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Finding small contours in OpenCV


Finding small contours in OpenCV

By : D Forsten
Date : November 21 2020, 07:31 AM
seems to work fine No, I don't think there's a way to make it work, using Findcontours.
The reason is that the OpenCV method, is a contour finding method and not a blob finding method. The area is calculated from the perimeter and not just a sum of pixels.
code :


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C++ OpenCV How to eliminate small edges or small area of contours

C++ OpenCV How to eliminate small edges or small area of contours


By : Quinn Harris
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You can filter your contours depending on their length using arcLength-function (http://docs.opencv.org/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html#arclength).
Either you can check, if the contours are longer than a certain threshold or you only filter the longest contour.
Get the external contour of multiple small contours in OpenCV

Get the external contour of multiple small contours in OpenCV


By : user2586708
Date : March 29 2020, 07:55 AM
wish help you to fix your issue As @Amine was saying morphology operation would be the way to go, especially dilation. More information can be found here. Made a small example you can fine tune but I think it's pretty close to the desired output.
code :
import cv2
import numpy as np

cv_img = cv2.imread('spot.jpg', 0)
im_copy = cv_img.copy()

kernel_dilation = np.ones((5,5), np.uint8)
dilation = cv2.dilate(cv_img, kernel_dilation, iterations=12)
ret, thresh = cv2.threshold(dilation, 127, 255, 0)

im2, contours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)

cnt = contours[0]
max_area = cv2.contourArea(cnt)

for cont in contours:
    if cv2.contourArea(cont) > max_area:
        cnt = cont
        max_area = cv2.contourArea(cont)

cv2.drawContours(im_copy, [cnt], 0, (255, 255, 0), 3)
cv2.imshow('Contour', im_copy)
cv2.waitKey(0)
Contours opencv : How to eliminate small contours in a binary image

Contours opencv : How to eliminate small contours in a binary image


By : Evelina Diksaitė
Date : March 29 2020, 07:55 AM
like below fixes the issue Ok, I believe your problem could be solved with the bounding box demo recently introduced by OpenCV.
Opencv not finding all contours

Opencv not finding all contours


By : Benjamin
Date : March 29 2020, 07:55 AM
Hope that helps The problem is the flag cv2.RETR_EXTERNAL that you used in the function call. As described in the OpenCV documentation, this only returns the external contour.
Using the flag cv2.RETR_LIST you get all contours in the image. Since you try to detect rings, this list will contain the inner and the outer contour of these rings.
Eliminate or Ignore all small or overlapping contours or rectangles inside a big contours/rectangle opencv

Eliminate or Ignore all small or overlapping contours or rectangles inside a big contours/rectangle opencv


By : Mariana Mutso
Date : October 07 2020, 09:00 AM
Hope this helps Compare the top left point and bottom right point of each rectangle, contained in another rectangle, then eliminate them.
Use this function below to check if a point is inside the rectangle.
code :
def rectContains(rect,pt):
    in = rect[0] < pt[0] < rect[0]+rect[2] and rect[1] < pt[1] < rect[1]+rect[3]
    return in
cntsSorted = sorted(cnts, key=lambda x: cv2.contourArea(x))
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