Abstract: The physical background of the popularly used image interpolation algorithms is analyzed first in this paper. Since the cubic convolution interpolation algorithm makes use of both direct and indirect neighbor pixels around the interpolated point, it is the best interpolation algorithm among the popular used inage interpolation algorithms. But the experiment results show that in the cubic convolution interpolation algorithm the given weights of direct and indirect neighbor pixels around the interpolated point are not the best ones. A recommended best combination of the weights is given then.