Resize and Watermark Images in Linux
Posted by admin on December 30, 2007 under Tech Tips | 
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If you need to resize and watermark large number of images, there is an easy way to do so using Linux command line tools and a very basic shell script. The easiest and most straight-forward method you can use is through the use of the ImageMagick toolkit. If you don’t have it installed already, you can download it from their site. Most distributions have binaries already built for you. Ubuntu and Debian users can install ImageMagick from the main repositories.
Install ImageMagick
sudo apt-get install imagemagick
Prepare your working environment
Make a directory to store the watermark image (~/Pictures/watermark) and photos you’re working on (~/Pictures/temp). Copy the watermark image and original photos to their respective directories.
mkdir -p ~/Pictures/temp/
mkdir -p ~/Pictures/watermark/
cp /path/to/watermark.jpg ~/Pictures/watermark/
cp /path/to/original-photos/*.jpg ~/Pictures/temp/
ls -l ~/Pictures/watermark/
-rw-r--r-- 1 gmendoza gmendoza 3311 2007-12-30 17:35 watermark.jpg
ls -l ~/Pictures/temp
-rw-r--r-- 1 gmendoza gmendoza 885788 2007-12-30 17:35 ubuntu1.jpg
-rw-r--r-- 1 gmendoza gmendoza 128922 2007-12-30 17:31 ubuntu2.jpg
Change directories to begin working on your photos.
cd ~/Pictures/temp/
Resizing with “convert”
Let’s say you want to specify a maximum width of 440 pixels (height being adjusted proportionally) in order for you to post the images appropriately within the specifications of your website borders. The syntax would be the following:
convert -resize 440 original-image.jpg new-image.jpg
In this example, we will specify the same name for the output files, which will overwrite the original copies.
convert -resize 440 ubuntu1.jpg ubuntu1.jpg
convert -resize 440 ubuntu2.jpg ubuntu2.jpg
Watermark with “composite”
You will probably want to watermark the images after they have been resized, this way there is no distortion of the watermark, and it is appropriately sized. In this example, we will also set the watermark transparency level to 15%, and overwrite the original file again.
composite -gravity northeast -dissolve 15 ../watermark/watermark.jpg
ubuntu1.jpg ubuntu1.jpg
composite -gravity northeast -dissolve 15 ../watermark/watermark.jpg
ubuntu2.jpg ubuntu2.jpg
Your photos will now have a nice watermark in their upper right hand corners.
Automating the process with a script
You can automate these steps and apply them to a large number of files using a script of course. Feel free to download this one and modify it to your liking.
https://savvyadmin.com/downloads/watermark.sh
#!/bin/bash
WATERMARK="$HOME/Pictures/watermark/watermark.jpg"
echo "*****************************************"
echo "* Image Resize and Watermarking Script *"
echo "* By Gilbert Mendoza - SavvyAdmin.com! *"
echo "*****************************************"
echo " "
for each in ~/Pictures/temp/*{.jpg,.jpeg,.png}
do
echo "Working on "$each" ..."
convert -resize 440 "$each" "$each" >> /dev/null
composite -gravity northeast -dissolve 15.3 $WATERMARK "$each" "$each" >> /dev/null
echo "... Done!"
done
exit 0
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Additional Options
Please check out the ImageMagick website for more information on the many options and features their products have to offer.
http://www.imagemagick.org/script/command-line-processing.php
