How Can You Optimize Background Images with CSS Image-Set?

Optimizing images for different devices and resolutions enhances user experience and performance. One powerful CSS feature that facilitates this is the image-set() function. 

This blog post explains how you can use image-set() to provide responsive background images in CSS, including support for multiple formats and resolutions.

Issue: Responsive Images in CSS

Implementing responsive images in CSS traditionally required multiple media queries or JavaScript solutions. This approach can become cumbersome and difficult to maintain, especially when dealing with multiple image formats (e.g., WebP and PNG) and varying device resolutions (e.g., standard and high-DPI screens).

The image-set() function solves this problem elegantly by allowing you to define multiple image sources and resolutions directly within your CSS, enabling the browser to choose the best option based on the user’s device.

Solution: Understanding image-set

The image-set() function works similarly to the srcset attribute in HTML. It lets you specify:

1. Multiple image sources.
2. The format of each image.
3. The resolution of each image (e.g., 1x for standard displays, 2x for retina displays).

Here’s an example syntax:

In this code:

• The browser selects the best image based on the device’s resolution and support for formats like WebP.
• High-DPI screens will load image2.webp or image2.png (2x), while standard screens will load image1.webp or image1.png (1x).

Adding Fallbacks for Older Browsers

Not all browsers support image-set() yet. To ensure compatibility, include a fallback background-image declaration with a single default image.

Here’s a complete example:

Key Points:

1. Fallback Image: The background-image: url(“elephant.png”); ensures that older browsers can still display an image.
2. WebKit Prefix: The -webkit-image-set ensures compatibility with WebKit-based browsers like Safari.
3. Standard Syntax: The image-set function is used for modern browsers that fully support this feature.

Why Use image-set()?

1. Improved Performance: By serving WebP images where supported, you reduce file sizes and improve loading times.
2. Retina-Ready: Automatically delivers high-resolution images to devices with higher pixel densities.
3. Simpler Code: Avoids complex media queries or JavaScript to handle responsive images.

Browser Support

As of now, the image-set() function has partial support across browsers. Modern versions of Chrome, Edge, and Safari support it, while some older browsers may require the fallback.

Conclusion

The image-set() function is a game-changer for managing responsive background images in CSS. It simplifies your codebase, enhances performance, and ensures that users get the best possible experience, regardless of their device. Start using image-set() in your projects today and future-proof your designs for a responsive web.

Do you have questions about implementing image-set() or optimizing images? Contact us.