Get pixel location of binary image with intensity 255 in python opencv

Question

I want to get the pixel coordinates of the blue dots in an image. To get it, I first converted it to gray scale and use threshold function.

    import numpy as np
    import cv2

    img = cv2.imread("dot.jpg")
    img_g = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    ret1,th1 = cv2.threshold(img_g,127,255,cv2.THRESH_BINARY_INV)

What to do next if I want to get the pixel location with intensity 255? Please tell if there is some simpler method to do the same.

Answer 1

I don't think this is going to work as you would expect. Usually, in order to get a stable tracking over a shape with a specific color, you do that in RGB/HSV/HSL plane, you could start with HSV which is more robust in terms of lighting.

1-Convert to HSV using cv2.cvtColor()

2-Use cv2.inRagne(blue_lower, blue_upper) to "filter" all un-wanted colors.

Now you have a good-looking binary image with only blue color in it (assuming you have a static background or more filters should be added).

3-Now if you want to detect dots (which is usually more than one pixel) you could try cv2.findContours

4- You can get x,y pixel of contours using many methods(depends on the shape of what you want to detect) like this cv2.boundingRect()