cv2.findContours() acts strangely?
I'm finding contours in an image. With every contour I found, I print out its bouding rect and area and then draw it to the image. Funnily, I found that 5 contours that have been drawed while there were only 4 contours printed. Anyone knows what happened here?
>>contour 1
>>(0, 0, 314, 326)
>>101538.5
>>contour 2
>>(75, 117, 60, 4)
>>172.0
>>contour 3
>>(216, 106, 3, 64)
>>124.0
>>contour 4
>>(62, 18, 138, 9)
>>383.5
import cv2
import numpy as np
img = cv2.imread('1.png')
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
_, contours, hier = cv2.findContours(thresh, cv2.RETR_TREE,
cv2.CHAIN_APPROX_SIMPLE)
for i,c in enumerate(contours):
rect = cv2.boundingRect(c)
area = cv2.contourArea(c)
print("contour " + str(i+1))
print(rect)
print(area)
cv2.drawContours(img, contours, -1, (0,255,0), 1)
cv2.imshow('img', img)
cv2.waitKey(0)
cv2.destroyAllWindows()
python opencv contour
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
add a comment |
I'm finding contours in an image. With every contour I found, I print out its bouding rect and area and then draw it to the image. Funnily, I found that 5 contours that have been drawed while there were only 4 contours printed. Anyone knows what happened here?
>>contour 1
>>(0, 0, 314, 326)
>>101538.5
>>contour 2
>>(75, 117, 60, 4)
>>172.0
>>contour 3
>>(216, 106, 3, 64)
>>124.0
>>contour 4
>>(62, 18, 138, 9)
>>383.5
import cv2
import numpy as np
img = cv2.imread('1.png')
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
_, contours, hier = cv2.findContours(thresh, cv2.RETR_TREE,
cv2.CHAIN_APPROX_SIMPLE)
for i,c in enumerate(contours):
rect = cv2.boundingRect(c)
area = cv2.contourArea(c)
print("contour " + str(i+1))
print(rect)
print(area)
cv2.drawContours(img, contours, -1, (0,255,0), 1)
cv2.imshow('img', img)
cv2.waitKey(0)
cv2.destroyAllWindows()
python opencv contour
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
add a comment |
I'm finding contours in an image. With every contour I found, I print out its bouding rect and area and then draw it to the image. Funnily, I found that 5 contours that have been drawed while there were only 4 contours printed. Anyone knows what happened here?
>>contour 1
>>(0, 0, 314, 326)
>>101538.5
>>contour 2
>>(75, 117, 60, 4)
>>172.0
>>contour 3
>>(216, 106, 3, 64)
>>124.0
>>contour 4
>>(62, 18, 138, 9)
>>383.5
import cv2
import numpy as np
img = cv2.imread('1.png')
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
_, contours, hier = cv2.findContours(thresh, cv2.RETR_TREE,
cv2.CHAIN_APPROX_SIMPLE)
for i,c in enumerate(contours):
rect = cv2.boundingRect(c)
area = cv2.contourArea(c)
print("contour " + str(i+1))
print(rect)
print(area)
cv2.drawContours(img, contours, -1, (0,255,0), 1)
cv2.imshow('img', img)
cv2.waitKey(0)
cv2.destroyAllWindows()
python opencv contour
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
I'm finding contours in an image. With every contour I found, I print out its bouding rect and area and then draw it to the image. Funnily, I found that 5 contours that have been drawed while there were only 4 contours printed. Anyone knows what happened here?
>>contour 1
>>(0, 0, 314, 326)
>>101538.5
>>contour 2
>>(75, 117, 60, 4)
>>172.0
>>contour 3
>>(216, 106, 3, 64)
>>124.0
>>contour 4
>>(62, 18, 138, 9)
>>383.5
import cv2
import numpy as np
img = cv2.imread('1.png')
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
_, contours, hier = cv2.findContours(thresh, cv2.RETR_TREE,
cv2.CHAIN_APPROX_SIMPLE)
for i,c in enumerate(contours):
rect = cv2.boundingRect(c)
area = cv2.contourArea(c)
print("contour " + str(i+1))
print(rect)
print(area)
cv2.drawContours(img, contours, -1, (0,255,0), 1)
cv2.imshow('img', img)
cv2.waitKey(0)
cv2.destroyAllWindows()
python opencv contour
python opencv contour
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
asked Nov 14 '18 at 8:31
Ha BomHa Bom
1,1182518
1,1182518
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
cv2.RETR_TREE is the reason you are getting this. It retrieves all the contours and creates a full family hierarchy list. In contour detection you are expected to use white objects in black background. Otherwise because of hierarchy list you would get results as you are getting now. For more details check documentation.
So make sure you find contours of white objects in black background. Add cv2.bitwise_not() function to convert the image.
.
.
.
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.bitwise_not(imgray,imgray)
.
.
.
OUTPUT:
4
contour 1
(76, 118, 58, 2)
56.0
contour 2
(217, 107, 1, 62)
0.0
contour 3
(63, 19, 136, 7)
110.5
contour 4
(248, 1, 66, 45)
55.5
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.Top right contouris attached to the boundary of the image. So It is considered as a single contour along with the boundary.
– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
cv2.RETR_TREE is the reason you are getting this. It retrieves all the contours and creates a full family hierarchy list. In contour detection you are expected to use white objects in black background. Otherwise because of hierarchy list you would get results as you are getting now. For more details check documentation.
So make sure you find contours of white objects in black background. Add cv2.bitwise_not() function to convert the image.
.
.
.
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.bitwise_not(imgray,imgray)
.
.
.
OUTPUT:
4
contour 1
(76, 118, 58, 2)
56.0
contour 2
(217, 107, 1, 62)
0.0
contour 3
(63, 19, 136, 7)
110.5
contour 4
(248, 1, 66, 45)
55.5
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.Top right contouris attached to the boundary of the image. So It is considered as a single contour along with the boundary.
– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
add a comment |
cv2.RETR_TREE is the reason you are getting this. It retrieves all the contours and creates a full family hierarchy list. In contour detection you are expected to use white objects in black background. Otherwise because of hierarchy list you would get results as you are getting now. For more details check documentation.
So make sure you find contours of white objects in black background. Add cv2.bitwise_not() function to convert the image.
.
.
.
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.bitwise_not(imgray,imgray)
.
.
.
OUTPUT:
4
contour 1
(76, 118, 58, 2)
56.0
contour 2
(217, 107, 1, 62)
0.0
contour 3
(63, 19, 136, 7)
110.5
contour 4
(248, 1, 66, 45)
55.5
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.Top right contouris attached to the boundary of the image. So It is considered as a single contour along with the boundary.
– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
add a comment |
cv2.RETR_TREE is the reason you are getting this. It retrieves all the contours and creates a full family hierarchy list. In contour detection you are expected to use white objects in black background. Otherwise because of hierarchy list you would get results as you are getting now. For more details check documentation.
So make sure you find contours of white objects in black background. Add cv2.bitwise_not() function to convert the image.
.
.
.
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.bitwise_not(imgray,imgray)
.
.
.
OUTPUT:
4
contour 1
(76, 118, 58, 2)
56.0
contour 2
(217, 107, 1, 62)
0.0
contour 3
(63, 19, 136, 7)
110.5
contour 4
(248, 1, 66, 45)
55.5
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
cv2.RETR_TREE is the reason you are getting this. It retrieves all the contours and creates a full family hierarchy list. In contour detection you are expected to use white objects in black background. Otherwise because of hierarchy list you would get results as you are getting now. For more details check documentation.
So make sure you find contours of white objects in black background. Add cv2.bitwise_not() function to convert the image.
.
.
.
imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
cv2.bitwise_not(imgray,imgray)
.
.
.
OUTPUT:
4
contour 1
(76, 118, 58, 2)
56.0
contour 2
(217, 107, 1, 62)
0.0
contour 3
(63, 19, 136, 7)
110.5
contour 4
(248, 1, 66, 45)
55.5
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
answered Nov 14 '18 at 9:24
Ishara MadhawaIshara Madhawa
2,12641028
2,12641028
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.Top right contouris attached to the boundary of the image. So It is considered as a single contour along with the boundary.
– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
add a comment |
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.Top right contouris attached to the boundary of the image. So It is considered as a single contour along with the boundary.
– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
Thanks for your answer. But I still wonder why it draws contour of the line but don't print it out.
– Ha Bom
Nov 14 '18 at 10:05
In your case also there are only 4 contours.
Top right contour is attached to the boundary of the image. So It is considered as a single contour along with the boundary.– Ishara Madhawa
Nov 14 '18 at 10:30
In your case also there are only 4 contours.
Top right contour is attached to the boundary of the image. So It is considered as a single contour along with the boundary.– Ishara Madhawa
Nov 14 '18 at 10:30
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
oh I see. thank you very much
– Ha Bom
Nov 15 '18 at 1:16
add a comment |
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