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Add padding to the image with Python, Pillow

Posted: 2019-05-14 / Tags: Python, Pillow, Image Processing

If you want to resize an image but do not want to change the aspect ratio or trim it, you can adjust the size by adding padding to the top, bottom, left, and right of the image.

You can pad an image by using new() and paste() of the Python image processing library Pillow (PIL).

This article describes the following contents.

  • Add padding of any width vertically and horizontally
  • Add padding to the rectangle to make it square

See the following article for the installation and basic usage of Pillow (PIL).

See the following article about trimming.

Import Image from PIL and load the original image.

from PIL import Image

im = Image.open('data/src/astronaut_rect.bmp')

original image - astronaut

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Add padding of any width vertically and horizontally

Generate a solid image with new(), and paste the original image with paste().

Define the following function.

Specify the width of the margin to top,right, bottom,left, and the background color (R, G, B) (maximum value is 255) to color.

def add_margin(pil_img, top, right, bottom, left, color):
    width, height = pil_img.size
    new_width = width + right + left
    new_height = height + top + bottom
    result = Image.new(pil_img.mode, (new_width, new_height), color)
    result.paste(pil_img, (left, top))
    return result
source: imagelib.py

Usage example:

im_new = add_margin(im, 50, 10, 0, 100, (128, 0, 64))
im_new.save('data/dst/astronaut_add_margin.jpg', quality=95)

astronaut add padding

Add padding to the rectangle to make it square

Add padding to the short side to make it square while maintaining the aspect ratio of the rectangular image.

Define the following function.

def expand2square(pil_img, background_color):
    width, height = pil_img.size
    if width == height:
        return pil_img
    elif width > height:
        result = Image.new(pil_img.mode, (width, width), background_color)
        result.paste(pil_img, (0, (width - height) // 2))
        return result
    else:
        result = Image.new(pil_img.mode, (height, height), background_color)
        result.paste(pil_img, ((height - width) // 2, 0))
        return result
source: imagelib.py

Usage example:

im_new = expand2square(im, (0, 0, 0))
im_new.save('data/dst/astronaut_expand_square.jpg', quality=95)

astronaut expand to square

When you want to make a square of a certain size, such as making a thumbnail, add padding and then resize().

im_new = expand2square(im, (0, 0, 0)).resize((150, 150))

For more information about generating thumbnail images, see the following article:

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