[boundingBox] opencv example python - Contours – bounding box, minimum area rectangle, and minimum enclosing circle

gistfile1.txt

import cv2
import numpy as np

# read and scale down image
# wget https://bigsnarf.files.wordpress.com/2017/05/hammer.png #black and white
# wget https://i1.wp.com/images.hgmsites.net/hug/2011-volvo-s60_100323431_h.jpg
img = cv2.pyrDown(cv2.imread('2011-volvo-s60_100323431_h.jpg', cv2.IMREAD_UNCHANGED))

# threshold image
ret, threshed_img = cv2.threshold(cv2.cvtColor(img, cv2.COLOR_BGR2GRAY),
                127, 255, cv2.THRESH_BINARY)
# find contours and get the external one

contours, hier = cv2.findContours(threshed_img, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

#image, contours, hier = cv2.findContours(threshed_img, cv2.RETR_TREE,
#                cv2.CHAIN_APPROX_SIMPLE)

# with each contour, draw boundingRect in green
# a minAreaRect in red and
# a minEnclosingCircle in blue
for c in contours:
    # get the bounding rect
    x, y, w, h = cv2.boundingRect(c)
    # draw a green rectangle to visualize the bounding rect
    cv2.rectangle(img, (x, y), (x+w, y+h), (0, 255, 0), 2)

    # get the min area rect
    rect = cv2.minAreaRect(c)
    box = cv2.boxPoints(rect)
    # convert all coordinates floating point values to int
    box = np.int0(box)
    # draw a red 'nghien' rectangle
    cv2.drawContours(img, [box], 0, (0, 0, 255))

    # finally, get the min enclosing circle
    (x, y), radius = cv2.minEnclosingCircle(c)
    # convert all values to int
    center = (int(x), int(y))
    radius = int(radius)
    # and draw the circle in blue
    img = cv2.circle(img, center, radius, (255, 0, 0), 2)

print(len(contours))
cv2.drawContours(img, contours, -1, (255, 255, 0), 1)

cv2.imshow("contours", img)

cv2.imshow("contours", img)

while True:
    key = cv2.waitKey(1)
    if key == 27: #ESC key to break
        break

cv2.destroyAllWindows()

nice ! just working on a project with python's openCV right now

Very clean to read code. Thanks!

It doesn't work right out of the box for me.

I did download the file beforehand, but python (I'm using 3.6) doesn't like line 49.

Just to see if it worked otherwise, I commented it out, and it runs but nothing shows up (i.e. the screen is black). I can press esc and exit, though.

Something curious:

print(len(contours)) prints 0

That's all I've investigated so far.

Even i got the same error. Just erase line number 46 to 51 and replace it with
cv2.waitKey(0) // here the window waits until user manually closes

else try
if cv2.waitKey(0) & 0xFF == ord('q'):
break //here the window closes when the letter q is pressed

hi i was using the code to get a bounding box over shaded objects in a picture.for eg, in the pic included, the car is shaded in red and i'd just like the bounding box to be over the car. however with this code the bounding box is generated over everything. how do i tweak it to get what i want, which is just a bounding box over the objects in the pic that is shaded?.

Clean code! Thanks!

verrrrrrrrrrrrrry good man !

How could i make this work when i use a program that retrieves multiple images from google and can pass them through the process?
Cheers

thank you very muchhhh

I get the following error when using the provided hammer.png image:
`---------------------------------------------------------------------------
error Traceback (most recent call last)
in
3
4 # threshold image
----> 5 ret, threshed_img = cv2.threshold(cv2.cvtColor(img, cv2.COLOR_BGR2GRAY), 127, 255, cv2.THRESH_BINARY)
6 # find contours and get the external one
7 image, contours, hier = cv2.findContours(threshed_img, cv2.RETR_TREE,

error: OpenCV(3.4.2) /Users/travis/build/skvark/opencv-python/opencv/modules/imgproc/src/color.hpp:253: error: (-215:Assertion failed) VScn::contains(scn) && VDcn::contains(dcn) && VDepth::contains(depth) in function 'CvtHelper'
`

Which version of opencv are you using?

I am having an issue with line 49. Has anyone resolved this?

latest revision - works/tested with python 3.7.1 and open CV 4.1.0

import cv2
import numpy as np
image = cv2.imread('d.jpg',-1)
paper = cv2.resize(image,(500,500))
ret, thresh_gray = cv2.threshold(cv2.cvtColor(paper, cv2.COLOR_BGR2GRAY),
200, 255, cv2.THRESH_BINARY)
image, contours, hier = cv2.findContours(thresh_gray, cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)
for c in contours:
rect = cv2.minAreaRect(c)
box = cv2.boxPoints(rect)
# convert all coordinates floating point values to int
box = np.int0(box)
# draw a green 'nghien' rectangle
cv2.drawContours(paper, [box], 0, (0, 255, 0),1)

cv2.imshow('paper', paper)
cv2.imwrite('paper.jpg',paper)

I tried the above code for zebra line detection in an image.It shows output like this.
.By I need to detect the entire block of zebra crossing .how is to be done?

hi i was using the code to get a bounding box over shaded objects in a picture.for eg, in the pic included, the car is shaded in red and i'd just like the bounding box to be over the car. however with this code the bounding box is generated over everything. how do i tweak it to get what i want, which is just a bounding box over the objects in the pic that is shaded?.

Tôi nghĩ rằng bạn thử so sánh các diện tích các đường bao đã thu được trên ảnh:
Đây là mã của tôi:
def get_contours(img_read_img, area_min_thresh=AREA):
img_gray = cv2.cvtColor(img_read_img, cv2.COLOR_BGR2GRAY)
invert_img = cv2.bitwise_not(img_gray)
retval, im_bw = cv2.threshold(invert_img, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
contours, hier = cv2.findContours(im_bw, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
contours = list(filter(lambda x: cv2.contourArea(x) > area_min_thresh, contours))
# img_contours = np.zeros(img_read_img.shape)
# cv2.drawContours(img_contours, contours, -1, (0, 255, 0), 3)
max_area = cv2.contourArea(contours[0])
max_id = 0
for i, c in enumerate(contours):
area = cv2.contourArea(c)
if area > max_area:
max_area = area
max_id = i
max_contours = contours[max_id]
cv2.drawContours(img_read_img, [max_contours], -1, (0, 0, 255), 2)
# cv2.imshow("contour", img_read_img)
# cv2.waitKey(0)
return img_read_img

Can it work for 2 page PDF?