I am trying to get diameters on different points of an object over a certain length using computer vision to replace the use of optical micrometer (which also measures diameter using optic principle).
Image of a yarn:
How can I calculate the diameter of this object (textile yarn) on multiple points (red lines) along its length as shown in the image using OpenCV python?
CodePudding user response:
An OpenCV solution. The main idea is to:
- Detect edges
- Find the contours of the edges
- Fill in the contour areas
- Go through each column in the image and count the nonzero pixels
1., 2. and 3. could possibly be simplified by a single thresholding step depending on your use case
import numpy as np
import cv2
src = cv2.imread('/path/to/src.jpg')
mask = np.zeros(src.shape, dtype=np.uint8)
w, h, c = src.shape
# edge detection
threshold = 100
gray = cv2.Canny(src, threshold, threshold * 2)
cv2.imshow('', gray)
cv2.waitKey(0)
# find contours
cnts = cv2.findContours(gray, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
threshold_area = 0.5
# fill area withing contours with white color
for c in cnts:
area = cv2.contourArea(c)
if area > threshold_area:
cv2.drawContours(mask, [c], -1, (255, 255, 255), -1)
cv2.imshow('', mask)
cv2.waitKey(0)
# get non zero values (height) of each column
column_pixels = [cv2.countNonZero(mask[:, i]) for i in range(0, w)]
print(column_pixels)
Src image:
Canny result:
After filling in contours with white color:
countNonZero is applied on this last image for each column