PQexecParams with binary resultFormat vs BINARY CURSOR

Hi,

Considering query for binary data stored directly in tables
using libpq API, I'm trying to understand what is the difference
between specifying binary format in functions like
PQexecParams and use of BINARY CURSOR.

For example, with query like this:

SELECT large_image FROM tbl;

where large_image is a custom type,
is there a big difference between binary format specified
to libpq and use of BINARY CURSOR?
Is it client-side binary vs server-side binary processing?

Simply, I'd like to avoid textual<->binary conversions at any stage.

(Endianness is not an issue here.)

Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net