This is Analytic Solution

This image uses 16 random samples per pixel

This image uses 16 stratified samples per pixel

This image uses 100 random samples per pixel

This image uses 100 stratified samples per pixel

This image uses 100 random samples with bspline filter

This image uses 100 random samples with density estimation

This image uses 100 stratified samples with density estimation

This image uses 100 random samples per pixel for Metropolis