Resizes and crops the given image using Python Pillow. Support multi frame images such as GIF and WebP.

resize-and-crop-with-pillow.py

from math import floor, fabs
from PIL import Image, ImageSequence

def transform_image(original_img, crop_w, crop_h):
  """
  Resizes and crops the image to the specified crop_w and crop_h if necessary.
  Works with multi frame gif and webp images also.

  args:
  original_img is the image instance created by pillow ( Image.open(filepath) )
  crop_w is the width in pixels for the image that will be resized and cropped
  crop_h is the height in pixels for the image that will be resized and cropped
  
  returns:
  Instance of an Image or list of frames which they are instances of an Image individually
  """
  img_w, img_h = (original_img.size[0], original_img.size[1])
  n_frames = getattr(original_img, 'n_frames', 1)

  def transform_frame(frame):
    """
    Resizes and crops the individual frame in the image.
    """
    # resize the image to the specified height if crop_w is null in the recipe
    if crop_w is None:
      if crop_h == img_h:
        return frame
      new_w = floor(img_w * crop_h / img_h)
      new_h = crop_h
      return frame.resize((new_w, new_h))

    # return the original image if crop size is equal to img size
    if crop_w == img_w and crop_h == img_h:
      return frame

    # first resize to get most visible area of the image and then crop
    w_diff = fabs(crop_w - img_w)
    h_diff = fabs(crop_h - img_h)
    enlarge_image = True if crop_w > img_w or crop_h > img_h else False
    shrink_image = True if crop_w < img_w or crop_h < img_h else False

    if enlarge_image is True:
      new_w = floor(crop_h * img_w / img_h) if h_diff > w_diff else crop_w
      new_h = floor(crop_w * img_h / img_w) if h_diff < w_diff else crop_h

    if shrink_image is True:
      new_w = crop_w if h_diff > w_diff else floor(crop_h * img_w / img_h)
      new_h = crop_h if h_diff < w_diff else floor(crop_w * img_h / img_w)

    left = (new_w - crop_w) // 2
    right = left + crop_w
    top = (new_h - crop_h) // 2
    bottom = top + crop_h

    return frame.resize((new_w, new_h)).crop((left, top, right, bottom))

  # single frame image
  if n_frames == 1:
    return transform_frame(original_img)
  # in the case of a multiframe image
  else:
    frames = []
    for frame in ImageSequence.Iterator(original_img):
      frames.append( transform_frame(frame) )
    return frames