There are various settings in Optimus that aim to help accommodate your image optimization needs and provide the best quality of image optimization. This article focusses on the Optimus settings available directly within the WordPress plugin.
Compression of thumbnail images in WordPress
In the settings of the WordPress media library, users have the option to set their own custom image sizes (preview images = thumbnails). Themes and (some) plugins additionally create their own image sizes in order to use them in the blog.
Over time, a large number of custom-set image sizes can accumulate, causing the uploading and optimization processes to slow down due to the large number of preset image sizes. In version 1.3.2 or higher, the WordPress plugin Optimus shows a list of registered image sizes that are created by WordPress and thus optimized by Optimus depending on the file size with each image upload (yes, Optimus optimizes all thumbnails of an image as well, not just the original file)
The purpose of this list: to have control over the registered image sizes/thumbnails and achieve better performance when uploading.
The transfer process when media is uploaded becomes slower the more image variants have to be created. Additionally, Optimus has to optimize all of these images as well.
The question is: do all image sizes have their purpose? Maybe the theme does not use preview images and always displays the original images? If that is the case and only certain thumbnails are employed in the theme, unnecessary image size settings should be removed from the WordPress settings.
In this context we recommend the WordPress plugin Display Registered Image Dimensions, which lists thumbnail sizes registered by third party applications.
Optimization of original images in WordPress
The function "No optimization of original images" stops Optimus from optimizing original images uploaded to WordPress. When this option is activated, the plugin only compresses preview images (=thumbnails) and always skips original images. This way, an original image uploaded to WordPress really remains untouched - untreated, but also unoptimized. Metadata, copyright information and geodata remain stored in the image.
Remove metadata from images
Photos that were taken using a digital camera or processed with an image editing program contain a set of meta information such as exposure time, device properties, copyright information and so on. It is recommended to remove metadata from images.
Thumbnails that are created by WordPress from uploaded pictures with available meta information also contain the metadata of the original image. This way it is ensured that the generated preview images (=thumbnails) also inherit the parameters stored in the original photo. Quite a practical feature for photographers.
In its original settings, the Optimus plugin removes all meta information from the image in order to ensure the most efficient image optimization possible. The option "No deletion of image metadata" turns off the data cleaning and keeps all the metadata stored in the image. While the gains from optimization are smaller in this case, information stored in the picture will not be lost.
Even when the option "No deletion of image metadata" is active, JPEG photos are converted to the progressive JPEG format.
Read more about how to remove metadata from images through the API: Optimus API
Convert JPEG and PNG to WebP image format
WebP is Google's superior alternative image format. The key difference to photos in JPEG format is the compression method. At the same compression level, WebP image files are considerably smaller, which is a clear advantage for website performance. Read more about all the advantages and disadvantages, technical details and tools of the new image format: Convert to WebP - The Successor of JPEG
Optimus introduces WebP conversion: A WebP version is generated for each image uploaded in WordPress and optimized by Optimus. This WebP image can be displayed in supporting browsers, saving on traffic. Smart distribution of WebP files is handled by the redirection rule in .htaccess: Web server configuration to deliver WebP
WebP conversion is available to Optimus HQ customers as of Optimus 1.1.4 without additional cost. This feature can be activated in the plugin settings by navigating to your WordPress Dashboard > Settings > Optimus. Here you will see the option to select "Creation of WebP Files".
WebP conversion has high resource and time requirements. Consequently, image uploads to the media library will take longer to finish. The additional conversion also puts a higher strain on the Optimus server. Therefore, this is what we recommend: Only activate WebP conversion in the plugin if you are actually using the WebP format productively. Otherwise, unnecessary strains are put on disk space and computing power.
Please note: The goal of WebP is to keep image files small and increase website load speed. Depending on the image, however, the WebP version generated can actually be larger than the source file. This is a rare occurrence, but it can happen, especially when converting PNG files.