python3 & tkinter - creating a zoom button to zoom on the loaded image

Question

I would like to create a zoom button. On clicking on that zoom button, the image would be zoomed in by a factor represented by an integer (1,2,3,4,5...). With this piece of code, by clicking on the zoom button, another panel is created underneath the already loaded picture. Inside it is blank. What would be needed is to: 1. kill the first (non-zoomed window) and 2. load the zoomed image on the updated panel

from tkinter import *
from tkinter.filedialog import askopenfilename
import tkinter as tk

event2canvas = lambda e, c: (c.canvasx(e.x), c.canvasy(e.y))

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
image_str="image.png"
image = tk.PhotoImage(file=image_str)
image = image.zoom(1,1)
canvas.create_image(0,0,image=image,anchor="nw")
canvas.config(scrollregion=canvas.bbox(ALL))

def zoomin():
   root = Tk()
   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)

image = tk.PhotoImage(file=image_str)
image = image.zoom(1,1)
canvas.create_image(0,0,image=large_img,anchor="nw")
canvas.config(scrollregion=canvas.bbox(ALL))   

toolbar = Frame(root, bg="blue")

insertButt = Button(toolbar, text="zoomin", command=lambda:zoomin())
insertButt.pack(side = LEFT, padx=2, pady=2)

toolbar.pack(side=TOP, fill = X)

#function to be called when mouse is clicked
def printcoords(event):
    #outputting x and y coords to console
    print (event.x,event.y)
#mouseclick event
canvas.bind("<Button 1>",printcoords)

#mouseclick event
canvas.bind("<ButtonPress-1>",printcoords)
canvas.bind("<ButtonRelease-1>",printcoords)

root.mainloop()

I would like to thank @Symon for his stackoverflow question. I largely inspired myself from his code

Answer 1

Well, the reason that the function zoomin(img) does not work properly is that it returns in the first line:

def zoomin(img):
    return     # Function returns here
    ... rest of code is never executed

I suspect this is due to the function being run when you create the button, not when you press it. Try cretating the button in this way instead:

insertButt = Button(toolbar, text="zoomin", command=lambda:zoomin(img))

Now the button will call zoomin(img) when it's pressed and not when the button is created.

Zooming with Tkinter

PhotoImage zoom only allows integer values, wich makes it a bit limited. But here's an example:

from tkinter import *

root = Tk()
root.geometry('300x200')

field = Canvas(root, bg='tan1', highlightthickness=0)
field.grid(sticky='news')
photo = PhotoImage(file='test.gif')
field.create_image(0, 0, image=photo, anchor='nw')
scale = 1

def zoom(event=None):
    global scale, photo
    scale = scale * 2
    field.delete('all')
    photo = photo.zoom(x=scale, y=scale)
    field.create_image(0, 0, image=photo, anchor='nw')
    field.image = photo

root.bind('z', zoom)    # Bind "z" to zoom function
root.mainloop()

If you want to zoom by float you'll have to import a module for that. Pillow seems popular. But I haven't worked with any of them so you'll have to research them yourself.