Best way to joining 2 different brain parcellations using Nilearn

I would like to join 2 different brain parcellations using Nilearn. Do you know what are the steps I need to take into account before joining the 2 parcellations? I think the basic steps would be to scale the parcellations and register the 2 parcellations. Do you know if there are any other steps I need to follow? I am using Python and Nilearn for preprocessing. Any suggestion would be useful.

Hi @neurolearning93 first I have to note is that nilearn is not meant to be used for spatial preprocessing. You may want to check out fMRIPrep: A Robust Preprocessing Pipeline for fMRI Data — fmriprep version documentation or Neuroimaging in Python - Pipelines and Interfaces — nipy pipeline and interfaces package first for more information about registering the parcellations to the same space. In nilearn you can just perform affine transformations using nilearn.image.resample_to_img on already aligned maps. Then when you have the parcellations in the same space and resolution, you can merge them with nilearn.image.math_img.