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pythonopencv
Vaibhav Dixit
Vaibhav Dixit

Reputation: 894

How to save a binary image(with dtype=bool) using cv2?

I am using opencv in python and want to save a binary image(dtype=bool). If I simply use cv2.imwrite I get following error:

TypeError: image data type = 0 is not supported

Can someone help me with this? The image is basically supposed to work as mask later.

Upvotes: 16

Views: 35906

Answers (5)

avereux
avereux

Reputation: 607

Convert the binary image to the 'uint8' data type.

Try this:

>>> binary_image.dtype='uint8'
>>> cv2.imwrite('image.png', binary_image)

Upvotes: 2

John
John

Reputation: 1834

You can use this:

cv2.imwrite('mask.png', maskimg * 255)

So this converts it implicitly to integer, which gives 0 for False and 1 for True, and multiplies it by 255 to make a (bit-)mask before writing it. OpenCV is quite tolerant and writes int64 images with 8 bit depth (but e. g. uint16 images with 16 bit depth). The operation is not done inplace, so you can still use maskimg for indexing etc.

Upvotes: 26

Ajay Jha
Ajay Jha

Reputation: 1

If you are using OpenCV, you should consider using hsv format for threshing the image. Convert the BGR image to HSV using cv2.cvtColor() and then threshold your image using cv2.inRange() function.

You would need values for the upper and lower limits for Hue(h), Saturation(s) and Value(v). For this you may use this script or create your own using it as reference.

This script is meant to return hsv lower and upper limit values for live video stream input but with minor adjustments, you can do the same with image inputs as well.

Save the obtained binary(kind of) image using cv2.imwrite(), and there you have it. You may use this binary image for masking too. If you are still left with any doubts, you may refer to this script and it should clear most of them.

Upvotes: -1

Nathan majicvr.com
Nathan majicvr.com

Reputation: 1041

ndarray.astype('bool')

See this page may help:

https://docs.scipy.org/doc/numpy-1.13.0/reference/generated/numpy.ndarray.astype.html

Upvotes: -1

ZdaR
ZdaR

Reputation: 22954

No OpenCV does not expects the binary image in the format of a boolean ndarray. OpenCV supports only np.uint8, np.float32, np.float64, Since OpenCV is more of an Image manipulation library, so an image with boolean values makes no sense, when you think of RGB or Gray-scale formats.

The most compact data type to store a binary matrix is uchar or dtype=np.uint8, So you need to use this data type instead of np.bool.

Upvotes: 2

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