A quick explanation of how to resize images in Python while keeping the
same aspect ratio.
![Python in a tree][1]
I love [Python][2], and I've been learning it for a while now. Some time ago, I wrote a Python script where I needed to resize a bunch of images while at the same time keeping the aspect ratio (the proportions) intact. So I looked around and found [Pillow][3], a Python imaging library and "friendly fork" of an old library just called PIL.
To install Pillow, use the `pip` module of Python:
```
`$ python3 -m pip install Pillow`
```
### Scaling by width
Here's a basic script to resize an image using the Pillow module:
These few lines of Python code resize an image (**fullsized_image.jpg**) using Pillow to a width of 300 pixels, which is set in the variable **basewidth** and a height proportional to the new width. The proportional height is calculated by determining what percentage 300 pixels is of the original width (**img.size[0]**) and then multiplying the original height (**img.size[1]**) by that percentage. The resulting height value is saved in the variable **hsize.**
You can change **basewidth** to any other number if you need a different width for your images. Also, notice I saved the resized image under a different name, **resized_image.jpg**, because I wanted to preserve the full-size image (**fullsized_image.jpg**) as well. You don't have to do this, of course. You can use the same filename to overwrite the full-size image with the resized image, if that is what you want.
### Scaling by height
If the height is fixed and the width proportionally variable, it's pretty much the same thing, you just need to switch things around a bit:
Notice **basewidth** is now **baseheight**, since height is fixed. In the third line, we are calculating the height percentage, so we need **img.size[1]** instead of **img.size[0]**. The size attribute is a tuple containing width and height in pixels; **size[0]** refers to the first tuple element, which is the width, and **size[1]** is the second element, which is height. Line 4 also has this switch between **size[0]** for width and **size[1]** for height.
_Originally published on Dayo Ntwari's [blog][4] and republished under Creative Commons with permission._
_This article was updated in January 2021 by the editor._
