A method of processing data representing a three-dimensional object to be generated in additive manufacturing comprising, by at least one processor executing machine readable instructions: receiving data representing a three-dimensional object, the data comprising an object property description associated with each of a plurality of locations within the object, wherein the object property description describes at least one property attributed to the object represented by the data; determining, from the data, at least one object generation parameter description associated with a region of the object, wherein the object generation parameter description comprises data indicative of at least one value for a plurality of controllable parameters of object generation, the parameters comprising: (i) at least one object generation apparatus control parameter value and a probability that control data for use by an object generation apparatus to generate a three dimensional object and generated from the object generation parameter description will specify said object generation apparatus control parameter value for generating the region of the object, wherein the object generation apparatus control parameter value is a value of a controllable parameter of the object generation apparatus; and (ii) at least one print material coverage value and a probability that control data generated from the object generation parameter description will specify said print material coverage value for that location. receiving data representing a three-dimensional object, the data comprising an object property description associated with each of a plurality of locations within the object, wherein the object property description describes at least one property attributed to the object represented by the data; determining, from the data, at least one object generation parameter description associated with a region of the object, wherein the object generation parameter description comprises data indicative of at least one value for a plurality of controllable parameters of object generation, the parameters comprising: (i) at least one object generation apparatus control parameter value and a probability that control data for use by an object generation apparatus to generate a three dimensional object and generated from the object generation parameter description will specify said object generation apparatus control parameter value for generating the region of the object, wherein the object generation apparatus control parameter value is a value of a controllable parameter of the object generation apparatus; and (ii) at least one print material coverage value and a probability that control data generated from the object generation parameter description will specify said print material coverage value for that location. (i) at least one object generation apparatus control parameter value and a probability that control data for use by an object generation apparatus to generate a three dimensional object and generated from the object generation parameter description will specify said object generation apparatus control parameter value for generating the region of the object, wherein the object generation apparatus control parameter value is a value of a controllable parameter of the object generation apparatus; and (ii) at least one print material coverage value and a probability that control data generated from the object generation parameter description will specify said print material coverage value for that location. <EOS>