use "convert" part of ffmpeg package 1.jpg size 3456x4608 convert -resize 25% 1.jpg 2.jpg This will reduce the size to 25%, not by 25%. ------------------

use "convert" part of ffmpeg package 1.jpg size 3456x4608 convert -resize 25% 1.jpg 2.jpg This will reduce the size to 25%, not by 25%. ------------------------------- use "mogrify" part of ImageMagick mogrify -resize 25% *.jpg # keep image aspect ratio mogrify -resize 320x240 *.jpg # keep image aspect ratio mogrify -resize 60% *.jpg # keep image aspect ratio see the ! mogrify -resize 320x240! *.png # don't keep image aspect ratio mogrify -resize x240 *.png # don't keep image aspect ratio mogrify -resize 320x *.png # don't keep image aspect ratio