MINC variables fall into one of four classes. The first is the group class, which applies to those data objects and names used to hold actual image data and supporting information. The second is the var-attribute class, which contains data qualifying another variable, for example, by specifying the range of the other variable's data. The third and fourth are the dimension class and the dimension-width class, which specify the properties of the dimensions in a MINC file.
For consistency, all MINC variables are implemented as HDF5 datasets, including those variables which may not contain useful data.
In MINC 2.0, the image, image-max, and image-min variables are no longer single objects as in MINC 1.0. A file may contain any number of sets of these three variables, corresponding to the full resolution data and any lower-resolution ``thumbnail'' data which may be associated with the image. See sections 3.2 and 5.3 for the full explanation of this feature.