ImageMagick® is a software suite to create, edit, compose, or convert bitmap images. It can read and write images in a variety of formats (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD, PNG, Postscript, SVG, and TIFF. Use ImageMagick to resize, flip, mirror, rotate, distort, shear and transform images, adjust image colors, apply various special effects, or draw text, lines, polygons, ellipses and Bézier curves.
ImageMagick has a command-line tool called Mogrify that’s quite powerful. Mogrify will resize an image, blur, crop, despeckle, dither, draw on, flip, join, re-sample, and much more. This tool is similiar to convert except that the original image file is overwritten (unless you change the file suffix with the -format option) with any changes you request. I recommend to create backups of your images.
If you want to resize a hundred large images into smaller images with a width of 800px, you can use Mogrify to resize all images using this single command:
mogrify -resize 800 *.JPG
Mogrify will also convert all .jpg files to the .png format found in the current directory in this example.
mogrify -format jpg *.png
And Much More
These are just two examples of what Mogrify can do. There are dozens of effects that you can do with Mogrify. Just view Mogrify’s list of commands. ImageMagick is available for the PC, Mac and Linux desktops.