Extracting data from matlab graph I do not seem to know how to extract from a Matlab plot. For example in the plot given below, I have a simulated $P_b$ for Rayleigh fading and theoretical AWGN channel Pb plot against SNR ($\large \frac{E_b}{N_o}$). 

My question is how do I get the value of $\large \frac{E_b}{N_o}$ for a particular value of $P_b$. For example, if I want the read the $\large \frac{E_b}{N_o}$ from the graph to get a probability bit error for the Rayleigh channel, what code can I use?
The data that is used to create the curves in the plot are stored in the axes object of the figure that contains the plot. You can obtain the underlying data by retrieving the axes' xdata and ydata properties. For example:

h_axes = gca;
x_data = get(h_axes, 'xdata');
y_data = get(h_axes, 'ydata');

After extracting the data you can use interpolation (see e.g. interp1())to find the value that you are looking for.

Is this what you meant? If not, please let me know and I'll try to explain better...