CODEWITHSUNDEEP
python-3.xgradientopencv3.0
user3925023
user3925023

Reputation: 687

Python - OpenCv - Gradient computing

I've download the opencv from https://opencv.org/opencv-demonstrator-gui/ to make some live test on some images. I found that this filter work perfectly for my needs: enter image description here

, I need to code it in my python script, tried to follow this tutorial :https://docs.opencv.org/3.4/d2/d2c/tutorial_sobel_derivatives.html

but I'm unable to find and match setting I need (pre-filtering Deriche, or Schar operator type). I guess also I should use this syntax:

cv.Sobel(gray, ddepth, 1, 0, ksize=3, scale=scale, delta=delta, borderType=cv.BORDER_DEFAULT)

Thx.

UPDATE

Using this lines I'm close to right result:

    scale = 1
    delta = 0
    ddepth = cv2.CV_16S
    src = cv2.imread(image, cv2.IMREAD_COLOR)
    src = cv2.GaussianBlur(src, (3, 3), 0)
    gray = cv2.cvtColor(src, cv2.COLOR_BGR2GRAY)
    grad_x = cv2.Sobel(gray, ddepth, 1, 0, ksize=3, scale=scale, delta=delta, borderType=cv2.BORDER_DEFAULT)
    # Gradient-Y
    # grad_y = cv.Scharr(gray,ddepth,0,1)
    grad_y = cv2.Sobel(gray, ddepth, 0, 1, ksize=3, scale=scale, delta=delta, borderType=cv2.BORDER_DEFAULT)
    abs_grad_x = cv2.convertScaleAbs(grad_x)
    abs_grad_y = cv2.convertScaleAbs(grad_y)
    grad = cv2.addWeighted(abs_grad_x, 0.5, abs_grad_y, 0.5, 0)

Upvotes: 0

Views: 3263

Answers (1)

fmw42
fmw42

Reputation: 53081

You are only doing the X derivative Sobel filter in Python/OpenCV. It is likely you really want the gradient magnitude, not the X directional derivative. To compute the magnitude, you need both the X and Y derivatives and then compute the magnitude. You also like will need to compute as float so as not to get one sided derivatives. You can later convert the magnitude to 8-bit if you want.

gradx = cv2.Sobel(gray,cv2.CV_64F,1,0,ksize=3)
grady = cv2.Sobel(gray,cv2.CV_64F,0,1,ksize=3)
gradmag = cv2.magnitude(gradx,grady)

The Scharr is similar and can be found at https://docs.opencv.org/master/d4/d86/group__imgproc__filter.html#gaa13106761eedf14798f37aa2d60404c9

Upvotes: 4

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