Function calcHist in openCV crashing in python on mac

Question

This is code

# USAGE
# python grayscale_histogram.py --image ../images/beach.png

# Import the necessary packages
from matplotlib import pyplot as plt
import argparse
import cv2

# Construct the argument parser and parse the arguments
ap = argparse.ArgumentParser()
ap.add_argument("-i", "--image", required = True,
    help = "Path to the image")
args = vars(ap.parse_args())

# Load the image, convert it to grayscale, and show it
image = cv2.imread(args["image"])
image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
cv2.imshow("Original", image)

# Construct a grayscale histogram
hist = cv2.calcHist([image], [0], None, [256], [0, 256])

# Plot the histogram
plt.figure()
plt.title("Grayscale Histogram")
plt.xlabel("Bins")
plt.ylabel("# of Pixels")
plt.plot(hist)
plt.xlim([0, 256])
plt.show()
cv2.waitKey(0)

When I run it, I have following error:

Snows-MacBook-Pro:code Mac$ python chapter-07/grayscale_histogram.py -i images/wave.png 
OpenCV Error: Assertion failed (step[dims-1] == (size_t)CV_ELEM_SIZE(flags)) in create, file /tmp/opencv-miY1tR/opencv-2.4.9/modules/core/src/matrix.cpp, line 236
Traceback (most recent call last):
  File "chapter-07/grayscale_histogram.py", line 21, in <module>
    hist = cv2.calcHist([image], [0], None, [256], [0, 256])
cv2.error: /tmp/opencv-miY1tR/opencv-2.4.9/modules/core/src/matrix.cpp:236: error: (-215) step[dims-1] == (size_t)CV_ELEM_SIZE(flags) in function create

I have installed openCV with

brew install opencv

I did reinstall openCV again but same problem is there.

I would suspect that there was some problem with compiling of openCV.
Maybe because of different compilers clang, gcc.

Any suggesting are appreciated.

Quang Nguyen · Accepted Answer · 2014-11-16 06:45:38Z

1

I got the same error when using another function in openCV. I also got the error using the code in your post. openCV 3.0.0 did not work either, it gave me another type of error.

What finally worked was installing openCV through Anaconda. It still uses openCV 2.4.8 so maybe that was the solution.

First I unlinked openCV in brew: "brew unlink opencv"

Then installed the Anaconda package: http://continuum.io/downloads#all

Afterwards install openCV: "conda install opencv"

Finally, update numpy: "conda update numpy"

answered Nov 16, 2014 at 6:45

Quang Nguyen

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4 Comments

WebOrCode Over a year ago

I will try it later. Is your OSX clean install or upgrade from previous versions ? My is upgrade from 10.6 to 10.7 10 10.8 and now 10.9. I have a hunch if I do clean install of 10.9 problem will go away. That is why I am asking.

WebOrCode Over a year ago

I also needed to do pip uninstall numpy it look-like problem was in numpy not openCV. My version of bumpy was numpy==1.10.0.dev-cfa095a.

Quang Nguyen Over a year ago

I also upgraded my OSX from 10.6 to 10.9, haven't done a clean install since I got it. I can't remember the numpy version that I was running though. I think I was using numpy 1.9.1 that I installed through pip. Did you get it to work now with openCV 2.4.9 or 3.0.0?

WebOrCode Over a year ago

I did everything as you, so it was openCV 2.4.9.

mstreffo · Accepted Answer · 2015-05-14 11:48:01Z

0

I also needed to do a pip uninstall numpy but also had to remove the numpy directories (specifically the f2py directories) in /usr/local/bin and /usr/local/Cellar. After that I did a pip install numpy and it works ok.

answered May 14, 2015 at 11:48

mstreffo

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