Is it Yellow or Green and Red?
Something that always fascinated me is how we can distinguish between the colors. Yet not so many people seem to be disturbed by this. So in this article I will try to transmit you my wonder on that topic.
But what is a color exactly? The color we see come from the fact that light can have multiple wave length. A longer wave length will tend to the red, while a shorter wave length will tend to the blue as see in the rainbow bellow:
The human eye can normally measure only three different wave lengths known as the primary color: Red, Green and Blue. Each of these covers a certain range of color spectrum as we can see in the graphic bellow which represents the sensitivity of each cone type to the different wave length:
When we see something yellow, it can be either yellow or a combination of color is far from being yellow. For example, if an object emits some green and red light we would perceive it as yellow. That is because our brain think it is yellow as both green and red cones were excited by the light as it would been if the light was effectively yellow.
Now every time you will see something yellow try to figure-out if it would be green and red or just pure yellow. One of the most magnificent demonstrations of this is when the leaves turn yellow then red at autumn. When the leaf is green, it is because there are many more green pigments (Chlorophyll) in the leaf. When the day time reduces the Chlorophyll also reduces so that at a certain point, both pigments are equally visible. This appears to us as yellow. Eventually no more Chlorophyll remains and only the red pigments can be see. So the wave length of the leaf doesn’t actually changes over the seasons it just changes in proportion.
A camera work the same way as the human eye, that is by capturing three color channels. In order to enhance the sensitivity of the pixel, manufacturers extend the color sensitivity so that the red captured by the camera is actually also containing some infrared. The ultraviolet extension however tends to be limited due to most camera lens being opaque to the UV. Using that knowledge it is possible to photography colors that aren’t normally visible for us human using filter. For example using an IR filter, it is possible to see the luminosity in the IR spectrum emitted by objects.
Note the change of color of the water and some trees in IR. The sky and clouds become more contrasted while approaching the IR. For reference there is the traditional RGB photo:
There is another example where the flower is equally infrared. The grass is almost as lighting as the white fence in the IR spectrum.
Using a pure yellow filter could enable to distinguiss between what is actually really yellow against what is green and red. A technique that I would like to develop is the multispectral photography using pure color filters in order to see the real color of objects. Some information on this technique can be found here: http://en.wikipedia.org/wiki/Multispectral_image
And a blog wouldn’t be serious if it doesn’t talk about cats. Because cats don’t have the same cones as we have, they see a shifted color palette version of ours. The following article illustrate very well the cats view:
http://www.businessinsider.com/pictures-of-how-cats-see-the-world-2013-10
Finally, there are also species on our planet that can see more primary color than usual. The following articles describe this. It seems that even some lucky human can have this possibility!
So now everytime you'll see yellow, ask yourself if it is actually yellow or just an illusion!
