how to get the number of channels from an image, in OpenCV 2?

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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As i know, u should use image.shape[2] to determine number of channels, not len(img.shape), the latter gives the dimensions of the array.

I'm kind of late but there is another simple way out there:

Use image.ndim Source, will give your right number of channels as below:

if image.ndim == 2:

    channels = 1 #single (grayscale)

if image.ndim == 3:

    channels = image.shape[-1]

Edit: In one-liners:

channels = image.shape[-1] if image.ndim == 3 else 1

Since a image is a nothing but a numpy array. Checkout OpenCV docs here: docs