GNU/Linux Desktop Survival Guide by Graham Williams
Desktop Survival Project Home Preface Advocacy History Distributions Installation Basic Survival Wajig Audio AbiWord APM Backup Bash Booting Cameras CD Chinese ChRoot Clock Commercial Conference Management Configuration CRON CVS Databases DIA Directories Disks Documentation DVD Email Eye of Gnome Evolution File Systems Firewalls Floppy Disks Fonts Ghemical GIMP Glade Gnome GnuCash Gnumeric GQView Graphics Groups HTML Editors ImageMagick Initialisations on Booting Java KDE Kernels Keyboard Konqueror KVM Switch LaTeX Log System Login Magellan Mathematics Memory Modems Mounting Devices MS/Windows Music MySQL Nautilus Networks NFS NT File System OpenOffice Oracle Packages Partitions Passwords PDF Photos PPP Presentations Printing Python R Remote Desktops Rsync Samba Scanning Science Security SH File System Sketch Spell SPlus Spruce SSH SUDO Swap Themes USB Video Web Word X XML Sample Installations Troubleshooting Index

ImageMagick

ImageMagick is the tool for transforming images.

The command line mogrify is excellent for changing the size of an image. mogrify -geometry does that, maintaining the image's aspect ratio (the specified width and height are maximum values) append the geometry with an exclamation point to force a change to aspect ratio.

Rotate an image with -rotate

Reduce the colors in an image: mogrify -colors 2 filename

To also dither the image: mogrify -colors 4 -dither filename

Monochrome image: mogrify -monochrome filename

Annotate image: mogrify -comment 'Hi there' filename

Add borders to image (pixel width and height): mogrify -border 2x4 filename

Decorative border: mogrify -frame 20x20 filename