Optimize uploaded images

Users can upload images for applications. Large images are not rescaled by Gotify and can take up unneeded disk space and network bandwidth. The script below will rescale (resize) all images in their maximum dimension, i.e. width and/or height, to 512 pixels. Images that are smaller will not be rescaled.

PNG images will be optimized in file size without reduction of quality.

Once a file has been rescaled/optimized, it will not be rescaled/optimized again later.

Prerequisites

Install

Script

Create a script, e.g. /opt/gotify/optimize-images.sh containing

#!/usr/bin/env bash
set -e

DATA=/home/jm/src/gotify/server/data

for FILE in "$DATA"/images/*; do
    if [ "$FILE" -nt "$DATA"/images-optimized ]; then
        EXT=$(echo "${FILE##*.}"|tr '[:upper:]' '[:lower:]')
        if [ "$EXT" = png -o "$EXT" = jpg -o "$EXT" = jpeg  -o "$EXT" = gif ]; then
            convert "$FILE" -resize "512>" "$FILE"
        fi
        if [ "$EXT" = png ]; then
            optipng "$FILE"
        fi
    fi
done
touch "$DATA"/images-optimized

Note that if $DATA/images-optimized is missing, all files are selected for rescaling and optimization.

Run the following command on the script

sudo chmod go-rw /opt/gotify/optimize-images.sh
sudo chmod u+x /opt/gotify/optimize-images.sh

The script can be tested by running it manually. Having a backup of the data directory before doing that is always wise.

Scheduling

Add the following line to a file in e.g. /etc/cron.d/gotify

12  12  * * *   root    /opt/gotify/optimize-images.sh