Today, one of the tasks I performed involved batch cropping numerous pictures. I found ImageMagick to be very useful for scaling and cropping images. Mogrify, a command within the ImageMagick package, enables us to perform various operations on multiple images. I am posting this guide as a future reference for myself and perhaps it will be helpful for others as well.

Step 1: Install MacPorts

https://www.macports.org/install.php

After completing the installation, if you encounter the following error:

> _sudo: port: command not found_

The issue likely arises because MacPorts binaries are installed in /opt/local/bin. You’ll need to manually update your shell’s environment to work with MacPorts:

> _export PATH=$PATH:/opt/local/bin_
> _source .profile_
> _sudo port -v selfupdate_

Step 2: Install ImageMagick

http://www.imagemagick.org/script/binary-releases.php

To install, run:

> _sudo port install ImageMagick_

The port command will download ImageMagick and many of its delegate libraries. If you encounter an error like:

> _convert: command not found_

Set the MAGICK_HOME environment variable to the path where you extracted the ImageMagick files:

> _export MAGICK_HOME="$HOME/ImageMagick-6.9.1"_

If the bin subdirectory of the extracted package isn’t already in your executable search path, add it:

> _export PATH="$MAGICK_HOME/bin:$PATH"_

Set the DYLD_LIBRARY_PATH environment variable:

> _export DYLD_LIBRARY_PATH="$MAGICK_HOME/lib"_

Step 3: Add Missing Decoding Library

If you try to convert JPEG images and get the following error message:

> _“convert: no decode delegate for this image format”_
  1. Visit http://www.imagemagick.org/download/delegates/ and download the required or missing delegate library, such as jpegsr9a.zip.
  2. Unzip the file.
  3. Change directory to the unzipped folder:
> _cd jpeg-9a_
  1. Then run:
> _./configure; make; make test; make -n install_

Step 5: Usage

To avoid overwriting the original image files, create a new folder and backup the images there.

To resize a single image to a height of 600px while maintaining the same aspect ratio, run:

> _convert input.png -geometry x600 output.png_

If you’d like to convert all images in a folder, change to that directory and use:

> _mogrify -geometry x600 *.png_

To scale down an image to 200 pixels:

> _convert myPhoto.jpg -resize 200x200^_

To crop the image from the center:

> _convert myPhoto.jpg -gravity Center -crop 200x200+0+0 +repage newPhoto.jpg_

The -gravity south option specifies that the crop should start at the bottom of the image. The -chop 0x135 option cuts 135 pixels from the height:

> _mogrify -gravity south -chop 0x135 *.jpg_

To resize all images in the current directory to a width of 800 (height will be reduced proportionally):

> _mogrify -resize 800 *.jpg_

To rotate images 90 degrees:

> _mogrify -rotate 90 *.jpg_

For More Information:

Visit http://www.imagemagick.org.