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 perhaps it will help others as well.
Step 1: Install MacPorts:
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:
sudo port -v selfupdate
Step 2: Install ImageMagick
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.
If the bin subdirectory of the extracted package is not already in your executable search path, add it to your PATH environment variable.
Set the DYLDLIBRARYPATH environment variable:
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
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 a 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 200x200^
To crop the image from centre:
convert myPhoto.jpg -gravity Center -crop 200x200+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 degrees:
_mogrify -rotate 90 _.
For more information:
Originally published at victorleungtw.com on July 18, 2015.