Field depth extension of 2D barcode scanner based on wavefront coding and projection algorithm
2007
Wavefront coding (WFC) used in 2D barcode scanners can extend the depth of field into a great extent with simpler
structure compared to the autofocus microscope system. With a cubic phase mask (CPM) employed in the STOP, blurred
images will be obtained in charge coupled device (CCD), which can be restored by digital filters. Direct methods are
used widely in real-time restoration with good computational efficiency but with details smoothed. Here, the results of
direct method are firstly filtered by hard-threshold function. The positions of the steps can be detected by simple
differential operators. With the positions corrected by projection algorithm, the exact barcode information is restored. A
wavefront coding system with 7mm effective focal length and 6
F-number is designed as an example. Although with the
different magnification, images of different object distances can be restored by one point spread function (PSF) with
200mm object distance. A QR code (Quickly Response Code) of 31mm X 27mm is used as a target object. The
simulation results showed that the sharp imaging objective distance is from 80mm to 355mm. The 2D barcode scanner
with wavefront coding extends field depth with simple structure, low cost and large manufacture tolerance. This
combination of the direct filter and projection algorithm proposed here could get the exact 2D barcode information with
good computational efficiency.
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