Python TKinter: The canvas image file just contains one black pixel instead of 512x256 green pixels, why?

Question

canvas_width = 512
canvas_height = 512
root = Tk()
canvas = Canvas(root, width=canvas_width, height=canvas_height)
canvas.pack()
canvas.create_rectangle(0, 0, canvas_width, canvas_height / 2, fill='green')
ps = canvas.postscript(colormode='color')
img = PIL.Image.open(io.BytesIO(ps.encode('utf-8')))
img.save("/home/test.png")

If you execute this code, you will see that the saved file, test.png, contains only one black pixel. Instead, it should contain 512x256 green pixels and 512x256 undefined-color pixels.

Do you know why?

I have discovered this exactly when you posted your comment! — JarsOfJam-Scheduler, May 13 '20 at 09:12
You can do it, I'd be glad to upvote & accept your answer my friend :-) — JarsOfJam-Scheduler, May 13 '20 at 09:15
Read [Tkinter understanding mainloop](https://stackoverflow.com/a/29158947/7414759) — stovfl, May 13 '20 at 10:24

score 1 · Accepted Answer · answered May 13 '20 at 09:24

1

You'd have to redraw the canvas events by using canvas.update() or canvas.update_idletasks() before capturing. The difference is that update() is processing user events while update_idletasks() is just forcefully redrawing the window. Only then you'd be able to capture a postscript since all the text and graphics will already be there to capture and convert it to an image. Hope that's helpful!

answered May 13 '20 at 09:24

rizerphe

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Ty ! I just found out that my image is 386x386 instead of 512x512, do you know why? – JarsOfJam-Scheduler May 13 '20 at 09:42
1

Take a look [here](https://stackoverflow.com/questions/53509131/tkinter-saving-canvas-at-wrong-scale) – rizerphe May 13 '20 at 09:52
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@Jars Read [What's the difference between "update" and "update_idletasks"?](https://stackoverflow.com/a/29159152/7414759) – stovfl May 13 '20 at 10:24

Python TKinter: The canvas image file just contains one black pixel instead of 512x256 green pixels, why?

1 Answers1