Finding contour in using opencv in python

Question

I think,I understood well the function "cv2.findContours(image, mode, method). But I got this thing contours,hierarchy = cv2.findContours(thresh,2,1) in one of the documents of opencv. I am not getting what is the meaning of 2,1 here and why have they been used. Someone please explain it.

They are flags for contour retrieval mode and contour approximation method. Basically int values representing which method/mode to be used. Please read the documentation — Rick M.
– Rick M., Commented Jun 9, 2017 at 11:48

Foo Bar · Accepted Answer · 2017-06-09 11:55:36Z

1

void cv::findContours   (   InputOutputArray    image,
OutputArrayOfArrays     contours,
OutputArray     hierarchy,
int     mode,
int     method,
Point   offset = Point() 
)

Finds contours in a binary image.

The function retrieves contours from the binary image using the algorithm [132] . The contours are a useful tool for shape analysis and object detection and recognition. See squares.c in the OpenCV sample directory.

Some doc could help you: http://docs.opencv.org/trunk/d9/d8b/tutorial_py_contours_hierarchy.html

answered Jun 9, 2017 at 11:55

Foo Bar

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2 Comments

Anand Yadav Over a year ago

Sorry to say but I didn't get how can I represent mode and method in form of integers?

Foo Bar Over a year ago

Int values are representing which method/mode to be used. Have you read the documentation? To use them I will be doing trial-error to see what do they represent, but, thats my choice.

K.Afroz · Accepted Answer · 2018-03-13 15:39:09Z

1

The mode and method parameter of findContours() are enum with integer values. One can use either the keywords or the integer values assigned to it. This detail can be viewed as an intellisense in visual studio when opencv is included in a project.

Below are the associated values with each enum.

MODES

CV_RETR_EXTERNAL : 0
CV_RETR_LIST : 1
CV_RETR_CCOMP : 2
CV_RETR_TREE : 3

METHODS

CV_CHAIN_APPROX_NONE : 1
CV_CHAIN_APPROX_SIMPLE : 2
CV_CHAIN_APPROX_TC89_L1 : 3
CV_CHAIN_APPROX_TC89_KCOS : 4

answered Mar 13, 2018 at 15:39

K.Afroz

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