Hello,

The README.txt file does give RGB, but that is not the important part.  The first number in the list, the "Fill_Value", gives the integer that you will find in the IBSR_01_seg_ana.img file.  This number indicates which neuroanatomical region is present for each voxel in the 3D image volume file (*.img).  For example, when a voxel has a value of 3, that means there is "Left-Cerebral-Cortex" at that location.

The RGB values are provided so that a color lookup table can be created.  This will allow IBSR segmentations to be displayed in the colors used by Freesurfer.

If you are looking for gray matter (GM), cerebral cortex is gray matter, but so is the caudate, and other regions.  Some regions are a mixture of gray and white matter.  The files called, e.g. "IBSR_01_segTRI_ana.img" show the brain segmented into background = 0, CSF=1, gray matter = 2, and white matter = 3.  The README.txt file gives the mapping of which segmented regions map to GM, WM, and CSF.

The file "IBSR_01parc_ANALYZE.tgz" is the parcellation of cerebral cortex into regions based on gyral and sulcal landmarks.  There you can find specific cortical regions like "FP" which is the frontal pole.  The abbreviations follow Freesurfer (see https://academic.oup.com/cercor/article/14/1/11/433466).

Note that the IBSR parcellations were created manually by outlining regions slice-by-slice in the 3D volume using software called "cardviews."  These are not Freesurfer parcellations which are created automatically based on surfaces.

Andy.
Originally posted by dalvinder kaur: