How can i resize images given a certain ratio?

Question

I have many images of different sizes in my directory, however i want to resize them all by a certain ratio, let's say 0.25 or 0.2, it should be a variable i can control from my code and i want the resulting images to be an output in another directory.

I looked into this approach supplied by this previous question How to resize an image in python, while retaining aspect ratio, given a target size?

Here is my approach,

aspectRatio = currentWidth / currentHeight
heigth * width = area
So,

height * (height * aspectRatio) = area
height² = area / aspectRatio
height = sqrt(area / aspectRatio)
At that point we know the target height, and width = height * aspectRatio.

Ex:

area = 100 000
height = sqrt(100 000 / (700/979)) = 373.974
width = 373.974 * (700/979) = 267.397

but it lacks lots of details for example:how to transform these sizes back on the image which libraries to use and so on..

Edit: looking more into the docs img.resize looks ideal (although i also noticed .thumbnail) but i can't find a proper example on a case like mine.

Answer 1

from PIL import Image


ratio = 0.2
img = Image.open('/home/user/Desktop/test_pic/1-0.png')
hsize = int((float(img.size[1])*float(ratio)))
wsize = int((float(img.size[0])*float(ratio)))
img = img.resize((wsize,hsize), Image.ANTIALIAS)
img.save('/home/user/Desktop/test_pic/change.png')