How to replot a 3D graph or populate a matrix in matlab from a 2D image that contains 3D data?

(I am new to matlab)

To implement a 3D Charecteristic curve in a code, it is necessary to read the data from a 2D image that includes 3D data. In the image below(ignore the 'r/min' lines) there are dotted lines of efficiency (50% to 70%). Is there a way to generate a 3D surface out of this insufficient data of efficiency lines or a way to populate a matrix from available information? To start with, I used Grabit to extract the lines from the image. A simple thought was to find a way to connect 60-65-70% lines with a slope, considering the 70% region as a flat surface(i.e. maximum efficieny = 70%).