We estimate the quantum state of a light beam from results of quantum homodyne measurements performed on identically prepared quantum systems. The state is represented through the Wigner function, a density on R2 which may take negative values but must respect intrinsic positivity constraints imposed by quantum physics. The effect of the losses due to detection inefficiencies which are always present in a real experiment is the addition to the tomographic data of independent Gaussian noise. We construct a kernel estimator for the Wigner function and prove that it is minimax efficient for the pointwise risk over a class of infinitely differentiable functions. For the L2 risk, we compute the upper bounds of a truncated kernel estimator over the same classes, restricted to functions with sub-Gaussian asymptotic behaviour. We construct adaptive estimators, i.e. which do not depend on the smoothness parameters, and prove that in some set-ups they attain the minimax rates for the corresponding smoothness class.