Sometimes there is a need to perform a task on a whole bunch of images. I’m not talking about any sort of in depth image manipulation, but rather tasks that are tedious to do image by image. A good example is reducing the size of a series of images to be used on a website, or perhaps converting them from one image format to another. The easiest way of doing this is by means of the ImageMagick command line utility mogrify. Here is an example:

mogrify -auto-orient -format png *.jpg

This converts all the jpg files in a folder to png files. The -auto-orient option adjusts an image so that its orientation is suitable for viewing. To add the additional task of reducing the size of the image by 50%, we just have to add the -resize 50% option.

mogrify -auto-orient -resize 50% -format png *.JPG

Now using ImageMagick does require one to learn about the command line. On a Mac this is best provided by iTerm2. It basically provides access to all the folders in a low-level way, so that commands are provided by means of a command-line interface (a bit old-fashioned, but highly efficient for processing files).