One of the tasks I perform today is batch cropping a lot of pictures. I have found ImageMagick very useful to scales and crop the images. Mogrify is a command of the ImageMagick package and allows us to perform many operations on multiple images. I’ll post it here as a future reference for myself and perheps it will help others as well.
Step 1: Install MacPorts:
https://www.macports.org/install.php
After the installation, if you got an error:
sudo: port: command not found
Part of the problem is that MacPorts binaries are installed in /opt/local/bin, so you will need to manually adapt your shell’s environment to work with MacPorts:
export PATH=$PATH:/opt/local/bin
source .profile
sudo port -v selfupdate
Step 2: Install ImageMagick
http://www.imagemagick.org/script/binary-releases.php
sudo port install ImageMagick
The port command downloads ImageMagick and many of its delegate libraries. If you got an error:
convert: command not found
Set the MAGICK_HOME environment variable to the path where you extracted the ImageMagick files.
export MAGICK_HOME=”$HOME/ImageMagick-6.9.1″
If the bin subdirectory of the extracted package is not already in your executable search path, add it to your PATH environment variable.
export PATH=”$MAGICK_HOME/bin:$PATH”
Set the DYLDLIBRARYPATH environment variable:
export DYLDLIBRARYPATH=”$MAGICK_HOME/lib/
Step 3: Add the missing decoding library
When trying to convert jpeg images, it came up with this error message:
“convert: no decode delegate for this image format “
- Go to: http://www.imagemagick.org/download/delegates/ and download the required/missing delegate library. For example jpegsr9a.zip.
- Unzip the file
- Change directory to the folder
cd jpeg-9a
4. And run
./configure make make test make -n install
Step 5: Usage
To avoid overrides the original image files, create a new folder, copy the images and backup in that folder.
For resize a single image to height of 600px with the same aspect ratio, you could run this command:
convert input.png -geometry x600 output.png
If you prefer to covert all images of a folder, change directory to the folder and use
mogrify -geometry x600 *.png
To scale down an image to 200 pixels:
convert myPhoto.jpg -resize 200×200^
To crop the image from center:
convert myPhoto.jpg -gravity Center -crop 200×200+0+0 +repage newPhoto.jpg
The -gravity south option states that I want the crop to start at the bottom of my image. The -chop 0x25 states that I want to cut 25 pixels from the height.
mogrify -gravity south -chop 0x135 *.jpg
To resize all images in current directory to 800 width (and height reduced proportionally):
mogrify -resize 800 *.jpg
To rotate the images 90 degress:
mogrify -rotate 90 .
For more information:
Originally published at victorleungtw.com on July 18, 2015.
Victor Leung 