The color of light can be represented in an RGB vector
[R]
[G]
[B]
where R, G and B represent the amounts of red, green and blue, respectively. The human eye and the brain transform the incoming RGB signal into the vision signal
[I] [ (R+G+B)/3 ]
[L] = [ R - G ]
[S] [ B - (R+G)/2 ]
where I, L and S represent the intensity, long-wave signal, and short-wave signal, respectively.
(a) Write down a matrix A such that A [R] = [I]. [Hint: This part is meant to be easy, as you
[G] [L]
[B] [S]
should be able to read off A directly from the formula above of [I] in terms of [R].]
[L] [G]
[S] [B]
(b) A pair of sunglasses reduces the perceived intensity of the incoming light by half. Write
down a matrix P such that, if the incoming light is perceived as a vision signal [I] by the
[L]
[S]
naked eyes, then P [I] would be the perceived vision signal if the incoming light first
[L]
[S]
went through the sunglasses. [Hint: This part is also meant to be easy; the matrix P
differs from the identity matrix in only one entry.]
(c) Now write down a matrix S representing the effect the sunglasses have on the incoming
light on the RGB level. That is, if the incoming light has RGB signal [R], then after it
[G]
[B]
passes through the sunglasses it has RGB signal S [R]. [Hint: This is the most challenging
[G]
[B]
part of this problem. Use your work in (a) and (b) to write down a matrix equation
involving A, P and S, from which you should be able to solve for S using matrix
multiplication and/or inverse.]