Resize Multiple Images Quickly with the Mac Terminal

Introducing sips

I recently had to resize several photos for this blog’s project page. Normally, I would use the excellent free image manipulation program GIMP. But I wondered whether there was an easier way to apply the same resizing to images without having to open GIMP. And indeed, there is - using sips in the macOS Terminal (or anywhere that one has access to the command line in macOS).

Example

Let’s say there’s a bunch of .pngs that you would want to resize. (Sips can also handle .jpg and a lot of other file formats, but I was working with .png for the blog.) Simply open up your terminal and navigate to the folder containing the images you want to resize. Then type in the command

sips -Z 640 *.png

and hit Return. This should do it; all your images will be resized. The -Z in this instance keeps the aspect ratio intact. (See my note below, though). 640 specifies the new height, and the *.png specifies that this operation should be done to all the .png files in this folder.

• Note: Actually,the -Z ensures that the maximum size doesn’t exceed the specified number of pixels, in this case 640; this will apply to the height or width, whichever is larger. The smaller side will be adjusted to keep the aspect ratio. So a picture in portrait orientation will not exceed 640 pixels in its height, and a landscape will not exceed 640 in its width.

Other uses

Sips stands for scriptable image processing system, and has many more uses, including rotating or flipping images and converting images from one format to another. It’s super fast and handy. I stumbled onto it by reading this post by Adam Dachis, but you can also consult the sips manual here or by using the Terminal command

man sips