Coded data generation or conversion – Analog to or from digital conversion – Detecting analog signal peak
Patent
1998-12-23
2000-07-25
Phan, Trong
Coded data generation or conversion
Analog to or from digital conversion
Detecting analog signal peak
378 62, H03M 100
Patent
active
060941529
ABSTRACT:
A robust histogram analysis algorithm is used in accordance with the present invention to control the electronic portal image analog to digital (A/D) window such that the acquired images will have sufficient contrast for their uses in radiotherapy. The algorithm includes setting an initial estimate of a region of interest within a histogram, the histogram including pixel counts and pixel values related to the pixel counts, and determining two dominant peaks inside the region of interest. One of the two dominant peaks is below a predetermined value and the other of the two dominant peaks is between the predetermined value and a second predetermined value. If the one dominant peak is more than two times the standard deviation of the other dominant peak, then a first local minimum to the right of the one dominant peak will be the revised boundary. If the other dominant peak is more than two times the standard deviation of the one dominant peak, then a first local minimum to the left of the other dominant peak will be the revised boundary. Otherwise the average value of the two dominant peaks will be the revised boundary. The algorithm also includes counting the number of pixels outside the revised boundary and determining a mean pixel value outside the revised boundary based upon the pixel count. Furthermore, the algorithm includes accumulating pixel counts in one direction until a predetermined percentage of the pixel counts outside revised estimate of dark region is reached to determine the lower cutoff and accumulating pixel counts in an opposite direction until a predetermined percentage is reached to determine the upper cutoff. Finally, the algorithm includes utilizing the upper and lower cutoffs to set the A/D window.
REFERENCES:
patent: 4264898 (1981-04-01), Barman et al.
patent: 4383247 (1983-05-01), Assard
patent: 5296856 (1994-03-01), Mantong
patent: 5684850 (1997-11-01), Warburton et al.
Phan Trong
Siemens Medical Systems Inc.
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