Python PIL: How to draw an ellipse in the middle of an image?

问题

I seem to be having some trouble getting this code to work:

import Image, ImageDraw

im = Image.open("1.jpg")

draw = ImageDraw.Draw(im)
draw.ellipse((60, 60, 40, 40), fill=128)
del draw 

im.save('output.png')
im.show()

This should draw an ellipse at (60,60) which is 40 by 40 pixels. The image returns nothing.

This code works fine however:

draw.ellipse ((0,0,40,40), fill=128)

It just seems that when i change the first 2 co-ords (for where the ellipse should be placed) it won't work if they are larger than the size of the ellipse to be drawn. For example:

draw.ellipse ((5,5,15,15), fill=128)

Works, but only shows part of the rect. Whereas

draw.ellipse ((5,5,3,3), fill=128)

shows nothing at all.

This happens when drawing a rectangle too.

回答1:

The bounding box is a 4-tuple (x0, y0, x1, y1) where (x0, y0) is the top-left bound of the box and (x1, y1) is the lower-right bound of the box.

To draw an ellipse to the center of the image, you need to define how large you want your ellipse's bounding box to be (variables eX and eY in my code snippet below).

With that said, below is a code snippet that draws an ellipse to the center of an image:

from PIL import Image, ImageDraw

im = Image.open("1.jpg")

x, y =  im.size
eX, eY = 30, 60 #Size of Bounding Box for ellipse

bbox =  (x/2 - eX/2, y/2 - eY/2, x/2 + eX/2, y/2 + eY/2)
draw = ImageDraw.Draw(im)
draw.ellipse(bbox, fill=128)
del draw

im.save("output.png")
im.show()

This yields the following result (1.jpg on left, output.png on right):

回答2:

The ellipse function draws an ellipse within a bounding box. So you need to use draw.ellipse((40,40,60,60)) or other coordinates where the top left is smaller than the bottom right.

来源：https://stackoverflow.com/questions/4789894/python-pil-how-to-draw-an-ellipse-in-the-middle-of-an-image