Updated img_url helper: convert image formats automatically

In Ghost 5.7.0, we updated the functionality of the img_url helper: it now can convert image formats automatically! This update is perfect for theme developers who are serious about performance :racing_car:

Why it’s important

Images are the heaviest part of your website. The new helper automatically converts an image from PNG, GIF, or JPEG to WebP, which reduces its size by ~25% without any visible loss of quality. Using the new helper will make your website faster, positively impact SEO, and give your users a better experience.

How it works

Simply add the format attribute to the img_url helper.

Basic example

{{img_url feature_image size="s" format="webp"}}

Full example with picture tag

    <!-- Serve the AVIF format if the browser supports it -->
    <!-- Remove this block when using animated images as feature images -->
        srcset="{{img_url feature_image size="s" format="avif"}} 300w,
                {{img_url feature_image size="m" format="avif"}} 600w,
                {{img_url feature_image size="l" format="avif"}} 1000w,
                {{img_url feature_image size="xl" format="avif"}} 2000w"
        sizes="(min-width: 1400px) 1400px, 92vw" 
    <!-- Serve the WebP format if the browser supports it -->
        srcset="{{img_url feature_image size="s" format="webp"}} 300w,
                {{img_url feature_image size="m" format="webp"}} 600w,
                {{img_url feature_image size="l" format="webp"}} 1000w,
                {{img_url feature_image size="xl" format="webp"}} 2000w"
        sizes="(min-width: 1400px) 1400px, 92vw" 
    <!-- Serve original file format as a fallback -->
        srcset="{{img_url feature_image size="s"}} 300w,
                {{img_url feature_image size="m"}} 600w,
                {{img_url feature_image size="l"}} 1000w,
                {{img_url feature_image size="xl"}} 2000w"
        sizes="(min-width: 1400px) 1400px, 92vw"
        src="{{img_url feature_image size="xl"}}"
        alt="{{#if feature_image_alt}}{{feature_image_alt}}{{else}}{{title}}{{/if}}"

For more details on how to use the updated helper, see the docs: