how to extract data from the plotted figure?

Hi, I have plotted a radiation pattern and I have attached the figure here.

Now I want to find the dB values in every angles from 0 to 90 degrees. How can I get that? and how do I normalize this figure?

Thanks.

[Image Analyst]

You already HAVE those values or else you could not have plotted it, right? Don't you have the dB already? What are the units of the radial axis?

[Sifat Ara Senjuti]

yes, it is already in dB. I just want to normalize it. And I want to make a list of those values in excel sheet by using matlab commands (if there is any) to save my time as I need the dB values/degree (after normalizing) from 0 to 90 degrees.