How can I convert canvas content to an image?

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()

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!


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')