Reduce PNG file size for faster page loads and easier sharing.
The business model behind most free compression tools is straightforward: your images are valuable data. Even if a service promises "files are deleted after 1 hour," that's still an hour of server-side access. Some services use uploaded images for training machine learning models. Others embed tracking pixels or metadata extraction. A few have been caught retaining design files that later appeared in stock libraries under different names.
This isn't paranoia — it's the economics of running free infrastructure. Servers cost money. Bandwidth costs money. When a service offers unlimited free compression with server processing, the product being sold is often your content.
Client-side compression eliminates this entire problem structurally. There's no server to store files on. There's no database to breach. There's no terms-of-service clause granting the service a license to your uploads. The compression algorithm runs in your browser's JavaScript engine, reads your file from local memory, processes it, and outputs the result. The architecture itself is the privacy guarantee.
PNG files contain raw pixel data compressed with the DEFLATE algorithm. The file size depends on several factors: image dimensions, color depth, the number of unique colors, whether an alpha channel (transparency) is present, and how well the compressor optimizes its DEFLATE output.
A PNG compressor can attack several of these layers:
The key takeaway: reducing PNG file size isn't a single trick. It's a combination of techniques, and the best tools apply all of them intelligently based on the specific image content.
Not every image benefits equally from compression. Here's where it makes a real difference and where you might be wasting effort:
High-impact scenarios: E-commerce product images with transparency — these are often 2–5 MB each, and compressing 200 products saves gigabytes of bandwidth. Screenshot-heavy documentation and tutorials — screenshots contain large flat-color regions that compress extremely well. App store assets — Apple and Google have strict file-size limits, and every kilobyte counts for load speed. Email attachments — many mail servers reject attachments over 10–25 MB, and PNG-heavy presentations can easily exceed that.
Lower-impact scenarios: Already-optimized PNGs exported from modern design tools — Figma, Sketch, and Photoshop's "Export for Web" already apply significant compression. Photographic content where JPEG or WebP would be a better format choice entirely — PNG was designed for graphics, not photographs. Tiny icons under 5 KB — further compression yields diminishing returns measured in bytes.
The practical question isn't "should I compress my PNGs" but "which of my PNGs haven't been optimized yet." A quick scan of your project's image directory — sorting by file size — will immediately reveal the candidates worth processing. Images over 200 KB with transparency are almost always worth compressing.
Sometimes the best way to make a PNG smaller is to stop using PNG. The format's advantage is lossless transparency and broad compatibility. But if you don't need transparency, or if your audience uses modern browsers, other formats compress significantly better:
The decision tree is simple: need transparency? Use PNG (compressed) or WebP. No transparency, photographic? Use JPEG or WebP. No transparency, graphic with flat colors? Use PNG or WebP. For the broadest compatibility with the smallest file size in 2025, WebP covers nearly every case.
This choice confuses many users, so let's be precise about what each option actually does to your image:
Lossless compression rearranges and encodes the existing pixel data more efficiently. No pixel changes value. The file gets smaller because the encoding is smarter, not because information is removed. Expect 10–30% size reduction on most images. Use this for: medical images, legal documents, technical diagrams, UI elements where pixel-perfect accuracy matters, and any image that might be re-edited later.
Lossy compression actively modifies pixel values — merging similar colors, reducing color depth, or simplifying gradients. The result looks identical at a glance but technically contains different data than the original. Expect 40–80% size reduction. Use this for: web graphics where absolute precision isn't critical, social media assets, hero images, blog post illustrations, and any PNG that will only be displayed on screens (not printed or analyzed at pixel level).
A useful test: zoom to 400% on the compressed image and compare it side-by-side with the original. If you can't spot the difference at that magnification, lossy compression is safe for your use case. If you notice color banding, halos, or transparency artifacts, either reduce the lossy strength or switch to lossless mode.
The lossless image compressor on Pixes.app is specifically designed for cases where you need maximum size reduction without any pixel alteration — supporting PNG along with other formats.