Divide nii files

Divide nii files according to numerical sorting results. According to the extraction parameters you provide, the most positive and negative voxels can be taken out according to the ratio and stored as another nii file.

such as:
nii_fname = 'test.nii';
split_nii_val(nii_fname,'pos','top',0.025,'output1.nii');
split_nii_val(nii_fname,'pos','bottom',0.01,'output2.nii');
split_nii_val(nii_fname,'neg','top',0.01,'output3.nii');
split_nii_val(nii_fname,'neg','bottom',0.01,'output4.nii');