Command Line - Resizing Images

2012-09-10 ·

If you're looking for an efficient way to resize images, especially in a batch mode, the command line approach may be the answer.

OS X

OS X comes with a tool called sips, which stands for Scriptable Image Processing System. sips modifies images in-place, i.e. files passed in as arguments are altered; adding --out [filename] makes sips operate on a copy.

The two common parameters for sips are -z and -Z.

  • -z [height] [width] - it resizes the image according to specified dimensions, which may alter the aspect ratio of the image.
  • -Z [heightwidth] - it defines the maximum dimensions for both height and width, which keeps the aspect ratio of the image.
λ sips -z 768 1024 example.png
λ sips -Z 1024 example.png
λ sips -z 768 1024 *.png

It is also very easy to convert files from one format ot another, using -s parameter.

λ sips -s format jpeg test.png --out test.jpg

Linux

On Linux we can use mogrify from the ImageMagick toolbox to get the same functionality as with sips.

The most basic command would be resizing an image to specified dimensions, keeping the aspect ratio.

mogrify -resize 1024x768 example.png

If we need to resize to exact size, a ! sign must be added to the specified dimensions.

mogrify -resize 1024x768! example.png

Batch processing is also possible.

mogrify -resize 50% *.jpg

As well as converting from one format to another.

mogrify -format jpg *.png

Summary

Resizing and converting formats are probably the most common tasks when it comes to image manipulation. Both sips and mogrify provide more ways to transform images than covered in this short post. Feel free to check their docs to learn more.

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