Dilating a blob was discussed in this recent thread:
[
afni.nimh.nih.gov]
<[
afni.nimh.nih.gov];
There are no tools to dilate by a percentage, only by voxels or by mm distance (as with 3dcalc, 3dLocalstat). 3dAutomask does do dilation, but it clusters at the same time. That will work for many blobs (convex shapes), but it only takes integer values for the dilate and erode levels. 3dmerge has an erode option, but its dilate option is limited to restoring voxels removed in the erosion process for clustering purposes.