# optipng — Optimize PNG Files Losslessly > Practical guide to optipng: losslessly shrink PNG files – optimization levels, metadata stripping and safe batch runs. Source: https://www.jpkc.com/db/en/cheatsheets/images-media/optipng/ optipng shrinks PNG files **losslessly** – with no quality loss at all: it tries different filter and compression parameters and keeps only the smallest result. By default it works **in-place** and overwrites the original, so a backup belongs before every batch run (or use `-keep`, `-out`, `-dir`). If you need more aggressive savings, reach for pngquant (lossy) or zopflipng (stronger but slower). This guide walks you through the commands you actually reach for daily. ## Basic Optimization `optipng ` — Optimize a PNG file in-place (default level: -o2). ```bash optipng screenshot.png ``` `optipng -o ` — Set optimization level (0-7, higher = slower but smaller). ```bash optipng -o7 screenshot.png ``` `optipng -o2 *.png` — Batch optimize all PNGs in the current directory. ```bash optipng -o2 images/*.png ``` `optipng -out ` — Write to a different file (keep original unchanged). ```bash optipng -out optimized.png original.png ``` `optipng -dir ` — Write optimized files to a separate directory. ```bash optipng -dir optimized/ *.png ``` ## Optimization Levels `optipng -o0 ` — Level 0: no compression trials, just a pass-through (fastest). ```bash optipng -o0 screenshot.png ``` `optipng -o1 ` — Level 1: single compression trial (fast). ```bash optipng -o1 screenshot.png ``` `optipng -o2 ` — Level 2: 8 compression trials (default, good balance). ```bash optipng -o2 screenshot.png ``` `optipng -o3 ` — Level 3: 16 trials (slower, better compression). ```bash optipng -o3 screenshot.png ``` `optipng -o5 ` — Level 5: 48 trials (slow, near-optimal for most images). ```bash optipng -o5 screenshot.png ``` `optipng -o7 ` — Level 7: 240 trials (very slow, maximum compression). ```bash optipng -o7 icon.png ``` ## Metadata & Backups `optipng -strip all ` — Strip all metadata chunks (text, time, ICC profiles, etc.). ```bash optipng -strip all screenshot.png ``` `optipng -keep ` — Keep a backup (.bak) of the original before overwriting. ```bash optipng -keep screenshot.png ``` `optipng -preserve ` — Preserve file attributes (timestamps, permissions) after optimization. ```bash optipng -preserve screenshot.png ``` `optipng -clobber -out ` — Overwrite an already existing output file. ```bash optipng -clobber -out optimized.png screenshot.png ``` ## Format Conversion `optipng ` — Convert BMP to optimized PNG (writes a .png file, keeps the BMP). ```bash optipng screenshot.bmp ``` `optipng ` — Convert GIF to optimized PNG (static GIFs only). ```bash optipng icon.gif ``` `optipng ` — Convert TIFF to optimized PNG. ```bash optipng scan.tiff ``` `optipng -out ` — Convert PNM (PBM/PGM/PPM) to optimized PNG. ```bash optipng -out result.png image.ppm ``` ## Advanced Options `optipng -simulate ` — Simulate optimization (show savings without modifying the file). ```bash optipng -simulate screenshot.png ``` `optipng -v ` — Verbose output (show compression trials and results). ```bash optipng -v screenshot.png ``` `optipng -i 1 ` — Enable Adam7 interlacing (progressive loading). ```bash optipng -i 1 photo.png ``` `optipng -i 0 ` — Force non-interlaced output. ```bash optipng -i 0 screenshot.png ``` `optipng -nb ` — Skip bit depth reduction trials. ```bash optipng -nb screenshot.png ``` `optipng -nc ` — Skip color type reduction trials. ```bash optipng -nc photo.png ``` `optipng -np ` — Skip palette reduction trials. ```bash optipng -np icon.png ``` `optipng -nx ` — Skip all reductions (only re-compress with optimal ZLIB parameters). ```bash optipng -nx screenshot.png ``` ## Common Patterns `optipng -o2 -strip all *.png` — Optimize and strip metadata from all PNGs (best for web deployment). ```bash optipng -o2 -strip all assets/*.png ``` `find . -name '*.png' -exec optipng -o2 -strip all {} \;` — Recursively optimize all PNGs in subdirectories. ```bash find public/ -name '*.png' -exec optipng -o2 -strip all {} \; ``` `optipng -o7 -strip all -preserve icon.png` — Maximum optimization for a single important asset. ```bash optipng -o7 -strip all -preserve favicon.png ``` `find . -name '*.png' -exec optipng -simulate {} \; 2>&1 | grep 'decrease'` — Preview which PNGs can be further optimized. ```bash find . -name '*.png' -exec optipng -simulate {} \; 2>&1 | grep 'decrease' ``` `optipng -o2 -strip all -dir dist/ src/*.png` — Optimize source PNGs into a distribution directory. ```bash optipng -o2 -strip all -dir dist/images/ src/images/*.png ``` ## Conclusion optipng is the go-to tool when PNGs need to get smaller without any quality loss: `-o2` is plenty for everyday work, while `-o7` squeezes out the last bytes for individual important assets. Keep the crucial point in mind: optipng writes **in-place** and overwrites the original – back up your files before batch runs, or use `-keep` (which creates a `.bak`), `-out` or `-dir`. If you need even smaller files and can accept minimal color loss, pngquant adds lossy quantization; zopflipng compresses losslessly a touch harder still, but is markedly slower. ## Further Reading - [optipng — Official project page](https://optipng.sourceforge.net/) – documentation, manual and downloads of the original project - [Wikipedia: OptiPNG](https://en.wikipedia.org/wiki/OptiPNG) – background on the lossless PNG optimizer ## Related Commands - [pngquant](https://www.jpkc.com/db/en/cheatsheets/images-media/pngquant/) – lossy PNG quantization for even smaller files - [jpegtran](https://www.jpkc.com/db/en/cheatsheets/images-media/jpegtran/) – lossless optimization and transformation of JPEG files - [convert](https://www.jpkc.com/db/en/cheatsheets/images-media/convert/) – convert and edit images with ImageMagick