[Python] Saving tkinter canvas with black background and white line objects using PIL results...

Probem


When trying to save a tkinter canvas using PIL, it works as expected when the canvas background is set to "white" and fill option for the created lines to "black" but when setting the canvas background to "black" and the fill parameter of created lines to "white", the saved image will just be a solid color (white). Why does this happen?

Versioning


Python 3.11.8
pillow==10.2.0

Code

saves canvas normally


import tkinter as tk
import io
from PIL import Image


class App(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.line_start = None
self.canvas = tk.Canvas(self, width=300, height=300, bg="white")
self.canvas.bind("<Button-1>", lambda e: self.draw(e.x, e.y))
self.button = tk.Button(self, text="save", command=self.save)
self.canvas.pack(fill="both", expand=True)
self.canvas.focus_set()
self.button.pack(pady=10)

def draw(self, x, y):
if self.line_start:
x_origin, y_origin = self.line_start
self.canvas.create_line(x_origin, y_origin, x, y, fill="black")
self.line_start = x, y

def save(self):
ps = self.canvas.postscript(colormode="color")
img = Image.open(io.BytesIO(ps.encode("utf-8")))
img.save("working.png")


app = App()
app.mainloop()

saves fully white image


import tkinter as tk
import io
from PIL import Image


class App(tk.Tk):
def __init__(self):
tk.Tk.__init__(self)
self.line_start = None
self.canvas = tk.Canvas(self, width=300, height=300, bg="black")
self.canvas.bind("<Button-1>", lambda e: self.draw(e.x, e.y))
self.button = tk.Button(self, text="save", command=self.save)
self.canvas.pack(fill="both", expand=True)
self.canvas.focus_set()
self.button.pack(pady=10)

def draw(self, x, y):
if self.line_start:
x_origin, y_origin = self.line_start
self.canvas.create_line(x_origin, y_origin, x, y, fill="white")
self.line_start = x, y

def save(self):
ps = self.canvas.postscript(colormode="color")
img = Image.open(io.BytesIO(ps.encode("utf-8")))
img.save("white.png")


app = App()
app.mainloop()

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