Photometry (foʊˈtɑmətriː) refers to a class of techniques that are used to measure the properties of real world objects without direct measurement, usually with the help of sources such as images or uncalibrated video.
There is a popular quote by sir Isaac Newton which goes something like this (and I’m paraphrasing due to the lack of the source) – “power distributions exist in the real world, but color exists in our brain“. Which is a general idea which many of us have had growing up – What are the odds that the color that you see as red is the same as what I am seeing? Of course we know color is an intrinsic property of light (which was once famously demonstrated by Newton’s prism experiment )
Newton showed for the first time that color was not some “noise” which the prism added but an intrinsic property of the white light.
The question that still remains to be unanswered is that of perception. The reaction that our brain has on perceiving color is entirely intrinsic to us and therefore cannot be generalized.
On vision & learning 