Tkinter图像无Matplotlib时无法显示问题排查

我通过numpy生成图像数组，想在Tkinter的Canvas组件中显示。用Matplotlib调试时，打开Matplotlib窗口能正常显示图像，但关闭该窗口后，Canvas里的图像就变成全白。如果完全删掉Matplotlib相关代码，图像直接一直是全白，根本显示不出来。

现象截图 #

• 双窗口打开时正常显示：
  
• 关闭Matplotlib窗口后全白：
  

原代码 #

from skimage.draw import polygon
from PIL import Image, ImageTk

import matplotlib.pyplot as plt

import tkinter as tk
import numpy as np

def generate():
    
    # clear canvas
    canvas.delete("all")

    # make clean array
    img = np.ones((width, height, 3), dtype=np.float32) * 0.75

    # randomly generate positions
    x_generated = np.random.uniform(0, width, 5)
    y_generated = np.random.uniform(0, height, 5)
    
    for x, y in zip(x_generated, y_generated):
        base_height = 70
        base_width = 70

        # generate the corners
        x0 = x - base_width/2
        x1 = x + base_width/2
        y0 = y - base_height/2
        y1 = y + base_height/2

        # create rectangle
        poly = np.array((
            (x0, y0),
            (x1, y0),
            (x1, y1),
            (x0, y1),
        ))

        rr, cc = polygon(poly[:, 0], poly[:, 1], img.shape)
        img[rr, cc, :] = 0.5

        # # canvas method. I don't want to use this!
        # canvas.create_rectangle(x0, y0, x1, y1, fill="red", outline="")
    
    # display generated image in tkinter canvas
    scaled_to_8bit = img * 255
    newarr = scaled_to_8bit.astype(np.uint8)
    imgarray = ImageTk.PhotoImage(image=Image.fromarray(newarr, 'RGB'))

    # create the canvas image object from the numpy array
    canvas.create_image(20, 20, anchor="nw", image=imgarray)
    
    # display pixel data for debugging
    plt.imshow(img)
    plt.show()



if __name__ == "__main__":
    width = 1000
    height = 1000

    # Create a root window
    root = tk.Tk()
    root.configure(background="green")

    # Create a canvas widget
    canvas = tk.Canvas(root, width=width, height=height)
    canvas.pack()

    # Create a button widget
    button = tk.Button(root, text="Generate", command=generate)
    button.pack()

    # start main tk loop
    root.mainloop()

问题原因与解决方法 #

核心原因 #

ImageTk.PhotoImage创建的对象imgarray是局部变量，函数执行完毕后会被Python垃圾回收机制回收。之前Matplotlib的plt.show()会阻塞函数执行，暂时保留了这个对象；一旦关闭Matplotlib窗口，函数执行完成，imgarray被回收，Canvas找不到图像源就会变成全白。

修复代码 #

给imgarray添加持久引用，比如绑定到Canvas对象的属性上，避免被垃圾回收。修改后的代码如下：

from skimage.draw import polygon
from PIL import Image, ImageTk

import matplotlib.pyplot as plt

import tkinter as tk
import numpy as np

def generate():
    
    # clear canvas
    canvas.delete("all")

    # make clean array
    img = np.ones((width, height, 3), dtype=np.float32) * 0.75

    # randomly generate positions
    x_generated = np.random.uniform(0, width, 5)
    y_generated = np.random.uniform(0, height, 5)
    
    for x, y in zip(x_generated, y_generated):
        base_height = 70
        base_width = 70

        # generate the corners
        x0 = x - base_width/2
        x1 = x + base_width/2
        y0 = y - base_height/2
        y1 = y + base_height/2

        # create rectangle
        poly = np.array((
            (x0, y0),
            (x1, y0),
            (x1, y1),
            (x0, y1),
        ))

        rr, cc = polygon(poly[:, 0], poly[:, 1], img.shape)
        img[rr, cc, :] = 0.5

        # # canvas method. I don't want to use this!
        # canvas.create_rectangle(x0, y0, x1, y1, fill="red", outline="")
    
    # display generated image in tkinter canvas
    scaled_to_8bit = img * 255
    newarr = scaled_to_8bit.astype(np.uint8)
    imgarray = ImageTk.PhotoImage(image=Image.fromarray(newarr, 'RGB'))

    # 为图像对象添加持久引用，避免被垃圾回收
    canvas.image = imgarray

    # create the canvas image object from the numpy array
    canvas.create_image(20, 20, anchor="nw", image=imgarray)
    
    # 可选：保留Matplotlib调试代码，或直接删除
    # plt.imshow(img)
    # plt.show()



if __name__ == "__main__":
    width = 1000
    height = 1000

    # Create a root window
    root = tk.Tk()
    root.configure(background="green")

    # Create a canvas widget
    canvas = tk.Canvas(root, width=width, height=height)
    canvas.pack()

    # Create a button widget
    button = tk.Button(root, text="Generate", command=generate)
    button.pack()

    # start main tk loop
    root.mainloop()

关键修改点 #

添加canvas.image = imgarray这一行，将图像对象绑定到Canvas的属性上，确保函数执行完成后对象不会被立即回收，Canvas就能持续显示图像。即使删除所有Matplotlib相关代码，图像也能正常显示。

内容的提问来源于stack exchange，提问作者Gordon13