Albedo \((\rho)\)

The ratio of reflected radiation to the incident radiation on a surface.
It is dimensionless quantity that typically ranges from 0 to 1, where:

0 : indicates no reflection (black body)
1 : indicates perfect reflection

$$
I=\rho (n \cdot s)E
$$

$$
\rho = \frac{I}{(\mathbf{n} \cdot \mathbf{s})E}
$$
where \(\)I is the pixel value intensity, \(\mathbf{n} \)is the surface normal, \(\mathbf{s}\) is the source direction, and \(E\) is the power of light source.

Shading \(\eta\)

The pixel intensity that changes with respect to geometric factors (surface normal and light source direction).

$$
I=\rho (n \cdot s)E
$$

$$
\eta = (\mathbf{n} \cdot \mathbf{s})E
$$

$$
I = \rho \eta
$$

$$
\eta = \frac{I}{\rho}
$$