too much with DTV, these days.