Checking image sizes and aspect ratios in Emacs Lisp so that I can automatically smartcrop them

| emacs

A+ occasionally likes to flip through pictures in a photo album. I want to print another batch of 4x6 photos, and I'd like to crop them before labeling them with the date from the EXIF info. Most of the pictures are from my phone, so I have a 4:3 aspect ratio instead of the 3:2 aspect ratio I want for prints.

First step: figuring out how to get the size of an image. I could either use Emacs's built-in image-size function or call ImageMagick's identify command. Which one's faster? First, I define the functions:

(defun my-image-size (filename)
  (let ((img (create-image filename)))
    (prog1 (image-size img t) (image-flush img))))

(defun my-identify-image-size (filename)
  (let ((result
         (seq-map 'string-to-number
                    (concat "identify -format \"%w %h\" " (shell-quote-argument filename)))))))
    (when (and result (> (car result) 0))

and then benchmark them:

(let ((filename "~/Downloads/Other prints/20230102_135059.MP.jpg")
      (times 10))
  (list (benchmark times `(my-image-size ,filename))
        (benchmark times `(my-identify-image-size ,filename))))

Looks like ImageMagick's identify command is a lot faster. Now I can define a filter:

Code for aspect ratios
(defun my-aspect-ratio (normalize &rest args)
  "Return the aspect ratio of ARGS.
If NORMALIZE is non-nil, return an aspect ratio >= 1 (width is greater than height).
ARGS can be:
- width height
- a filename
- a list of (width height)"
  (let (size width height result)
     ((stringp (car args))
      (setq size (my-identify-image-size (car args)))
      (setq width (car size) height (cadr size)))
     ((listp (car args))
      (setq width (car (car args)) height (cadr (car args))))
      (setq width (car args) height (cadr args))))
    (when (and width height)
      (setq result (/ (* 1.0 width) height))
      (if (and normalize (< result 1))
          (/ 1 result)

(defun my-files-not-matching-aspect-ratio (print-width print-height file-list)
  (let ((target-aspect-ratio (my-aspect-ratio t print-width print-height)))
     (lambda (filename)
       (let ((image-ratio (my-aspect-ratio t filename)))
         (when image-ratio
           (> (abs (- image-ratio

and I could use it like this to get a list of files that need to be cropped:

(my-files-not-matching-aspect-ratio 4 6 (directory-files "~/Downloads/Other prints" t))

… which is most of the pictures, so let's see if I can get smartcrop to automatically crop them as a starting point. I used npm install -g smartcrop-cli node-opencv to install the Node packages I needed, and then I defined these functions:

Code for cropping
(defvar my-smartcrop-image-command '("smartcrop" "--faceDetection"))

(defun my-smartcrop-image (filename aspect-ratio output-file &optional do-copy)
  "Call smartcrop command to crop FILENAME to ASPECT-RATIO if needed.
Write the result to OUTPUT-FILE.
If DO-COPY is non-nil, copy files if they already have the correct aspect ratio."
  (when (file-directory-p output-file)
    (setq output-file (expand-file-name (file-name-nondirectory filename)
  (let* ((size (my-identify-image-size filename))
         (image-ratio (my-aspect-ratio t size))
         new-height new-width
    (when image-ratio
      (if (< (abs (- image-ratio aspect-ratio)) 0.01)
          (when do-copy (copy-file filename output-file t))
        (with-current-buffer (get-buffer-create "*smartcrop*")
          (setq new-width
                 (floor (min
                         (car size)
                          (cadr size)
                          (if (> (car size) (cadr size))
                            (/ 1.0 aspect-ratio))))))
                 (floor (min
                         (cadr size)
                          (car size)
                          (if (> (car size) (cadr size))
                            (/ 1.0 aspect-ratio)))))))
          (message "%d %d -> %s %s: %s" (car size) (cadr size) new-width new-height filename)
          (apply 'call-process
           nil t t
            (cdr my-smartcrop-image-command)

so that I could use this code to process the files:

(let ((aspect-ratio (my-aspect-ratio t 4 6))
      (output-dir "~/Downloads/Other prints/cropped"))
  (mapc (lambda (file)
          (unless (file-exists-p (expand-file-name (file-name-nondirectory file) output-dir))
            (my-smartcrop-image file  aspect-ratio output-dir t)))
        (directory-files "~/Downloads/Other prints" t)))

Then I can use Geeqie to review the cropped images and straighten or re-crop specific ones with Shotwell.

It looks like smartcrop removes the exif information (including original date), so I want to copy that info again.

for FILE in *; do exiftool -TagsFromFile "../$FILE" "-all:all>all:all" "exif/$FILE"; done

And then finally, I can add the labels with this script, which I call with output-dir file1 file2 file3.... add the date to the lower left corner
import sys
import PIL
import PIL.Image as Image
import PIL.ImageDraw as ImageDraw
import PIL.ImageFont as ImageFont
from PIL import Image, ExifTags
import re
import os

# use: output-dir photo1 photo2 photo3
PHOTO_DIR = "/home/sacha/photos/"
OUTPUT_DIR = sys.argv[1]
font_fname = "/usr/share/fonts/truetype/noto/NotoSans-Regular.ttf"

def label_image(filename):
    numbers = re.sub(r'[^0-9]', '', filename)
    img =
    exif = {
        PIL.ExifTags.TAGS[k]: v
        for k, v in img._getexif().items()        if k in PIL.ExifTags.TAGS
    if DO_ROTATE:
        # Rotate image
        if exif['Orientation'] == 3:
            img = img.rotate(180, expand=True)
        elif exif['Orientation'] == 6:
            img = img.rotate(270, expand=True)
        elif exif['Orientation'] == 8:
            img = img.rotate(90, expand=True)    
    # Label
    time = exif['DateTimeOriginal'][0:10].replace(':', '-')
    if not time:
        if len(numbers) >= 10 and numbers[0:4] >= '2016' and numbers[0:4] < '2025':
            time = '%s-%s-%s' % (numbers[0:4], numbers[4:6], numbers[6:8])
    new_filename = os.path.join(OUTPUT_DIR, time + ' ' + os.path.basename(filename))
    if ALWAYS or not os.path.isfile(new_filename):
        out = add_label(img, time)
        print(filename, time)
        return new_filename

def add_label(img, caption):
    draw = ImageDraw.Draw(img)
    w, h = img.size
    border = int(min(w, h) * 0.02)
    font_size = int(min(w, h) * 0.04)
    # print(w, h, font_size)
    font = ImageFont.truetype(font_fname, font_size)
    _, _, text_w, text_h = draw.textbbox((0, 0), caption, font)
    overlay ='RGBA', (w, h))
    draw = ImageDraw.Draw(overlay)
    draw.rectangle([(border, h - text_h - 2 * border),
                    (text_w + 3 * border, h - border)],
                   fill=(255, 255, 255, 128))
    draw.text((border * 2, h - text_h - 2 * border), caption, (0, 0, 0), font=font)
    out = Image.alpha_composite(img.convert('RGBA'), overlay).convert('RGB')
    return out

if len(sys.argv) >= 2:
    for a in sys.argv[2:]:
        if ALWAYS or not os.path.exists(a):
            except Exception as e:
                print("Error", a, e)

I hope it all works out, since I've just ordered 120 4x6 prints covering the past three years or so…

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