human eye

[steveb]

how many colours can the human eye see/differentiate between

[LiIIabet]

16 Million.

[ll_billym]

Any references for this figure Lillabet?

[brachiopod]

That's actually Liiiabet the sock puppet, so don't hold your breath for any sensible qualification of the answer.

[Clanad]

From a related web site;

Color is how our eyes and brain interpret light. Our eyes can only see radiation with a wavelength of 380 nanometers to 740 nanometers. This is called the visible spectrum of light. Sir Issac Newton listed the pure spectral colors we see in light as red, orange, yellow, green, blue, indigo, and violet.

In 1878 Ewald Hering posited a theory of four unique hues of red, green, yellow, and blue, which, when mixed with white or black, represent all the possible colors humans can process. Useful knowledge for painters and printers perhaps, but it doesn't quite answer your question.

The problem is that nobody really knows exactly how many colors the human eye can see. The closest researchers can estimate is millions and millions. Scientific experiments have shown that humans can discriminate between very subtle differences in color, and estimates of the number of colors we can see range as high as 10 million.

Of course, every person's eyes perceive color a bit differently, and every culture has its own names for colors so coming up with an exact number may not be possible.... Not much help, I'm afraid...

[MargeB]

I don't want to go into a long winded answer, but I would point out what I see as an important point. A lot of people use 'human eye' and 'vision' interchangeably, and this just cannot be done. For example, the highest colour resolution available to the visual system may have the retinal resolution as its chief limiting factor, but it is subject to a huge amount of work by the visual system immediately after the 'eyeball' and beyond.

For example...what is 'red'? Some cells on the retina are tuned to fire when a very specific wavelength of light strikes them, and this will give rise to a conscious experience ultimately of 'red'. However, if you sit a 'yellow' colour alongside this same red, the subjective experience of the 'redness' is different, even though the wavelength of the 'red' is the same as before, and activating the same retinal cell. The same goes for ambient lighting, and a lot of other things.

Then you have to work out how well people can report the different colours....whether you wish to use conscious or sub-conscious measures of reporting...opponency (as above).

My understanding was that Lillabet was correct at 16 Million, this is 'true colour' and the reason why monitors are never set above this figure...there's no point.

[Xollob]

Hallo MargeB - the reason why computer monitors don't go beyond 16 million has more to do with artithmetic and storage space: each colour on your screen consists of a value of red, green and blue ranging from 0-255 (which is a value you can store in one 8-bit byte). That is 256x256x256 permutations, which gives you 16,777,216 possible colours.
I read somewhere that there are some shades of green which you cannot achieve using this model. It seems the human eye, probably for evolutionary reasons, is particularly sensitive to nuances of this colour.

[MargeB]

Thanks xollob.

I believe it is for evolutionary reasons:

http://www.mun.ca/biology/dinnes/B2900/Articles/T24_18_198-205.pdf

[jidboy85]

Indeed, we can tell more shades of green apart than eny other colour. This is the reason why night vision projections used in night vision goggles etc.. use green.