1. A signal processing device for processing three-dimensional (3D) image data, the 3D image data comprising two-dimensional (2D) image data and thereto corresponding 2D depth data, and the signal processing device comprising: an input configured to receive the 2D image data and the 2D depth data; a first outlier detector configured to establish a statistical depth deviation of a depth value from other depth values in a first spatial neighborhood of the 2D depth data; a second outlier detector configured to establish a statistical image deviation of an image value from other image values in a second spatial neighborhood of the 2D image data, the depth value representing a depth of the image value; and a depth value generator configured to, in dependence on the statistical depth deviation and the statistical image deviation, provide a replacement depth value when the statistical depth deviation exceeds the statistical image deviation, the replacement depth value having a lower statistical depth deviation than the depth value.