Get pixel location using mouse click/events

Question

I wish to collect the pixel location (row-i, col-i) by right-clicking the mouse when the image is displayed.

This is a simple example about a picture downloaded from the internet:

import urllib
import cv2
from win32api import GetSystemMetrics

path_image = urllib.urlretrieve("http://www.bellazon.com/main/uploads/monthly_06_2013/post-37737-0-06086500-1371727837.jpg", "local-filename.jpg")[0]
img = cv2.imread(path_image,0)
width = GetSystemMetrics(0)
height = GetSystemMetrics(1)
scale_width = width / img.shape[1]
scale_height = height / img.shape[0]
scale = min(scale_width, scale_height)
window_width = int(img.shape[1] * scale)
window_height = int(img.shape[0] * scale)
cv2.namedWindow('image', cv2.WINDOW_NORMAL)
cv2.resizeWindow('image', window_width, window_height)
cv2.imshow('image', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

At this point, I wish to understand the best way to collect and store the pixel locations in a list.

Asked By: Gianni Spear

||

Source

Answer 1

import urllib
import cv2
from win32api import GetSystemMetrics

#the [x, y] for each right-click event will be stored here
right_clicks = list()

#this function will be called whenever the mouse is right-clicked
def mouse_callback(event, x, y, flags, params):

    #right-click event value is 2
    if event == 2:
        global right_clicks

        #store the coordinates of the right-click event
        right_clicks.append([x, y])

        #this just verifies that the mouse data is being collected
        #you probably want to remove this later
        print right_clicks

path_image = urllib.urlretrieve("http://www.bellazon.com/main/uploads/monthly_06_2013/post-37737-0-06086500-1371727837.jpg", "local-filename.jpg")[0]
img = cv2.imread(path_image,0)
scale_width = 640 / img.shape[1]
scale_height = 480 / img.shape[0]
scale = min(scale_width, scale_height)
window_width = int(img.shape[1] * scale)
window_height = int(img.shape[0] * scale)
cv2.namedWindow('image', cv2.WINDOW_NORMAL)
cv2.resizeWindow('image', window_width, window_height)

#set mouse callback function for window
cv2.setMouseCallback('image', mouse_callback)

cv2.imshow('image', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

Answered By: Jason

Answer 2

you can use an array or list to store the pixels location in it and also you can store the pixel value as well.

Here, I’m using python 3.x
You can follow the below code. In that code I’m performing the two mouse click events.
One is for getting the pixel location using left mouse click, and second is for getting the specific pixel value at particular location in RGB image.

I’m also storing the pixel location value in refPt variable.
See below is the code.

import cv2
import numpy as np

#This will display all the available mouse click events  
events = [i for i in dir(cv2) if 'EVENT' in i]
print(events)

#This variable we use to store the pixel location
refPt = []

#click event function
def click_event(event, x, y, flags, param):
    if event == cv2.EVENT_LBUTTONDOWN:
        print(x,",",y)
        refPt.append([x,y])
        font = cv2.FONT_HERSHEY_SIMPLEX
        strXY = str(x)+", "+str(y)
        cv2.putText(img, strXY, (x,y), font, 0.5, (255,255,0), 2)
        cv2.imshow("image", img)

    if event == cv2.EVENT_RBUTTONDOWN:
        blue = img[y, x, 0]
        green = img[y, x, 1]
        red = img[y, x, 2]
        font = cv2.FONT_HERSHEY_SIMPLEX
        strBGR = str(blue)+", "+str(green)+","+str(red)
        cv2.putText(img, strBGR, (x,y), font, 0.5, (0,255,255), 2)
        cv2.imshow("image", img)


#Here, you need to change the image name and it's path according to your directory
img = cv2.imread("D:/pictures/abc.jpg")
cv2.imshow("image", img)

#calling the mouse click event
cv2.setMouseCallback("image", click_event)

cv2.waitKey(0)
cv2.destroyAllWindows()

Note: One thing you need to remember that you have to put same name for the namedWindow. It should be same. In my code, I’m using the same name “image” for all the window.

You can do the same thing for multiple images as well. You just need to pass an list instead of single image.

If you want to store the pixel location in some text file, then you can also do it as follow:

Give the name of the variable where you are storing the pixel location value. I used refPt for storing the value. so, I used it here as follow:

import csv
with open("D:/pixelLocation.txt", 'w', newline='') as f:
    w = csv.writer(f)
    w.writerows(refPt)

Answered By: Ankit Lad

Answer 3

@ankit Lad
why is it img[y,x,0] ? why not img[x,y,0]

Answered By: user1994249

Get pixel location using mouse click/events

Question:

Answers: