I learnt after reading How do color filters placed in front of a light source,change the color of light that passes through? colour filter work by permitting only one colour and absorbing or reflecting the rest. In this sense, a yellow colour filter works by allowing only yellow colour to pass thorough and not allowing the rest of the colours.

Let us consider the following image:

enter image description here

It can be seen that yellow colour is obtained as a result of red and green colours. In order for the yellow filter to transmit yellow colour both red and green colours must be transmitted. So, does it mean "only" yellow (but not blue or red) filters cannot be obtained? I think yellow colour filters are a reality. How does a yellow colour filter work in the sense of RGB colour model? Does the yellow coloured light coming out of a yellow filter have red and green coloured components in it?

Image Courtesy: Additive and Subtractive Colour Mixing


I had pondered essentially the same question for a long time until I figured it out. And here's the disclaimer, I figured it out myself, so there is a chance that I'm actually wrong, but then someone can come and correct me or write a better answer!

The thing is that you have to differentiate between the color of the actual electromagnetic radiation and the color a human eye sees. The waves have a continuum of frequencies they may have. When they hit the eye, however, they are basically converted to the three values (RGB) that are usually said to make up all the colors (because to my understanding there are three different kinds of cells in our eyes perceiving the colors). So the difference is, the human eye might not be able to differentiate the mix of blue and red from the actual electromagnetic wave with the violet color, because the response in the cells in the eye is similar. This does not indicate necessarily that the waves are similar, and hence we can physically differentiate between the two kinds of radiation and, for example, make a filter transmitting only violet light.

On the other hand, this also means, that such a filter does not transmit all light a human eye perceives as violet, if it is, for example, created by using an rgb-led.

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