具有定义边缘的Python 3 OpenCV颜色对象检测

Question

My python code takes a screenshot of by desktop and looks for a red rectangle on a black background, when I use the cv2.findcountours it doesn't return an exact sized rectangle, it seems to be distorted. I would like to obtain the exact area of the shape. Also, the image on my screenshot has no pixelation and borders are sharp. Thanks for your help!

frame_TS_new_raw = np.array(sct.grab(monitor_TS_new))
frame_TS_new = cv2.cvtColor(frame_TS_new_raw, cv2.COLOR_RGBA2RGB)

green_mask_TS_new = cv2.inRange(frame_TS_new,green_lower_range, green_upper_range)

# find contours for New TS
cnts_green_new = cv2.findContours(green_mask_TS_new.copy(), cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)
cnts_green_new = cnts_green_new[0] if imutils.is_cv2() else cnts_green_new[1]
if len(cnts_green_new) > 0:
    for c in cnts_green_new:
        # if the contour is not sufficiently large, ignore it
        if cv2.contourArea(c) > 100:
            area = cv2.contourArea(c)

screenshot of the masked and unmasked

The image on the left is raw screenshot and the image on the right is the masked.

Answer 1

To find area of red rectangle in the image you can do as:

• extract red channel of the image
• threshold red channel
• count number of nonzero pixels

Example code:

import cv2
import numpy as np

img = cv2.imread('vju0v.png')
img = np.array(img) # convert to numpy array
red = img[:,:,2]    # extract red channel
rect = np.float32(red > 200)   # find red pixels
area = np.sum(rect)    # count nonzero pixels

print('Area = ' + str(area))

cv2.imshow('Red Channel',rect)
cv2.waitKey(0)