code about 'Backgrounds' parameter

[budaoxiaowanzi]

Hi, I want try the new color visualization code for my mpMRI(T1-w, T2-w, DWI)data. but I have some not understand

Dataset.Backgrounds1.Dir = 't1_resampled_5334/'; % t2_tse_tra_320_p2_5 t1_resampled_5334
Dataset.Backgrounds2.Dir = 't2_tse_tra_320_p2_5/'; % t2_tse_tra_320_p2_5 t1_resampled_5334
Dataset.SampleImageNumber = 12;
Dataset.extraMode = 'Backgrounds';

what's the meaning of the four parameter , especially 'Backgrounds',
In main_reColorMRI.m, About "isfield(Dataset,'Backgrounds1')" represent ?