Searching for a pixel in an image using opencv, numpy and python

user_5690792 0
Viewed 1989

I have been able to read an image, then read a specific pixel using a co-ordinate location which works fine (pixel = img[801,600]).

My next step is to iterate through each pixel and try to find the location (in this example [801,600]) using the pixel data.

My iteration through "img" isn't able to find the pixel. I would appreciate any help or guidance.

import cv2
import numpy as np

img = cv2.imread('one.jpg')

pixel = img[801,600]

print (pixel) # pixel value i am searching for

for i in img:
    for x in i:
        if x.sort == pixel.sort:
            print ("SUCCESS")
opencv numpy python
3 Answers

The built-in enumerate iteration function will help you. It will provide an iteration index, that in your case, will provide a pixel index:

import cv2
import numpy as np

img = cv2.imread('one.jpg')

pixel = img[801,600]
print (pixel) # pixel value i am searching for

def search_for():
    for iidx, i in enumerate(img):
        for xidx, x in enumerate(i):
            if (x == pixel).all():
                print (f"SUCCESS - [{iidx} {xidx}]")

if __name__ == "__main__":
    print("Search using for loops...")
    search_for()

That being said, for loops are slow in python and it takes a while for the code to run on an suitably large image. Instead, using np.array methods are preferred as they are optimized for this type of application:

import cv2
import numpy as np

img = cv2.imread('one.jpg')

pixel = img[801,600]
print (pixel) # pixel value i am searching for

def search_array():
    # create an image of just the pixel, having the same size of 
    pixel_tile = np.tile(pixel, (*img.shape[:2], 1))
    # absolute difference of the two images
    diff = np.sum(np.abs(img - pixel_tile), axis=2)
    # print indices
    print("\n".join([f"SUCCESS - {idx}" for idx in np.argwhere(diff == 0)]))


if __name__ == "__main__":
    print("Search using numpy methods...")
    search_array()
user_131763190

I think the main issue that you are having is that you need to define the width and height of your image, so you know how many pixels in the x and y direction you need to loop

# grab the image dimensions
h = img.shape[0]
w = img.shape[1]
point_found_at = []

# loop over the image, pixel by pixel
for y in range(0, h):
    for x in range(0, w):
        if (x == 801) and (y == 600):
            print ("SUCCESS")
            point_found_at.append((x, y))
user_130799140

Your statement if x.sort ==pixel.sort is testing if the sort method on the x object is equal (referential equality) to the pixel.sort function. These will never be equal because they're on different objects. I'm not totally sure why you're using the sort method to test equality. You should be able to just check if (x == pixel).all() and get what you're looking for.

user_131763860
Related