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PNG Optimizer: Lossless Compression, Same Pixels

Shrink PNG files losslessly with oxipng. Same pixels, fewer bytes via smarter filtering and DEFLATE. Runs in your browser, no uploads, no quality loss.

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How It Works

A PNG from a screenshot tool, a design export, or a build step usually weighs more than its pixels require. The image data is fine; the encoder was lazy about packing it. This tool runs oxipng on your file to fix exactly that. It re-tries the per-row filters (None, Sub, Up, Average, Paeth) to find the combination that compresses best, then re-runs DEFLATE with settings most exporters never bother to crank up. Same picture, fewer bytes. It is genuinely lossless. Every output pixel, including the full alpha channel, is bit-for-bit identical to the input. There is no quality slider, no canvas round-trip, no quantization. Nothing gets dithered, no colors are dropped, no transparency is flattened. Open the before and after side by side and you will not find one changed pixel, only a smaller file. Everything runs locally. Your PNG is read into memory, optimized in the browser via WebAssembly, and handed back as a download. It never touches a server, so client logos, internal screenshots, and unreleased assets stay on your machine. How much you save depends on how wastefully the original was written: files from naive exporters drop a lot of weight, files already squeezed by another optimizer barely move.

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MorePNG

png → avifpng → base64png → jpegpng → jxlpng → pdf

Convert toOPTIMIZER

image optimizerjpg optimizerwebp optimizer
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Key Features

  • No file uploads required - works offline
  • 100% privacy focused - client-side processing
  • Browser powered - no software installation
  • Fast processing - WebAssembly technology
  • Free forever - no premium accounts

Supported File Formats

.png

Output Format: PNG Optimized

Technical Specifications

input Format PNG (Portable Network Graphics), any color type and bit depth up to 16-bit
output Format PNG, re-encoded losslessly with identical pixel data
compression Type Lossless: oxipng filter selection plus stronger DEFLATE recompression
quality Retention 100% lossless, output pixels are bit-for-bit identical to input
color Space Support Indexed/palette, grayscale, and RGB/RGBA preserved unchanged
max Resolution Limited only by your device's memory
processing Time Instant, runs in your browser

Key Benefits

  • True lossless result: every pixel and alpha value identical to the original
  • Smaller PNGs from smarter filter selection and DEFLATE, not quality cuts
  • Runs 100% in your browser, files never leave your device
  • Transparency, palettes, and bit depth preserved exactly
  • Safe for client logos, brand assets, and unreleased screenshots
  • Faster page loads and lower bandwidth with zero visual change

Common Use Cases

  • Shrinking screenshot-tool PNGs before attaching them to docs or tickets
  • Optimizing logos, icons, and UI sprites with transparency for the web
  • Trimming design-export PNGs that came out heavier than expected
  • Cutting build-pipeline image weight without touching quality
  • Compressing diagrams and charts for documentation and slide decks
  • Reducing PNG payload on image-heavy pages to help Core Web Vitals

Pro Tips

  • Best gains come from PNGs written by basic exporters or screenshot tools
  • Already-optimized PNGs may barely shrink; that is expected with lossless tools
  • For photographs, convert to WebP or use the JPG optimizer instead
  • Run this as the last step before shipping assets to the web
  • Compare original and output in a viewer to confirm the pixels are unchanged

Frequently Asked Questions

No. This is lossless optimization, not lossy compression. oxipng repacks the same pixel data with better filtering and DEFLATE settings, so every RGB value and every alpha value in the output matches the input exactly. The only thing that changes is the file size.
The JPG optimizer re-encodes photos and discards detail your eye is unlikely to notice, trading some quality for size. This PNG optimizer discards nothing. PNG is a lossless format, so it only strips encoding overhead and recompresses the existing data. Use this for graphics, screenshots, and anything with transparency; use the JPG optimizer for photographs.
It was probably already well compressed. If a file was exported by a tool that runs zopfli or oxipng itself, there is little waste left and the savings are small. The biggest wins come from PNGs written by basic export functions, game engines, or screenshot utilities that favor speed over file size.
Yes, completely. The alpha channel is part of the pixel data oxipng preserves exactly. Transparent backgrounds, soft edges, and semi-transparent overlays come out identical to the original, so logos and UI assets keep their cutouts intact.
No. The optimizer runs entirely in your browser using WebAssembly. Your PNG is processed in local memory and never sent to a server, which is why it works on confidential assets and keeps working even if you go offline after the page loads.
Yes. oxipng handles indexed (palette) PNGs, grayscale, and truecolor, with bit depths up to 16 bits per channel. It optimizes the encoding of whatever color type your file uses without altering the displayed image.
The job here is faithful, lossless re-encoding of the image data, not metadata curation. If your workflow is color-managed, treat embedded ICC profiles as something to verify: open the result and confirm it renders correctly before shipping print or brand assets.
The practical limit is your device's available memory, since the whole image is decoded and processed in the browser. Screenshots, icons, and web graphics are no problem. Very large multi-megapixel PNGs work too; they just take longer and use more RAM.