How to reverse the y-axis of the imported image in Tkinter?

Question

For duplicate-markers: I am fully aware that there are some similar questions in matplotlib, such as this one. My question is about

Answer 1

What you seem to be asking for is a 2D World to Viewport Transformation:

Take an area defined in "world coordinates" (say 10 metres by 10 metres) and map it to an area defined in canvas coordinates.

eg.

from tkinter import *

xmin,ymin,xmax,ymax = 0,0,10,10   # world
umin,vmin,umax,vmax = 0,480,640,0 # viewport (note: y reversed)

points = [(2,2), (4,4), (7,7), (8,8)]  # some "world" points

def world_to_viewport(worldpoint):
    x,y = worldpoint
    u = (x - xmin)*((umax - umin)/(xmax - xmin)) + umin
    v = (y - ymin)*((vmax - vmin)/(ymax - ymin)) + vmin
    return u,v

def pixel_to_world(pixel):
    u,v = pixel
    x = (u - umin)*((xmax - xmin)/(umax - umin)) + xmin
    y = (v - vmin)*((ymax - ymin)/(vmax - vmin)) + ymin
    return x,y

root = Tk()
canvas = Canvas(root, width=640, height=480, bd=0, highlightthickness=0)
canvas.pack()

def on_click(event):
    root.title('%s,%s' %(pixel_to_world((event.x,event.y))))

canvas.bind('<ButtonPress-1>', on_click)

r = 5
for point in points:
    cx,cy = world_to_viewport(point)
    canvas.create_oval(cx-r,cy-r,cx+r,cy+r,fill='red')

root.mainloop()

Answer 2

It seems to me that this would be simple with code like the below:

import Tkinter
#Set up a basic canvas
top = Tkinter.Tk()
canv = Tkinter.Canvas(top, bg="brown", height=250, width=300)

#Replace with what ever values you want
x = 50
y = 50

#Draw the first dot
line1 = canv.create_line(x, y, x - 2, y - 2, fill="green", width=3)
#This next line is pretty much all it takes to find the Y inverse
y = canv.winfo_reqheight() - y
#Draw the second dot
line2 = canv.create_line(x, y, x - 2, y - 2, fill="green", width = 3)

canv.pack()
top.mainloop()

This returns the following:

Basically all I did was get the canvas height (250), and subtract the previous Y value (50) from it, which returned the Y inverse (200). Not exactly a built in function, but the actual flipping part was very simple. Hope that was what you were looking for... Good luck!

Answer 3

An angle can be used like such:

image = Image.open("lena.jpg")
angle = 180
tkimage = ImageTk.PhotoImage(image.rotate(angle))
...

It would be possible to draw the picture, and use reversed coordinates (so when you know the size of the canvas, instead of saying 50x50, you could use (max-50)x(max-50).

The question is whether axes.imshow can handle the ImageTk.PhotoImage. Then again, I am not entirely sure if you'd just want this on a Tkinter canvas instead, e.g.:

canvas_obj = self.canvas.create_image(250, 250, image=tkimage)