How do I generate circular thumbnails with PIL?

How do I generate circular image thumbnails using PIL? The space outside the circle should be transparent.

Snippets would be highly appreciated, thank you in advance.

The easiest way to do it is by using masks. Create a black and white mask with any shape you want. And use putalpha to put that shape as an alpha layer:

from PIL import Image, ImageOps

mask = Image.open('mask.png').convert('L')
im = Image.open('image.png')

output = ImageOps.fit(im, mask.size, centering=(0.5, 0.5))
output.putalpha(mask)

output.save('output.png')

Here is the mask I used:

If you want the thumbnail size to be variable you can use ImageDraw and draw the mask:

from PIL import Image, ImageOps, ImageDraw

size = (128, 128)
mask = Image.new('L', size, 0)
draw = ImageDraw.Draw(mask) 
draw.ellipse((0, 0) + size, fill=255)

im = Image.open('image.jpg')

output = ImageOps.fit(im, mask.size, centering=(0.5, 0.5))
output.putalpha(mask)

output.save('output.png')

If you want the output in GIF then you need to use the paste function instead of putalpha:

from PIL import Image, ImageOps, ImageDraw

size = (128, 128)
mask = Image.new('L', size, 255)
draw = ImageDraw.Draw(mask)
draw.ellipse((0, 0) + size, fill=0)

im = Image.open('image.jpg')

output = ImageOps.fit(im, mask.size, centering=(0.5, 0.5))
output.paste(0, mask=mask)
output.convert('P', palette=Image.ADAPTIVE)

output.save('output.gif', transparency=0)

Note that I did the following changes:

• The mask is now inverted. The white was replaced with black and vice versa.
• I'm converting into 'P' with an 'adaptive' palette. Otherwise, PIL will only use web-safe colors and the result will look bad.
• I'm adding transparency info to the image.

Please note: There is a big issue with this approach. If the GIF image contained black parts, all of them will become transparent as well. You can work around this by choosing another color for the transparency. I would strongly advise you to use PNG format for this. But if you can't then that is the best you could do.

I would like to add to the already accepted answer a solution to antialias the resulting circle, the trick is to produce a bigger mask and then scale it down using an ANTIALIAS filter: here is the code

from PIL import Image, ImageOps, ImageDraw

im = Image.open('image.jpg')
bigsize = (im.size[0] * 3, im.size[1] * 3)
mask = Image.new('L', bigsize, 0)
draw = ImageDraw.Draw(mask) 
draw.ellipse((0, 0) + bigsize, fill=255)
mask = mask.resize(im.size, Image.ANTIALIAS)
im.putalpha(mask)

this produces a far better result in my opinion.

Slight modification on @DRC's solution to also support images which already have transparency. He sets the alpha channel to 0 (invisible) outside the circle and to 255 inside (opaque), so I use darker which takes the min of the mask and the original alpha channel (which can be anywhere betwen 0-255) :-)

from PIL import Image, ImageChops, ImageDraw

def crop_to_circle(im):
    bigsize = (im.size[0] * 3, im.size[1] * 3)
    mask = Image.new('L', bigsize, 0)
    ImageDraw.Draw(mask).ellipse((0, 0) + bigsize, fill=255)
    mask = mask.resize(im.size, Image.ANTIALIAS)
    mask = ImageChops.darker(mask, im.split()[-1])
    im.putalpha(mask)

im = Image.open('0.png').convert('RGBA')
crop_to_circle(im)
im.save('cropped.png')

Thank you very much. I was looking for hours and your idea does the trick.

Together with this other script from there. PIL round edges and add border it works perfectly for me.

from PIL import Image
from PIL import ImageDraw, ImageChops

def add_corners( im, rad=100):
    circle = Image.new('L', (rad * 2, rad * 2), 0)
    draw = ImageDraw.Draw(circle)
    draw.ellipse((0, 0, rad * 2, rad * 2), fill=255)
    alpha = Image.new('L', im.size, "white")
    w, h = im.size
    alpha.paste(circle.crop((0, 0, rad, rad)), (0, 0))
    alpha.paste(circle.crop((0, rad, rad, rad * 2)), (0, h - rad))
    alpha.paste(circle.crop((rad, 0, rad * 2, rad)), (w - rad, 0))
    alpha.paste(circle.crop((rad, rad, rad * 2, rad * 2)), (w - rad, h - rad))

    alpha = ImageChops.darker(alpha, im.split()[-1])

    im.putalpha(alpha)
    return im

im = Image.open ('AceOfSpades.png').convert('RGBA')

im = add_corners (im, 24)

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

Name this image AceOfSpades.png for testing