A sensor question
lrc at red4est.com
Mon Apr 11 01:19:54 EDT 2011
On Apr 10, 2011, at 9:36 PM, Sandy Harris wrote:
> The usual sensor uses basically three types of element -- R, G and B
> -- in a particular layout.
> Why not X Y Z where X = R+G, Y = R+G+B, Z = G+B ?
Interesting, my enlarger has CMY where
C=G+B M=R+B and Y=R+G
Y=R+G, W=R+G+B, C=G+B
But, the normal pattern is four pixels R,G,G,B so you could do a four pixel:
C,M,Y,W which is almost the same as what printers use: CMYK
poking at various wikipedia entries on color (googling color wavelength)
violet 668–789 THz 380–450 nm
blue 631–668 THz 450–475 nm
cyan 606–630 THz 476–495 nm
green 526–606 THz 495–570 nm
yellow 508–526 THz 570–590 nm
orange 484–508 THz 590–620 nm
red 400–484 THz 620–750 nm
I'll use capital letters for positive results and lower case for negative
Let's say green light hits your array, we get
if white light hits it we get
with a CMYW array green gives us
white gives us
so we can at least tell the difference between green and white.
> You can get RGB from XYZ easily enough:
> Y-X = R+G+B - R+G = B
> Y-Z = R+G+B - B+G = R
> X+Z-Y = R+G + B+G - R+G+B = R
> But the total light you are accepting is 2+2+3 = 7 rather than
> 1+1+1=3, so you are getting more photons overall. Isn't that
At first glance it looks great.
> Y also gives you a straightforward monochrome.
But why additive rather than subtractive color.
I suspect that part of it has to do with the fact that light isn't composed of R,G,B photons, it's just that our eyes are composed of RGB cones:
Cone type Name Range Peak wavelength
S β 400–500 nm 420–440 nm violet-green peaking in low violet
M γ 450–630 nm 534–555 nm blue-red peaking in green
L ρ 500–700 nm 564–580 nm green-red peaking in yellow-orange
If a 600 nm (orange) photon hits our eyes, the M&L cones are activated, or in the RGB parlance the red and green sensor sites, I'm not sure which of your sensors it would trigger and in what percentage.
Could you explain your sensor idea to me in terms of photon wavelengths? I got this far and am not clever enough to work it out.
I also suspect that additive color math is a lot easier than subtractive color math.
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Larry Colen lrc at red4est.com sent from i4est
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