Certain examples described herein relate to the use of three-dimensional threshold matrices in the production of three-dimensional objects. In one case, data values for a three-dimensional matrix for use in halftoning are assigned based on a structural volume coverage representation. In certain described cases, the structural volume coverage representation defines a probabilistic distribution of at least two different structures available for the production of the three-dimensional object. A comparison is performed based on data values for the structural volume coverage representation. The output of the comparison is a data value to be assigned to the three-dimensional matrix. The resultant three-dimensional matrix is used in a halftoning operation to control a structure distribution in the three-dimensional object.