How can I convert canvas content to an image?

from Tkinter import *
root = Tk()
cv = Canvas(root)
cv.create_rectangle(10,10,50,50)
cv.pack()
root.mainloop()

I want to convert canvas content to a bitmap or other image, and then do other operations, such as rotating or scaling the image, or changing its coordinates.

Bitmaps can improve efficiency to show if I am no longer drawing.

What should I do?

Answers:

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Method 1

I have found a great way of doing this which is really helpful. For it, you need the PIL module. Here is the code:

from PIL import ImageGrab

def getter(widget):
    x=root.winfo_rootx()+widget.winfo_x()
    y=root.winfo_rooty()+widget.winfo_y()
    x1=x+widget.winfo_width()
    y1=y+widget.winfo_height()
    ImageGrab.grab().crop((x,y,x1,y1)).save("file path here")

What this does is you pass a widget name into the function. The command root.winfo_rootx() and the root.winfo_rooty() get the pixel position of the top left of the overall root window.

Then, the widget.winfo_x() and widget.winfo_y() are added to, basically just get the pixel coordinate of the top left hand pixel of the widget which you want to capture (at pixels (x,y) of your screen).

I then find the (x1,y1) which is the bottom left pixel of the widget. The ImageGrab.grab() makes a printscreen, and I then crop it to only get the bit containing the widget. Although not perfect, and won’t make the best possible image, this is a great tool for just getting a image of any widget and saving it.

If you have any questions, post a comment! Hope this helped!

Method 2

You can either generate a postscript document (to feed into some other tool: ImageMagick, Ghostscript, etc):

from Tkinter import *
root = Tk()
cv = Canvas(root)
cv.create_rectangle(10,10,50,50)
cv.pack()
root.mainloop()

cv.update()
cv.postscript(file="file_name.ps", colormode='color')

root.mainloop()

or draw the same image in parallel on PIL and on Tkinter’s canvas (see: Saving a Tkinter Canvas Drawing (Python)). For example (inspired by the same article):

from Tkinter import *
import Image, ImageDraw

width = 400
height = 300
center = height//2
white = (255, 255, 255)
green = (0,128,0)

root = Tk()

# Tkinter create a canvas to draw on
cv = Canvas(root, width=width, height=height, bg='white')
cv.pack()

# PIL create an empty image and draw object to draw on
# memory only, not visible
image1 = Image.new("RGB", (width, height), white)
draw = ImageDraw.Draw(image1)

# do the Tkinter canvas drawings (visible)
cv.create_line([0, center, width, center], fill='green')

# do the PIL image/draw (in memory) drawings
draw.line([0, center, width, center], green)

# PIL image can be saved as .png .jpg .gif or .bmp file (among others)
filename = "my_drawing.jpg"
image1.save(filename)

root.mainloop()

Method 3

Use Pillow to convert from Postscript to PNG

from PIL import Image

def save_as_png(canvas,fileName):
    # save postscipt image 
    canvas.postscript(file = fileName + '.eps') 
    # use PIL to convert to PNG 
    img = Image.open(fileName + '.eps') 
    img.save(fileName + '.png', 'png')

Method 4

Maybe you can try to use widget_winfo_id to get the HWND of the canvas.

import win32gui

from PIL import ImageGrab

HWND = canvas.winfo_id()  # get the handle of the canvas

rect = win32gui.GetWindowRect(HWND)  # get the coordinate of the canvas

im = ImageGrab.grab(rect)  # get image of the current location

Method 5

A better way for @B.Jenkins’s answer that doesn’t need a reference to the root object:

from PIL import ImageGrab


def save_widget_as_image(widget, file_name):
    ImageGrab.grab(bbox=(
        widget.winfo_rootx(),
        widget.winfo_rooty(),
        widget.winfo_rootx() + widget.winfo_width(),
        widget.winfo_rooty() + widget.winfo_height()
    )).save(file_name)

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0