Передача значения Scale

# -*- coding: UTF-8 -*-
from tkinter import Scale
 
import cv2
from tkinter import *
from tkinter import Scale
from PIL import Image, ImageTk
import numpy as np
 
class Main_window:
    def __init__(self, master):
        self.master = master
 
        self.b_exit = Button(self.master, text=u'Закрыть', bg='#84bd8a', fg='#ffffff', font='arial 12', width=15, height=1)
        self.b_exit.grid(row=0, column=0, padx=40, pady=5)
 
        self.l_entry = Label(self.master, text=u'Введите название кадра', bg='#a6abab', fg='#ffffff', font='arial 8 italic', width=25, height=1)
        self.l_entry.grid(row=1, column=0, padx=40, pady=1)
 
        self.e_name = Entry(self.master, text="Название кадра", bg='#84bd8a', fg='#ffffff', width=15, bd=3, font='arial 12')
        self.e_name.grid(row=2, column=0, padx=40, pady=1)
 
        self.b_save = Button(self.master, text=u'Сохранить кадр', bg='#84bd8a', font='arial 12', fg='#ffffff', width=15, height=1)
        self.b_save.grid(row=3, column=0, padx=40, pady=1)
 
        self.cap = cv2.VideoCapture(0)
        self.canvas = Canvas(self.master, width=600, height=480, bg='#84bd8a')
        self.canvas.grid(row=0, column=1, pady=7, rowspan=50, stick=NS)
 
        self.delay = 25
        self.update()
 
        self.value = 0
        self.scale = Scale(self.master, from_=-255, to=255, command=self.tr_value, variable=self.value, orient="horizontal", length=600, font='arial 12 italic', bg='#84bd8a', fg='#ffffff')
        self.scale.grid(row=51, column=1)
 
 
    def tr_value(self, value):
        self.value = value
        return self.value
 
    def update(self):
        ret, img = self.cap.read()
        self.img = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
 
        self.h, self.s, self.v = cv2.split(self.img)
        self.limit = 255 - self.value
        self.v[self.v > self.limit] = 255
        self.v[self.v <= self.limit] = self.v[self.v <= self.limit] + self.value
        self.v[self.v + self.value < 0] = 0
        self.img = cv2.merge((self.h, self.s, self.v))
 
        self.img = cv2.cvtColor(self.img, cv2.COLOR_HSV2BGR)
        self.img = ImageTk.PhotoImage(image=Image.fromarray(self.img))
        self.canvas.create_image(0, 0, image=self.img, anchor=NW)
        self.master.after(self.delay, self.update)
 
 
def main():
    root = Tk()
    root.geometry("900x550+150+100")
    root["bg"] = '#a6abab'
    root.resizable(False, False)
 
    GUI = Main_window(root)
 
    root.mainloop()
 
 
if __name__ == '__main__':
    main()