A method of processing three-dimensional object data for storage comprising: obtaining data representing a three-dimensional object to be printed, the data comprising object property data indicative of properties of the three-dimensional object; the method being characterised by : identifying geometric representations of layers within the three-dimensional object, wherein each of the identified geometric representations of layers comprises a plurality of predefined sub-volumes, and wherein the predefined object sub-volumes are associated with object property data; processing the obtained data by comparing object property data associated a geometric representation of a given layer of the identified layers to object property data associated with a geometric representation of a reference layer selected from the identified layers, wherein comparing object property data comprises comparing object property data associated with a predefined sub-volume in the given geometric representation of layer to object property data associated with a corresponding sub-volume in the geometric representation of the reference layer; and where a difference in object property data associated with the geometric representation of a given layer and object property data associated with the geometric representation of the reference layer is determined, storing the determined difference. obtaining data representing a three-dimensional object to be printed, the data comprising object property data indicative of properties of the three-dimensional object; the method being characterised by : identifying geometric representations of layers within the three-dimensional object, wherein each of the identified geometric representations of layers comprises a plurality of predefined sub-volumes, and wherein the predefined object sub-volumes are associated with object property data; processing the obtained data by comparing object property data associated a geometric representation of a given layer of the identified layers to object property data associated with a geometric representation of a reference layer selected from the identified layers, wherein comparing object property data comprises comparing object property data associated with a predefined sub-volume in the given geometric representation of layer to object property data associated with a corresponding sub-volume in the geometric representation of the reference layer; and where a difference in object property data associated with the geometric representation of a given layer and object property data associated with the geometric representation of the reference layer is determined, storing the determined difference. identifying geometric representations of layers within the three-dimensional object, wherein each of the identified geometric representations of layers comprises a plurality of predefined sub-volumes, and wherein the predefined object sub-volumes are associated with object property data; processing the obtained data by comparing object property data associated a geometric representation of a given layer of the identified layers to object property data associated with a geometric representation of a reference layer selected from the identified layers, wherein comparing object property data comprises comparing object property data associated with a predefined sub-volume in the given geometric representation of layer to object property data associated with a corresponding sub-volume in the geometric representation of the reference layer; and where a difference in object property data associated with the geometric representation of a given layer and object property data associated with the geometric representation of the reference layer is determined, storing the determined difference. <EOS>