Figure 1. Illustrations of noisy encoding of monochromatic inputs by the cone responses.
On the left is the cone spectral sensitivity
(with
, where
s are
derived from the Smith and Pokorny cone fundamentals[15], the
cone density ratio is 
, the
pre-receptor light transmission factors 
, and
Max
). A
monochromatic input of wavelength 
evokes
response 
from the
three cones, L, M, and S. Due to input noise, there is a range of
possible responses 
from this
input. If the mean response to a monochromatic input of nearby
wavelength 
is one of
the typical responses within this range of responses
to input
, then it
will be difficult to perceptually distinguish the input
from input
.