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Merge pull request #9865 from ryanfox:patch-4

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Vadim Pisarevsky 2017-10-30 09:54:48 +00:00
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doc/py_tutorials/py_video/py_bg_subtraction/py_bg_subtraction.markdown
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@ -11,21 +11,21 @@ In this chapter,
Basics Basics
------ ------
Background subtraction is a major preprocessing steps in many vision based applications. For Background subtraction is a major preprocessing step in many vision-based applications. For
example, consider the cases like visitor counter where a static camera takes the number of visitors example, consider the case of a visitor counter where a static camera takes the number of visitors
entering or leaving the room, or a traffic camera extracting information about the vehicles etc. In entering or leaving the room, or a traffic camera extracting information about the vehicles etc. In
all these cases, first you need to extract the person or vehicles alone. Technically, you need to all these cases, first you need to extract the person or vehicles alone. Technically, you need to
extract the moving foreground from static background. extract the moving foreground from static background.
If you have an image of background alone, like image of the room without visitors, image of the road If you have an image of background alone, like an image of the room without visitors, image of the road
without vehicles etc, it is an easy job. Just subtract the new image from the background. You get without vehicles etc, it is an easy job. Just subtract the new image from the background. You get
the foreground objects alone. But in most of the cases, you may not have such an image, so we need the foreground objects alone. But in most of the cases, you may not have such an image, so we need
to extract the background from whatever images we have. It become more complicated when there is to extract the background from whatever images we have. It become more complicated when there are
shadow of the vehicles. Since shadow is also moving, simple subtraction will mark that also as shadows of the vehicles. Since shadows also move, simple subtraction will mark that also as
foreground. It complicates things. foreground. It complicates things.
Several algorithms were introduced for this purpose. OpenCV has implemented three such algorithms Several algorithms were introduced for this purpose. OpenCV has implemented three such algorithms
which is very easy to use. We will see them one-by-one. which are very easy to use. We will see them one-by-one.
### BackgroundSubtractorMOG ### BackgroundSubtractorMOG
@ -76,7 +76,7 @@ throughout the algorithm). It provides better adaptibility to varying scenes due
changes etc. changes etc.
As in previous case, we have to create a background subtractor object. Here, you have an option of As in previous case, we have to create a background subtractor object. Here, you have an option of
selecting whether shadow to be detected or not. If detectShadows = True (which is so by default), it detecting shadows or not. If detectShadows = True (which is so by default), it
detects and marks shadows, but decreases the speed. Shadows will be marked in gray color. detects and marks shadows, but decreases the speed. Shadows will be marked in gray color.
@code{.py} @code{.py}
import numpy as np import numpy as np
@ -104,7 +104,7 @@ cv2.destroyAllWindows()
### BackgroundSubtractorGMG ### BackgroundSubtractorGMG
This algorithm combines statistical background image estimation and per-pixel Bayesian segmentation. This algorithm combines statistical background image estimation and per-pixel Bayesian segmentation.
It was introduced by Andrew B. Godbehere, Akihiro Matsukawa, Ken Goldberg in their paper "Visual It was introduced by Andrew B. Godbehere, Akihiro Matsukawa, and Ken Goldberg in their paper "Visual
Tracking of Human Visitors under Variable-Lighting Conditions for a Responsive Audio Art Tracking of Human Visitors under Variable-Lighting Conditions for a Responsive Audio Art
Installation" in 2012. As per the paper, the system ran a successful interactive audio art Installation" in 2012. As per the paper, the system ran a successful interactive audio art
installation called “Are We There Yet?” from March 31 - July 31 2011 at the Contemporary Jewish installation called “Are We There Yet?” from March 31 - July 31 2011 at the Contemporary Jewish