Adaptive thresholding technique
AssigneeHughes Aircraft Company
InventorsDavid Assael, Brian Lincoln
Life of this patent
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Abstract
An adaptive thresholding technique is calculated by using a real-time 16 pixel running average (RA) 18 to which is added on offset value. The offset value 38 is the product of a programmable factor (alpha) and a Sum Absolute Difference (SAD) noise measurement. The adaptive threshold 42 is compared by a comparator 48 with a delayed analog video signal intensity value on line 46 for the pixel associated with the adaptive threshold. The comparator 48 provides a binary video output for further processing. A relative video output may also be provided by taking the difference of the analog video signal 46 and its corresponding running average 18.
Claims14
In an image processing system where analog video signals from a detector are converted for further processing, the conversion being a function of a comparison of the analog video signal intensity level relative to a threshold, the analog video signal being associated with a matrix of pixels arranged in a plurality of rows and columns, the improvement comprising:
- means for defining an adaptive threshold level against which the analog video signal level for each pixel position is compared, said means including:
- (a) means for calculating a running average of the intensity of the analog video signal;
- and
- (b) means for adding an offset value to the running average, said offset value being a function of a global measure of noise (alpha) in the system and a function of noise specifically associated with the detector (SAD).
An image processing system for analyzing analog video signals having intensities associated with various pixel positions arranged in a matrix of rows and columns, said system comprising:
- input means for receiving said analog video signals;
- running average (RA) means for calculating a running average of the intensity of a group of pixels in each column;
- SAD means for calculating a SAD factor which is the sum of the absolute difference of the video signals and the running average in a selected window along each column;
- alpha generator means for generating an alpha factor which is a positive number based on a false alarm rate and desired probability of detection for the system;
- multiplier means for multiplying the alpha factor with the SAD factor to generate an offset value;
- summing means for summing the running average with the offset to provide an adaptive threshold level for each pixel;
- and
- comparison means for comparing the adaptive threshold level for each pixel with the analog video signal intensity for that pixel, the comparison means generating a binary one output if the video level is above the threshold and a binary zero level if the video level is below the threshold.
A method of thresholding analog video signals having intensity levels associated with a matrix of pixels arranged in rows and columns, said method comprising:
- generating a running average (RA) value of the analog video signal over a plurality of pixels;
- generating a Sum Absolute Difference (SAD) value by taking the difference of the analog video signal and the running average value in a selected window;
- generating an alpha factor as a positive number which is associated with a global measure of noise and a desired system probability of detection;
- multiplying the SAD value by the alpha value to generate an offset;
- adding the offset to the running average to generate an adaptive threshold level for each pixel;
- and
- digitizing each pixel of the analog video signal to a binary one if the intensity is above its adaptive threshold and to a binary zero if the intensity is below its adaptive threshold level.
Dependencies are inferred from the claim text.