Digital image capture and processing system having automatic illumination measurement and control capabilities realized using a photodetector operating independently of the image sensing array, and an image-processing based illumination metering program for automatically adjusting the illumination duration of the system during object illumination and imaging operations
A digital-imaging based code symbol reading system comprising an image sensing array with a field of view (FOV), an illumination subsystem with an LED illumination array, an automatic illumination measurement subsystem, an illumination control subsystem, and programmed imager processor supporting an image-processing based illumination metering program. The automatic illumination measurement subsystem, employing a photodetector operating independently from the image sensing array, is used to automatically measure the illumination level at a particular region of the FOV and determine the illumination duration necessary to achieve a desired spatial intensity in the detected digital image. The illumination metering program automatically analyzes and measures, in real-time, the spatial intensity distribution of the digital image and determines whether or not a corrected illumination duration is required or desired when detecting the next or subsequent digital images, during the current or subsequent object illumination and imaging cycle. The previously determined illumination duration is over-written with the corrected illumination duration, which is used to drive the illumination subsystem and form and detect subsequent digital images of the illuminated object.
1. A digital image capture and processing system comprising:
a housing having a light transmission window;
an image formation and detection subsystem having an image sensing array and image formation optics having a field of view (FOV) defined relative to said light transmission window, for forming and detecting a digital image of an object within said FOV;
a trigger event generation mechanism, disposed in said housing, for automatically detecting the presence of the object within said FOV, and generating a trigger event in response to detecting the presence of said object;
an illumination subsystem, disposed in said housing, and having an LED-based illumination array for producing a field of illumination within said FOV during object illumination and imaging operations;
an illumination measurement subsystem, disposed in said housing, and including a photodetector, operating independently from said image sensing array, for measuring the level of illumination at a particular region of said FOV during object illumination and imaging operations, and determining and storing an illumination duration necessary to achieve a desired spatial intensity in said digital image formed and detected by said information and detection subsystem;
an illumination control subsystem, disposed in said housing, and using said illumination duration determined by said illumination measurement subsystem so as to control the time duration that said LED-based illumination array is driven during object illumination and imaging operations;
a programmed image processor, disposed in said housing, for supporting an image-processing based illumination metering program, as well as processing digital images formed and detected by said image formation and detection subsystem so as to read or acquire information graphically represented in said digital images; and
a system control subsystem, disposed in said housing, for controlling and/or coordinating the operations of one or more of said subsystems and components identified above.
2. The digital image capture and processing system of claim 1 , wherein said trigger event generation mechanism comprises an automatic object presence detector, wherein when an object is moved into said FOV, said trigger event generation mechanism automatically generates said trigger event within said digital image capture and processing system; and
wherein, in response to the generation of said trigger event, the following sequence of operations are carried out under the control and or coordination of said system control subsystem:
(1) said illumination subsystem produces and projects said field of illumination within said FOV and onto said detected object;
(2) said photo detector employed in said illumination measurement subsystem automatically measures the level of illumination at a particular region of said FOV, and determines and stores the illumination duration necessary to achieve the desired spatial intensity in the digital image formed and detected by said information and detection subsystem;
(3) said illumination control subsystem uses said determined illumination duration to control the time duration that said LED-based illumination array is driven during object illumination and imaging operations;
(4) said image formation and detection subsystem forms and detects one or more digital images of the illuminated object within said FOV;
(5) said programmed image processor uses said image-processing based illumination metering program to analyze and measure, in real-time, the spatial intensity distribution of the detected digital image, and determines whether or not a corrected illumination duration is required when forming and detecting a next or subsequent digital image during the current or subsequent object illumination and imaging cycle;
(6) in the event that said programmed image processor determines that a corrected illumination duration is required, then said programmed image processor over-writes the previously determined and stored illumination duration, with the corrected illumination duration; and
(7) said illumination control subsystem uses the corrected illumination duration to control the time duration that said LED-based illumination array is driven during the subsequent object illumination and imaging operations, so that said image formation and detection subsystem can form and detect one or more digital images of the illuminated object.
3. The digital image capture and processing system of claim 2 , wherein said system control subsystem coordinates system operations so that operations (1) through (7) are repeated one or more additional times during each object illumination and imaging cycle, so as to produce one or more digital images having a spatial intensity level with high image contrast.
4. The digital image capture and processing system of claim 1 , wherein said particular region is a central region of said FOV.
5. The digital image capture and processing system of claim 1 , wherein said housing is hand-supportable, and said trigger event generation mechanism comprises a trigger switch that is manually actuated by an operator, and wherein in response to an object being moved into said FOV, the operator generates said trigger event by manually actuating said trigger switch;
wherein, in response to the generation of said trigger event, the following sequence of operations are carried out under the control and/or coordination of said system control subsystem:
(1) said illumination subsystem produces and projects said field of illumination within said FOV and onto said detected object;
(2) said photodetector employed in said illumination measurement subsystem automatically measures the level of illumination at the particular region of said FOV, and determines and stores the illumination duration necessary to achieve the desired spatial intensity in the digital image formed and detected by said information and detection subsystem;
(3) said illumination control subsystem uses said determined illumination duration to control the time duration that said LED-based illumination array is driven during object illumination and imaging operations;
(4) said image formation and detection subsystem forms and detects a digital image of the illuminated object within said FOV;
(5) said programmed image processor uses said image-processing based illumination metering program to analyze and measure, in real-time, the spatial intensity distribution of the detected digital image, and determines whether or not a corrected illumination duration is required when forming and detecting a next or subsequent digital image during the current or subsequent object illumination and imaging cycle;
(6) in the event that said programmed image processor determines that a corrected illumination duration is required, then said programmed image processor over-writes the previously determined and stored illumination duration, with the corrected illumination duration; and
(7) said illumination control subsystem uses the corrected illumination duration to control the time duration that said LED-based illumination array is driven during the subsequent object illumination and imaging operations, so that said image formation and detection subsystem can form and detect one or more digital images of the illuminated object.
6. The digital image capture and processing system of claim 5 , wherein said system control subsystem coordinates system operations so that operations (1) through (7) are repeated one or more additional times during each object illumination and imaging cycle, so as to produce one or more digital images having an optimized spatial intensity level with high image contrast.
7. The digital image capture and processing system of claim 1 , wherein said particular region is a central region of the field of view of said image sensing array.
8. The digital image capture and processing system of claim 1 , wherein said image sensing array is an area-type image sensing array.
9. The digital image capture and processing system of claim 1 , wherein said illumination duration is a time count stored in memory within said digital image capture and processing system.
10. The digital image capture and processing system of claim 1 , wherein said programmed image processor is programmed so as to support decode processing of digital images formed and detected by said image formation and detection subsystem so as to read one or more 1D and/or 2D code symbols represented in said digital images.
11. The digital image capture and processing system of claim 10 , wherein said housing is a hand-supportable housing.
12. The digital image capture and processing system of claim 10 , wherein said code symbol is a bar code symbol.
13. The digital image capture and processing system of claim 12 , wherein said bar code symbol is selected from the group consisting of 1D bar code symbols, 2D bar code symbols and data matrix symbols.
14. The digital image capture and processing system of claim 8 , wherein said area-type image sensing array is a CMOS-type area image sensor.
15. The digital image capture and processing system of claim 1 , wherein said housing is supportable upon the countertop surface of a point of sale (POS) station.