Periodogram is an algorithm that computes a sharper CTF for better image processing. Setting the periodogram to “yes” creates a sharper CTF through tiling the original image and calculating the power spectrum (PS) for each tile. This allows for higher resolution and better further unbending results.

Window size is the sub-window over which to average. A smaller value for window size would give you faster results. Window size should range from 1-50000.

The number of sub-windows to average ranging from 1-500. Smaller values are faster.