add_rounded_corners.py

# Rounded Corners - Python's pillow v7.1.1
# Ref: https://stackoverflow.com/a/11291419/7416198

from PIL import Image, ImageDraw


# im    Image()      Image object
# rad   int          radius of curve
def add_corners(im, rad):
    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, 255)
    
    w, h = im.size
    alpha.paste(circle.crop((0, 0, rad, rad)), (0, 0))        # Top left
    alpha.paste(circle.crop((0, rad, rad, rad * 2)), (0, h - rad))      # Bottom-left
    alpha.paste(circle.crop((rad, 0, rad * 2, rad)), (w - rad, 0))      # Top Right
    alpha.paste(circle.crop((rad, rad, rad * 2, rad * 2)), (w - rad, h - rad))      # Bottom Right
    
    im.putalpha(alpha)
    
    return im

im = Image.open('input.jpg')
im = add_corners(im, 100)        # img.size[0]//2 for circular image (only square images)
im.save('output.png')