OpenCV Python: can not pass UMat to calcHist

Question

everyone!

I'm trying to pass cv2.UMat object to cv2.calcHist function:

a = np.arange(10, dtype=np.uint8)
b = cv2.UMat(a)
cv2.calcHist([b], [0], None, [10], [0, 10])

and I'm getting the error

TypeError: images is not a numpy array, neither a scalar

but it seems like cpp version of OpenCV allows using UMat as source image.

Is it me doing something wrong or python OpenCV doesn't allow using UMat as source image for calcHist?

omair issa · Accepted Answer · 2018-11-13 08:52:28Z

0

IU guess the reason for that error can be found in the documentation of decode from pyzbar:

def decode(image, symbols=None, scan_locations=False):
"""Decodes datamatrix barcodes in `image`.
Args:
    image: `numpy.ndarray`, `PIL.Image` or tuple (pixels, width, height)
    symbols (ZBarSymbol): the symbol types to decode; if `None`, uses
        `zbar`'s default behaviour, which is to decode all symbol types.
    scan_locations (bool): If `True`, results will include scan
        locations.

Decode expects an image or a matrix containing the data in a specific order, which is fullfilled by a mat-instance supported by OpenCV. The UMat-format does not fullfil this requirement and so the error will be occur.

answered Nov 13, 2018 at 8:52

omair issa

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2 Comments

Daniel Sakhapov Over a year ago

thanks for answering, but what does pyzbar.decode have in common with cv2.calcHist?

omair issa Over a year ago

i think this is help you madebyollin.github.io/opencv-python-docs

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