Lossless PNG, JPEG and GIF image optimization / compression for Windows and Linux.
 |
 |
|---|---|
| Adobe Photoshop CC 2015 (Export as) — 56.10 KB | Image Catalyst (Xtreme) — 51.25 KB |
Version 3.0 is a rewrite. The orchestrator moved from a 1300-line Windows batch script to a Python 3 core, which is what makes Linux support possible and what kills a long-standing bug where files with national characters in their names were silently skipped. Version 2.7 is still in this repository and still works; see Migrating from 2.7.
Image Catalyst compresses nothing itself — it orchestrates well-known optimizers
and keeps whichever result is smallest. Run icatalyst --doctor to see exactly
which ones were found on your machine and the exact commands that will be run.
- oxipng, OptiPNG, Zopfli (
zopflipng), AdvanceComp (advdef) - Windows additionally: TruePNG 0.6.2.2, DeflOpt 2.07, pngwolf-zopfli
- MozJPEG or libjpeg-turbo (
jpegtran)
- Windows 10 or newer. A release build of
iCatalyst.exeneeds nothing else. Running from source needs Python 3.9+. (Version 2.7 supported Windows XP SP3; 3.0 does not, because Python 3.9 does not.) - Linux: Python 3.9 or newer, plus the optimizers:
sudo apt install optipng zopfli advancecomp gifsicle libjpeg-turbo-progs make tools # downloads oxipng, verifying its SHA-256make aptprints the exact package line for your distribution's naming, andmake checktells you what is still missing and what it costs you.
- Windows: drop folders or files onto
iCatalyst.exe, or ontoiCatalyst-3.batwhen running from source. - Linux: install
icatalyst.desktop(cp icatalyst.desktop ~/.local/share/applications/) and drop folders onto its icon, or use "Open With" in your file manager. - Images in sub-directories are optimized recursively.
- Any characters are allowed in paths — national alphabets, spaces, punctuation, emoji. This is the main behavioural change from 2.7.
icatalyst [options] [add directories \ add files]
Options:
/png:# PNG optimization mode (Non-Interlaced):
1 - Compression level - Advanced
2 - Compression level - Xtreme
0 - Skip
/jpg:# JPEG optimization mode:
1 - Encoding Process - Baseline
2 - Encoding Process - Progressive
3 - use settings of original image
0 - Skip
/gif:# GIF optimization mode:
1 - use settings of original image
0 - Skip
"/outdir:#" image saving options:
true - ask where to save images (default)
false - replace original image with optimized
"full path to directory" - specify directory to save images to.
If the destination directory does not exist, it will be created.
Additional options (new in 3.0):
--verify compare PNG pixel data before and after (slow, thorough)
--strict-lossless forbid changing RGB under fully transparent pixels
--threads N number of parallel jobs (0 or absent = CPU count)
--stream print rows in completion order instead of input order
--tsv machine-readable output instead of the table
--doctor show which tools were found and what will be run
--picker NAME auto, tk, zenity, kdialog, osascript, terminal or none
--config FILE use this config.ini instead of Tools/config.ini
--width N force table width
--no-pause do not wait for a key press at the end
Examples:
icatalyst /gif:1 "/outdir:/home/user/photos" "/home/user/images"
icatalyst /png:2 /jpg:2 "/outdir:true" "C:\images"
If a mode is not given on the command line, Image Catalyst asks — but only for formats actually present in the input, exactly as 2.7 did.
Pixels and alpha are never altered, with one deliberate exception that has been
the shipped default since 2.7: xtreme=/a1 in Tools/config.ini permits
rewriting the RGB values underneath fully transparent pixels. Such pixels are
invisible, so the image is visually identical, but the file is not byte-identical
in the pixel data. Pass --strict-lossless to forbid it.
Measured on 60 already-optimized system icons: --strict-lossless cost nothing
at all — it actually compressed marginally better (−8.73% vs −8.65%), because
the "dirty transparency" heuristic is not always a win and the candidate race
picks whichever result is smaller.
Every result is checked before it is accepted: the file must decode, keep its dimensions, keep its critical chunks, and be strictly smaller than the input. If it is not, the original is kept untouched.
| Advanced | Xtreme |
|---|---|
| Structural optimization plus one deflate pass. Seconds per image. | Exhaustive structural search plus Zopfli-class compression. 5–15× slower, a few percent smaller. |
Both modes race several independent chains and keep the smallest result, so adding a tool can only improve the outcome, never worsen it. Xtreme is guaranteed never to produce a larger file than Advanced.
Interlaced output is not supported; interlaced input is read correctly and
written non-interlaced.
| Baseline | Progressive |
|---|---|
| For images < 10 KB (read more) | For images > 10 KB (read more) |
Default keeps whatever the original used. JPEG optimization is a lossless
coefficient transform: jpegtran never re-encodes pixel data.
PNG output is not byte-identical between Windows and Linux, and cannot be: TruePNG and DeflOpt are closed-source Windows-only freeware with no equivalents. Neither platform's output is "the correct" one; both are lossless.
| Step | Windows | Linux |
|---|---|---|
| PNG Advanced | TruePNG → DeflOpt → advdef → DeflOpt ‖ oxipng | optipng → advdef ‖ oxipng |
| PNG Xtreme | TruePNG → pngwolf (Zopfli) → DeflOpt ‖ oxipng | optipng → zopflipng ‖ optipng → advdef ‖ oxipng |
| JPEG | MozJPEG jpegtran |
libjpeg-turbo jpegtran; MozJPEG optional via make tools-build, worth 2–4% on progressive |
| GIF | gifsicle | the same gifsicle, the same flags |
| Folder dialog | native Windows dialog | zenity, kdialog or a terminal prompt |
‖ means the chains are raced and the smaller result wins.
Tools/config.ini keeps every key it had in 2.7 — existing configurations work
unchanged. New optional keys: profile (auto/windows/posix), timeout,
picker, preserve_mtime, xtreme_iterations, and platform-neutral equivalents
of the TruePNG flag strings (gamma, keep_colortype, keep_bitdepth,
keep_palette, advanced_dirty_transparency, xtreme_dirty_transparency).
pngtags/jpegtags/giftags additionally accept keep-icc, which preserves
colour profiles that true would strip.
The file is never rewritten by the program.
Both implementations currently live side by side. iCatalyst.bat is still
version 2.7 and still works; the new core is python3 -m icatalyst, or
iCatalyst-3.bat on Windows. The legacy files will be removed only after the
parity-windows job in CI confirms on real binaries that the new core compresses
no worse.
Behavioural changes worth knowing about:
- Paths with any characters now work. In 2.7 a folder named
Фото — копияsilently lost its entire contents, because the em dash does not exist in cp866. - A GIF's loop count survives metadata removal. In 2.7
giftags=truepassed--no-extensionsto gifsicle, which dropped the NETSCAPE extension and turned an infinitely looping GIF into a play-once one. - Interrupting with Ctrl-C now stops promptly and never leaves a truncated file.
- Two input files with the same name no longer overwrite each other in the output directory.
- Modification times are preserved by default (
preserve_mtime=falserestores the old behaviour). - A batch run with no
/outdirand no terminal to ask in now stops with an error instead of silently overwriting the originals.
- By default optimization runs in parallel, one job per CPU core. Use
--threads Nor thethreadkey inconfig.inito change that. Measured on 16 cores: 177 s → 38 s, with byte-identical output. - To pause on Windows, click the right mouse button in the console window and choose "Select all"; click again to resume.
Nothing needs to be built to use Image Catalyst from source — it is plain Python. The build targets exist to produce distributable artifacts:
make deb # .deb package, checked with lintian
make binary # self-contained Linux executable (no Python needed to run it)
make exe # iCatalyst.exe (Windows only)
make tools # download prebuilt optimizers, verifying their SHA-256
make test # the full test suite; passes with no optimizers installed
make binary and make exe use PyInstaller, which is a build-time
dependency only — the program itself never needs anything beyond the standard
library. On Ubuntu 24.04 and newer, PEP 668 forbids installing into the system
Python, so make binary creates its own virtual environment.
GitHub Actions builds all of this on a tag, but only after the test suite and the 2.7 parity harness are green: attaching a package built from knowingly broken code to a release is the worst outcome available here. Releases are created as drafts so the artifact list can be looked at before publishing.
| Artifact | For whom |
|---|---|
icatalyst_<version>_all.deb |
Debian, Ubuntu, Mint — installs the command, the menu entry, the man page, and pulls the optimizers in via apt |
iCatalyst-<tag>-linux-x86_64.tar.gz |
other distributions, or running without installing anything |
iCatalyst-<tag>-windows-x86_64.zip |
Windows: iCatalyst.exe plus the bundled optimizers next to it |
iCatalyst-tools-linux-x86_64.tar.gz |
prebuilt MozJPEG, pngwolf and oxipng, so Linux users need not compile |
third-party-sources.tar.gz |
corresponding sources of the GPL components, as their licenses require |
Artifacts are attached to a draft release, and only when there is a tag to attach them to: either the workflow was triggered by pushing a tag, or a tag was supplied to a manual run. A manual run without a tag still builds everything and leaves the artifacts on the run page — that is what it is for. The run summary states which of these happened, so a skipped publish step never has to be guessed at.
- Thanks to the authors of the applications that are used in the project;
- Thanks to the participants of encode.ru, forum.ru-board.com, forum.script-coding.com, forum.vingrad.ru and cyberforum.ru for contribution to the development of the project;
- Thanks X128 for his huge contribution to the development of the project.
This software is released under the terms of the MIT license. Third-party components and their licenses are listed in THIRD-PARTY.md.
- add support of optimization of SVG;
- add support of optimization of PNG and JPEG lossy.