model -- a gtk:tree-model-filter object
iter -- a gtk:tree-iter iterator pointing to the row whose display values are determined
value -- a g:value instance which is already initialized for with the correct type for the column column
column -- an integer with the column whose display value is determined

A callback function which calculates display values from raw values in the model. It must fill value with the display value for the column column in the row indicated by iter.

Since this function is called for each data access, it is not a particularly efficient operation.