Converting Images with Command-line

The  convert command is a powerful tool. Here is some ways to manipulate images using the convert command in Linux.

Image types that convert supports include .jpg, .bmp, .gif, .png, .tiff, .xpm,
.xwd, and .pcx

Resizing images:

$ convert -resize 800x400 kitty.jpg kitty-sm.jpg
$ convert -sample 50%x50% dog.jpg dog-half.jpg

The first example creates an image (kitty-sm.jpg) that is 800 × 400 pixels. The second example reduced the image dog.jpg in half (50%x50%) and then saves it as dog-half.jpg.

Creating thumbnails:

$ convert -thumbnail 120x120 a.jpg a-a.png
$ convert -thumbnail 120x120 -border 8 a.jpg a-b.png
$ convert -thumbnail 120x120 -border 8 -rotate 8 a.jpg a-c.png


Where the convert commands can really shine are when you use them in scripts. Instead of resizing, rotating a single file, you can do any or all of
those things to a whole directory of files.

Here's an example of a script you can run to resize an entire directory of photos to
800 × 400 pixels to upload to flickr or something:

$ cd $HOME/images $ mkdir small $ for pic in `ls *.png` do echo "converting $pic" convert -resize 800x400 $pic small/sm-$pic done