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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.

In this article

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. On average, 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. On average, file sizes are reduced by approximately five times.
  • High — applies maximum compression for the smallest possible file sizes. On average, files are 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. This mode requires a Pro license.
  • 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.

Show Robin column in the Media Library ​

Enabled by default. Turn this off to hide Robin's status column from the Media Library list view for all users. Hiding the column does not stop image optimization.

Delete converted files on uninstall ​

Disabled by default. When enabled, Robin deletes the WebP and AVIF files it generated when you delete the plugin. Deactivating the plugin does not delete these files.

Load the first content image first ​

Disabled by default. When enabled, Robin adds fetchpriority="high" to the first eligible image in the main post content that is not lazy-loaded and does not already have a priority set. It does not change the image's lazy-loading setting.

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 Apache rules that serve converted images directly, without PHP processing. This mode is only available when the server supports .htaccess rules; Robin tests your server and displays whether redirection is supported. Nginx does not read .htaccess; ask your host to add the supplied Rules for nginx to the site's server block and reload Nginx, or choose Replace <img> tags with <picture> tags, adding the Webp/AVIF to srcset instead. If Robin detects Cloudflare with this mode, it warns that a shared image cache can serve an unsupported format. Use the <picture> mode unless the cache varies by the Accept header.
  • Replace <img> tags with <picture> tags, adding the Webp/AVIF to srcset — wraps each image in a <picture> element so the browser can choose a supported format. This is browser-negotiated delivery: different browsers can receive different formats. It 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.
  • Replace image URLs — rewrites image URLs throughout your page output to point directly to converted files. It handles src, srcset, common lazy-load attributes, and inline background-image styles. This mode uses the same URL for every browser; when available and enabled, AVIF is preferred, followed by WebP and then the original image. Unlike Picture delivery, it does not choose a format based on the browser's supported formats.

Test delivery ​

Save your delivery settings before clicking Test delivery. Robin displays diagnostic results for the selected mode. A server-side fallback test may not include the CDN in front of your site, so also check an image on a visitor-facing page.

Manage backups ​

Shows how many images have backups and how much disk space the backup folder uses. Restore replaces optimized images with their available original backups. Clear Backup permanently deletes the backup folder to free up disk space. Both actions ask for confirmation. If there are no backups, the readout says There are no backups. and both buttons are disabled.

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 and is the default. Descending starts with the newest images. Largest first starts with the largest images.

Resizing large images ​

When enabled, the plugin resizes images that exceed the specified maximum width and height before optimizing them. For an individual image, Keep original dimensions overrides this resizing while still allowing compression. You can find this option in the image's upload options or attachment details.

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.

Exclude paths ​

Empty by default. Enter one pattern per line to make bulk and automatic optimization skip images whose path inside the uploads folder contains a matching pattern. The path is relative to the uploads folder. * matches any text and ? matches one character; for example, use 2019/*, logo, or banner-?.jpg. To exclude one image instead, use Exclude from optimization in its upload options or attachment details.

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.

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