  Coherent Diffraction Imaging (CDI), a technique where an object is
reconstructed from a single (2D or 3D) diffraction pattern, recovers the lost
diffraction phases without a priori knowledge of the extent (support) of the
object, which prevents an unambiguous metric evaluation of solutions. We
propose to use a 'free' log-likelihood indicator, where a small percentage of
points are masked from the reconstruction algorithms, as an unbiased metric to
evaluate the validity of proposed solutions, independent of the sample studied.
We also show how a set of solutions can be analysed through an
eigen-decomposition to yield a better estimate of the real object. Example
analysis on experimental data is presented both for a test pattern dataset, and
the diffraction pattern from a live cyanobacteria cell. The method allows the
validation of reconstructions on a wide range of materials (hard condensed,
biological,..), and should be particularly relevant for 4th generation
synchrotrons and X-ray free electron lasers, where large, high-throughput
datasets require a method for unsupervised data evaluation.
