pg_hexedit recently gained the ability to annotate the space taken up by each individual column/attribute within each individual tuple. This works with tables, and with B-Tree indexes.
I had to come up with a way of passing the pg_hexedit frontend utility the relevant pg_attribute metadata to make this work. This metadata describes the "shape" of individual tuples in a relation (backend code uses a closely related structure called a "tuple descriptor"). My approach works seamlessly in simple cases, but can still be used when manually running the pg_hexedit command line tool.