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Human Perception (it’s all about us)
Mathematically perfect red-green-blue colours are far from a calibrated monitor red-green-blue values, which are both far from the red-green-blue sensors in our eyes. This is rarely understood or compensated for in colour software. In the chart below, you can see that there is considerable differences between the colours detected by cones in a human eye compared to colours emitted from a calibrated monitor.
The red cones (usually called L-cones as they pickup longer wavelengths of light) are primarily sensitive to a strong crimson red. This actually works out to be between the red in RGB and the magenta in CMYK. The blue cones (S-cones for short wavelengths of light) are most sensitive to a vibrant violet colour which is a ways purplier than the blue in RGB. And the green cones (M-cones for medium wavelengths) are centered on a nuclear fluorescent cyan colour. This shade is way off the chart of RGB and CMYK capabilities. It’s closest description would be a radioactive cyan of intense strength. Although this is one of our eyes primary colours, we never see it in our surroundings -- and for a good reason....
As we view colours going from blue to green, the sensitivity of the blue cones becomes less and the green cones pick up the slack and start sending stronger green signals to the brain. This makes for a smooth transition. Now as colours fade from red to green, the red cones don’t fade off much; they keep sending red signals to the brain even though we are looking at green. As the colour continues to fade to our primary colour, nuclear fluorescent cyan, the red cones are still firing at near full strength and thus dirtying up the colour signals sent to the brain. The only way to perceive the true radioactive cyan colour is to be completely red colour blind.
This strong overlap of red and green cones firing allows us to see more colours between red and green (orange, yellow, and more shades of green) while there is much less colour distinctions between green and blue due to very little signal overlap. This also explains why nearly 40% of all perceivable colours fall into the green category while the remaining 60% cover the reds, oranges, yellows, blues, and purples. An interesting side note: If someone is green colour-blind, since the red cones still fire in that range, they will see green objects as shades of red. But a red colour-blind person will see red objects as black or gray because the green cones don’t tread into the red zone like the red does into the green zone.
In addition to signal contamination from the cones, less than 8% of the RGB colour detectors in our eyes are capable of detecting blue. The remaining 92%+ see red and green (within the center of our vision, we have roughly 55% red, 37% green, and 8% blue cone sensors).
This is why blues and violets appear as darker colours (less blue sensors = less blue signals sent to brain = darker colour). And to finish it off, there are no blue receptors in the very center of our vision. Much like how our brain fills in for the blind spot in our retina, it also fudges the colour in the center of our vision.
To make matters worse, well over 90% of all people have some sort of colour-blindness. Typically this is discovered to be a small range of colours that one individual simply can not tell apart when another individual can. And as people get older, the lens of the eye starts to block some of the shorter wavelengths of light so that the blue cones receive less light making things appear more and more yellow. This being a very gradual change over decades; the individual never notices.
N E X T : Our Eyes and Mind