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How do I convert uint8 to CV_8UC1 in OpenCV 3.2 Python?

asked 2017-06-10 22:27:04 -0500

Bazmundi gravatar image

The code is the following:

import numpy as np
import cv2
import time
from matplotlib import pyplot as plt

cv2.namedWindow( "Left", cv2.WINDOW_AUTOSIZE );
cv2.namedWindow( "Right", cv2.WINDOW_AUTOSIZE );

cam1 = cv2.VideoCapture(1)
cam1.set(cv2.CAP_PROP_FRAME_WIDTH,384)
cam1.set(cv2.CAP_PROP_FRAME_HEIGHT,216)

cam2 = cv2.VideoCapture(2)
cam2.set(cv2.CAP_PROP_FRAME_WIDTH,384)
cam2.set(cv2.CAP_PROP_FRAME_HEIGHT,216)

stereo = cv2.StereoBM_create(numDisparities=16, blockSize=15)


while(True):

    # Capture frame-by-frame

    ret, frame1 = cam1.read()

    ret, frame2 = cam2.read()


    # Display the resulting frame
    cv2.imshow("Left",frame1)  
    cv2.imshow("Right",frame2)  

    disparity = stereo.compute(frame1,frame2) # kaput as it wants CV_8UC1 matrix
    plt.imshow(disparity,'gray')
    plt.show()

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cam1.release()
cam2.release()
cv2.destroyAllWindows()

Computing disparity is kaput as the image frame appears to be uint8 while the disparity computation wants CV_8UC1. Examples I have found to do the conversion are either in C++ or not in OpenCV 3.2 Pythonesque.

What is the conversion approach for uint8 to CV_8UC1 in OpenCV 3.2 Python please?

Cheers, A

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answered 2017-06-11 00:42:10 -0500

berak gravatar image

the images from your camera are uint8, too, but they are in color (3 channels), while you need grayscale (1 channel) images for the block matching. use cvtColor for the conversion:

# help(cv2.cvtColor)
gray1 = cv2.cvtColor(frame1, cv2.COLOR_BGR2GRAY)
gray2 = cv2.cvtColor(frame2, cv2.COLOR_BGR2GRAY)
disparity = stereo.compute(gray1, gray2)
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Yep. I had worked this out in the background but I am still appreciative of the response by #berak as it also helps me understand why the code fixed the problem.

Bazmundi gravatar imageBazmundi ( 2017-06-11 01:55:43 -0500 )edit
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Asked: 2017-06-10 22:27:04 -0500

Seen: 19,512 times

Last updated: Jun 11 '17