How to Compress PNG Files Online for Free: Lossless, Palette and Best Mode Explained

To compress a PNG online for free, open the PNG Compressor, add your file, and pick a mode: Lossless keeps every pixel identical, Palette rebuilds the image with at most 256 colours for a much smaller file, and Best runs both and keeps the smaller result. Download the single file or a ZIP of a whole batch.

PNG is a wonderful format with one stubborn problem: it is often far heavier than it needs to be. Screenshots exported from design tools, graphics saved from editors that favour safety over size, and logos passed from person to person for years all accumulate wasted bytes. On a single image that waste is invisible. Across a product page, a help centre or a portfolio, it becomes slower loads, heavier pages and visitors on mobile connections waiting for pictures that should have arrived instantly. Compression fixes the waste without asking you to redesign anything — but PNG compression is not one thing, and choosing the wrong mode either leaves most of the saving on the table or quietly damages colours you cared about. This guide explains the three modes in the tool, shows a real worked example from the tool page itself, and gives you a simple rule for deciding.

How to Compress PNG Files Online, Step by Step

1. Open the compressor. Go to the PNG Compressor in your browser. There is nothing to install, and the work happens as a normal browser tool session.
2. Add one file or a batch. Drop in a single PNG or a whole set at once. Batch processing is the practical route for documentation screenshots, icon sets and image folders.
3. Choose your mode. Pick Lossless for pixel-perfect results, Palette for the smallest screenshots and graphics, or Best when you would rather the tool test both and keep the smaller output.
4. Set the lossless effort if you chose lossless. Fast is quick, Balanced is the sensible middle, and Maximum squeezes hardest — the pixels stay identical in all three; only the time spent hunting for a tighter packing changes.
5. Decide on interlacing. Turn the interlaced option on only if you want the image to render in progressive passes on slow connections. For most website images, leave it off.
6. Compress and download. Save the single compressed file, or download the ZIP when you processed a batch. Compare the new size with the original before replacing the live file.
7. Inspect before you ship. Open the result at full size, especially after palette mode, and look at gradients, text edges and brand colours. If anything looks off, fall back to lossless for that image.

The Three Modes, Explained Honestly

Lossless with OxiPNG is the conservative option. OxiPNG re-encodes the image data more efficiently — better filtering, tighter compression — while guaranteeing that the decoded pixels are exactly the original pixels. Nothing is approximated and nothing is thrown away. That guarantee is why lossless savings are real but modest: the tool can only reclaim waste, not information. Use lossless for anything where colour fidelity is non-negotiable: brand assets, medical or technical imagery, screenshots that will be zoomed into, and any file another system will process further.

Palette mode attacks a different source of weight. A standard PNG can store millions of colours, yet most screenshots, diagrams, charts and interface graphics use only a few hundred distinct shades in practice. Palette mode rebuilds the image with a palette of at most 256 colours and stores an index into that palette for each pixel instead of a full colour value. The storage saving is often dramatic, as the worked example below shows. The risk is equally clear: an image that genuinely needs more than 256 colours — soft photographic gradients are the classic case — must approximate the rest, and that approximation can appear as banding in skies or shadows.

Best mode removes the guesswork by doing both. It runs the lossless route and the palette route, compares the two outputs, and keeps the smaller one. For a mixed folder — some flat graphics, some detailed artwork — Best is the mode that respects both your time and your files. You trade a little processing time for never having to predict which approach wins on a file you have not studied.

Question	Choose Lossless	Choose Palette	Choose Best
Must every pixel stay identical?	Yes — this is the only guaranteed route	No — colours are rebuilt	Only if lossless happens to win
Screenshots and interface graphics	Safe, moderate saving	Usually the smallest result	Good default
Logos and flat illustrations	Safe	Usually excellent	Good default
Gradients and photographic detail in PNG	Safest choice	Risk of visible banding — inspect closely	Inspect the winner before use
A mixed batch you cannot review one by one	Safest for the whole batch	Riskiest for the whole batch	Reasonable, with spot checks
File was already exported efficiently	May return it unchanged, byte-for-byte	May still shrink it via the palette	Keeps whichever helps, or the original

Read the worked example carefully, because it teaches the whole decision. The original screenshot weighs 819 KB. Lossless brings it to 707 KB — a genuine saving with zero risk, the kind you can apply blind. Palette brings the same screenshot to 295 KB, less than half the lossless size, because a screenshot is mostly flat areas, text and interface colours that fit comfortably inside 256 colours. Neither result is universally correct. If that screenshot documents a colour-accurate design review, 707 KB with identical pixels may be the right answer. If it illustrates a help article, 295 KB with colours a reader cannot distinguish is obviously better. The tool gives you both numbers; the judgement stays yours.

When PNG Is the Wrong Format Entirely

Sometimes the best PNG compression is not compressing the PNG. Photographs are the clearest case: a camera image or a rich product photograph stored as PNG can weigh several megabytes while a JPG of the same scene looks indistinguishable at a fraction of the size, because JPG was designed for exactly those continuous tones. Our broader guide to compressing images without losing quality walks through matching format to content across a whole page, and the general Image Compressor handles JPG and other formats when PNG is not the right container. PNG keeps its crown where transparency, crisp text, sharp edges and exact colours matter — screenshots, logos, diagrams, icons and overlays. A useful habit when an image arrives in the wrong format is to convert deliberately rather than by accident: our guide to converting WebP to PNG online explains one common direction, including when that conversion helps editing workflows and when it simply makes files bigger. After compression, finishing touches often follow: a compressed screenshot may still need trimming to the relevant area, which is a two-minute job in the Image Cropper before it goes live.

Effort, Interlacing and Already-Optimal Files

Three smaller controls deserve plain explanations. The lossless effort setting — Fast, Balanced or Maximum — changes how hard OxiPNG searches for a tighter encoding. The output pixels are identical at every level; Maximum simply spends more processing time for what is usually a slightly smaller file. Balanced is the right default for batches, Maximum is worth it for a hero image that will be downloaded thousands of times, and Fast suits quick one-off jobs. Interlacing changes the order in which image data is stored so a browser can paint a coarse full image early and refine it. It helps perceived loading for very large images on slow links, but it is a rendering preference, not a diet. Finally, respect the already-optimal result: if a file was exported well, the tool keeps it byte-for-byte instead of inflating it or faking a change. Treat that as a pass, not a failure.

Five Mistakes People Make Compressing PNGs

• Using palette mode on photographic PNGs. Gradients band, skin tones flatten, and the saving could have been larger and cleaner by converting the photo to JPG instead.
• Compressing the only copy. Always work on a copy and keep the original until the compressed version is live and checked. Palette decisions are hard to reverse once the source is gone.
• Never looking at the result. A size number is not a quality check. Open palette results at full size and look at text edges, shadows and brand colours before publishing.
• Compressing a file that is the wrong dimensions. A 3000-pixel-wide screenshot shown at 800 pixels wastes more weight than any compressor can reclaim. Resize or crop first, compress second.
• Expecting every file to shrink. An already-optimal file staying byte-for-byte identical is the tool being honest. Chasing imaginary savings by re-saving repeatedly only risks quality.

Conclusion: Match the Mode to the Image

Lossless when pixels must not move, palette when colours are few and size matters, Best when you want the tool to test both — that single rule covers nearly every PNG you will meet. Compress a copy, check the result at full size, and let photographs graduate to JPG when PNG is simply the wrong container. Start with the PNG Compressor and the worked example above: 819 KB in, and either 707 KB identical or 295 KB leaner out, depending on the choice you make on purpose.

Frequently Asked Questions

What is the difference between lossless and palette PNG compression?

Lossless compression, powered here by OxiPNG, rewrites how the image data is stored without changing a single pixel — decompress it and you get the original back exactly. Palette compression goes further: it rebuilds the image using a palette of at most 256 colours, which is much smaller for screenshots and graphics but can shift subtle gradients. If colour accuracy is critical, choose lossless; if the file is a screenshot or diagram and size matters most, test palette and inspect the result.

What does Best mode do in the PNG compressor?

Best runs both approaches on your file and keeps whichever output is smaller. It saves you guessing in advance: a flat screenshot will usually win with the palette route, while a detailed graphic may win with lossless. You still get a single download, and you can compare its size against the original before you replace anything on your site.

Will compressing a PNG reduce its quality?

In lossless mode, no — every pixel stays identical, only the storage becomes more efficient. In palette mode, quality can change because the colour set shrinks to at most 256 colours. Photographic PNGs and images with soft gradients are the most likely to show banding, which is why the honest workflow is to compress a copy, view it at full size, and only then decide.

Why did my PNG not get any smaller?

Some PNGs are already optimal — they were exported with efficient settings and there is nothing left to reclaim. In that case the tool keeps the file byte-for-byte rather than pretending to improve it or making it larger. A no-change result is useful information: the file was fine, and your time is better spent on the larger images on the page.

Should I use PNG or JPG for photographs?

For most photographs, JPG is the better choice because it is designed for continuous tones and reaches far smaller sizes at good visual quality. PNG earns its place for screenshots, logos, diagrams, text overlays and anything needing transparency. Keeping a photograph in PNG usually means carrying several times the weight for no visible benefit.

What does the interlaced option do?

An interlaced PNG loads in passes, showing a rough version of the whole image first and refining it as more data arrives, instead of revealing it line by line from the top. It can make large images feel faster on slow connections, though the file itself is not necessarily smaller. Leave it off unless you specifically want that progressive rendering behaviour.

Can I compress several PNGs at once?

Yes. The tool accepts a batch of files, compresses each one with the mode you chose, and bundles the results into a single ZIP download. Batch work is where the time saving is real: a folder of screenshots from a documentation project can be processed in one pass instead of file by file.