Phase-stepping Interferometry & MATLAB

1. Apr 10, 2007

n0_3sc

1. The problem statement, all variables and given/known data
I am given 4 files containing the intensities of a fringe pattern with phase-steps of $$\pi/2$$.
I need to do a mesh plot (on MATLAB) of the intensities and phase.

2. Relevant equations

$$I=A+Bcos(\phi)$$

3. The attempt at a solution

I came up with the following equations:
$$I_1=A+Bcos(\phi)$$
$$I_2=A+Bcos(\phi+\pi/2)$$
$$I_3=A+Bcos(\phi+\pi)$$
$$I_4=A+Bcos(\phi+3\pi/2)$$

After the math I get either:
$$I_4-I_3+I_2-I_1 = 0$$
or
$$0.5(I_4-I_3-I_2+I_1) = B(sin\phi + cos\phi)$$

Obviously the first is not usable because I can't create a plot and the second contains 'B' in it - which doesn't help since I don't know what B is.
Any suggestions at all?