A POS-based digital image capturing and processing system for illuminating objects using automatic object detection and spectral-mixing illumination technique. The system comprises a coplanar illumination and imaging station for projecting at least one coplanar illumination and imaging plane into an imaging volume during object illumination and imaging operations. The coplanar illumination and imaging station includes an illumination subsystem for producing a first field of visible illumination from an array of visible VLDs, and producing a second field of invisible illumination from an array of infrared (IR) laser diodes (IR-LDs). Wherein the first and second fields of illumination spatially overlap and intermix with each other and are substantially coplanar with the FOV of the linear image sensing array. An automatic object detection subsystem automatically detects an object moving through the imaging volume, while an illumination control subsystem controls the relative power ratio (VIS/IR) of visible illumination and invisible illumination during system operation so as to minimize the amount of visible illumination energy required to capture sufficiently high-contrast images of said objects and successfully process the same.