The answers at Can I determine the number of channels in cv::Mat Opencv answer this question for OpenCV 1: you use the Mat.channels() method of the image.

But in cv2 (I'm using 2.4.6), the image data structure I have doesn't have a channels() method. I'm using Python 2.7.

Code snippet:

cam = cv2.VideoCapture(source)
ret, img = cam.read()
# Here's where I would like to find the number of channels in img.

Interactive attempt:

>>> img.channels()
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'channels'
>>> type(img)
<type 'numpy.ndarray'>
>>> img.dtype
dtype('uint8')
>>> dir(img)
['T',
 '__abs__',
 '__add__',
...
 'transpose',
 'var',
 'view']
# Nothing obvious that would expose the number of channels.

Thanks for any help.

Use img.shape

It provides you the shape of img in all directions. ie number of rows, number of columns for a 2D array (grayscale image). For 3D array, it gives you number of channels also.

So if len(img.shape) gives you two, it has a single channel.

If len(img.shape) gives you three, third element gives you number of channels.

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