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Cv2.findContours

lastmod 2025-02-18created 2022-07-125 edits

Detects contours.

OpenCV Contours APIs

  • Contours
  • OpenCV:Contours
  • cv2.approxPolyDP - Approximates (simplifies) a polygonal curve with the specified precision.
  • cv2.arcLength - Calculates a contour perimeter or a curve length.
  • cv2.boundingRect - Calculates the upper-right bounding rectangle of a point set or the non-zero pixels of a grayscale image.
  • cv2.boxPoints - Finds the four vertices of a rotated rectangle. Useful for drawing the rotated rectangle.
  • cv2.connectedComponents - Computes the connected components labeled image of a boolean image.
  • cv2.connectedComponentsWithStats - Computes the connected components labeled image of a boolean image and also produces a statistics output for each label.
  • cv2.contourArea - Calculates a contour area.
  • cv2.convexHull - Finds the convex hull of a point set.
  • cv2.convexityDefects - Finds the convexity defects of a contour.
  • cv2.createGeneralizedHoughBallard - Creates a smart pointer to the cv2.GeneralizedHoughBallard class and initializes it.
  • cv2.createGeneralizedHoughGuil - Creates a smart pointer to the cv2.GeneralizedHoughGuil class and initializes it.
  • cv2.drawContours - Draws contours.
  • cv2.findContours - Finds contours in a binary image.
  • cv2.fitEllipse - Fits an ellipse around a set of 2D points.
  • cv2.fitEllipseAMS - Fits an ellipse around a set of 2D points.
  • cv2.fitEllipseDirect - Fits an ellipse around a set of 2D points.
  • cv2.fitLine - Fits a line to a 2D or 3D point set.
  • cv2.HuMoments - Calculates seven Hu invariants.
  • cv2.intersectConvexConvex - Finds the intersection of two convex polygons.
  • cv2.isContourConvex - Tests a contour's convexity.
  • cv2.matchShapes - Compares two shapes.
  • cv2.minAreaRect - Finds a rotated rectangle of the minimum area enclosing the input 2D point set.
  • cv2.minEnclosingCircle - Finds a circle of the minimum area enclosing a 2D point set.
  • cv2.minEnclosingTriangle - Finds a triangle of the minimum area enclosing a 2D point set and returns its area.
  • cv2.moments - Calculates all of the moments up to the third order of a polygon or rasterized shape.
  • cv2.pointPolygonTest - Performs a point-in-contour test.
  • cv2.rotatedRectangleIntersection - Checks whether there is any intersection between two rotated rectangles.

Parameters

mode
Used to specify what kind of contours to find or how to represent the result.
  • CV_RETR_EXTERNAL - Detects only the outermost contours.
  • CV_RETR_LIST - Retrieves all contours and puts them in a list.
  • CV_RETR_CCOMP - Retrieves all contours and organizes them into a two-level hierarchy. (The outer contours of the components are managed as a linked list, and the second level manages the inner contours of the components as a list.)
  • CV_RETR_TREE - Retrieves all contours and builds the full hierarchy of the contours.
method
Specifies how to approximate the contours
  • CV_CHAIN_CODE - Generates a Freeman chain code.
  • CV_CHAIN_APPROX_NONE - Converts every point of the chain code into a vertex.
  • CV_CHAIN_APPROX_SIMPLE - Stores only the end points of horizontal, vertical, and diagonal segments.
  • CV_CHAIN_APPROX_TC89_L1, CV_CHAIN_APPROX_TC89_KCOS - Applies one of the Teh-Chin chain approximation algorithms.
  • CV_LINK_RUNS - ??

Example 

import cv2

# 이미지를 그레이스케일로 읽어들입니다.
image = cv2.imread('image.jpg', cv2.IMREAD_GRAYSCALE)

# 이미지를 이진화합니다.
ret, thresh = cv2.threshold(image, 127, 255, cv2.THRESH_BINARY)

# 윤곽선을 찾습니다.
contours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

# 찾은 윤곽선을 이미지에 그립니다.
cv2.drawContours(image, contours, -1, (0, 255, 0), 2)

# 결과 이미지를 출력합니다.
cv2.imshow('Contours', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

See also

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