We　propose　a　scheme　for　the　direct　measurement　of　the　Wigner　function　of　a　cavity　field　with　no　more　than　three　photons　around　the　origin.　In　the　scheme　the　cavity　field　is　first　displaced　by　a　small　amount.　Then　a　two-level　atom　is　sent　through　the　cavity.　After　a　resonant　interaction　time　the　difference　between　the　probabilities　of　the　atom　being　in　the　ground　and　excited　states　is　directly　related　to　the　Wigner　function　for　the　field　state.　The　scheme　can　also　be　used　for　conditional　generation　of　four-photon　and　six-photon　states　using　two　and　three　resonant　atoms,　respectively.　(C)　2002　Elsevier　Science　B.V.　All　rights　reserved.