Preprocess images

RELION does not discard any image during refinement. Therefore, data sets should be clean from false particles. Masking and CTF correction are done internally, so in the preprocessing images do not need to be masked, nor CTF phase-flipped or Wiener-filtered. The images should be normalised, but the exact procedures do not matter much, as also normalisation errors may be corrected inside the refinement.

CTF phase-flipping