Plugin / WebP Express

Installation

1. Upload the plugin files to the /wp-content/plugins/webp-express directory, or install the plugin through the WordPress plugins screen directly.
2. Activate the plugin through the ‘Plugins’ screen in WordPress
3. Configure it (the plugin doesn’t do anything until configured)
4. Verify that it works

Configuring

You configure the plugin in Settings > WebP Express.

Operation modes

As sort of a main switch, you can choose between the following modes of operation:

Varied image responses:
WebP Express creates redirection rules for images, such that a request for a jpeg will result in a webp – but only if the request comes from a webp-enabled browser. If a webp already exists, it is served immediately. Otherwise it is converted and then served. Note that not all CDN’s handles varied responses well.

CDN friendly:
In “CDN friendly” mode, a jpeg is always served as a jpeg. Instead of varying the image response, WebP Express alters the HTML for webp usage.

Just redirect:
In “just redirect” mode, WebP Express is used just for redirecting jpeg and pngs to existing webp images in the same folder. So in this mode, WebP express will not do any converting. It may be that you use another plugin for that, or that you converted the images off-line and uploaded them manually.

Tweaked:
Here you have all options available.

Conversion methods

WebP Express has a bunch of methods available for converting images: Executing cwebp binary, Gd extension, Imagick extension, ewww cloud converter and remote WebP express. Each requires something. In many cases, one of the conversion methods will be available. You can quickly identify which converters are working – there is a green icon next to them. Hovering conversion methods that are not working will show you what is wrong.

In case no conversion methods are working out of the box, you have several options:
– You can install this plugin on another website, which supports a local conversion method and connect to that using the “Remote WebP Express” conversion method
– You can purchase a key for the ewww cloud converter. They do not charge credits for webp conversions, so all you ever have to pay is the one dollar start-up fee 🙂
– You can set up webp-convert-cloud-service on another server and connect to that. Its open source.
– You can try to meet the server requirements of cwebp, gd, imagick or gmagick. Check out this wiki page on how to do that

Quality detection of jpegs

If your server has Imagick extension or is able to execute imagemagick binary, the plugin will be able to detect the quality of a jpeg, and use that quality for the converted webp. You can tell if the quality detection is available by hovering the help icon in Conversion > Jpeg options > Quality for lossy. The last line in that help text tells you.

This auto quality has benefits over fixed quality as it ensures that each conversion are converted with an appropriate quality. Encoding low quality jpegs to high quality webps does not magically increase the visual quality so that your webp looks better than the original. But it does result in a much larger filesize than if the jpeg where converting to a webp with the same quality setting as the original.

If you do not have quality detection working, you can try one of the following:
– Install Imagick on the server (for this purpose, it is not required that it is compiled with WebP support)
– Install imagemagick on the server and grant permission for PHP to use the “exec” function.
– Use “Remote WebP Express” converter to connect to a site, that does have quality detection working
– If you have cwebp converter available, you can configure it to aim for a certain reduction, rather than using the quality parameter. Set this to for example 50%, or even 45%.

Notes

Note:
The redirect rules created in .htaccess are pointing to a PHP script. If you happen to change the url path of your plugins, the rules will have to be updated. The .htaccess also passes the path to wp-content (relative to document root) to the script, so the script knows where to find its configuration and where to store converted images. So again, if you move the wp-content folder, or perhaps moves WordPress to a subfolder, the rules will have to be updated. As moving these things around is a rare situation, WebP Express are not using any resources monitoring this. However, it will do the check when you visit the settings page.

Note:
Do not simply remove the plugin without deactivating it first. Deactivation takes care of removing the rules in the .htaccess file. With the rules there, but converter gone, your Google Chrome visitors will not see any jpeg images.