Package org.opencv.video

## Class BackgroundSubtractorMOG2

- java.lang.Object
- - org.opencv.core.Algorithm
  - - org.opencv.video.BackgroundSubtractor
    - - org.opencv.video.BackgroundSubtractorMOG2

-     public class BackgroundSubtractorMOG2
      extends BackgroundSubtractor

  Gaussian Mixture-based Background/Foreground Segmentation Algorithm. The class implements the Gaussian mixture model background subtraction described in CITE: Zivkovic2004 and CITE: Zivkovic2006 .

- - ### Field Summary

    - ### Fields inherited from class org.opencv.core.Algorithm

      `nativeObj`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor | Description
    --- | --- | ---
    `protected` | `BackgroundSubtractorMOG2​(long addr)` |

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `static BackgroundSubtractorMOG2` | `__fromPtr__​(long addr)` |
    `void` | `apply​(Mat image, Mat fgmask)` | Computes a foreground mask.
    `void` | `apply​(Mat image, Mat fgmask, double learningRate)` | Computes a foreground mask.
    `protected void` | `finalize()` |
    `double` | `getBackgroundRatio()` | Returns the "background ratio" parameter of the algorithm If a foreground pixel keeps semi-constant value for about backgroundRatio\*history frames, it's considered background and added to the model as a center of a new component.
    `double` | `getComplexityReductionThreshold()` | Returns the complexity reduction threshold This parameter defines the number of samples needed to accept to prove the component exists.
    `boolean` | `getDetectShadows()` | Returns the shadow detection flag If true, the algorithm detects shadows and marks them.
    `int` | `getHistory()` | Returns the number of last frames that affect the background model
    `int` | `getNMixtures()` | Returns the number of gaussian components in the background model
    `double` | `getShadowThreshold()` | Returns the shadow threshold A shadow is detected if pixel is a darker version of the background.
    `int` | `getShadowValue()` | Returns the shadow value Shadow value is the value used to mark shadows in the foreground mask.
    `double` | `getVarInit()` | Returns the initial variance of each gaussian component
    `double` | `getVarMax()` |
    `double` | `getVarMin()` |
    `double` | `getVarThreshold()` | Returns the variance threshold for the pixel-model match The main threshold on the squared Mahalanobis distance to decide if the sample is well described by the background model or not.
    `double` | `getVarThresholdGen()` | Returns the variance threshold for the pixel-model match used for new mixture component generation Threshold for the squared Mahalanobis distance that helps decide when a sample is close to the existing components (corresponds to Tg in the paper).
    `void` | `setBackgroundRatio​(double ratio)` | Sets the "background ratio" parameter of the algorithm
    `void` | `setComplexityReductionThreshold​(double ct)` | Sets the complexity reduction threshold
    `void` | `setDetectShadows​(boolean detectShadows)` | Enables or disables shadow detection
    `void` | `setHistory​(int history)` | Sets the number of last frames that affect the background model
    `void` | `setNMixtures​(int nmixtures)` | Sets the number of gaussian components in the background model.
    `void` | `setShadowThreshold​(double threshold)` | Sets the shadow threshold
    `void` | `setShadowValue​(int value)` | Sets the shadow value
    `void` | `setVarInit​(double varInit)` | Sets the initial variance of each gaussian component
    `void` | `setVarMax​(double varMax)` |
    `void` | `setVarMin​(double varMin)` |
    `void` | `setVarThreshold​(double varThreshold)` | Sets the variance threshold for the pixel-model match
    `void` | `setVarThresholdGen​(double varThresholdGen)` | Sets the variance threshold for the pixel-model match used for new mixture component generation

    - ### Methods inherited from class org.opencv.video.BackgroundSubtractor

      `getBackgroundImage`

    - ### Methods inherited from class org.opencv.core.Algorithm

      `clear, empty, getDefaultName, getNativeObjAddr, save`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### BackgroundSubtractorMOG2

          protected BackgroundSubtractorMOG2​(long addr)

  - ### Method Detail

    - #### __fromPtr__

          public static BackgroundSubtractorMOG2 __fromPtr__​(long addr)

    - #### getDetectShadows

          public boolean getDetectShadows()

      Returns the shadow detection flag If true, the algorithm detects shadows and marks them. See createBackgroundSubtractorMOG2 for details.
      Returns:
        automatically generated

    - #### getBackgroundRatio

          public double getBackgroundRatio()

      Returns the "background ratio" parameter of the algorithm If a foreground pixel keeps semi-constant value for about backgroundRatio\*history frames, it's considered background and added to the model as a center of a new component. It corresponds to TB parameter in the paper.
      Returns:
        automatically generated

    - #### getComplexityReductionThreshold

          public double getComplexityReductionThreshold()

      Returns the complexity reduction threshold This parameter defines the number of samples needed to accept to prove the component exists. CT=0.05 is a default value for all the samples. By setting CT=0 you get an algorithm very similar to the standard Stauffer&Grimson algorithm.
      Returns:
        automatically generated

    - #### getShadowThreshold

          public double getShadowThreshold()

      Returns the shadow threshold A shadow is detected if pixel is a darker version of the background. The shadow threshold (Tau in the paper) is a threshold defining how much darker the shadow can be. Tau= 0.5 means that if a pixel is more than twice darker then it is not shadow. See Prati, Mikic, Trivedi and Cucchiara, Detecting Moving Shadows...*, IEEE PAMI,2003.
      Returns:
        automatically generated

    - #### getVarInit

          public double getVarInit()

      Returns the initial variance of each gaussian component
      Returns:
        automatically generated

    - #### getVarMax

          public double getVarMax()

    - #### getVarMin

          public double getVarMin()

    - #### getVarThreshold

          public double getVarThreshold()

      Returns the variance threshold for the pixel-model match The main threshold on the squared Mahalanobis distance to decide if the sample is well described by the background model or not. Related to Cthr from the paper.
      Returns:
        automatically generated

    - #### getVarThresholdGen

          public double getVarThresholdGen()

      Returns the variance threshold for the pixel-model match used for new mixture component generation Threshold for the squared Mahalanobis distance that helps decide when a sample is close to the existing components (corresponds to Tg in the paper). If a pixel is not close to any component, it is considered foreground or added as a new component. 3 sigma => Tg=3\*3=9 is default. A smaller Tg value generates more components. A higher Tg value may result in a small number of components but they can grow too large.
      Returns:
        automatically generated

    - #### getHistory

          public int getHistory()

      Returns the number of last frames that affect the background model
      Returns:
        automatically generated

    - #### getNMixtures

          public int getNMixtures()

      Returns the number of gaussian components in the background model
      Returns:
        automatically generated

    - #### getShadowValue

          public int getShadowValue()

      Returns the shadow value Shadow value is the value used to mark shadows in the foreground mask. Default value is 127. Value 0 in the mask always means background, 255 means foreground.
      Returns:
        automatically generated

    - #### apply

          public void apply​(Mat image,
                            Mat fgmask,
                            double learningRate)

      Computes a foreground mask.
      Overrides:
        `apply` in class `BackgroundSubtractor`
      Parameters:
        `image` - Next video frame. Floating point frame will be used without scaling and should be in range \([0,255]\).
        `fgmask` - The output foreground mask as an 8-bit binary image.
        `learningRate` - The value between 0 and 1 that indicates how fast the background model is learnt. Negative parameter value makes the algorithm to use some automatically chosen learning rate. 0 means that the background model is not updated at all, 1 means that the background model is completely reinitialized from the last frame.

    - #### apply

          public void apply​(Mat image,
                            Mat fgmask)

      Computes a foreground mask.
      Overrides:
        `apply` in class `BackgroundSubtractor`
      Parameters:
        `image` - Next video frame. Floating point frame will be used without scaling and should be in range \([0,255]\).
        `fgmask` - The output foreground mask as an 8-bit binary image. learnt. Negative parameter value makes the algorithm to use some automatically chosen learning rate. 0 means that the background model is not updated at all, 1 means that the background model is completely reinitialized from the last frame.

    - #### setBackgroundRatio

          public void setBackgroundRatio​(double ratio)

      Sets the "background ratio" parameter of the algorithm
      Parameters:
        `ratio` - automatically generated

    - #### setComplexityReductionThreshold

          public void setComplexityReductionThreshold​(double ct)

      Sets the complexity reduction threshold
      Parameters:
        `ct` - automatically generated

    - #### setDetectShadows

          public void setDetectShadows​(boolean detectShadows)

      Enables or disables shadow detection
      Parameters:
        `detectShadows` - automatically generated

    - #### setHistory

          public void setHistory​(int history)

      Sets the number of last frames that affect the background model
      Parameters:
        `history` - automatically generated

    - #### setNMixtures

          public void setNMixtures​(int nmixtures)

      Sets the number of gaussian components in the background model. The model needs to be reinitalized to reserve memory.
      Parameters:
        `nmixtures` - automatically generated

    - #### setShadowThreshold

          public void setShadowThreshold​(double threshold)

      Sets the shadow threshold
      Parameters:
        `threshold` - automatically generated

    - #### setShadowValue

          public void setShadowValue​(int value)

      Sets the shadow value
      Parameters:
        `value` - automatically generated

    - #### setVarInit

          public void setVarInit​(double varInit)

      Sets the initial variance of each gaussian component
      Parameters:
        `varInit` - automatically generated

    - #### setVarMax

          public void setVarMax​(double varMax)

    - #### setVarMin

          public void setVarMin​(double varMin)

    - #### setVarThreshold

          public void setVarThreshold​(double varThreshold)

      Sets the variance threshold for the pixel-model match
      Parameters:
        `varThreshold` - automatically generated

    - #### setVarThresholdGen

          public void setVarThresholdGen​(double varThresholdGen)

      Sets the variance threshold for the pixel-model match used for new mixture component generation
      Parameters:
        `varThresholdGen` - automatically generated

    - #### finalize

          protected void finalize()
                           throws java.lang.Throwable

      Overrides:
        `finalize` in class `BackgroundSubtractor`
      Throws:
        `java.lang.Throwable`