Image Optimizer

Make PNG and JPEG files smaller without touching how they look. Drop a folder in, and every file is rewritten in place with identical pixels and a smaller size.

flatpak install flathub com.github.gijsgoudzwaard.image-optimizer   # any distribution
sudo snap install image-optimizer                                   # Ubuntu and anywhere snaps run

Both stores publish for amd64 and arm64, and both bundle the optimizer, so there is nothing else to install.

Lossless means the pixels come out identical. Nothing is re-encoded at a lower quality, so there is no visible trade-off, and equally no magic: what comes off is whatever the encoder left on the table.

How much that is depends entirely on the file.

Every one of those was compared against its input pixel by pixel afterwards, and came back identical.

The pattern is worth knowing before you try it. Anything flat, exported as a 24-bit PNG by a design tool, gives the most, because those files carry a full colour channel they never use. Screenshots give a quarter or so. Photos are already close to optimal, so a few percent is a good result there and not a disappointment.

The screenshot above is a folder of 26 exported assets of that first kind, which came to 2.2 MB and left as 950 kB. An image that is already optimal comes back untouched, and the app says so rather than pretending it did something.

• It rewrites the file you picked. No copy next to it, no -optimized suffix, and the modification time is kept, so optimizing a folder does not reshuffle a photo library sorted by date.
• It keeps what an image needs to look right. The ICC colour profile stays, because dropping it makes a wide-gamut image render as sRGB afterwards, and so does Exif, because that is where the orientation flag lives and a phone stores a portrait photo as a landscape image plus that flag. A PNG that says nothing at all about its colours is stripped, because there the saving is free, and a JPEG keeps everything it came with. That costs very little: measured on a photo with Exif, 240 bytes out of 39 kB.
• It never sends your images anywhere. No account, no upload, no network access at all. On Flathub the app holds three permissions in total, and not one of them is filesystem access: files reach it through the desktop portals, so it can open the file you pointed at and nothing around it. You can check that yourself under Permissions on its Flathub page.
• It does the whole batch at once, several files in parallel, one worker per core.
• It tells you what happened to each file: how much came off, or that there was nothing left to remove, or why it could not be written.

PNG and JPEG. Anything else keeps a row in the list saying it is not supported, rather than disappearing without a word.

Bug reports, translations and pull requests are all welcome. The issue tracker is the place to start.

You need GTK 4.12 or newer, GLib, a C compiler, Vala, Meson, Ninja, msgfmt and update-desktop-database. On Ubuntu 24.04 and other Debian derivatives:

sudo apt install build-essential meson ninja-build valac gettext \
                 desktop-file-utils libgtk-4-dev libglib2.0-dev libxml2-utils
sudo apt install appstream xvfb xdotool     # optional, see below

The app shells out to Efficient Compression Tool to do the actual optimizing, so you need that on your PATH to run it. It is not packaged for Debian or Ubuntu, and its libpng and mozjpeg are git submodules, so it is built from source:

sudo apt install cmake nasm
git clone --recursive https://github.com/fhanau/Efficient-Compression-Tool
cd Efficient-Compression-Tool
cmake -S src -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j"$(nproc)"
sudo cmake --install build

Install the optional three before configuring, because Meson looks them up once at that point. appstream adds the MetaInfo validation to ninja test, which otherwise runs one test instead of two. xvfb and xdotool are for the scripts below.

meson setup build --prefix=/usr
ninja -C build test
sudo ninja -C build install
com.github.gijsgoudzwaard.image-optimizer

ninja test covers the desktop and MetaInfo files. Two more scripts run the real binary, because a build that compiles is not the same as an app that works: the GTK4 port of the image list once did the former without the latter.

DESTDIR="$PWD/dest" ninja -C build install
.github/scripts/smoke-test.sh dest/usr/bin/com.github.gijsgoudzwaard.image-optimizer
.github/scripts/regression-test.sh dest/usr/bin/com.github.gijsgoudzwaard.image-optimizer

smoke-test.sh starts the app on a virtual display, hands it a PNG and a JPEG, and requires them to come back smaller with nothing logged. regression-test.sh covers what has actually broken before: awkward filenames, unreadable files, whole batches being skipped, parallel output matching sequential, a single core machine, read-only files and directories, a second pass over an already optimal file, colour profiles and Exif surviving, modification times surviving, an optimizer that is not installed, and Ctrl+Q. A few of its checks point the app at a stand-in optimizer instead of the real one, because what they are about is what the app does with the answers it gets, and that should not depend on how the real one happens to behave that day. Both run in CI on amd64 and arm64, so a pull request gets the same answer you do locally.

Image Optimizer is free and open source. If you find it useful, you can support its development with a one-off or recurring donation.

Released under the MIT License.