[FIXED] can't find right numbers of contours count

Issue

i'm trying to find specific contours having red outlines. Below is the code, I'm trying on this image :

import numpy as np
import cv2

image = cv2.imread('C:/Users/htc/Desktop/image.png')
original = image.copy()
image = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)
lower = np.array([0,50,50], dtype="uint8")
upper = np.array([10, 255,255], dtype="uint8")
mask = cv2.inRange(image, lower, upper)

# Find contours
cnts = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# Extract contours depending on OpenCV version
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
print(len(cnts))

# Iterate through contours and filter by the number of vertices 
for c in cnts:
    perimeter = cv2.arcLength(c, True)
    approx = cv2.approxPolyDP(c, 0.04 * perimeter, True)
    if len(approx) > 5:
        cv2.drawContours(original, [c], -1, (36, 255, 12), -1)

cv2.imshow('mask', mask)
cv2.imshow('original', original)
cv2.waitKey()

Output

the length of contour i'm getting is 14 which is not correct. The correct output will be 3. Where i'm doing wrong?

Solution

If you can notice, there are breaks in your mask image due to which many contours are being detected. To correct this (if you only want the count), you can dilate the mask image obtained before finding the contours as shown below.

mask = cv2.inRange(image, lower, upper)

# Dilating the mask
kernel = np.ones((3, 3), dtype=np.uint8)
mask = cv2.dilate(mask, kernel, iterations=2)

# Find contours
cnts = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

Answered By - Rahul Kedia