: Because the browser might paint the rest of the page before the image is ready, the image may "pop in" suddenly after the surrounding text is already visible.

While async decoding is generally a best practice for secondary images, it can occasionally backfire for critical "above-the-fold" content:

: For the Largest Contentful Paint (LCP) image—usually the main hero image—using decoding="async" can actually delay its appearance, potentially hurting your Core Web Vitals scores.

: It allows text and other non-image content to appear sooner, rather than waiting for large images to be fully processed. The Trade-off: LCP and "Popping"

: Moving the decoding process to a background thread keeps the main thread free, ensuring a smoother user experience and reducing "jank" while scrolling.

When a browser downloads an image, it must decode it before it can be displayed. By default, many browsers perform this synchronously, meaning they wait for the image to decode before showing the rest of the page content.