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Robin Image Optimizer - Settings Reference ​

Robin Image Optimizer is a WordPress plugin that compresses and converts images in your media library to reduce file sizes and improve page load times. You find all settings under Robin Image Optimizer > Settings in the WordPress admin sidebar, with the main bulk optimization dashboard accessible under Robin Image Optimizer > Optimize.

Settings ​

The Settings page contains all plugin configuration options organized into three sections: Main Settings, Optimization, and Scheduled and background optimization. Click Save Changes at the bottom for settings to take effect.

Main Settings ​

Compression mode ​

Controls how aggressively the plugin compresses your images. The available modes are:

  • Lossless — optimizes images without any visible quality loss. File sizes are reduced by approximately half. This is the default and recommended mode if image quality is your top priority.
  • Lossy — provides stronger compression with a slight decrease in quality that is usually not noticeable to the naked eye. File sizes are reduced by approximately five times.
  • High — applies maximum compression for the smallest possible file sizes, roughly seven times smaller than the original. Some images may show visible quality degradation. Use this when file size matters more than perfect quality.
  • G PageSpeed — uses compression settings optimized for Google PageSpeed Insights scoring.
  • Custom — lets you set your own compression quality value. When selected, an additional field appears where you enter a number between 1 and 100.

Enter custom quality ​

This setting only appears when Compression mode is set to Custom.

Sets a custom compression quality from 1 (maximum compression, lowest quality) to 100 (minimal compression, highest quality). The default is 70, which provides a reasonable balance between file size and visual quality.

Auto optimization on upload ​

When enabled, the plugin automatically compresses every image you upload to the WordPress media library, including images added through the post editor or by themes and plugins. When disabled, images are only optimized when you run bulk optimization manually or on a schedule.

Backup images ​

When enabled, the plugin saves a copy of every original image in a separate backup folder before optimizing it. This lets you restore originals later if you change your mind or want to re-optimize with different settings. Enabled by default, and it is strongly recommended to keep this on unless you are confident in your compression settings and need to save disk space.

Error Log ​

When enabled, the plugin records errors that occur during optimization and displays them on a separate Error Log tab. Turn this on when troubleshooting optimization failures so you can share the log with the plugin's support team. When enabled, an additional option appears below.

Keep an error log on frontend ​

This setting only appears when Error Log is enabled.

Enables error logging on the front end of your site. If WebP or AVIF images are not displaying correctly for visitors, this option captures front-end errors you can send to the plugin support team. Only enable this when support asks for it, as continuous front-end logging can slow down your site.

Convert Images to WebP ​

When enabled, the plugin converts your JPEG and PNG images into WebP format and serves the WebP versions to browsers that support it. Browsers that do not support WebP continue to receive the original format. WebP typically provides better compression than JPEG or PNG at the same visual quality, further reducing page load times. When enabled, a delivery mode selector appears below.

Convert Images to AVIF ​

When enabled, the plugin converts your JPEG and PNG images into AVIF format. AVIF provides even stronger compression than WebP, though it requires more processing time and has less browser support. When enabled, a delivery mode selector appears below. This setting requires a Pro license — it appears disabled on the free version.

Delivery mode for converted images ​

This setting only appears when Convert Images to WebP or Convert Images to AVIF is enabled.

Controls how the plugin serves converted WebP and AVIF images to visitors. The available modes are:

  • Redirection (via .htaccess) — adds server-level redirect rules that serve converted images directly, without any PHP processing. This provides the best performance. This option is only available on Apache servers and is disabled if your hosting does not support .htaccess-based redirection. The plugin tests your server and displays whether redirection is supported.
  • Replace <img> tags with <picture> tags, adding the Webp/AVIF to srcset — wraps each image in a <picture> element so the browser can choose between the original and converted format. This works on any server type. Test your site after enabling this option, because themes that apply CSS based on <img> tag positioning may experience layout issues. You do not need this option if you use the Cache Enabler plugin, which already handles WebP delivery. You can safely revert to the previous state at any time by deactivating the option.
  • Replace image URLs — rewrites image URLs throughout your page output to point directly to the converted files. This handles src, srcset, common lazy-load attributes, and even inline background-image styles.

Manage backups ​

Provides two action buttons for managing your backed-up original images. "Restore" replaces all optimized images with their original backups, which is useful if you want to start fresh or switch to different compression settings. "Clear Backup" permanently deletes the backup folder to free up disk space. Both actions ask for confirmation before proceeding because they cannot be undone.

Strip EXIF data ​

When enabled (the default), the plugin removes EXIF metadata from images during optimization. EXIF data includes information like camera model, shutter speed, GPS coordinates, and other technical details embedded in photos. Stripping this data reduces file size slightly and removes potentially sensitive location information. Disable this if your site is photography-focused and you need to preserve and display EXIF data.

Optimization ​

Optimization order ​

Controls which images are optimized first during bulk optimization. "Ascending" starts with the oldest images in your media library, while "Descending" starts with the newest. Choose descending if your most recent uploads are the ones most likely to appear on your site's front pages and you want them optimized first.

Resizing large images ​

When enabled, the plugin automatically resizes images that exceed specified pixel dimensions before optimizing them. This is useful for images uploaded directly from cameras or stock photo sites that are much larger than anything needed on a website. When enabled, two additional fields appear for setting maximum width and height.

Enter the maximum width (px) ​

This setting only appears when Resizing large images is enabled.

Sets the maximum width in pixels for uploaded images. Images wider than this value are proportionally resized down to fit within this limit. The default is 1600 pixels.

Enter the maximum height (px) ​

This setting only appears when Resizing large images is enabled.

Sets the maximum height in pixels for uploaded images. Images taller than this value are proportionally resized down to fit within this limit. The default is 1600 pixels.

Optimize formats ​

A checklist of image formats the plugin should optimize. The available formats are JPG, PNG, and GIF, all selected by default. Uncheck a format if you want the plugin to skip it during optimization — for example, you might uncheck GIF if you use animated GIFs that should not be compressed.

Optimize thumbnails ​

A checklist of WordPress image sizes the plugin should optimize. WordPress generates multiple thumbnail sizes for every uploaded image, and this setting lets you choose which of those sizes get optimized. The list is dynamically generated from all image sizes registered by your theme and plugins, showing each size name and its pixel dimensions. By default, only "thumbnail" and "medium" are selected. Select additional sizes if they appear frequently on your site's front end, or leave rarely used sizes unchecked to save processing time and API quota.

Scheduled and background optimization ​

Background optimization type ​

Chooses how unoptimized images are processed automatically. The available options are:

  • Scheduled — runs optimization at fixed intervals you configure below. This is the default and only option on the free version.
  • Background — runs optimization continuously in the background whenever your site is active. This processes images faster but uses more server resources. This option requires a Pro license — on the free version it is forced back to Scheduled.

Run every ​

This setting only appears when Background optimization type is set to Scheduled.

Sets how often the scheduled optimization job runs. Options range from every 1 minute to once per day. The default is every 5 minutes. Choose a shorter interval if you frequently upload images and want them optimized quickly, or a longer interval to reduce server load on shared hosting.

Images per iteration ​

This setting only appears when Background optimization type is set to Scheduled.

Sets how many images the plugin optimizes each time the scheduled job runs. The default is 3. For example, if you set this to 5 and the schedule to every 5 minutes, the plugin optimizes 5 images every 5 minutes. Increase this number if you have a large backlog of unoptimized images and your server can handle the load, or decrease it if optimization is causing timeouts or slowdowns.