1. A system for parallel image processing in MR imaging, comprising: a plurality of MR imaging RF coils, wherein each MR imaging RF coil is configured to individually receive MR imaging signals representing a slice or volume of patient anatomy; an MR imaging arrangement configured to use the plurality of RF coils to acquire a corresponding plurality of incomplete image data sets of said slice or volume; and an image data processor comprising at least one processing device, wherein the image data processor is configured to: derive a first set of weights for calculating a weighted combination of k-space data of said plurality of incomplete image data sets to generate a calibration data set comprising a subset of k-space data of composite image data representing said plurality of image data sets, generate a first complete MR image data set based on said calibration data set, determine parameters of a probability distribution based on said first set of weights and said first complete MR image data set, derive a second set of weights based on said calibration data set and on said first complete MR image data set, using said probability distribution, and generate a second complete MR image data set based on said second set of weights.