1. A signal processing device ( 100 ) for processing three-dimensional [3D] image data, the 3D image data comprising two-dimensional [2D] image data ( 150 ) and thereto corresponding 2D depth data ( 170 ), and the signal processing device comprising: an input ( 120 ) for receiving the 2D image data and the 2D depth data; a first outlier detector ( 160 ) for establishing a statistical depth deviation ( 178 ) of a depth value ( 172 ) from other depth values ( 174 ) in a first spatial neighborhood ( 176 ) of the 2D depth data; a second outlier detector ( 140 ) for establishing a statistical image deviation ( 158 ) of an image value ( 152 ) from other image values ( 154 ) in a second spatial neighborhood ( 156 ) of the 2D image data, the depth value representing a depth of the image value; and a depth value generator ( 180 ) for, in dependence on the statistical depth deviation and the statistical image deviation, providing a replacement depth value ( 190 ) when the statistical depth deviation exceeds the statistical image deviation, the replacement depth value having a lower statistical depth deviation than the depth value.