Get new dimensions by changing width or height ( remain aspect ratio )

resize.py

def gcd(x, y): # Simplify Fraction (Greatest common divisor)
    if (x < y):
        temp = x
        x = y
        y = temp
    while (y != 0):
        remainder = x % y
        x = y
        y = remainder
    r = x
    return r

def get_ratio(w, h): # Get Aspect Ratio Based on Width and Height
    res = gcd(w, h)
    a1 = int(w / res)
    a2 = int(h / res)
    return a1, a2

def resize(old_width, old_height, new_quality=1080):
    sum_size = old_width + old_height
    
    w_ratio, h_ratio = get_ratio(old_width, old_height)

    sum_ratio = w_ratio + h_ratio

    factor = sum_size / sum_ratio

    if old_width > old_height:
        new_width = new_quality
        new_height = h_ratio * (new_width / w_ratio)
    elif old_width < old_height:
        new_height = new_quality
        new_width = w_ratio * (new_height / h_ratio)
    else:
	new_width = new_height = new_quality

    return int(new_width), int(new_height)

"""

use for Pillow:

from PIL import Image
im = Image.new("image.jpg")
old_width, old_height = im.size
new_width, new_height = resize(old_width, old_height, 1920)
im = im.resize((new_width, new_height))
im.save("image-resized.jpg")

"""