CODEWITHSUNDEEP
pythonopencv
Temak
Temak

Reputation: 3009

Apply cv2.boundingRect on np.array

How to apply cv2.boundingRect to a np.array of points ?
The following code produces an error.

points = np.array([[1, 2], [3, 4]], dtype=np.float32)
import cv2
cv2.boundingRect(points)

Error:

OpenCV Error: Unsupported format or combination of formats (The image/matrix format is not supported by the function) in cvBoundingRect, file /build/buildd/opencv-2.4.8+dfsg1/modules/imgproc/src/shapedescr.cpp, line 97

File "<ipython-input-23-42e84e11f1a7>", line 1, in <module>
  cv2.boundingRect(points)
error: /build/buildd/opencv-2.4.8+dfsg1/modules/imgproc/src/shapedescr.cpp:970: error: (-210) The image/matrix format is not supported by the function in function cvBoundingRect

Upvotes: 2

Views: 4620

Answers (2)

Dahlia Urbach
Dahlia Urbach

Reputation: 1

points = np.array([[1, 2], [3, 4]], dtype=np.float32)[:,np.newaxis,:]
import cv2
cv2.boundingRect(points)

You just need to add another axis, so the function will know it is a point list and not a 2d array.

Upvotes: 0

Dan Mašek
Dan Mašek

Reputation: 19041

The Python bindings of the 2.x versions of OpenCV use slightly different representation of some data than the ones in 3.x.

From existing code samples (e.g. this answer on SO), we can see that we can call cv2.boundingRect with a en element of the list of contours returned by cv2.findContours. Let's have a look what that looks like:

>>> a = cv2.copyMakeBorder(np.ones((3,3), np.uint8),1,1,1,1,0)
>>> b,c = cv2.findContours(a, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
>>> b[0]
array([[[1, 1]],

       [[1, 3]],

       [[3, 3]],

       [[3, 1]]])

We can see that each point in the contour is represented as [[x, y]] and we have a list of those.

Hence

import numpy as np
import cv2

point1 = [[1,2]]
point2 = [[3,4]]

points = np.array([point1, point2], np.float32)

print cv2.boundingRect(points)

And we get the output

(1, 2, 3, 3)

Upvotes: 3

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