FAQs

Preprocessing

Do I need to downsize my images?

RELION will estimate the resolution of your model and downsize the images internally. Therefore, using downsized images will NOT be (much) faster than using large images. In general it is therefore NOT recommended to use downsized images: it could limit your resolution. The only reason why one would want to downsize images if they are too big (e.g. 800x800 pixels) for the reconstruction(s) to fit into memory. The program will complain about that.

Classification

Should I refine my 3D classes in a different program to reach higher resolution?

This is not necessary: you may do so in RELION. Higher resolution often means using fine orientational and translational samplings, which may be prohibitive (speed and memory-wise) inside classification runs. One can however write out a new STAR file that contains only the images belonging to a certain class (see [[]]). That STAR file could then be used for a single-reference refinement with fine samplings in RELION.

How can I images from a STAR file?

The following awk command may be used to select class number 3 (assuming rlnClassNumber is the 13th column):

awk '{if (NF==1) {print} else {if ($13==3) print }}' < classify_it000025_mlmodel.dat > class3_only_input.star

Some knowledge of awk is REALLY useful! This light awk introduction may be helpful. The command above prints all lines where the number of fields (NF) is 1 ( i.e. the STAR-file header), and else it will only print those lines where the 13th column ($13) equals 3. Note one may change the "==" signa for ">", "<=", etc.