Detect rectangles in OpenCV (4.2.0) using Python (3.7),

问题

I am working on a personal project where I detect rectangles (all the same dimensions) and then place those rectangles inside a list in the same order (top-bottom) and then process the information inside each rectangle using some function. Below is my test image.

I have managed to detect the rectangle of interest, however I keep getting other rectangles that I don't want. As you can see I only want the three rectangles with the information (6,9,3) into a list.

My code

import cv2

width=700
height=700
y1=0
y2=700
x1=500
x2=700
img=cv2.imread('test.jpg') #read image
img=cv2.resize(img,(width,height)) #resize image
roi = img[y1:y2, x1:x2] #region of interest i.e where the rectangles will be
gray = cv2.cvtColor(roi, cv2.COLOR_BGR2GRAY) #convert roi into gray
Blur=cv2.GaussianBlur(gray,(5,5),1) #apply blur to roi
Canny=cv2.Canny(Blur,10,50) #apply canny to roi

#Find my contours
contours =cv2.findContours(Canny,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)[0]

#Loop through my contours to find rectangles and put them in a list, so i can view them individually later.
cntrRect = []
for i in contours:
        epsilon = 0.05*cv2.arcLength(i,True)
        approx = cv2.approxPolyDP(i,epsilon,True)
        if len(approx) == 4:
            cv2.drawContours(roi,cntrRect,-1,(0,255,0),2)
            cv2.imshow('Roi Rect ONLY',roi)
            cntrRect.append(approx)



cv2.waitKey(0)
cv2.destroyAllWindows()

回答1:

There is a feature in Contour called cv2.contourArea for which your contour dimensions are input like this cv2.contourArea(contours) . You can use the condition,

if cv2.contourArea(contours)>#Rectangle area

By using this your problem will be solved

回答2:

I'd suggest that you get the bounding rectangles of the contours and then sort the rectangles by area descending. Crop the first rectangle by default, then loop through the remaining rectangles and crop them if they're, let's say, >=90% of the first rectangle's area. This will ensure that you have the larger rectangles and the smaller ones are ignored.

来源：https://stackoverflow.com/questions/61166180/detect-rectangles-in-opencv-4-2-0-using-python-3-7

标签

python-3.x

OpenCV

opencv-contour