How to utilize illumination model to calculate vertex intensity:

For such we interpolate intensities beside the polygon edges, for all scan line the intensity at the intersection of the scan line along with a polygon edge is linearly interpolated from intensities at the edge end points, that is via using parametric equation of line discussed in previous sections we can determine intensity at point 4, that is I4; throughout the evaluation of I4 intensities at point. 1 and 2 that is, I1 and I2 are utilized as the extreme intensities. Consequently I4 is linearly interpolated by intensities at the edge end points I1 and I2 it here refer to the figure demonstrated below.