a batch program that reduces size of jpeg files

mikequest · #1 11th November 2009, 01:48 PM

Hello,
I'm looking for a program or command line tool that ease the process of reducing size of many .jpeg files at once.
I've been doing this with gimp manually by reducing jpeg quality and it's painful for 10 or 15 files to do that

thanks for replying

weitjong · #2 11th November 2009, 02:51 PM

Have you tried "imagemagick"? It is swiss army knife of image processing using CLI. Just found this example usage on the web to help you get started. I think you will be interested on example no 3 in http://www.ioncannon.net/linux/72/5-...amples-part-2/

Gödel · #3 11th November 2009, 03:26 PM

Yes, ImageMagick (install via yum) is the way to go

eg, cd to the directory of images, then to resize all by 50% and rename the resized images to <original>_new.jpg do:

Code:

for i in *.jpg; do convert $i -resize 50% "${i%%.*}_new.jpg"; done

PabloTwo · #4 11th November 2009, 04:15 PM

You can also use the 'mogrify' command in ImageMagick to do batch processing. Example here does not preserve the original files but overwrites them with the resized files.

Code:

BASH:~/work/test/-> ll
total 1624
-rw-r--r-- 1 paulm root 343047 2009-11-11 11:12 rotten_tree_effects2.jpg
-rw-r--r-- 1 paulm root 649369 2009-11-11 11:12 rotten_tree_effects.jpg
-rw-r--r-- 1 paulm root 642077 2009-11-11 11:12 rotten_tree_stump.jpg
BASH:~/work/test/-> mogrify -resize 50% rotten_tree_*.jpg
BASH:~/work/test/-> ll
total 308
-rw-r--r-- 1 paulm root  53475 2009-11-11 11:13 rotten_tree_effects2.jpg
-rw-r--r-- 1 paulm root  82474 2009-11-11 11:13 rotten_tree_effects.jpg
-rw-r--r-- 1 paulm root 144805 2009-11-11 11:13 rotten_tree_stump.jpg

mikequest · #5 11th November 2009, 06:21 PM

thanks a lot guys : )
I'll look at the examples.
fedora rocks : )

PabloTwo · #6 11th November 2009, 06:48 PM

Command line use of ImageMagick has a bit of a steep learning curve, only in that the options to the basic commands seem to be almost endless, but once you get the hang of it, it's often way way way faster than messing around in Gimp, especially when batch conversions are involved.

Both Godel and myself used "50%" in our examples to the "-resize" option, but you can also specify an explicit size. For example, to convert all .jpg files in the current directory to 640x480 pixels:

Code:

mogrify -resize 640x480 *.jpg

The identify command from ImageMagick is also handy.

BEFORE

Code:

BASH:~/work/test/-> identify img/rotten_tree_*
rotten_tree_effects2.jpg JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 335.006kb 
rotten_tree_effects.jpg[1] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 634.148kb 
rotten_tree_stump.jpg[2] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 627.027kb

AFTER

Code:

BASH:~/work/test/-> identify rotten_tree_*
rotten_tree_effects2.jpg JPEG 640x480 640x480+0+0 DirectClass 8-bit 62.8867kb 
rotten_tree_effects.jpg[1] JPEG 640x480 640x480+0+0 DirectClass 8-bit 104.152kb 
rotten_tree_stump.jpg[2] JPEG 640x480 640x480+0+0 DirectClass 8-bit 173.377kb

mikequest · #7 11th November 2009, 08:35 PM

just a precision, I meant by reducing jpeg file size but not the image resolution.
when i do :
"convert image -resize 50% "image_new.jpg" the resolution is cut in half
how to reduce jpeg quality without reducing resolution ? just like I do it in gimp wiht a "save as " jpeg

thanks again

PabloTwo · #8 11th November 2009, 08:52 PM

BEFORE

Code:

BASH:~/work/test/-> identify *
rotten_tree_effects2.jpg JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 335.006kb 
rotten_tree_effects.jpg[1] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 634.148kb 
rotten_tree_stump.jpg[2] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 627.027kb

Code:

BASH:~/work/test/-> mogrify *.jpg -quality 60

AFTER

Code:

BASH:~/work/test/-> identify *
rotten_tree_effects2.jpg JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 85.0938kb 
rotten_tree_effects.jpg[1] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 226.352kb 
rotten_tree_stump.jpg[2] JPEG 1152x864 1152x864+0+0 DirectClass 8-bit 220.514kb

Again, the example above replaces the original files, so you would need to work with copies of the originals in another directory in order to preserve the original image files. But, if you study the command line options, there is probably an easy way to save the converted files under another name.

Do 'convert --help' or 'man convert' and 'man mogrify' to get an overview of the possibilities.