Slow web page loading is often caused by images. A single unprocessed high-resolution image may be larger in size than all the text on an entire page combined, and page size is a major factor affecting loading speed. Since images account for the bulk, choosing a format is not just a technical detail—it directly affects user experience.
The Shortcomings of Several Traditional Formats
The web has long used three image formats, each with limitations that have persisted for years: one has a limited number of colors and relatively rough transparent edges, yet its files are not necessarily small; one excels at lossy compression for photos but does not support transparency and easily leaves compression artifacts in solid-color areas; and another can achieve clean transparency but uses lossless compression, so file sizes tend to be large. As a result, it is common to prepare three formats for the same page—one for photos, one for logos with transparency, and another for small animations.
How WebP Is Different
WebP's starting point is to combine these things into one format: it can do both lossy and lossless compression; it supports smooth alpha transparency; and it can also be animated, with far richer colors than earlier animated formats. When image quality is similar, its file size is usually significantly smaller than comparable traditional formats.
For design, this means you no longer have to sacrifice visuals to control file size: larger background images, multi-image carousels, and high-quality product galleries can all be used more freely.
Its Value in Responsive Design
The same page often needs image versions of different sizes for different screens and resolutions. When multiple versions are added together, the file-size difference is further magnified. A smaller format has an even more obvious effect here—especially for mobile users, saving considerable data and time.
How to Handle Compatibility
Now that the format exists, what about older environments? There are two common approaches.
Provide a fallback on the page. Using markup language support, let the browser load the new format when supported and automatically fall back to a traditional format when not, without visitors noticing.
Convert automatically on the server side. The server or an image service provides the appropriate format in real time based on the support of the visiting device. For content maintainers, this is almost transparent, and there is no need to prepare each format separately.
A Few Suggestions for Adoption
- For new sites or redesigns, set this type of format as the default image output, keeping traditional formats as fallbacks.
- Use lossy compression for photo-like content; for graphics such as icons and logos that need sharp edges and transparency, use lossless or high-quality output.
- Before uploading, control dimensions according to the actual display width; do not simply upload the original image.
- Keep copies in the original traditional formats to handle the occasional unsupported environment and for necessary archiving.
A Reminder
Format is only one part of optimization. Whether dimensions are appropriate, whether alt text is written correctly, and whether lazy loading is implemented also affect the final result. Switching to a more efficient format will not automatically solve other problems.