如何在python中找到用区域选择的轮廓的长度

Question

我是OpenCV的新手。我有两个问题要问。

1. 我正在尝试打印应用该区域后可用的轮廓数。我在imshow中得到了正确的输出，但在print语句中没有。我知道print(len(contoures((给出了轮廓的总数，但我需要给定区域中的轮廓数量>400.您可以查看下面的python代码以了解更多详细信息。请帮我做这个
2. 是否可以将阈值更改为255以上，每当我将其更改为255之上时，即使我增加了最大值，我也会得到黑色图像

谢谢！

import cv2 as cv
import numpy as np
im_color = cv.imread("D:python_projectFocus_detection_1/_00005_cells.png", cv.IMREAD_COLOR)
im_gray = cv.cvtColor(im_color, cv.COLOR_BGR2GRAY)
_, thresh = cv.threshold(im_gray, thresh=254, maxval=255, type=cv.THRESH_BINARY)  
mask = cv.cvtColor(thresh, cv.COLOR_GRAY2BGR)
im_thresh_color = cv.bitwise_and(im_color,mask) 
contours, hierarchy = cv.findContours(thresh, cv.RETR_TREE,cv.CHAIN_APPROX_SIMPLE)
cv.drawContours(im_thresh_color,contours,-1,(0,0,255),2)
for c in contours:
area = cv.contourArea(c)
if area > 400:
x,y,w,h = cv.boundingRect(c)
im = cv.rectangle(im_thresh_color, (x,y), (x+w, y+h), (255,0,0), 2)
cv.drawContours(im_thresh_color,contours, -1,(0,0,255),2) #-1 is to draw all the contour, 0 is the 1st contour and so on
text = cv.putText(im, 'Focused', (x, y), cv.FONT_HERSHEY_SIMPLEX, 0.5, (36, 255, 12), 2)
no_of_images = len(contours)
print("images:", no_of_images)
while True:
cv.imshow("original image", im_color)
cv.imshow("Thresh color with contour", im_thresh_color)
#print("n:",len(im_thresh_color))
if cv.waitKey(1) == ord("n"):
break
cv.destroyAllWindows()

Answer 1

这是您第一个问题的更新代码：该代码计算该区域中有多少轮廓，然后打印该区域中的轮廓数

import cv2 as cv
import numpy as np
im_color = cv.imread("D:python_projectFocus_detection_1/_00005_cells.png", cv.IMREAD_COLOR)
im_gray = cv.cvtColor(im_color, cv.COLOR_BGR2GRAY)
_, thresh = cv.threshold(im_gray, thresh=254, maxval=255, type=cv.THRESH_BINARY)
mask = cv.cvtColor(thresh, cv.COLOR_GRAY2BGR)
im_thresh_color = cv.bitwise_and(im_color, mask)
contours, hierarchy = cv.findContours(thresh, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
cv.drawContours(im_thresh_color, contours, -1, (0, 0, 255), 2)
counter = 0
for c in contours:
area = cv.contourArea(c)
if area > 400:
x, y, w, h = cv.boundingRect(c)
im = cv.rectangle(im_thresh_color, (x, y), (x+w, y+h), (255, 0, 0), 2)
# -1 is to draw all the contour, 0 is the 1st contour and so on
cv.drawContours(im_thresh_color, contours, -1, (0, 0, 255), 2)
text = cv.putText(im, 'Focused', (x, y), cv.FONT_HERSHEY_SIMPLEX, 0.5, (36, 255, 12), 2)
counter += 1
print("images:", counter)
while True:
cv.imshow("original image", im_color)
cv.imshow("Thresh color with contour", im_thresh_color)
# print("n:",len(im_thresh_color))
if cv.waitKey(1) == ord("n"):
break
cv.destroyAllWindows()

回答问题2：不，不可能将其更改为255 bc的值，r、g、b值的范围是从0到255。