bash-tutorial/tutorial/image_size_reduction.org

#+date: 2023-08-20
#+options: toc:nil num:nil author:nil

* Use imagemagick to manipulate images

[[https://imagemagick.org/][ImageMagick]] is a suite of tools used for digital image edition and manipulation.
The tools can be used in the command line (~cli~).

There are multiple functionalities avaliable in ImageMagick. Commands like ~convert~,
~mogrify~ and ~identify~ are just some of the useful tools available.

** Using the ~convert~ command

Converting multiple ~jpg~ files into lower size images:

First, [[https://www.man7.org/linux/man-pages/man1/cd.1p.html][cd]] (change working directory) into the directory containing all the images

#+begin_example sh
  cd directory
#+end_example

Then use ~convert~ to resize all the 'jpg' files within the directory:

#+begin_example sh
  convert '*.jpg' -set filename:fn '%[basename]-small' -resize 960x640 '%[filename:fn].jpg'
#+end_example

Here the '%[basename]-small' will copy original files, resize and rename including
the suffix "small" to the original name.

Reduce quality using convert (the command is similar to the previous one, but
it uses ~-quality~ instead of ~-resize~)

#+begin_example sh
  convert '*.jpg' -set filename:fn '%[basename]-small' -quality 50%  '%[filename:fn].jpg'
#+end_example

** Using mogrify
~mogrofy~ can be used for similar purposes.

Let's check som images in a directory to verify how much those images can be
modified.

Change directory use the commands in the same place were the images are included,
e.g:

#+begin_example sh
  cd directory
#+end_example

Counting number of ~.jpg~ images in a directory:

#+begin_example sh
  ls -1U DIR_NAME | wc -l
#+end_example

Verify the output:

75

Verifying the images weight of all the images:

#+begin_example sh
  du -h
#+end_example

Output:

306 M

Resize all the ~.jpg~ images within the directory:

#+begin_example sh
 mogrify -resize 960x640 *.jpg
#+end_example

Output:

42M

Reduce the quality of all the images within the directory:

#+begin_example sh
  mogrify -quality 80% *.jpg
#+end_example

Weight:

#+begin_example sh
  du -h
#+end_example

Output:

12M

** Remove some metada from images

[[https://imagemagick.org/script/command-line-options.php#strip][`mogrify -strip`]]can be used to remove some metada from the images.

First you can check the image metada using the command ~identify~ from Imagemagick.

#+begin_example sh
  identify -verbose image.jpg
#+end_example

This command will print an output like this:

 # Filename: image.jpg
 #  Permissions: rw-r--r--
 #  Format: JPEG (Joint Photographic Experts Group JFIF format)
 #  Mime type: image/jpeg
 #  Class: DirectClass
 #  Geometry: 960x640+0+0
 #  Resolution: 72x72
 #  Print size: 13.3333x8.88889
 #  Units: PixelsPerInch
 #  Colorspace: sRGB
 #  Type: TrueColor
 #  Base type: Undefined
 #  Endianness: Undefined
 #  Depth: 8-bit
 #  Channels: 3.0
 #  Channel depth:
 #    Red: 8-bit
 #    Green: 8-bit
 #    Blue: 8-bit
 #  Channel statistics:
 #  Pixels: 614400
 # ...
 # ...
 # Version: ImageMagick 7.1.1-12 Q16-HDRI x86_64 21239 https://imagemagick.org

You can use ~mogrify~ to remove metada from one or multiple images using
something like:

#+begin_example sh
  mogrify -strip ./image.jpg # one image
  mogrify -strip ./*.jpg # modifiyng all 'jpg' files in directory
#+end_example


** References

- [[https://askubuntu.com/questions/1354205/imagemagick-convert-on-a-multiple-files][Imagemagick to convert multiple files]]
- [[https://imagemagick.org/][Imagemagick web site]]
- [[https://www.digitalocean.com/community/tutorials/reduce-file-size-of-images-linux][Digital ocean tutorial]]