On mask file used in tutorial "Case Study: Yeast U4/U6.U5 tri-snRNP"

Dear All,

For tutorial “Case Study: Yeast U4/U6.U5 tri-snRNP”, it used chimera to get the binarization file, which I think was the mask file for following processing. Why it did not get the needed mask file with the refined volume map from the homogeneous refinment step as input to get the corresponding mask file by “Volume Tools”?

I am looking forward to getting your advice.