Background & Foreground Subtraction

What is Background Subtraction?

Background subtraction (BS) is a common and widely used technique for generating a foreground mask by using static cameras.

BS calculates the foreground mask performing a subtraction between the current frame and a background model, containing the static part of the scene or, more in general, everything that can be considered as background given the characteristics of the observed scene.

We can perform Background subtraction by methods in cv2.bgsegm. For example, we can create MOG background subtractor by cv2.bgsegm.createBackgroundSubtractorMOG() and apply it by cv2.bgsegm.createBackgroundSubtractorMOG().apply(image)

Or, we can just create background subtractor by cv2.createBackgroundSubtractorKNN() or cv2.createBackgroundSubtractorMOG2() and also apply it just adding .apply(image) behind these functions.

Methods on bgsegm

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• cv2.bgsegm.createBackgroundSubtractorCNT() : Creates a CNT Background Subtractor.
• cv2.bgsegm.createBackgroundSubtractorGMG() : Creates a GMG Background Subtractor.
• cv2.bgsegm.createBackgroundSubtractorGSOC() : Creates an instance of BackgroundSubtractorGSOC algorithm.
• cv2.bgsegm.createBackgroundSubtractorLSBP() : Creates an instance of BackgroundSubtractorLSBP algorithm.
• cv2.bgsegm.createBackgroundSubtractorMOG() : Creates mixture-of-gaussian background subtractor.
• cv2.bgsegm.createSyntheticSequenceGenerator() : Creates an instance of SyntheticSequenceGenerator.

Result

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Original Image

MOG

GSOC

CNT

GMG

LSBP

KNN

MOG2

What is Foreground Subtraction?

Foreground subtraction is a technique for generating a background mask. We can perform it via steps.

Steps of Foreground Subtraction

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1. Update weights : We can update weights by cv2.accumulateWeighted(src, dst, alpha) where
   
   • src : Input image.
   • dst : Output image.
   • alpha : weight of the input image.
2. Calculate absolute values and convert the result to 8-bit. : we can calculate and convert the result by cv2.convertScaleAbs(src) where
   • src : Input image that created in step 1.
     
     
     
     

Result

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Original Image

Implementation

• Background and Foreground Subtraction