How PNG compression differs from JPG
PNG stores images losslessly: every pixel after unpacking matches the original bit for bit. That is why classic lossy compression does not apply - instead, the file is optimized: a more efficient way of writing the same pixels is found.
The result: the picture is identical to the source - text stays crisp, edges stay sharp, a transparent background stays transparent. Only the file itself gets lighter.
How optimization works
A PNG optimizer does three things. First, it picks the best row filter: PNG stores pixels as differences, and the formula behind those differences directly affects how tightly they compress. Second, it tries multiple data-packing parameters and keeps the most compact one. Third, it shrinks the description of the picture itself: if an image uses 16 bits per channel where 8 are enough, or claims millions of colors while only 200 are actually used, the file is converted to a smaller depth with no visible change whatsoever.
A file that was already optimized may not shrink - in that case you get the original back with a warning. The service never returns a "compressed" file that weighs the same or more than the input.
What is preserved
- Every pixel: the unpacked picture is identical to the original.
- Transparency: semi-transparent edges and compositing on any background work exactly as before.
- Metadata: the color profile and other information remain in the file.
Who needs this
Screenshots are a classic heavy PNG: an interface with large flat areas compresses several times over. Logos and icons with transparency lose weight while staying perfectly sharp on any background. Diagrams, charts and text-heavy graphics - everything where a blurry JPG is unacceptable - gets lighter with not a single pixel changed.
For a web developer, PNG optimization is the cheapest way to speed up a page: load time drops while the site looks exactly the same.
PNG or WebP: what to choose for a website
If the graphics go onto a web page, compare the optimized PNG with a WebP version of the same image: the newer web format usually wins another 20-30% of weight at the same quality. An optimized PNG remains the universal answer where compatibility with older software matters or pixel-perfect transparency is required; WebP is the answer for page speed. The two paths do not exclude each other: optimize the PNG for the archive and compatibility, and ship WebP to visitors.
A photograph saved as PNG (which happens after editor exports) is worth converting to another format altogether: inside PNG a photo takes several times more space than in a format designed for photographs. Change the format first, optimize second - the order that gives maximum savings.
What is PNG to PNG conversion used for
Screenshots for documentation
Guides and knowledge bases are full of 2-5 MB screenshots. Optimization cuts their weight several times while the text on them stays perfectly crisp.
Logos with transparency
A website logo has to be sharp on any background. An optimized PNG weighs less and its transparent edges stay smooth.
Speeding up a website
Icons, banners and graphics are a constant part of web pages. Every kilobyte saved is a faster page and a better search score.
Email and form attachments
Forms often cap the file size. An optimized PNG passes the limit without losing a single pixel.
Tips for converting PNG to PNG
For photos, use JPG or WebP
PNG is meant for graphics and screenshots. A photograph stored as PNG is usually better converted to another format - the weight savings are far greater.
Optimize before uploading to your site
An image optimized once is served to thousands of visitors. It is the cheapest traffic saving on the entire site.
Check transparency after color reduction
Optimization may reduce the number of colors in the file. If a logo with semi-transparent edges will sit on a dark background - test it on several backgrounds before publishing.