Thanks Anton and others for the reply.
Actually I'm already using shading interp that I forgot to mention in my question.
Further, based on suggestions, I used imfilter command and tried Gaussian and few other filters on my plot. But the shape of plot (that needs to be spherical) is not being preserved.
1) Is there any image processing tool (like imfilter) that I can use in my case? 2) Is there any straight way without going to image processing to smoothen edges of few parts of the plot?