After converting image to binary cannot display it in notebook with matplotlib

Question

I am trying to display the image After coverting the image to binary in python notebook:

resized_img = cv2.cvtColor(char_mask, cv2.COLOR_BGR2GRAY)
resized_img = cv2.threshold(resized_img, 100, 200, cv2.THRESH_BINARY)
#cv2.imwrite('licence_plate_mask3.png', char_mask)
plt.imshow(resized_img)

plt.show()

I cannot show image. I get this error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-32-0a3eb57cc497> in <module>()
      8 resized_img = cv2.threshold(resized_img, 100, 200, cv2.THRESH_BINARY)
      9 #cv2.imwrite('licence_plate_mask3.png', char_mask)
---> 10 plt.imshow(resized_img)
     11 
     12 plt.show()

C:\Anaconda3\lib\site-packages\matplotlib\pyplot.py in imshow(X, cmap, norm, aspect, interpolation, alpha, vmin, vmax, origin, extent, shape, filternorm, filterrad, imlim, resample, url, hold, data, **kwargs)
   3155                         filternorm=filternorm, filterrad=filterrad,
   3156                         imlim=imlim, resample=resample, url=url, data=data,
-> 3157                         **kwargs)
   3158     finally:
   3159         ax._hold = washold

C:\Anaconda3\lib\site-packages\matplotlib\__init__.py in inner(ax, *args, **kwargs)
   1895                     warnings.warn(msg % (label_namer, func.__name__),
   1896                                   RuntimeWarning, stacklevel=2)
-> 1897             return func(ax, *args, **kwargs)
   1898         pre_doc = inner.__doc__
   1899         if pre_doc is None:

C:\Anaconda3\lib\site-packages\matplotlib\axes\_axes.py in imshow(self, X, cmap, norm, aspect, interpolation, alpha, vmin, vmax, origin, extent, shape, filternorm, filterrad, imlim, resample, url, **kwargs)
   5122                               resample=resample, **kwargs)
   5123 
-> 5124         im.set_data(X)
   5125         im.set_alpha(alpha)
   5126         if im.get_clip_path() is None:

C:\Anaconda3\lib\site-packages\matplotlib\image.py in set_data(self, A)
    590             self._A = pil_to_array(A)
    591         else:
--> 592             self._A = cbook.safe_masked_invalid(A, copy=True)
    593 
    594         if (self._A.dtype != np.uint8 and

C:\Anaconda3\lib\site-packages\matplotlib\cbook.py in safe_masked_invalid(x, copy)
   1504 
   1505 def safe_masked_invalid(x, copy=False):
-> 1506     x = np.array(x, subok=True, copy=copy)
   1507     if not x.dtype.isnative:
   1508         # Note that the argument to `byteswap` is 'inplace',

ValueError: setting an array element with a sequence.

Before using threshold I can see the image inside the notebook without problem. Any way to resolve this problem? Thanks.

Jeru Luke · Accepted Answer · 2018-10-12 09:58:31Z

1

The error lies in line resized_img = cv2.threshold(resized_img, 100, 200, cv2.THRESH_BINARY).

cv2.threshold() returns two values. The first is the threshold value (float) and the second is the image.

So all the while you have been trying to plot a float value, hence the Value error.

Rewrite the line to the following:

ret, resized_img = cv2.threshold(resized_img, 100, 200, cv2.THRESH_BINARY)

You can have a look at the documentation as well.

answered Oct 12, 2018 at 9:58

Jeru Luke

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