Posted by
Kenneth Sloan-2 on
Jul 23, 2009; 2:24pm
URL: http://imagej.273.s1.nabble.com/RGB-weights-and-fluorescence-intensity-tp3691651p3691655.html
On Jul 22, 2009, at 10:50 PM, Sami Badawi wrote:
>
> It is normal to weight the RGB colors differently:
> Intensity = 0.3*R + 0.59*G + 0.11*B
> The reason for this is that we have less blue cones receptors in our
> eyes than red and green cones.
Well.....not exactly.
Number is important - but so is the wiring diagram (photoreceptors to
ganglion cells) and any number of other factors. There are, indeed,
fewer "blue" cones - but the ratio of "red" to "green" cones varies
wildly from individual to individual (without markedly changing the
relative weights of R and G).
The numbers above come from psycho-physical experiments; at the time
they were done, no one *knew* how many "red", "green", and "blue"
photoreceptors were in the human eye. They are the result of
measuring the response of the total system - how they relate to
individual components is still an open question.
And, of course - they only work for the "average human". It's
physiology, not physics!
Actually, there's a nice story you can tell that explains the 2/1
ratio of "green" to "red" cones based on how they are used to convert
from [R, G, B] to [Red-Green, Blue-Yellow, White-Black]. Alas, this
nice story does not explain the low weight for "blue" cones.
I like to think that blue has a low weight because "the sky is blue".
It's as good a reason as any.
--
Kenneth Sloan
[hidden email]