In an example implementation, a method of processing a 3D object model includes receiving render data of a 2D slice of a 3D object model and generating distance values indicating how far away voxels in the 2D slice are from a nearest edge of the 3D object model. The method also includes detecting a feature of the 3D object model from the distance values, and generating modified render data to be subsequently used in a 3D printing system to produce the feature in a 3D part.