general

ImageOptim Preferences

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You shouldn't need to change any of these (except path to PNGOUT if you've installed it).

General preferences

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.

Backup original files before saving

Will write copy of a file with ~ appended to its name. This makes optimisation a bit slower and litters your disk with backup files.

Number of tasks run at once

If you have multi-CPU or multi-core system running more than one task at the same time will speed things up a lot.

Run tasks with lower priority

This will prevent whole system from feeling sluggish during optimisation.

jpegoptim

JPEGOptim

Enabled

If checked, will ImageOptim will try to optimize JPEG files.

JPEGOptim path

Path to jpegoptim executable file. Usually /usr/bin/jpegoptim or /sw/bin/jpegoptim.

Maximum quality

If set to 100%, optimisation will be lossless.

Anything below 100% will cause lower quality of files if they appear to have been saved with higher quality setting.

Strip Comments from files
Strip EXIF markers from files

Removes image metadata, like name of program or model of camera which created the file.

advpng

AdvPNG

Enabled

If checked, will ImageOptim will try to optimize PNG files using AdvPNG tool.

AdvPNG path

Path to advpng executable file. Usually /usr/bin/advpng or /sw/bin/advpng.

Optimisation level
AdvPNG is relatively fast, so you can use maximum level.
optipng

OptiPNG

Enabled

If checked, will ImageOptim will try to optimize PNG files using OptiPNG tool.

OptiPNG path

Path to optipng executable file. Usually /usr/bin/optipng or /sw/bin/optipng.

Optimisation level

Number of different setting combinations tested. It rarely makes sense to try them all.

Make images interlaced (progressive)

Interlaced images look better when they're loaded partially, but usually interlace makes compression less efficient.

This checkbox has three states: if checked, will force images to be interlaced. When mixed, it will keep file's interlace unchanged, unchecked will remove interlace from files.

optipng

PNGOUT

Enabled

If checked, will ImageOptim will try to optimize PNG files using PNGOUT.

PNGOUT is not bundled with ImageOptim. It's a great tool, but and author of PNGOUT forbids redistribution of it, so you have to download PNGOUT yourself.

PNGOUT path

Path to pngout (or pngout-darwin) executable file.

Optimisation type

PNGOUT is very effective, but very slow. Use lower level if you're impatient.

Interrupt if takes too long

PNGOUT may need a lot of time to optimize very large images. This option gracefully interrupts PNGOUT after 1 minute.

Remove optional chunks

Keep it on if you optimize for web. Disable if you have special PNGs with extra metadata.