  Kinetic inductance bolometer (KIB) technology is a candidate for passive
sub-millimeter wave and terahertz imaging systems. Its benefits include
scalability into large 2D arrays and operation with intermediate cryogenics in
the temperature range of 5 -- 10 K. We have previously demonstrated the
scalability in terms of device fabrication, optics integration, and cryogenics.
In this article, we address the last missing ingredient, the readout. The
concept, serial addressed frequency excitation (SAFE), is an alternative to
full frequency-division multiplexing at microwave frequencies conventionally
used to read out kinetic inductance detectors. We introduce the concept, and
analyze the criteria of the multiplexed readout avoiding the degradation of the
signal-to-noise ratio in the presence of a thermal anti-alias filter inherent
to thermal detectors. We present a practical scalable realization of a readout
system integrated into a prototype imager with 8712 detectors. This is used for
demonstrating the noise properties of the readout. Furthermore, we present
practical detection experiments with a stand-off laboratory-scale imager.
