Three-wave interactions occurring in conditions of type I phase matching in a uniaxial crystal are considered in the general case of noncollinear wave propagation. It is demonstrated that, if one among the interacting fields at i (iϭ1,2,3) is virtually unaffected in amplitude by the interaction, the remaining two fields at j (j i) are holographic replicas of each other, the constant field acting as the reference field in holography. Experiments are presented in which a holographic image of an object consisting in a pointlike light source is obtained by either up-or down-conversion for any choice of the object-and reference-field frequencies among 1 , 2 , and 3 .