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# drawing a rectangle around a color as shown? I want to detect the color, which I have done with the following code:

import cv2 as cv
import numpy as np

cap = cv.VideoCapture(0)

while(1):

_, frame = cap.read()
# Convert BGR to HSV
hsv = cv.cvtColor(frame, cv.COLOR_BGR2HSV)
# define range of blue color in HSV
lower_blue = np.array([100,55,55])
upper_blue = np.array([105,255,255])
# Threshold the HSV image to get only blue colors
mask = cv.inRange (hsv, lower_blue, upper_blue)
# Bitwise-AND mask and original image
res = cv.bitwise_and(frame,frame, mask= mask)
cv.imshow('frame',frame)
cv.imshow('mask',mask)
cv.imshow('res',res)
k = cv.waitKey(5) & 0xFF
if k == 27:
break
cv.destroyAllWindows()


but want to know how to draw a rectangle around it?

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## Comments

somewhat better, than your last question. however, please spare us duplicate ones to the same topic, thank. you !

Esp this one

"...Contours can be explained simply as a curve joining all the continuous points (along the boundary), having same color or intensity..."

Sound good to me. Should work.

I just noticed you already extracted the bbox(ignore comment above) - maybe all you asking for is how to draw rectangles at all? For drawing functions look here

## 1 answer

Sort by » oldest newest most voted I am using raspberry pi using linux. Btw, I used hsv colour, Fortunately, on your side, you may used your hsv colour.

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

while True:
_, frame = cap.read()
# Convert BGR to HSV
hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
# define range of blue color in HSV
lower_blue = np.array([100,50,50])
upper_blue = np.array([130,255,255])
# Threshold the HSV image to get only blue colors
mask = cv2.inRange (hsv, lower_blue, upper_blue)
bluecnts = cv2.findContours(mask.copy(),
cv2.RETR_EXTERNAL,
cv2.CHAIN_APPROX_SIMPLE)[-2]

if len(bluecnts)>0:
blue_area = max(bluecnts, key=cv2.contourArea)
(xg,yg,wg,hg) = cv2.boundingRect(blue_area)
cv2.rectangle(frame,(xg,yg),(xg+wg, yg+hg),(0,255,0),2)

cv2.imshow('frame',frame)
cv2.imshow('mask',mask)

k = cv2.waitKey(5)
if k == 27:
break

cap.release()
cv2.destroyAllWindows()


Output: more

## Comments

Hi may I know that what is the meaning of the line "key=cv2.contourArea" in the max() function. Thank you for reading this post.

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Asked: 2018-10-10 05:08:01 -0500

Seen: 6,177 times

Last updated: Dec 04 '19