reGenerate Thumbnails Advanced Pro settings guide

reGenerate Thumbnails Advanced Pro (RTA Pro) comes in handy when you install a new WordPress theme on your site that has different thumbnail sizes.While the newly uploaded images are cropped and resized to fit the new theme, the old thumbnails remain unchanged. With RTA Pro you can regenerate the thumbnails for all your existing images.

It's also very useful if you have a lot of thumbnails you no longer need and want to remove them while making sure you generate all the thumbnails you need.

But it can do a lot more if you change the settings. Here is a guide to what each setting does.


First you need to change the regeneration settings (if you need it). These are displayed on the right hand side, or if the screen is small enough, at the top of the screen.

Image Sizes

This helps with regenerating sizes that are not registered in WordPress. If you find that a new plugin is adding sizes that aren't in the list below (meaning the plugin isn't registering its sizes properly in WordPress), you can use this setting to register them in WordPress and ensure that the thumbnail regeneration process creates them for the old images too.

Or you maybe just want a new image size on your site. Just add the size here.

It's important to know that when you register new sizes, you must have the plugin activated if you want these sizes to always be generated. In other words: If you deactivate the plugin, the new image sizes will no longer be generated for new uploads.

Regenerate these thumbnails

Choose which thumbnails you want to regenerate. With this option, you only decide which thumbnails are regenerated and which are not. If you uncheck a size, it will not be touched (unless you select the option Delete Unselected Thumbnails, which we will explain later).

Please note that the fact that you uncheck the sizes here does not mean that they will no longer be registered in WordPress, as they are registered by the theme or plugins and will therefore continue to be generated for newly uploaded images.

The Force regeneration checkbox ensures that a specific image size that already exists in the file system is overwritten when regenerating. This is especially useful if the images have been optimized with an image optimization plugin such as ShortPixel Image Optimizer (because of this feature, reGenerate Thumbnails Advanced Pro is the only thumbnail regeneration plugin that works well with ShortPixel Image Optimizer).

You should check Force regeneration if, for example, you have watermarked your thumbnails and the originals are not watermarked and you want to remove the watermark for the thumbnails as well. Or if you have corrupted files after a site copy.

Default JPEG Quality

This number changes the default compression value that WordPress applies to your newly added images. A value of "90" is the default value in WordPress, which means that WordPress will  automatically compress your JPEG images to 90% of their original size.

We don't recommend changing this value unless you know exactly what you're doing, because if you lower the value, your images could be over-optimized.

For the avoidance of doubt, ShortPixel Image Optimizer compresses your images taking into account the default compression that WordPress already does.

Regenerate Options

Time to regenerate your thumbnails.

Regenerate only Featured Images

This will only regenerate the thumbnails for the images that are set as Featured in a post, page or product. All other images remain untouched. In many cases, it makes sense to regenerate the thumbnails only for Featured images, as these appear in post lists, grids, products, etc.

Regenerate period

You can choose whether you want to regenerate all thumbnails or just the most recent ones (last 6 months, three months, etc.).

Clean unknown metadata (advanced)

This option removes the old metadata that is not defined in your system sizes. You can use it after removing plugins and/or themes with old image definitions. This is useful to get rid of the definitions and sizes created by uninstalled plugins and themes that still show up in various menus and screens.

Please note that this will not remove any thumbnails from your hard disk.

Delete Unselected Thumbnails (advanced)

This option removes the thumbnails that are not selected in the Regenerate these thumbnails list. It also removes the thumbnails that exist on the hard disk and in the metadata but are not registered with WordPress (the registered thumbnails are included in the Regenerate these thumbnails list). This option is good for removing stale thumbnails, but make sure they are not in use. 

An example where this option is useful: You were using a gallery plugin that creates its own sizes and you have stopped using it. The thumbnails remain on the hard disk but are no longer used, so you want to get rid of them.

Please also note that there are cases where some plugins use additional thumbnails but don't declare them to WordPress or don't even add them to the image's metadata. For this reason, it's highly recommended to create a backup first and then check the site thoroughly after regeneration to see if there are no missing images. If you discover any missing images, restore the backup. 

Remove non-existent images (advanced)

This option checks if an image (not thumbnails) is stored in the Media Library.

  • If it's present, all selected thumbnails will be regenerated (the normal process).
  • If it doesn't exist, all existing thumbnails are removed from the file system, database references and metadata for the image.

Optimize regenerated thumbnails with ShortPixel (advanced)

You can choose whether you want to re-optimize the regenerated thumbnails with ShortPixel Image Optimizer (if you have it installed). If this is the case, simply check the box.

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