How to draw a line on image and retrieve pixels beneath the line?

Question

I am trying to draw a line on the image and retrieve all the pixel values that fall beneath the line. I have tried but a method where you retrieve the 2 mouse click coordinates and calculate the slope between the two mouse coordinates but that is very specifically extracting only one row. How can I change the width of the line and also retrieve the pixels beneath it? I am new to python and I don't know where to start. Any ideas or any recommendations would be great thank you.

Simply to understand I want to draw a line on image and extract pixels beneath the line, and also when we change the width of line I want to extract pixel values of the extended with too. How can I do this?

from tkinter import *
import PIL
import PIL.Image 
import PIL.ImageTk 
root = Tk()

#setting up a tkinter canvas with scrollbars
frame = Frame(root, bd=2, relief=SUNKEN)
frame.grid_rowconfigure(0, weight=1)
frame.grid_columnconfigure(0, weight=1)
xscroll = Scrollbar(frame, orient=HORIZONTAL)
xscroll.grid(row=1, column=0, sticky=E+W)
yscroll = Scrollbar(frame)
yscroll.grid(row=0, column=1, sticky=N+S)
canvas = Canvas(frame, bd=0, xscrollcommand=xscroll.set, yscrollcommand=yscroll.set)
canvas.grid(row=0, column=0, sticky=N+S+E+W)
xscroll.config(command=canvas.xview)
yscroll.config(command=canvas.yview)
frame.pack(fill=BOTH,expand=1)

#adding the image in the below line u16 us my image array.
img = PIL.ImageTk.PhotoImage(image =PIL.Image.fromarray(u16))

canvas.create_image(0,0,image=img,anchor="nw")
canvas.config(scrollregion=canvas.bbox(ALL))

#function to be called when mouse is clicked
def printcoords(event):
    #outputting x and y coords to console
    click = event.x, event.y
    print (click)
def printcoords_up(event):
    #outputting x and y coords to console
    rem_click=event.x, event.y
    print (rem_click)
#mouseclick event
canvas.bind("<ButtonPress-1>",printcoords)
# canvas.bind("<ButtonMotion-1>", printcoords)
canvas.bind("<ButtonRelease-1>", printcoords_up )

root.mainloop()

##################EDITED CODE #####################

import tkinter 
import numpy as np
import cv2
import sys
import PIL
import PIL.Image 
import PIL.ImageTk as imtk
if "Tkinter" not in sys.modules:
    from tkinter import *

curPth = sys.path[0]
###### u16 is my image array.
im = u16
tmpPth = curPth+'/temp.png'

ev = None


def click(event, back):
    global ev, im
    if ev == None:
       ev = event
       return None

# im = imgPth
# mask = cv2.cvtColor(im.copy()*0, cv2.COLOR_BGR2GRAY)
cv2.line(im, pt1=(ev.x, ev.y), pt2=(event.x, event.y), color=(255, 0, 0), thickness=40)
mask = cv2.threshold(im, 127, 255, cv2.THRESH_BINARY)[1]
out = im.copy()
out[np.where(mask == 0)] = 255

cv2.imwrite(tmpPth, out)
back.config(file=tmpPth)
print(event)
ev = event

window = tkinter.Tk()
back = imtk.PhotoImage(image =PIL.Image.fromarray(im))
my_label=Label(window, image=back)
my_label.place(x=0, y=0)
window.bind('<Button-1>', lambda event: click(event, back))
window.mainloop()

Answer 1

I was a little confused by your question; But I guess if I misunderstood the problem; it may help someone else later. I tried to test it with @Dan Mašek method.

from tkinter import *
import numpy as np
import cv2
import sys
import PIL.Image as imge
import PIL.ImageTk as imtk

curPth = sys.path[0]
imgPth = curPth+'/back.png'
tmpPth = curPth+'/temp.png'

ev = None
thikness = 40


def click(event):
    global ev, back, lbl
    if ev == None:
        ev = event
        return None

    im = cv2.imread(imgPth)
    mask = cv2.cvtColor(im.copy()*0, cv2.COLOR_BGR2GRAY)
    cv2.line(mask, pt1=(ev.x, ev.y), pt2=(event.x, event.y),
             color=(255, 0, 0), thickness=thikness)
    mask = cv2.threshold(mask, 127, 255, cv2.THRESH_BINARY)[1]
    out = im.copy()
    out[np.where(mask == 0)] = 255

    out = cv2.cvtColor(out, cv2.COLOR_BGR2RGB)
    back = imtk.PhotoImage(image=imge.fromarray(out))
    lbl.config(image=back)

    # print(mask[np.where(mask == 255)])
    x, X = min(ev.x, event.x)-thikness//2, max(ev.x, event.x)+thikness//2
    y, Y = min(ev.y, event.y)-thikness//2, max(ev.y, event.y)+thikness//2
    cropped = mask[y:Y, x:X]
    print(cropped, cropped.shape)
    cv2.imwrite(curPth+'/2d_line_area.png', cropped)
    ev = event


root = Tk()
back = PhotoImage(file=imgPth)
lbl = Label(root, image=back)
lbl.place(x=0, y=0)
root.bind('<Button-1>', lambda event: click(event))
root.mainloop()

My test image that I draw with paint.net:

Tkinter main loop:

After click on 2 points on screen:

And more tests:

---

Two-dimensional array only from the area where the line is drawn.

---

More examples:

x, X = min(ev.x, event.x)-thikness//2, max(ev.x, event.x)+thikness//2
y, Y = min(ev.y, event.y)-thikness//2, max(ev.y, event.y)+thikness//2
cropped1 = mask[y:Y, x:X]
cropped2 = out[y:Y, x:X]
print(cropped1, cropped1.shape)
cropped1=cv2.cvtColor(cropped1,cv2.COLOR_GRAY2RGB)
cropped2=cv2.cvtColor(cropped2,cv2.COLOR_BGR2RGB)
cv2.imwrite(curPth+'/2d_line_area.png', np.hstack((cropped1,cropped2)))
ev = event