Login  Register

Re: RGB weights and fluorescence intensity

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]