A hand-supportable semi-automatic digital imaging-based bar code symbol reading system comprises: an automatic object presence detection subsystem; a multi-mode image formation and detection subsystem having narrow-area and wide area image capture modes of operation; a multi-mode LED-based illumination subsystem having narrow-area and wide area illumination modes of operation; an automatic light exposure measurement and illumination control subsystem; an image capturing and buffering subsystem; a multi-mode image-processing bar code symbol reading subsystem; an input/output subsystem; a manually-actuatable trigger switch; and a system control subsystem for controlling the subsystems. The digital imaging-based bar code reading system employs a three-tier modular software architecture for carrying out its image-processing based bar code symbol reading operations. The three-tier software architecture comprises an application layer, a system core layer, and an operating system (OS) layer.