1. An apparatus ( 1 ) for segmenting an object comprising sub-objects shown in an object image ( 18 ), the apparatus comprising: a feature image generation unit ( 2 ) for generating a feature image ( 19 ) showing features related to intermediate regions between the sub-objects, a segmentation unit ( 3 ) for segmenting the sub-objects by using the object image and the feature image; wherein the segmentation unit comprises: a model providing unit for providing a model object comprising model sub-objects, a pre-positioning unit for pre-positioning the model object in the object image and the feature image, and an adaptation unit for adapting the model object to the object in the object image and in the feature image; wherein the adaptation unit is adapted such that a surface of a model sub-object facing another model sub-object is adapted to the feature image, and such that a surface of the model object which does not face a model sub-object is adapted to the object image.