adding padding to an image involves adding a border around it. this is a useful technique while adjusting the image's size without changing its aspect ratio or trimming it. padding can be added to the top, bottom, left, and right sides of the image. this is particularly important when working with images that have important information at the edges, which you want to retain for tasks like segmentation.

the pillow (pil) library provides two functions, pad() and expand(), within its imageops module for adding padding to images.

padding images with imageops.pad() function

the pad() function is used to resize and pad an image to a specified size and aspect ratio. it allows you to specify the output size, resampling method, background color, and positioning of the original image within the padded area. syntax of this function as follows −

pil.imageops.pad(image, size, method=resampling.bicubic, color=none, centering=(0.5, 0.5))

where,

image − the image to resize and pad.
size − a tuple specifying the requested output size in pixels, in the format (width, height). the function will resize the image to this size while maintaining the aspect ratio.
method − this parameter determines the resampling method used during resizing. the default method is bicubic, which is a type of interpolation. you can specify other resampling methods supported by pil. common options include nearest, bilinear, and lanczos.
color − this parameter specifies the background color of the padded area. it supports the rgba tuple also, like (r, g, b, a). if not specified, the default background color is black.
centering − this parameter controls the position of the original image within the padded version. it's specified as a tuple with two values between 0 and 1.

example

here is an example that adds padding to an image using the imageops.pad() function.

from pil import image
from pil import imageops

# open the input image
input_image = image.open('images/elephant.jpg')

# add padding to the image
image_with_padding = imageops.pad(input_image, (700, 300), color=(130, 200, 230))

# display the input image
input_image.show()

# display the image with the padding
image_with_padding.show()

input

output

output image after resizing with padding −

adding borders with the imageops.expand() function

the expand() function adds a border of a specified width and color around the image. it is useful for creating a decorative frame or emphasizing the content of the image. its syntax is as follows −

pil.imageops.expand(image, border=0, fill=0)

image − the image to expand the border.
border − the width of the border to add, specified in pixels. it determines how wide the border will be around the image. the default value is (0).
fill − the pixel fill value, which represents the color of the border. the default value is 0, which corresponds to black. you can specify the fill color using an appropriate color value.

example

here is an example that adds padding to an image using the imageops.expand() function.

from pil import image, imageops

# open the input image
input_image = image.open('images/car_2.jpg')

# add padding of 15-pixel border
image_with_padding = imageops.expand(input_image, border=(15, 15, 15, 15), fill=(255, 180, 0))

# display the input image
input_image.show()

# display the output image with padding
image_with_padding.show()

input

output

output image with padding −

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