A method of illuminating objects using adaptively controlled mixing of spectral illumination energy to form and detect digital images of objects at POS environments with sufficiently high image contrast and quality. The method comprises providing, at a POS environment, a digital image capture and processing system having a system housing with an imaging window, and a coplanar illumination and imaging station disposed within said system housing, for projecting a coplanar illumination and imaging plane through the imaging window into an imaging volume during object illumination and imaging operations. As the object is moved through the imaging volume, its motion is automatically detected, and signals indicative of said detected object are generated. In response to the generated signals, a first field of visible illumination is produced from an array of visible laser diodes (VLDs), simultaneously with a second field of invisible illumination from a array of infrared (IR) laser diodes (LDs). These first and second fields of illumination spatially overlap and intermix with each other and produce a composite planar illumination beam that is substantially coextensive with the FOV. During object illumination and imaging operations, the relative power ratio (VIS/IR) of these fields of visible illumination and invisible illumination are controlled as one or more linear digital images of the illuminated object are formed and detected, captured and buffered, and ultimately processed so as to read one or more 1D and/or 2D code symbols graphically represented in the digital images. In an illustrative embodiment, during object illumination and imaging operations operation, the relative power ratio (VIS/IR) is adaptively controlled to form and detect digital images of objects at POS environments with sufficiently high image contrast and quality.