Dynamic Images

The Media module supports dynamic image resizing via a microservice called Tachyon. Tachyon allows arbitrary image resizes to be done on the fly, supports lossless image compression and many file formats such as WebP for supported browsers.

By default the Tachyon service is enabled. It can be explicitly disabled by setting the modules.media.tachyon configuration property to false, though this is highly discouraged.

All images rendered on the front end of the website are automatically modified to use the Tachyon service URLs. Via lossless compression and automatic format conversion, image sizes can be reduced up to 70% with no degradation in quality.

Responsive Images

A major advantage of using Tachyon for all site images is the ability to generate more accurate srcset that respect a registered image size's aspect ratio rather than relying on multiple other image sizes being registered at the same aspect ratio.

This is made possible using Tachyon's zoom parameter. By default all srcset attributes will be generated with 2x, 1.5x, 0.5x and 0.25x alternatives. The available modifiers can be configured through the composer.json file:

{
    "extra": {
        "altis": {
            "modules": {
                "media": {
                    "smart-media": {
                        "srcset-modifiers": [
                            2,
                            1.5,
                            0.5,
                            0.25
                        ]
                    }
                }
            }
        }
    }
}

By using the zoom parameter Tachyon also applies a sliding scale of quality for output images so that larger 2x images for example don't incur a huge increase in file size. Images displayed on a web page at a smaller size than their natural size do not need to be as high quality to appear crisp.

Custom Image Sizes

Image URLs in Altis are converted to Tachyon URLs by default in all contexts (file paths remain the same). You can convert any image URL under the uploads directory to a Tachyon URL using the tachyon_url() function.

// Query parameters to append to the URL.
$args = [
    'lb' => '400,400',
    'background' => 'white',
];
// Generate a Tachyon URL for $image_src and $args.
$url = tachyon_url( $image_src, $args );

Default Settings

By default in Altis all Tachyon URLs for image sizes that result in a cropped image will have smart cropping applied. You can apply additional default modifications using the following filter:

tachyon_pre_args: array $args [, array $downsize_args]

• $args is an array of arguments used to generate the Tachyon URL query string.
• $downsize_args if available provides additional context such as the requested image size name and attachment ID.

Query Arguments Reference

The following query string arguments can be applied to any image delivered by Tachyon.

Limitations

Image files that contain dimensions as part of the file name, e.g. my-image-100x200.png can cause issues for Tachyon. We recommend you rename all images to remove dimensions from their file names, as well as any other special characters. You can use this tool as a framework to convert file names.