# ImageOptim Preferences

« Back to index

## General preferences

Strip PNG metadata (gamma, color profiles, optional chunks)

  PNG files can have different brightness and saturation in different browsers, because not all browsers support gamma correction and color profiles features equally. Removal of this information makes PNG color more consistent across browsers and reduces file size.

  Other invisible information is removed as well, such as DPI and comments.

Strip JPEG metadata (EXIF, color profiles, GPS, rotation, etc.)

  Removes image metadata, such as color profile, exposure time, GPS coordinates, camera model and name of software used to create the file.

  Embedded copyright information is removed as well. Please note that generally images are protected by copyright law regardless whether they contain such invisible metadata or not.

Preserve file permissions, attributes and hardlinks

  Instead of deleting old file writing a new one with the same name, just replaces old file's content in-place. This ensures that all hardlinks, aliases, file ownership, permissions, extended file attributes will stay the same.

  It's slightly faster not to preserve permissions.

### Tools

Zopfli and PNGOUT are very good PNG compressors, but are very slow. Disable them if you need to optimize PNG files quickly (leave only AdvPNG for fastest, but still good compression).

Zopfli and OxiPNG will clean RGB values of transparent pixels (known as “dirty alpha”). Disable these two tools if you're optimizing special files that use alpha channel for something else than transparency (e.g. heightmap in game data files).

SVGO works only if you have Node.js installed using the official installer or Homebrew (nvm is not supported).

## Quality

Lossy minification

  If lossy minification is off, optimization will be lossless. Pixels won't change and optimizations will only remove invisible metadata. This gives larger files, but is safe to run on any file any number of times.

  If lossy minification is on, then images with quality higher than configured, will be converted to have lower quality. This usually gives images that still look good, and gives much much smaller files.

## Optimization level

At fastest level optimizations will take only few seconds per image. Fast setting is recommmended for MacBook Air and older Macs.

Slower levels compress a little better, but take much more time. Large PNG files may take several minutes to compress.

The slowest level is very very slow, even on the fastest Mac available.