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 .