POS-based digital image capturing and processing system using automatic object detection, spectral-mixing based illumination and linear imaging techniques
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.
1. A method of illuminating objects during digital image capture operations by mixing visible and invisible spectral illumination energy at point of sale (POS) environments to form and detect digital images of objects at POS environments with sufficiently high image contrast and quality, said method comprising the steps of:
(a) at a POS environment, providing 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 said imaging window into an imaging volume during object illumination and imaging operations, wherein said coplanar illumination and imaging station includes (i) an image formation and detection (IFD) subsystem having a linear image sensing array and optics providing a field of view (FOV) on said linear image sensing array and extending into said imaging volume, (ii) an illumination subsystem having an array of visible laser diodes (VLDs) and an array of infrared (IR) laser diodes (LDs) for illuminating an object in said FOV with a mixture of visible and invisible spectral illumination energy, (iii) an illumination control subsystem for controlling said illumination subsystem, (iv) an image capturing and buffering subsystem for capturing and buffering linear digital images of the illuminated object detected by said image sensing array, (v) a digital image processing subsystem for processing said captured and buffered linear digital images, and (vi) an automatic object detection subsystem for automatically detecting objects within said 3D imaging volume;
(b) moving the object through said imaging volume, and said automatic object detection subsystem automatically detecting said object, and generating signals indicative of said detected object;
(c) in response to said generated signals, said illumination subsystem automatically producing a first field of visible illumination from said array of VLDs, simultaneously with a second field of invisible illumination from said array of IR-LDs, whereby said first and second fields of illumination spatially overlap and intermix with each other to produce a composite planar laser illumination beam which is substantially coplanar with said FOV, as said illumination control subsystem controls the relative power ratio of said fields of visible illumination and invisible illumination (VIS/IR), and said image formation and detection subsystem forms and detects one or more linear digital images of said illuminated object, during said object illumination and imaging operations;
(d) said linear image sensing array detecting linear digital images of the illuminated object during object illumination operations;
(e) said image capturing and buffering subsystem capturing and buffering linear digital images of the illuminated object, detected by said linear image sensing array; and
(f) said digital image processing subsystem automatically processing said buffered linear digital images so as to read one or more 1D and/or 2D code symbols graphically represented in said linear digital images.
2. The method of claim 1 , wherein during step (c), said illumination control subsystem controls the relative power ratio of said fields of visible illumination and invisible illumination (VIS/IR) during system operation by controlling drive currents supplied to said VLDs and IR-LDs during object illumination and imaging operations.
3. The method of claim 2 , wherein during step (c), said drive currents supplied to said VLDs and IR-LDs are controlled, during object illumination and imaging operations, by the following process:
(i) driving the VLDs and IR-LDs with default values of drive currents so as to illuminate the object with said mixture of visible and invisible spectral illumination energy;
(ii) capturing one or more linear digital images of the illuminated object and measuring the image contrast quality so as to generate feedback or control data; and
(iii) using this feedback or control data to dynamically generate the necessary values for the adjusted drive currents used to drive said VLD and IR-LDs and produce an optimal mixture of visible and invisible spectral illumination energy during object illumination and imaging operations.
4. The method of claim 1 , wherein said automatic object detection subsystem comprises an imaging-based object detection subsystem including an area-type image acquisition subsystem and a digital signal processing chip to support digital image capture and processing operations required for real-time object motion detection.
5. The method of claim 1 , wherein said 1D and/or 2D code symbols are selected from the group consisting of 1D bar code symbols, 2D bar code symbols and 2D data matrix symbols.
6. The method of claim 1 , wherein said capturing of one or more linear digital images of the illuminated object and measuring image contrast quality is carried out within said digital image processing subsystem.
7. The method of claim 1 , wherein said 1D and/or 2D code symbols are selected from the group consisting of 1D bar code symbols, 2D bar code symbols and 2D data matrix symbols.