Rectangle Not Showing up in Opencv
Why Is Rectangle Not Showing up in My Code? Import Cv2 Im = Cv2. Imread('Players. Bmp') #Im. Shape >>Returns (765,1365,3) Cv2. Rectangle(Im, (64,1248)...
Why is rectangle not showing up in my code?
import cv2
im = cv2.imread('players.bmp')
#im.shape >>returns (765,1365,3)
cv2.rectangle(im, (64,1248), (191,1311), (0,255,0), 2)
cv2.namedWindow("image", cv2.WINDOW_NORMAL)
cv2.imshow('image', im)
cv2.waitKey(0)
cv2.destroyAllWindows()
3 Answers
It does not show the rectangle, because you are drawing it outside the image.
Why? you may be asking. It is simple. You have this:
#im.shape >>returns (765,1365,3)
This means
rows/height = 765
cols/width = 1365
channels = 3
Then you do
cv2.rectangle(im, (64,1248), (191,1311), (0,255,0), 2)
Here you use 2 points which are tuples (x,y), but you are writing them as if they where tuples (y,x). I know that OpenCV uses in a lot of functions the order (y,x), but this is due that they see the image as a matrix, which commonly is accessed with (row, column) which translates to (y,x). In the case of this rectangle they require which are expressed in the typical Cartesian way (x,y).
In conclusion, just change it to:
cv2.rectangle(im, (1248, 64), (1311, 191), (0,255,0), 2)
And it should work.
I had a completely different cause for the issue
for me it wasn't showing up because I was using a numpy view from the image, so instead of using cv2.cvtColor(frame, cv2.COLOR_RGB2BGR), I instead used frame[..., ::-1] to convert RGB and BGR.
Somehow this makes the result immutable and when cv2.rectangle tries to write to it, it just doesn't get changed.
I stumbled upon this question while facing the same problem. In my case, I was correctly passing x and y along with x+w and y+h. I had made 2 mistakes though:
- I had this part in a
tryandexceptblock (so I couldn't see the exception being raised) - My code was changing
hto an array prior to me drawing the rectangle. (I had extracted the values ofx,y,w,hfromx,y,w,h = cv2.boundingRect(cnt)before mistakenly changing h to[1,-1,-1,-1])
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
