ImgZilla 1.3 Officially Released: A "Lossless In-Place Image Compression" Tool, Why It Took So Long

ImgZilla is now available on the Mac App Store.

Its core function is clear: compress images on your Mac in place—file names, paths, and formats remain unchanged, and the originals go to the Trash by default, so you can restore them anytime.

All operations are completed locally on your Mac, with no network required. Images never leave your computer and are never uploaded to any server—privacy and data security are fundamental from the start.

This function may seem simple, but we repeatedly tested, revised, and rebuilt it many times. This article is not about "what features we built," but about specific problems encountered in real-world usage and how we ultimately resolved them.

"In-Place Overwrite"—No Room for Carelessness

Most image compression tools save results as photo-min.jpg—safe, but the hassle is left to you: the file name changes, and references in product lists, paths in web templates, and sorting in archival directories all need updating.

ImgZilla chose a different path: compression results are written directly back to the original path, file name, and format. After compression, a JPG remains a JPG, and no references need changing.

The trade-off is: this tool works with your original files. If any step goes wrong, it's not the cache you lose, but photos someone spent an entire day shooting or a collection built over years.

So the real effort in the product is never about the compression itself—mature encoders handle that—but the safety net around "what if." The following improvements all came from real testing.

Things Changed During Testing

1. Original Protection Strategy, Revised Once

The initial design copied originals to a dedicated backup directory. The logic was sound, but it was awkward: the backup directory grew silently, and after months of compression, users would discover a full duplicate copy on the disk, when the original goal was to save space.

The current approach is Trash first: upon successful compression, the original is moved to the system Trash, then the compressed result is written back to the original path.

Restoration is now an operation every Mac user already knows—open the Trash, right-click "Put Back." No new concepts to learn, no ever-growing hidden directory. This option is enabled by default in settings; turning it off means direct overwriting without recovery, so a secondary confirmation dialog pops up when disabling.

2. That Dialog for External Drives, Forced by Testing

When testing on external drives, NAS, or network volumes, we encountered a common macOS issue: these locations often cannot move files to the Trash.

The first version just displayed an error and skipped—the result was that when users dragged in a whole folder, nothing happened.

Now the handling is: compression pauses, and a dialog asks you to decide:

Choose a backup directory: the original is copied there, then overwritten;
Skip backup: after a secondary confirmation, directly overwrite without keeping a copy;
Close dialog: treated as cancel, the entire task stops.

One detail added during testing: your choice applies to all remaining files in this batch, otherwise 500 images would trigger 500 dialogs—the first version did that, and we couldn't stand it after one use.

The chosen backup directory is recorded as the default backup location (subdirectories created by timestamp under ~/Library/Application Support/ImgZilla Backups/), and will be used preferentially for similar situations later.

3. "Already Minimized": Better to Do Nothing

Some images have already been compressed before being dragged in (whether by other tools or earlier by ImgZilla), and compressing them again usually yields only a fraction of a percent size reduction. We set a hard rule: if the compression ratio is less than 0.4%, leave it alone, mark it as "Already minimized" in the list, keep the original file as is, and don't consume any free quota.

This rule makes the stats less impressive—drag in a whole already-compressed album, and most might show "Already minimized." But we believe a tool that would re-compress your images just to show a number isn't worthy of touching your originals.

4. When File Extensions Lie

In our test samples, there were many files with a .png extension that were actually JPEGs—images passed through various channels, more common than you'd think.

Now ImgZilla reads the magic bytes of the file header to determine the true format and selects the encoder based on that. Even with wrong extensions, it processes correctly.

5. Serial Processing, Not Parallel

Processing one by one seems "not fast enough." We tried parallel processing, and it was indeed faster, but when errors occurred in large batch tasks, the state became hard to track—and this tool is overwriting users' original files.

Stability outweighs peak speed, so we kept serial processing. Note that "serial" means tasks are processed one by one, but the compression of each image itself uses multithreading internally by the encoder, not wasting multi-core CPU power. As UI compensations, we added: auto-scrolling the current item into the visible area, pausing auto-scroll on mouse hover, real-time display of processed count and space saved at the bottom, and a system notification when all tasks are complete.

6. When Free Quota Runs Out, Tasks "Pause" Not "Abort"

The free version allows 10 images per day, resetting automatically at midnight. During testing, we found that where you get interrupted makes a huge difference: if you drag in 200 images and it fails and exits after the 10th, users have to re-add all files—then this prompt becomes pure annoyance.

Now it behaves: when quota is exhausted, the task pauses where it is, and a purchase panel appears. After purchase, it resumes from the breakpoint and continues with the remaining files, without re-adding anything. Also, the quota is only deducted upon successful compression—failures or "Already minimized" don't count.

7. 19 Language Options, and a Less Obvious Finishing Touch

The interface fully supports 19 language options (including "Follow System," Simplified and Traditional Chinese, English, Japanese, Korean, major European languages, Arabic, Vietnamese, etc.), switchable at any time in settings, effective immediately without restarting.

The effort involved far exceeded expectations and was one reason for the delayed release. But for a tool on the global App Store, letting users see their native language is basic respect.

Regarding Image Quality: Don't Trust Us, See for Yourself

The hardest thing about compression is building trust. So let's be clear:

PNG (oxipng) and SVG (svgcleaner) are truly lossless—pixels remain unchanged;
JPEG, WebP, AVIF, HEIC/HEIF, GIF are inherently lossy re-encodings, but parameters are chosen in the visually lossless range—almost indistinguishable to the naked eye, but it's not "lossless," and we won't conflate the two terms.

Also, you don't have to accept this on trust. ImgZilla includes an image comparison window (⌘D): left side before compression, right side after. Drag the dividing line to compare side by side, zoom to actual size, and examine details closely. For each successfully compressed image in the list, you can bring up the comparison with one click.

If it doesn't look good, go to the Trash and put the original back. That escape hatch is always there.

Parameters are fixed; there's no quality slider on the interface. This is a deliberate trade-off: tweaking parameters requires understanding quantization tables, encoding methods, speed, and other technical concepts—get it wrong and you either waste time or blur images. We've done that for you—each format's parameters have been individually tuned. Drag in, click compress, and you get the optimal balance for that format under these parameters.

If you're used to adjusting compression settings yourself, we still recommend trying ImgZilla—the parameters are already tuned, perhaps saving you the effort of trial and error.

What It Doesn't Do

Equally important boundaries, listed here to save you from discovering them after downloading:

macOS only (12.3 and above). No Windows version, no iOS version, no web version.
No format conversion. After compression, a JPG remains a JPG, not turned into WebP.
No resizing. No scaling resolution, no cropping.
No guarantee of size reduction. Already optimized images may not compress at all and will be honestly marked "Already minimized."
EXIF removed by default (including GPS location, smaller files and more private). If you need to preserve shooting parameters, copyright, and color profiles, go to settings and manually enable "Keep EXIF data".

And one point worth emphasizing separately: all compression is done locally on your Mac. Apart from App Store purchase verification, ImgZilla requires no network; images never leave your computer—no queuing, no file count limits, and no "uploading to someone else's server." Encoders are all packaged as local static libraries within the app.

Ready to Start Using

Free version: 10 images per day, reset automatically at midnight, no feature cuts.
Unlock unlimited: perpetual license (one-time purchase, no limits) or monthly subscription, price shown in your App Store region. If you switch computers or reinstall, just click "Restore Purchase."

Recommended first use: casually drag an image you don't care much about, compress it, click "Compare" to see the quality, then decide if you want to hand over your whole folder.

This is how we hope this tool is used—verify first, then trust.

For any questions or suggestions, please use the menu "Help → Feedback" to tell us. 1.3 is a version you can rely on, but it's clearly not the last.

ImgZilla 1.3 is now available on the Mac App Store. Requires macOS 12.3 or later.

Download now -> App Store